Machining of Aluminum and Aluminum Alloys / 763

Home , 1060 aluminium alloy, 2218 aluminium alloy, 2219 aluminium alloy, 5154 aluminium alloy, 5454 aluminium alloy, 5456 aluminium alloy

MachJning of Aluminum and AlumJnum Alloys

ALUMINUM ALLOYS can be ma- -r.. _ . lul Tools with small rake angles can normally chined rapidly and economically. Because be used with little danger of burring the part ," ,' ,,'7.,','_ ' , '~: £,~ " ~ ! f / "' " of their complex metallurgical structure, or of developing buildup on the cutting their machining characteristics are superior ,, A edges of tools. Alloys having silicon as the to those of pure aluminum. major alloying element require tools with The microconstituents present in alumi- larger rake angles, and they are more eco- num alloys have important effects on ma- nomically machined at lower speeds and chining characteristics. Nonabrasive con- feeds. stituents have a beneficial effect, and ,o IIR Wrought Alloys. Most wrought alumi- insoluble abrasive constituents exert a det- num alloys have excellent machining char- rimental effect on tool life and surface qual- acteristics; several are well suited to multi- ity. Constituents that are insoluble but soft B pie-operation machining. A thorough and nonabrasive are beneficial because they e,,{' , understanding of tool designs and machin- assist in chip breakage; such constituents s,~ ,.t ing practices is essential for full utilization are purposely added in formulating high- of the free-machining qualities of aluminum strength free-cutting alloys for processing in alloys. high-speed automatic bar and chucking ma- Strain-hardenable alloys (including chines. " ~ ~p /"~ commercially pure aluminum) contain no In general, the softer ailoys~and, to a alloying elements that would render them lesser extent, some of the harder al- c • o c hardenable by solution heat treatment and ,p loys--are likely to form a built-up edge on precipitation, but they can be strengthened the cutting lip of the tool. This edge consists "/a to some extent by cold work. In machining, of aluminum particles that have become a continuous chip is formed that must be welded to the tool edge because they were directed away from the workpiece by tools melted by the heat generated in cutting. with generous side and back rake angles, Edge buildup can be minimized by using thus preventing scratching of the finished effective cutting fluids and by employing D :/ D surface with the work-hardened chips. tools with surfaces that are free of grinding These alloys machine easily, although tool marks and scratches. pressures are high as a result of high fric- Alloys containing more than 10% Si are tion. To obtain good surface finish, sharp the most difficult to machine because hard tools are mandatory because the alloys are particles of free silicon cause rapid tool gummy. Machinability is improved by cold wear. Alloys containing more than 5% Si working; alloys in the full-hard temper are ~. easier to machine to a good finish than those will not finish to the bright machined sur- ~. 0 faces of other high-strength aluminum al- in the annealed condition. loys, but will have slightly gray surfaces , ] Heat-Treatable Alloys. Most of the al- with little luster. Chips are torn rather than loys of this group contain fairly high per- sheared from the work, and special precau- centages of alloying elements such as cop- tions (such as the use of lubricant-contain- Machinabllity ndmin Feed, mndrev (in./rev) per, silicon, magnesium, and zinc. They can ing cutting fluids) must be taken to avoid the rating Alloy (sfm) Left photo Right photo be machined to a good finish with or without cutting fluid, but a cutting fluid is rec- buildup of burrs on cutting edges. A ...... 2011-T3 120 0.066 0. ! 52 (400) (0.0026) (0.0060) ommended for most operations. Turnings B ...... 2024-T4 30 O. 152 0.264 usually occur as long, continuous curls, Classification of (100) (0.0(0) (0.0104) except for the free-machining alloys, which C ...... 6061-T6 120 0.152 0.264 contain chip-breaking constituents. Heat- Aluminum Alloys (400) (0.0060) (0.0104) D ...... 3004-H32 120 O. 152 0.264 treatable alloys are more machinable in the Cast, wrought, strain hardenable, and (400) (0.0060) (0.0104) heat-treated tempers than in the softer as- heat treatable are the four major classifica- E ...... 1100-HI2 120 0.152 0.264 fabricated or annealed solution. tions of aluminum alloys. Machinability (400) (0.0060) (0.0104) Machinability groupings for aluminum groupings are also used. alloys are useful in specifying tool forms. Typical chips for machinability ratings A to E Cast alloys containing copper, magne- F'U ° I (Table 1)for aluminum alloys. All chips were For this purpose, alloys are classified into sium, or zinc as the principal alloying ele- made with 20 ° rake tool and 2.54 mm (0.100 in.) depth five groups: A, B, C, D, and E, in increasing ments impose few machining problems. of cut. order of chip length and in decreasing order 762 / Machining of Specific Metals and Alloys

Table l(a) Machinability ratings of wrought aluminum alloys Hardness, HB Hardness, HB Alloy (500 kg load, Machinabflity Alloy (500 kg load, Machinability designation Temper Product form 10 nun ball) rating(a) designation Temper Product form 10 mm ball) rating(a) 1060 ...... O Extruded rod, bar, 19 E 5154 ...... O Sheet, plate; welding wire 58 D HI2 extruded and drawn 23 E H32 and rod 67 D HI4 tube, pipe 26 D H34 73 C HI6 30 D H36 78 C HI8 35 D H38 80 C 1100 ...... O Sheet, plate; rolled and 23 E H112 63 D HI2 extruded rod, bar; 28 E 5252 ...... H25 Sheet 68 C HI4 extruded and drawn 32 D H38 75 C H 16 tube, pipe; other 38 D 5254 ...... O Sheet, plate 58 D H 18 44 D H32 67 D 2011 ...... T3 Rod, bar, tube, pipe 95 A H34 73 C T8 100 A H36 78 C 2014 ...... O Plate, rod, bar, tube, pipe; 45 D H38 80 C T4 other 105 B H 112 63 D T6 135 B 5257 ...... H25 Sheet 32 C 2017 ...... O Rolled rod, bar; other 45 C H28 43 C T4 105 B 5357 ...... O Sheet, plate 32 D 2018 ...... T61 Forging stock 120 B H25 50 C 2024 ...... O Sheet, plate, rod, bar, tube, 47 D H28 55 C T3 pipe; other 120 B 5454 ...... O Sheet, plate; other 62 D T4 120 B H32 73 D T61 130 B H34 81 C 2025 ...... T6 Forging stock I l0 B HI 11 70 D 2117 ...... T4 Rivet wire, rod 70 C HI 12 62 D 2218 ...... T72 Forging stock 95 B 5456 ...... O Sheet, plate; extruded rod 70 D 2219 ...... O Sheet, plate; extruded rod, • ..... Hill bar; extruded tube, pipe; 75 D T42 bar; extruded and drawn ...... H112 forgings 70 D T351 tube, pipe; forging stock 100 B HI 16 90 D T37 117 B 5457 ...... O Sheet 32 E T62 I 15 B H25 48 C T851 130 B H28 55 C T87 130 B 5557 ...... O Sheet 27 E 2618 ...... T61 Forgings 115 B H25 46 D 3002 ...... O Sheet 25 -.. H28 55 D H25 ...... 5652 ...... O Sheet, plate 47 D 3003 ...... O Sheet, plate; rolled and 28 E H32 60 D HI2 extruded rod, bar; 35 E H34 68 C H 14 extruded and drawn 40 D H36 73 C HI6 tube, pipe; other 47 D H38 77 C H 18 55 D 5657 ...... H25 Sheet 40 D 3004 ...... O Sheet, plate; drawn tube, 45 D H28 50 D H32 pipe 52 D 6005 ...... T5 Extruded rod, bar 95 C H34 63 C 6061 ...... O Sheet, plate, rod, bar, tube, 30 D H36 70 C T4 pipe; forging; other 65 C H38 77 C T6 95 C 4032 ...... T6 Forging stock 120 B 6063 ...... O Extruded rod, bar; 25 D 5005 ...... O Sheet, plate; rolled rod and 28 E T l extruded and drawn 42 D H 12 bar; other 36 E T4 tube, pipe 60 D H14 41 D T5 60 C H 16 46 D T6 73 C H 18 51 D T83 82 C H32 36 E T831 70 C H34 41 D T832 95 C H36 46 D 6066 ...... O Extruded rod, bar; forging 43 D H38 51 D T4 stock 90 C 5050 ...... O Sheet, plate; drawn tube, 36 E T6 120 B H32 pipe 46 D 6070 ...... T6 Rod, bar, tube, pipe 120 C H34 53 D 6151 ...... T6 Forging stock 100 • • • H36 58 C 6262 ...... T9 Rod, bar, tube, pipe 120 B H38 63 C 6463 ...... TI Extruded rod, bar; 42 D 5052 ...... O Sheet, plate; rolled rod, 47 D T5 extruded and drawn 60 C H32 bar; drawn tube, pipe; 60 D T6 tube, pipe 74 C H34 other 68 C 6951 ...... O Sheet 28 • • • H36 73 C T6 82 • • • H38 77 C 7001 ...... O Extruded rod, bar 60 B 5056 ...... O Rivet rod, wire 65 D T6 160 B HI8 105 C 7005 ...... T53 Rod, bar, tube, pipe ...... H38 100 C 7075 ...... O Sheet, plate, rod, bar, tube, 60 D 5083 ...... O Sheet, plate, rod, bar, tube, 67 D T6 pipe; forging stock 150 B H321 pipe, forgings 82 D 7079 ...... O Sheet, plate, rod, bar, tube, • ..... 5086 ...... O Sheet, plate; extruded rod, 60 D T6 pipe; forging stock 145 B H32 bar; extruded and drawn 72 D 7178 ...... O Sheet, plate, rod, bar, tube, 60 • • • H34 tube, pipe 82 C T6 pipe 160 B HI 12 64 D T76 ...... 8280 ...... O Sheet, plate • • • B HI2 • • • A (a) A, B, C, D, and E are relative ratings in increasing order of chip length (see Fig. 1) and decreasing order of quality of finish. A, free cutting, very small broken chips and excellent finish; B, curled or easily broken chips and good-to-excellent finish; C, continuous chips and good finish; D, continuous chips and satisfactory finish; E, optimum tool design and machine settings required to obtain satisfactory control of chip and finish. Source: Ref 1 Machining of Aluminum and Aluminum Alloys / 763

Table I (b) Machinability ratings of cast aluminum alloys Hardness, HB Hardness, HB Alloy (500 kg load, Machinability Alloy (S00 kg load, Machinablllty designation Temper Casting type 10 mm bali) rating(a) designation Temper Casting type 10 mm bali) rating(a) 208 ...... F Sand 55 B A356 ...... T6 Permanent mold 80 213 ...... F Permanent mold 85 • • • T61 Permanent mold 80 B

222 ...... T52 Permanent mold 100 • • • 357 ...... F Permanent mold • • • • . o

T551 Permanent mold 115 • • • T51 Permanent mold • • • • o . T65 Permanent mold 140 • • • T6 Sand 90 B 238 ...... F Permanent mold 100 B T6 Permanent mold 85 B A240 ...... F Sand 90 A T7 Sand 60

242 ...... F Sand ...... T7 Permanent mold 70 • o °

T21 Sand 70 B A357 ...... T6 Sand 85 • . .

T571 Sand 85 B T6 Permanent mold 85 • . . T571 Permanent mold 105 B B358 ...... T6 Permanent mold 90 B T61 Permanent mold 110 B T62 Permanent mold • • • T77 Sand 75 B 359 ...... T61 Permanent mold 90 A242 ...... T77 Sand 70 • • • T62 Permanent mold 100 B 295 ...... T4 Sand 60 B 360 ...... F Die 75 C T6 Sand 75 B A360 ...... F Die 75 C T62 Sand 90 B 364 ...... F Die ... C B295 ...... T4 Permanent mold 75 B 380 ...... F Die 80 B T6 Permanent mold 90 B A380 ...... F Die 80 B T7 Permanent mold 80 B 384 ...... F Die • • • C 308 ...... F Permanent mold 70 B 390 ...... F Die 120 319 ...... F Sand, permanent mold 70 C A390 ...... F Sand 100 T5 Sand 80 B F Permanent mold 110 T6 Sand 80 B T5 Sand 100 T6 Permanent mold 95 B T5 Permanent mold 110 A332 ...... T551 Permanent mold 105 C T6 Sand 140 T65 Permanent mold 125 C T6 Permanent mold 145 F332 ...... T5 Permanent mold 105 C T7 Sand 115 333 ...... F Permanent mold 90 C T7 Permanent mold 120 T5 Permanent mold 100 B 413 ...... F Die 80 E T6 Permanent mold 105 B A413 ...... F Die 80 T7 Permanent mold 90 B 443 ...... F Sand 40 E 354 ...... T61 Permanent mold 100 B F Permanent mold 45 E T62 Permanent mold 110 B F Die 50 E

355 ...... F Sand ...... A444 ...... F Sand ... • . .

T51 Sand 65 B F Permanent mold 44 • . . T51 Permanent mold 75 B T4 Sand • • •

T6 Sand 80 B T4 Permanent mold 45 • . . T6 Permanent mold 90 B 514 ...... F Sand 50 B T61 Sand 90 B A514 ...... F Permanent mold 60 B T62 Permanent mold 105 B F Die • • • B

T7 Sand 85 B B514 ...... F Sand 50 • . . T7 Permanent mold 85 B F514 ...... F Sand 50 B

T71 Sand 75 B L514 ...... F Die • • • • . . T71 Permanent mold 85 B 518 ...... F Die 80 B C355 ...... T6 Sand 85 • • • 520 ...... T4 Sand 75 B

T6 Permanent mold 90 • • • 535 ...... F Sand 70 • . . T61 Permanent mold 100 B A535 ...... F Sand 65 B 356 ...... F Sand ...... B535 ...... F Sand 65 A F Permanent mold ...... 705 ...... F Sand 65 B T51 Sand 60 C 707 ...... F Sand 85 B T51 Permanent mold • • • C A712 ...... F Sand 75 B T6 Sand 70 C C712 ...... F Permanent mold 70 B T6 Permanent mold 90 C D712 ...... F Sand 75 B T7 Sand 75 C 713 ...... F Sand 75 B T7 Permanent mold 70 C 850 ...... T5 Sand 45 A T71 Sand 60 C T5 Permanent mold 45 A A356 ...... F Sand ...... A850 ...... T5 Sand, permanent mold 45 A T51 Sand ...... B850 ...... T5 Sand 65 A T6 Sand 75 • • • T5 Permanent mold 70 A (a) A, B, C, D, and E are relative ratings in increasing order of chip length (see Fig. /) and decreasing order of quality of finish. A, free cutting, very small broken chips and excellent finish; B, curled or easily broken chips and good-to-excellent finish; C, continuous chips and good finish; D , continuous chips and satisfactory finish; E, optimum tool design and machine settings required to obtain satisfactory control of chip and finish. Source: Ref I

of finish quality, as defined in the footnotes is less than might be expected on the ba- cutting force required in turning aluminum of Tables l(a) and l(b). Ratings for most sis of its mechanical properties. Although is only about 35% of that required in turn- commercial aluminum alloys are given in the cutting force required to machine simi- ing low-carbon steel• Consequently, as Tables l(a) and l(b), and typical chips for lar metals is often in direct proportion to shown in Fig. 3, the number of cubic milli- each rating are illustrated in Fig. 1. tensile strength, this proportion is not meters of metal that can be removed per necessarily valid with dissimilar metals. minute per unit kilowatt expended is Cutting Force and Power For example, the common mechanical prop- approximately three times as great for erties of 2017-T4 aluminum alloy and of aluminum alloy 2017-T4 as for hot-rolled The cutting force, and therefore the hot-rolled low-carbon steel are quite simi- low-carbon steel of closely similar tensile power, required to machine aluminum lar (Table 2), but as Fig. 2 shows, the strength. 764 / Machining of Specific Metals and Alloys

Table 2 Comparison of common finely broken. Alloy 2011 is therefore rec- Feed, in./rev mechanical properties of 2017-T4 ommended for all general and high-produc- 0.001 0.01 875 5000 tion machining where a free-cutting alloy is HotLrolled " J j,~,-" aluminum alloy and hot-rolled E ._ low-carbon steel~J;~, low-carbon steel desired. Alloy 2011 is especially desirable z.t: .C). e~ Aluminum Hot-roiled for multiple-operation machining, mainly ~ 175 1000 ~ ~ alloy low-carbon because it machines with a broken chip. o'3 Mechanical property 2017-T4 steel Stock for multiple-operation machining is (3~ o .=_ "5 I' "-2017-T4 Tensile strength, MPa (ksi)... 440 (63.8) 449 (65.2) also available in alloys 2017, 2024, 6061, and "5 "5 0.2% yield strength, 6262 in several heat-treated tempers. o 17.5 100 0 MPa (ksi) ...... 278 (40.3) 277 (40.2)(a) Alloys 2024-T4, 2017-T4, and 7075-T6 0.025 0.25 Elongation in four Feed, mm/rev diameters, % ...... 26.0 32.7 produce continuous chips that must be bro- Shear strength, MPa (ksi) .... 279 (40.5) 324 (47.0) ken by a chip breaker in the tool. Alloys "'l~g"n .~ The effect of feed on cutting force for Hardness, HB 6061-T6 and 5056-H38 are slightly more low-carbon steel and aluminum alloy 2017- 500 kg, 10 mm ball ...... 113 110 difficult to machine, and they produce chips T4 with comparable mechanical properties 3000 kg, 10 mm ball ...... 132 128 that are difficult to control. The softer al- (a) Yield point is 309 MPa (44.8 ksi). loys 5052, 3003, and 1100 are likely to produce gummy chips. Wrought alloy 4032 Bar Versus Tubing and cast alloys 220, 13, and A132 are quite abrasive, and high rates of tool wear result. Many parts can be machined equally well Selection of The following example describes an appli- from either bar stock or tubing. When either Alloy and Temper cation in which a change to an alloy and of these product forms can be used, cost per temper having better machinability im- piece machined is the determining factor. An application often dictates the use of a proved results. Initial cost of bar versus tube, cost of addi- specific alloy or temper or both. Under Example 1: Change of Alloy 6061-T6 tional machining to make the part from bar these conditions, composition cannot be to 6262-T9 to Improve Machinability of stock, and value of the additional scrap that changed for the sake of improving machin- Hexagonal Nut. When alloy 6061-T6 was results from machining bar stock must be ability. However, there is often a marked used for a hexagonal nut (Fig. 4), a lead of considered to determine cost. Because of difference in machinability among different three threads chamfer on the tap form was the high cost of producing small tubing, tempers of the same alloy. Therefore, it required to produce a thread without tear- total cost per piece machined may be great- may be feasible to do some or all of the ing. A length of 4.8 mm (3/16 in.) had to be er when tubing of small sizes (less than machining operations with the alloy in the cut off after tapping. After changing to the about 32 mm, or 11/4 in., in diameter) is most favorable condition for machining and freer-cutting 6262-T9, lead was reduced to used. For parts requiring a diameter greater then to convert the alloy to the temper 11/2 threads, so that only 3.2 mm (I/8 in.) had than 32 mm (I !/4 in.), tubing is usually less specified for the end use. to be cut off. Material savings was 8.5%. expensive. For some applications, two or more al- Because 6262-T9 produced fewer burrs on loys are equally acceptable. Under these the tapped threads, frequency of tool grind- General Machining conditions, machinability can be a major ing was reduced. Conditions consideration in making the final selection. With 6061-T6, the workpiece before tap- For example, high-strength, free-cutting al- ping weighed 0.0254 kg (0.0560 lb), and with Power requirements for machining are loy 2011 can be machined to an excellent 6262-T9, it weighed 0.0232 kg (0.0512 Ib). proportional to speed and cutting force, and surface finish at high speed and feed, with a Production rate was 890 pieces per hour the power lost in the bearings and gears of low rate of tool wear. The chips formed are with both alloys. the machine increases with speed. Power requirements for machining aluminum decrease somewhat as the rake angle of the cutting tool is increased. Table 3 lists typi- Feed, in./rev cal power requirements for several wrought 0.001 0.002 0.004 0.006 0.01 0.02 and cast alloys, as measured at the cutter 61 5.0 with single-point tools having 0 and 20 ° rake 4.0 angles. The cutting force for aluminum alloys 2017-T4 can vary widely at low speeds, such as 30 to 3.4 ~-' (i.) V : 9.94f025 60 rrdmin (100 to 200 sfm), rising momen- ¢- NHP tarily to peak values several times higher ~t.¢-~d C~..- 2.0 ~"~ than normal. At higher speeds, the cutting a~ E ~'~ E > _ S=S °E, E,_- E Hot-rolled low-carbon steel s_ x 15 Original alloy" _JL-. 4-, 12 V : 2.24f017 1.0 ~ 6061-T6 NHP ~ O~.,~,--,,,~1r -'"~" Changed to: 0.8 ~ 5 6262-T9

0.6 § --I I thread 6.1 0.5 0.025 0.05 0.10 0.15 0.25 0.50 Feed, mm/rev F i g. 4 Hexagonal nut for which a change from alloy 6061-T6 to 6262-T9 resulted in a savings of Fig. 3 The effect of feed on metal removal rate per net power for low-carbon steel and aluminum alloy 2017-T4 material and less burring of the tapped thread. Dimen- with comparable mechanical properties. V/NHP, volume per net horsepower sions given in inches Machining of Aluminum and Aluminum Alloys / 765

Table 3 Power requirements for machining aluminum alloys Speed, sfm 200 400 600 800 1000 Power ] 1550 w 350 J 0 ° rake 20 ° rake Alloy ~kW/mm3/min) x 10-4 hp/in.~/minj ~kW/mm3/min)x 10-4 hp/in.3/mi2 Tools: high-speed steel 1330 Tool form: ASA 300 FI32-T5 ...... 0.16--0.32 0.20--0.40 0.16--0.41 0.20--0.50 0 °,0 °,7 °,15 ° ,15 ° , 356-T51 ...... 0.20--0.36 0.25--0.45 0.24--0.81 0.30-1.00 0.40 mm 2011 -T3 ...... 0.12-0.20 0.15--0.25 0.16-0.24 0.20--0.30 1110 Feed: 0.264 mm/rev 250 2024-T351 ...... 0.16--0.32 0.20--0.40 0.24-0.41 0.30--0.50 Depth of cut: 2.54 mm 6061 -T651 ...... 0.20-0.28 0.25--0.35 0.24--0.41 0.30--0.50 z 890 ~q I I 200 -~ a; 6061-T651 o O ,1 2024-T351- 150 o Table 4 Design of single-point tools for machining aluminum alloys of A and B machinability ratings 100 \ ;356-T51 High-speed steel I l Carbide I 2011-T3 Tool details J Roughing Finishing Roughing Finishing F132-T5 220 50 Back rake, degrees ...... 20 20 20 20 Side rake, degrees ...... 20 20 20 20 0 End relief, degrees ...... 10 10 7 7 30 90 150 215 275 335 Side relief, degrees ...... 10 10 7 7 End cutting edge, degrees ...... 5 5 5 5 Speed, m/min Side cutting edge, degrees ...... 10 10 10 10 Nose radius, mm (in.) ...... 1.6 (0.063) 5.1 (0.20) 1.6 (0.063) 5.1 (0.20) •1~;"- 5 The effect of speed on cutting force for five F aluminum alloys

force for machining 2011-T3 alloy rises aerospace applications (see the article chucking equipment, power of the ma- slightly with increasing speed, but for most "High-Speed Machining" in this Volume). chine tool, and amount of stock to be re- alloys it decreases. The overall effect of Even higher speeds have been achieved moved in order to minimize the number speed on cutting force is small. As speed with experimental equipment. However, in of cuts required. As depth of cut is in- increases up to about 300 m/min (1000 sfm), most practice, mainly because of the limita- creased, cutting force increases. Depth cutting force changes slightly; above 300 m/ tions imposed by available spindle speed, of cut must be limited to a value that will min (1000 sfm), the effect of speed is negli- available horsepower, and dynamic balance not distort the workpiece or cause it to gible. Increasing the speed does not pro- of the part, machining speeds are seldom slip, nor overload the machine. Depth of duce much more heat, but it does shorten higher than 900 m/min (3000 sfm) and they cut in roughing may be as high as 6.35 mm the time available for removing the heat are more commonly less than 300 m/min (0.250 in.) for small work or up to 38.10 from the tool. The effect of speed on cutting (1000 sfm), as indicated by the examples in mm (1.500 in.) for medium or large work. force for several aluminum alloys is plotted this article. At the opposite extreme, depth of cut in in Fig. 5. Heating of tool surfaces is not Cutting speed should be as high as is finishing is often less than 0.635 mm (0.025 sufficient to have a harmful effect on a practical in order to save time and to mini- in.). high-speed steel tool until the speed ex- mize temperature rise in the part, as de- Feed will depend on the finish desired and ceeds about 215 m/min (700 sfm). High- scribed in the section "Thermal Expan- on the strength and rigidity of the workpiece speed steel can be used for speeds well sion" in this article. As cutting speed is and of the machine. Finishing cuts require a beyond this limit, but carbide tools are increased above 30 to 60 m/min (100 to 200 light feed of 0.05 to 0.15 mm/rev (0.002 to recommended for long tool life. sfm), the probability of forming a built-up 0.006 in./rev); rough cuts may use a feed of The culling speed for aluminum alloys is edge on the cutter is reduced, chips break 0.15 to 2.03 mm/rev (0.006 to 0.080 in./rev). determined by the limits of the machine tool more readily, and finish is improved. Alloys with machinability ratings of D and and by the workpiece. Speeds as high as Depth of cut should be as great as E are best machined with a feed in the lower 4600 m/min (15 000 sfm) have been used in possible within the limits of part strength, end of the range.

Table 5 Current machining practice for 390 aluminum alloy Speed, Depth, Operation Tool mm/min (shn) Feed mm (in.) Coolant Turning ...... Tungsten carbide, with J polish 30-150 0.13--0.51 mm/rev 0.13-5.1 Soluble oil (20-1) (SPG 422 insert) (100--500) (0.005-0.02 in./rev) (0.005-0.20) Diamond (SPG 422 insert) 310-910 0.08--0.38 mm/rev 0.13-3.8 Soluble oil (20-1) (1000-3000) (0.003-0.015 in./rev) (0.005-0.15) Milling ...... Tungsten carbide, C-2 or C-3, 5-10 ° 99-175 0.10--0.30 mm/tooth 0.13-5.1 Soluble oil (15" 1) or dry rake, 7-15 ° shear (325-575) (0.004--0.012 in./tooth) (0.005-0.20) Diamond, 5-10 ° rake, 7-15 ° shear 400-790 0.10-0.20 mm/tooth 0.20-I .0 Soluble oil (15"1) or dry (1300-2600) (0.004-0.008 in./tooth) (0.OO8--O.O40) Drilling ...... High-speed steel, high helix 20 381 mm/min 6 x diam Soluble oil (20:1), 19 L/min (5 (70) (15 in./min) gal./min) at 170 kPa (25 psi) Tungsten carbide tipped, coolant fed 90 508 mm/min 6 x diam Soluble oil (20:1), 34 L/min (9 (300) (20 in./min) gai./min) at 3.4 MPa (500 psi) Tapping ...... Form taps, with four lobes 20 By pitch 6 x diam Soluble oil (20:1), 19 L/rain (5 (70) gal./min) at 170 kPa (25 psi) Broaching ...... Tungsten carbide, 0 ° shear, 5 ° rake 45 229 mm/min 0.13 Soluble oil (20:1) or dry (150) (9 in./min) (0.005) Source: Ref 2 766 / Machining of Specific Metals and Alloys

Table 6 Cutting fluids for aluminum Type of lubricant Principal ingredients Viscosity range Application; mlntemmce Relative effectiveness Necessary precautions Mineral oils Mineral oil, lard, or 40 SUS at 40 °C Generous flow at all Good lubricity and chip Control air above oil where (fatty-additive type neats-foot oil; oleic acid (100 °F) for cutting edges; keep flushing; fair cooling; mist application endangers preferred) or butyl stearate high-speed machining recirculating fluid excellent finish as shop air; remove oil from to 300 SUS for low clean and cool. built-up edge is finished parts (also from speeds minimized chips to reclaim and reduce fire hazard). Soluble oils Soluble oil, petroleum Generally low Generous flow at all Good chip flushing; For high-speed machining, (emulsions) (3--5% sulfonate emulsifying cutting edges; keep lubrication adjustable cooling is more important soluble oil in water) agents, water (oil is recirculating fluid by varying than lubrication; where added); rust inhibitor, clean; cool when concentration; emulsion is applied as mist, germicide, stain inhibitor necessary, excellent cooling; keep oil content as low as good finish possible to reduce air and shop contamination. Aqueous chemical Water; soluble synthetics Generally low Generous flow at all Good chip flushing; Keep oil content low; control solutions (usually clear); cutting edges; keep excellent visibility of mist; consider cost sometimes, fatty recirculating fluid cut; excellent cooling; (significantly higher than materials; rust inhibitors; clean; cool as adjustable lubrication; soluble-oil emulsions). germicides required, good finish Stick lubricants Mineral compounds, animal Various hardnesses Applied as required to Prevents the loading of Application is intermittent, but fats, waxes, synthetics blades, wheels, abrasive surfaces or should be monitored and disks, or files or to of teeth of saws and made as required throughout workpiece files run. Source: Ref 1

Tool Design angles, as related to alloy machinability Clearance angle is important to proper rating (Table l), are: functioning of the tool. Too small a clear- Tools intended for machining aluminum ance will permit the side or heel of the tool and its softer alloys should be ground to to rub the work and generate heat, while too Rating Rake angle, degrees allow considerably more side rake and back large an angle will cause the tool to dig into rake than are customary when machining A ...... 0-20 the work and chatter. This angle must be B ...... 20 steel. Therefore, they approach the con- C ...... 20-30 carried around the side of the tool that tours of tools designed for cutting hard- D ...... 40 advances into the work. For most applica- wood. The larger rake angles are recom- E ...... 40 tions, clearance angles of 6 to l0 ° are suit- mended for finishing tools and for the able. The side rake angle imparts to the tool machining of alloys that are not free cutting, a slicing action that assists materially in especially the softer alloys, which require Tool forms for machining aluminum al- sheafing the chip from the stock. This angle exceptionally acute and keen cutting edges. loys with machinability ratings of A and B is important and should be held within the Smaller rake angles can be used for the with single-point tools are given in Table 4. ranges recommended in subsequent sec- free-cutting alloys and for roughing cuts, Variations of these may be desirable, de- tions of this article. which require a sturdy tool for the heavier pending on machining conditions or shape Cutting Edge Finish. For maximum per- cuts and feeds employed. Suggested rake of the workpiece. formance, it is essential that tool cutting edges be keen, smooth, and free of grinding- wheel scratches, burrs, or wire edges. Keen edges can be obtained by finish grinding on a fine abrasive wheel and then lapping, or hand stoning with a fine oilstone. Neither the angles nor the contour of the cutting edge should be appreciably modified during tool finishing.

Tool Material Water-hardening tool steel, such as W I, heat treated to 65 to 68 HRC, is an adequate cutting tool material when production runs are short and speeds are low. However, tool steels of this type soften rapidly if the temperature of the cutting edge exceeds 150 °C (300 °F). In addition, tools made from water-hardening tool steel have low resistance to edge wear. High-speed steel tools are generally satisfactory for machining all but the high- silicon alloys, which are quite abrasive and should be machined with carbide or diamond tools, unless runs are short. For short runs, high-speed steel is usually satisfacto- Fig. 6 Typical spar mill defect at a section change. Courtesy of McDonnell Douglas Canada, Ltd. ry. Complexly shaped cutters such as twist Machining of Aluminum and Aluminum Alloys / 767

drills, reamers and counterbores, taps and other thread-cutting tools, end mills and many other types of milling cutters, and form tools are widely used in turning operations. For general machining and for relatively short-run production, single-point tools of high-speed steel are also commonly used. Grade M2 high-speed tool steel is commonly used in machining aluminum, although M7 is sometimes preferred because it is more suitable for fine-edge tools and is more abrasion resistant. Grade T2 is also used sometimes, as are high-speed steels containing cobalt. (a) Carbide Tools. Because of the brittleness of the tool tip, the lip angle for carbide tools is usually greater than those recommended for high-speed steel tools in order to provide maximum support to the edge. This is indicated in Table 4, in which smaller relief angles are given for carbide tools. The rake angles can also be decreased to zero or negative to increase the lip angle, but negative rake angles are generally not recommended. When very light finishing cuts are made, it is sometimes feasible to reverse

this practice and use higher rake angles and ...... smaller lip angles. Carbide tools retain sharp edges over a (b) longer period between regrinds than carbon .m~l~|emo 7 Typical end mill defect associated with vertical plunge cut pocketing operations. (a) Front view. (b) Back or high-speed steel tools, provided they are view. Courtesy of McDonnell Douglas Canada, Ltd. not used for heavy, intermittent cuts. A better finish is obtained because of the hardness of the tool tip compared to that of the stock. Carbide tools are particularly useful for machining high-silicon alloys, many of which cannot otherwise be machined satisfactorily under production conditions. For longer production runs, cemented tungsten carbide tooling is generally the choice for machining low-silicon alloys and is often used for high-silicon alloys. The primary advantage offered by carbides in the machining of easily machined aluminum alloys is the greatly increased cutting speed possible compared to high-speed steel tooling--double or more the metal removal rates possible with the latter. Both brazed-tip and indexable inserts are suitable. Straight-tungsten carbides are recommended in the C-2 to C-3 application categories. Some carbide specialists recommend fine-grain carbides for aluminum because a keener edge can be produced and because any edge chipping is small and therefore has a smaller effect on sharpness. Edge sharpness is desirable for cutting alu- Fig. 8 Milling defect associated with the NC machining of 7075-T7651 aluminum plate with a 75 mm (3 in.) diam minum. milling cutter. Courtesy of McDonnell Douglas Canada, Ltd. Coatings, which have proved to be highly advantageous in many steel machining operations, do not appear to provide any ben- Diamond tools are used only in opera- Single-crystal natural diamond cutting efits in the machining of aluminum alloys. tions requiring an exceptionally high finish, tools have long been used for producing Indeed, vacuum-deposited coatings have a particularly on high-silicon alloys, in which very smooth finishes on turned aluminum detrimental effect on the smoothness of the particles of free silicon will in time slightly workpiecesmfinishes of the order of 0.125 rake face of an insert, and all aluminum dull the cutting edge of even carbide tools. ixm (5 I~in.) roughness and better. For ex- machining specialists stress the need for Finishing cuts with diamond tools seldom ample, the lens barrels of even relatively highly polished cutters in any material. exceed a few thousandths of an inch. inexpensive cameras are often turned with 768 / Machining of Specific Metals and Alloys

practical limit, which is acceptable in most applications. Because the crystal orientation is ran- dom, impact resistance is high, and the properties are essentially omnidirectional. In contrast, single-crystal stones require careful orientation of the crystal for optimum utilization of properties. Another advantage over natural stones is that tool tips can be produced virtually to final shape, Fig. 9 Attachmenttee madeof 7075-T6aluminum with the soft spot area havinga hardness of 73 to 83 HRB saving considerable effort for the toolmak- comparedto 90 HRB for the rest of the structure. Courtesy of McDonnell Douglas Canada, Ltd. er, and the use of a carbide substrate permits easy brazing of the polycrystalline tip c-" to a tool steel shank or standard-size insert. Q Initially introduced in the United States in 1972, polycrystalline diamond tooling has Milling cutter gained an important position in the machining of the highly abrasive silicon-aluminum

f alloys. Typical production operations in- f Tee clude turning, boring, and milling. Reports \ of polycrystalline diamond tools outlasting Soft spot tungsten carbide by factors as great as 100 t ti/If in the machining of high-silicon aluminum f are not uncommon. More detailed informa- J/7 t tion on polycrystalline diamond tooling can toolinglnsufficient~backut~,f ~/// ::iiii i/~////~ J~~ be found in the article "Ultrahard Tool Materials" in this Volume. Application data for aluminum-silicon alloys follow. f f

Dwell Machining of High-Silicon • Direction Aluminum Alloy 390 (Ref 2) of cut Microstructural Considerations. Be- cause of the presence of primary silicon in the microstructure, the machining of aluminum-silicon alloys such as 390 must be approached somewhat differently from the machining of conventional aluminum casting alloys. The major alloying ingredients are 17% Si, 4.5% Cu, and 0.5% Mg. The Fig. 10 Schematic of the milling cutter path in machiningthe attachmenttee shown in Fig. 9 eutectic composition is approximately 12% Si; the remaining 5 to 6% Si occurs as a primary phase. This primary-phase silicon single-crystal diamond tools, and no further having a major effect in many aluminum is desirable in wear parts, but it affects finishing operations are performed. machining operations has been the intro- cutting tool life drastically when machining The principal advantages of single-crystal duction of compacted polycrystalline dia- alloy 390. The 390 silicon-aluminum alloy diamond for machining aluminum are the mond cutting tools. Polycrystalline dia- machines differently from other cast alumi- ability to take an extremely fine edge, the mond is produced by a technique that num alloys, such as 319 (5.5 to 6.5% Si), and highest known hardness and wear resis- includes pressing gritlike diamond particles 380 (7.5 to 9.5% Si), in that the primary tance, and an extremely low coefficient of in a mold under pressures and temper- silicon causes rapid tool wear. Alloy 390 friction with no tendency to adhere. In atures approaching those necessary to con- was originally developed for use in engines addition, there is no chemical reaction be- vert carbon into synthetic diamond. Natural in which the cylinder bore is finished in tween the carbon of diamond and alumi- or synthetic diamond particles can be such a manner that primary silicon stands in num. used as the raw material, and it is possible relief and prevents piston tings, and so on, Diamond tools are usually made with to produce a compacted polycrystalline from contacting the aluminum matrix. either circular or faceted cutting edges, the diamond surface on a tungsten carbide sub- Most aluminum casting alloys contain sil- latter being the more common. With the strate. icon as a major alloying element. Silicon, in faceted cutter, there may be as many as five Polycrystalline diamond, being true dia- either eutectic or primary form, is much facets on one cutting edge, each varying in mond, possesses the basic physical and harder than any other phase of the micro- size from 0.5 to 1.5 mm (0.02 to 0.06 in.). chemical properties that make single-crystal structure. The hardness of silicon crystals Cutting angles of 74 to 90 ° and top rake diamond a valuable tool material for ma- generally ranges from 1000 to 1300 HK, angles of 6 to 10° are used. Rake should not chining aluminum, but it does differ in sev- while the microhardness of an aluminum be less than -6 ° . The tool should be set on, eral respects. Because it is polycrystalline, casting alloy matrix seldom exceeds 180 or slightly above, the centerline of the it cannot produce as fine an edge as single- HK. Silicon, like the heavy-element inter- work. crystal diamond. Therefore, it is not suit- metallic impurity phases of iron, manga- Polycrystalline Diamond Tooling (Ref able for producing the finest finishes; about nese, and chromium, is a very abrasive 1). A development of recent years that is 0.125 to 0.25 I~m (5 to 10 Ixin.) is the material in an otherwise soft matrix and is Machining of Aluminum and Aluminum Alloys / 769

41P

•~i:i ~:iii~:i;!~!}i ii:: :iiiiiiii~:~i~iii~i~iii~!!i~!i~i~i~ii~!!~ii~!~iii!~!~!i!i!~i~i~i~i~i!i~i}!~.~i~i!~i~3!~i~i~!~ .~,~ ....::+

"'IiI1~|'" I 2 Two views of a milling defect on an unsupported vertical flange in a 7075- T651 aluminum plate. Courtesy of McDonnell Douglas Canada, Ltd.

cutting tools. Turning with carbide should be limited to relatively slow cutting speeds (30 to 150 m/min, or 100 to 500 sfm) to ensure adequate tool life. Tool life can be greatly improved and cutting speeds sub- stantially increased through the use of poly- Fig. 1 I Occurrence of soft spots in the same location on each of three 7075-T651 aluminum plate components. crystalline diamond tools. The productivity Of the 19 parts produced, 13 had a soft zone hardness of 68 to 87 HRB and conductivity of 36 to 39%. increase (300 to 900 m/min, or 1000 to 3000 Unaffected regions of the plate had a hardness of 90 to 91 HRB and conductivity of 31 to 32%. Courtesy of McDonnell Douglas Canada, Ltd. sfm) can more than offset the higher cost of the diamond. Similar results have been experienced for Causes of overheating milling alloy 390. Milling with carbide during mach~mng should be done at slow speeds (99 to 175 m/ min, or 325 to 575 sfm) with or without I coolant. Milling with polycrystalline dia- I I mond can be done at speeds of 400 to 790 m/ Frict0on Low heat absorpt0on min (1300 to 2600 sfm) (with or without coolant) and with much longer tool life. The drilling of alloy 390 can be accom- Slow feed rateI (dwell0ng) Inadequate backupI fixtures plished using high-speed steel, high-helix Less-than-opt0mum cutter Poor clamp0ng drills with parabolic flutes at a speed of 20 m/min (70 sfm) for holes up to six times Lack of cutting fluid Part vibrat0on diameter in depth. Much better productivity Heavy end m011 plunge culs can be achieved by using tungsten-carbide- Fig. 1 3 Causes of overheating during machining process attributable to friction and low heat absorption tip, coolant-fed drills at 90 m/rain (300 sfm). problems In addition, diamond-tip, coolant-fed gun drills have achieved even higher productivity gains with much better tool life in holes the element that singularly has the greatest size in conventional die castings is very up to eight times diameter. tendency to decrease cutting tool life. small even without phosphorus refinement, Thread forming taps have the longest tool A fine, well-modified eutectic silicon and the silicon size and distribution are life and can be run at speeds to 20 m/min (70 structure is far less detrimental to tool life controlled by such process parameters as sfm). They also produce stronger threads than heavy-element intermetallic impurity melt temperature, die temperature, and die than thread cutting taps. phases. However, the rate of wear on cut- fill rate. The use of generous quantities of coolant ting tools increases as silicon particle size Regardless of the casting method em- is imperative when drilling and tapping alloy increases. If the eutectic silicon structure is ployed, primary silicon acts as a chip break- 390. The coolant must be in sufficient vol- coarse, tool life suffers. Primary silicon er. Although primary silicon crystals are ume and pressure to reach the bottom of the crystals, even if well refined and distribut- very hard, they are also quite friable. When hole and flush out the chips. These chips are ed, are more detrimental than eutectic sili- the cutting tool passes through the matrix of very abrasive to the cutting tool. con, and large unrefined primary crystals the alloy, it fractures primary silicon parti- The broaching of alloy 390 can be accom- can seriously degrade tool life. cles. This fracturing, along with the natural plished with the same speeds, tool geome- In permanent mold or sand casting, pri- hardness of the alloy and work hardening of tries, and materials used to broach gray mary silicon is controlled by a refinement the chips, causes the close, tightly curled iron. Tool life will be much better, and the treatment, adding a small amount of phos- chips to break into short ringlets similar in surface finish will be comparable to, or phorus to the molten alloy. Unrefined pri- appearance to gray iron chips. better than, the finish typical of gray iron. mary silicon is eight to ten times the size of Machining Parameters. Table 5 lists in- The machining of alloy 390 in recent refined silicon crystal, and it drastically formation regarding tools and cutting con- years has been much improved. This has affects machinability. ditions for machining alloy 390. The turning been accomplished through the application In conventional die casting, a refinement of alloy 390 can be performed using C-3 of new technology in cutting tool materials treatment is not necessary. Primary silicon tungsten carbide or polycrystalline diamond and in tool designs, optimization of cutting 770 / Machining of Specific Metals and Alloys

Table 7 Suggested practices for both are seldom used and are not usually Cutting speed, sfm turning aluminum on required for machining aluminum. In addi- 500 1000 2000 4000 6000 general-purpose equipment tion, many of them will stain the work. 300 t,~ Table 6 lists various cutting fluids and their The suggested practices are commonly used, but higher 200 390 die cas speeds, feeds, and depths of cut can be employed in applications. diamond, ,,,,,~ many cases (depending on the nature of the part, Soluble oil mixed with water in ratios of wet ~X machine tool, tool design, lubrication, and other l part oil to 20 to 30 parts water is the cutting conditions) to increase production rates. 380 die cast, \ cutting fluid most widely used for machin- tungsten carbide, \ Variable and condition Suggested practice ing aluminum alloys. Soluble-oil emulsions 1O0 ~ wet Back rake angle, degrees ...... 5-15 are inexpensive, highly efficient for cooling ._ \ E Side rake angle, degrees and removing chips, and are usually ade- 60 \ Machinability rating A ...... 0-20 quate for preventing built-up edges. - Machinability rating B ...... 20 -o \ \ Machinability rating C ...... 20-30 Mineral oil used as a cutting fluid may ~- 40 / ~ \ \ Machinability rating D, E ... 40 contain a fatty additive, such as lard oil, End relief angle clearance, ~ 390 die castX ~~x \ \ neat's-foot oil, oleic acid, or butyl stearate. tungsten degrees However, mineral oil that contains no addi- carbide, \ ~, X High-speed steel tool ...... 8-15 tive and that has a viscosity of 40 to 300 20 ~'\\ wet I \ \ Carbide tool ...... 6-8 \ I Side relief angle, degrees Saybolt universal seconds (SUS) at 40 °C 390 sand cast, 390 sand cast, High-speed steel tool ...... 8-15 (100 °F) is most often used. As cutting speed tungsten carbide, diamond, Carbide tool ...... 6--8 is increased, the viscosity of the oil should dry dry End cutting edge angle, o I i degrees ...... 5 be decreased to provide easier flow and 150 300 610 1200 1800 Side cutting edge angle, therefore greater cooling. Straight mineral Cutting speed, m/min degrees ...... 5-15 seal oil (--40 SUS at 40 °C, or 100 °F) has Nose radius, mm (in.) been effective in many applications. Kero- -,ul::"- 1 4 Tool li~e curves for the dry turning of sand Rough cutting ...... 0.8-3.2 (I/32-1/8) sene, which is slightly less viscous than cast alloy 390 using carbide and dia- Finish cutting ...... 0.25--0.76 (0.010-0.030) mond, the wet turning of die cast alloy 390 using carbide Depth of cut, mm (in.) mineral seal oil, is also used. and diamond, and the wet turning of die cast alloy 380 Small work ...... 0.4-6.4 (I/6~--!/4) Chemical solutions are effective as cut- using carbide. Source: Ref 2 Large work ...... 13-38 (I/2-1 I/2) ting fluids for machining aluminum and are Feed, mm/rev (in./rev) Rough cutting ...... 0.15-2.0 (0.006-0.080) especially desirable when a transparent flu- Finish cutting ...... 0.05-0.15 (0.002-0.006) id is needed to permit viewing the work of a mist, while not equal to that of a Speed, m/min (sfm) during machining. These solutions vary in copious flood, is considerable because the High-speed steel tool ...... -<300 (-< 1000) composition, but most contain amines, ni- rapid evaporation of the finely divided drop- Carbide tool ...... -<4600 (-< 15 000) tildes, phosphates, borates, soaps, wetting lets adds the latent heat of vaporization to Source: Ref 4 agents, glycols, and germicides. Some of the cooling capability of the liquid. these solutions stain aluminum alloys. Proponents of the compressed air method Stick grease is sometimes used in band also claim that the high velocity of the Table 8 Nominal speeds for sawing, circular sawing, and abrasive belt, droplets tends to get the fluid into the cut- turning aluminum alloys abrasive disk, or abrasive wheel polishing ting zone effectively and that the evapora- I Speed, m/min (sfm) I and grinding when requirements are not too tion of the water increases the iubricity at Nonheat-treated All other alloys severe and a flood of lubricant is not re- the cut. Visibility into the cutting area is cast alloys and tempers Operation quired. improved, and splash shielding does not High-speed steel tools (M2 or T5) Continuous filtering of cutting fluids for pose as much of a problem as flooding does. the removal of chips, slivers, grindings, and Most experts recommend the use of auto- Single-point roughing ...... 230 (750) 180 (600) Single-point finishing ...... 300 (1000) 240 (800) other foreign material is especially desirable matic shutoff devices for mist systems and Forming and cutoff ...... 170 (550) 140 (450) because aluminum alloys are relatively soft venting to prevent potential air contamina- Carbide tools (C-2) and are easily damaged by a contaminated tion. cutting fluid. Single-point roughing(a) Brazed tips ...... 490 (1600) 340 (I I00) The mist application of cutting fluids is Disposable tips ...... 610 (2000) 430 (1400) sometimes preferred for machining alumi- Distortion and Forming and cutoff ...... 360 (1200) 250 (825) num, especially on such machine tools as Dimensional Variation Note: Speeds for single-point turning are based on a 3.81 mm small, vertical mills and high-speed routers. (0.150 in.) depth of cut and a feed of 0.38 mm/rev (0.015 in./rev) for roughing and a 0.64 mm (0.025 in.) depth of cut and a feed of Compressed air, at pressures ranging from Because aluminum alloys have a low O. 18 mm/rev (0.007 in./rev) for finishing. Speeds for form turning 70 to 550 kPa (10 to 80 psi) is used to modulus of elasticity (---70 GPa, or l0 x l0 6 are based on feeds of 0.089, 0.08, and 0.05 mm/rev (0.0035, 0.003, and 0.002 in./rev) for tool widths of 13, 25, and 50 mm (½, I, and atomize the cutting fluid and propel it into psi), they will distort more than most metals 2 in.), respectively. Speeds for cutoff are based on a feed rate of 0.05 mm/rev (0.002 in./rev). (a) For finish turning, use the maxi- the cutting zone. The technique can be used for a given clamping or chucking force. mum speed of the machine and C-3 carbide. with straight oils (especially of lower vis- Moderate clamping forces should be used to cosities), emulsions, or chemical solutions avoid dimensional variations due to distor- as long as there are no solid additives con- tion. High clamping pressures are not re- conditions, and the replacement of outdated tained in the fluid. Some producers of quired, because cutting forces are low. transfer lines with machine tools designed spray-mist equipment, however, recom- Thermal Expansion. The coefficient of for aluminum alloys. mend the use of water-base fluids over oils thermal expansion of aluminum alloys (l 8 to because the latter may tend to clog and may 25 ixm/m" K, or l0 to 14 i~in./in.PF) is higher Cutting Fluids present a hazard. than that of most metals commonly ma- Although the use of compressed air adds chined. Therefore, the dimensional accura- A cutting fluid for aluminum can be a a new element of cost, the overall cost can cy of finished parts requires that the part be soluble-oil emulsion, a mineral oil, or an often be reduced because of the smaller kept cool during machining. When turning aqueous chemical solution. Cutting oils that volume of fluid used and lower losses of between centers, it is important to avoid contain compounds of sulfur or chlorine or fluid carried out by chips. The cooling effect expansion, which will put excessive pres- Machining of Aluminum and Aluminum Alloys / 771

Table 9 Nominal speeds and feeds for the boring of aluminum alloys with high-speed tool steels and carbide tools I High-speed steel tool I [ Uncoated carbide tool Tool material [ Speed ] Tool material Hardness, Depth of cut Speed Feed grade Brazed Indexable Feed grade Material HB (500 kg) Condition mm in. m/mln sfm mm/rev in./rev iSO AISI m/rain sfm m/min sfm mm/rev in./rev ISO C

Wrought EC 3005 6066 30-80 Cold drawn 0.25 0.010 305 1000 0.075 0.003 $4, $5 M2, M3 610 2000 Max Max 0.15 0.006 K01, MI0 C-3 1060 4032 6070 1.25 0.050 245 800 0.13 0.005 $4, $5 M2, M3 550 1800 Max Max 0.20 0.008 KI0, MI0 C-2 1100 5005 6101 2.5 0.100 215 700 0.30 0.012 $4, $5 M2, M3 365 1200 Max Max 0.40 0.015 K20, M20 C-2 1145 5050 6151 75-150 Solution treated 0.25 0.010 305 1000 0.075 0.003 $4,$5 M2, M3 610 2000 Max Max 0.15 0.006 K01, MI0 C-3 1175 5052 6253 and aged 1.25 0.050 245 800 0.13 0.005 $4, $5 M2, M3 550 1800 Max Max 0.20 0.008 KI0, MI0 C-2 2011 5083 6463 2.5 0.100 215 700 0.30 0.012 $4, $5 M2, M3 365 1200 Max Max 0.40 0.015 K20, M20 C-2 1235 5056 6262 2014 5086 6951 2017 5154 7001 2018 5252 7004 2021 5254 7005 2024 5454 7039 2025 5456 7049 2117 5457 7050 2218 5652 7075 2219 5657 7079 2618 6053 7175 3003 6061 7178 3004 6063

Cast Sand and permanent mold AI40 F332.0 520.0 40-100 As-cast 0.25 0.010 305 1000 0.075 0.003 $4,$5 M2, M3 550 1800 Max Max 0.15 0.006 K01, MI0 C-3 201.0 333.0 535.0 1.25 0.050 245 800 0.13 0.005 $4, $5 M2, M3 365 1200 Max Max 0.20 0.008 KI0, MI0 C-2 208.0 354.0 705.0 2.5 0.100 215 700 0.30 0.012 $4, $5 M2, M3 305 1000 Max Max 0.40 0.015 K20, M20 C-2 213.0 355.0 707.0 70-125 Solution treated 0.25 0.010 230 750 0.075 0.003 $4,$5 M2, M3 550 1800 Max Max 0.15 0.006 K01, MI0 C-3 222.0 C355.0 A712.0 and aged 1.25 0.050 185 600 0.13 0.005 $4, $5 M2, M3 365 1200 Max Max 0.20 0.008 KI0, MI0 C-2 224.0 356.0 D712.0 2.5 0.100 170 550 0.30 0.012 $4, $5 M2, M3 305 1000 Max Max 0.40 0.015 K20, M20 C-2 242.0 A356.0 713.0 295.0 357.0 771.0 B295.0 359.0 850.0 308.0 B443.0 A850.0 319.0 514.0 B850.0 328.0 A514.0 A332.0 B514.0 Hiduminium RR-350

Die castings 360.0 A380.0 40-100 As-cast 0.25 0.010 305 1000 0.075 0.003 $4, $5 M2, M3 550 1800 Max Max 0.15 0.006 K01, M I0 C-3 A360.0 C443.0 1.25 0.050 245 800 0.13 0.005 $4, $5 M2, M3 365 1200 Max Max 0.20 0.008 KI0, MI0 C-2 380.0 518.0 2.5 0.100 215 700 0.30 0.012 $4, $5 M2, M3 305 1000 Max Max 0.40 0.015 K20, M20 C-2 70-125 Solution treated 0.25 0.010 230 750 0.075 0.003 $4, $5 M2, M3 490 1600 Max Max 0.15 0.006 K01, M I0 C-3 and aged 1.25 0.050 185 600 0.13 0.005 $4, $5 M2, M3 425 1400 Max Max 0.20 0.008 KI0, MI0 C-2 2.5 0.100 145 550 0.30 0.012 $4, $5 M2, M3 245 800 Max Max 0.40 0.015 K20, M20 C-2

383.0 413.0 40-100 As-cast 0.25 0.010 230 750 0.075 0.003 $4, $5 M2, M3 490 1600 Max Max 0.15 0.006 K01, M I0 C-3 A384.0 A413.0 1.25 0.050 185 600 0.13 0.005 $4, $5 M2, M3 425 1400 Max Max 0.20 0.008 KI0, MI0 C-2 2.5 0.100 170 550 0.30 0.012 $4, $5 M2, M3 245 800 Max Max 0.40 0.015 K20, M20 C-2 70-125 Solution treated 0.25 0.010 205 675 0.075 0.003 $4, $5 M2, M3 410 1350 Max Max 0.15 0.006 K01, M I0 C-3 and aged 1.25 0.050 170 550 0.13 0.005 $4, $5 M2, M3 335 II00 Max Max 0.20 0.008 KI0, MI0 C-2 2.5 0.100 145 480 0.30 0.012 $4, $5 M2, M3 260 850 Max Max 0.40 0.015 K20, M20 C-2

390.0 40-100 As-cast 0.25 0.010 46 150 0.075 0.003 $4,$5 M2, M3 125 410 145 480 0.15 0.006 KI0, MI0 C-2 392.0 1.25 0.050 37 120 0.13 0.005 $4, $5 M2, M3 100 325 115 385 0.20 0.008 Ki0, MI0 C-2 2.5 0.100 34 i10 0.30 0.012 $4, $5 M2, M3 90 300 105 350 0.30 0.012 K20, M20 C-2 70--125 Solution treated 0.25 0.010 43 140 0.075 0.003 $4,$5 M2, M3 105 350 125 410 0.15 0.006 KI0, MI0 C-2 and aged 1.25 0.050 34 110 0.13 0.005 $4, $5 M2, M3 85 280 100 330 0.20 0.008 KI0, MI0 C-2 2.5 0.100 30 100 0.30 0.012 $4, $5 M2, M3 70 230 84 275 0.30 0.012 K20, M20 C-2 Source: Ref 5

sure on the centers. High cutting speed Dull tools cause a heat rise in the work- The distortion resulting from machining helps keep the part cool because most of the piece; therefore, cutting tools should be stresses can be minimized or eliminated heat introduced into the part during a given kept sharp, either by employing a series of light cuts as rotation is removed with the chip during the Residual stress can be induced by a dull the part approaches finished size or by next rotation, and the time for diffusion of or improperly designed cutter that cold stress relieving the part between rough and heat is short. A cutting fluid is effective in works the surface, by excessive chucking or finish machining. For heat-treatable alloys, removing heat that is not removed with the clamping force, or by faulty clamping. Dis- it is preferable to do all rough machining on chips. Live centers are recommended to tortion from residual stress is most notice- material in the solution-treated and aged minimize frictional heating at the center, able in slender parts, condition, rather than in the annealed con- 772 / Machining of Specific Metals and Alloys

Table 10 Nominal speeds and feeds for the boring of aluminum alloys i__ 2.3805 -==- with diamond tools 2024-T4 ~- 2.3795 I---,,22 ~ ~om20 ~ T6---'~o0.767 Speed, /~/ Hardness, Depth of cut, m/rain Feed, mm/rev Workpiece -~ I 0 28 Material HB (500 kg) Condition mm (in.) (sfm) (in./rev)

Wrought )~~ / 0.015 EC 2218 5252 6253 30-150 All 0.13-0.40 460 0.075--0.15 1060 2219 5254 6262 (0.005--0.015) (1500) (0.003-0.006) ,.oo,o, .I H 1100 2618 5454 6463 0.40-1.25 305 0.15--0.30 1145 3003 5456 6951 (0.015--0.050) (1000) (0.0064).012) diom I ~/' 1175 3004 5457 7001 1.25-3.2 150 0.30--0.50 1235 3005 5652 7004 (0.050-0.125) (500) (0.012-0.020) 2011 4032 5657 7005 0.5625 tool 2014 5005 6053 7039 2017 5050 6061 7049 diom A and B .L within 0.0003 2018 5052 6063 7050 (typical both ends) 2021 5056 6066 7075 B and C @ within 0.0004 TIA, II within 0.0003 (typical both ends) 2024 5083 6070 7079 2025 5086 6101 7175 Speed, at 1200 rev/min, m/min (sfm).. 97 (318) 2117 5154 6151 7178 Feed, mm/min (in./min) ...... 35.6 (1.4) Cutting fluid ...... Kerosene plus Cast proprietary oil Sand and permanent mold Production rate, pieces/h ...... 9 AI40 319.0 357.0 A712.0 40-100 As-cast 0.13-0.40 760 0.075-0.15 Tool life/grind, lineal m (lineal in.) ... 20 (800) 201.0 328.0 359.0 D712.0 (0.005-0.015) (2500) (0.003-0.006) 208.0 A332.0 B443.0 713.0 0.40-1.25 610 0.15--0.30 ,u:'- 1 5 eoughand finish boring of a heat-treated 213.0 F332.0 514.0 771.0 (0.015--0.050) (2000) (0.006-0.012) F aluminum alloy forging. Dimensions in 222.0 333.0 A514.0 850.0 1.25-3.2 305 0.30--0.50 figure given in inches 224.0 354.0 B514.0 A850.0 (0.050--0.125) (1000) (0.012-0.020) 242.0 355.0 520.0 B850.0 70-125 Solution treated 0.13--0.40 670 0.075-0.15 295.0 C355.0 535.0 and aged (0.005-0.015) (2200) (0.003-0.006) B295.0 356.0 705.0 0.40-I .25 520 O. 15-0.30 chined in the postsolution heat treatment 308.0 A356.0 707.0 (0.015-0.050) (1700) (0.0(04).012) tempers, the resultant effect is overaging, Hiduminium RR-350 1.25-3.2 215 0.30--0.50 softening, and therefore loss of strength. (0.050-0.125) (700) (0.012-0.020) Such defects, referred to as soft spots, Die castings 360.0 A380.0 40-100 As-cast 0.13-0.40 915 0.075-0.15 are usually invisible and may remain unde- A360.0 C443.0 (0.005-0.015) (3000) (0.003-0.006) tected at this stage except where hardness 380.0 518.0 0.40-1.25 760 0. ! 5--0.30 and/or conductivity testing is performed in 383.0 (0.015-0.050) (2500) (0.006-0.012) the overheated area. However, anodizing 1.25-3.2 610 0.30--0.50 (0.050-0.125) (2000) (0.012-0.020) has the capability to reveal these defects. Locally overheated and softened areas are A384.0 40-100 As-cast O. 13--0.40 760 0.075-0.15 indicated by a color contrast against the 413.0 (0.005-0.015) (2500) (0.003-0.006) background of the normal anodic film. The A413.0 0.40-1.25 610 0.15-0.30 390.0 (0.015-0.050) (2000) (0.006--0.012) area is always very local on the parts, and !.25-3.2 460 0.30--0.50 its shape is usually related to the machine (0.050-0.125) (1500) (0.012-0.020) cutting tool that profiled the particular area. Frequently, the soft areas are at or near 392.0 40-100 As-cast 0.13-0.40 610 0.075-0.15 (0.005--0.015) (2000) (0.003-0.006) changes of section thickness. In addition, 0.40-1.25 460 0.15--0.30 there is often exact repeatability of the soft (0.015--0.050) (1500) (0.006--0.012) spot location in all other parts of the batch. 1.25-3.2 305 0.30-0.50 Figure 6 illustrates a half-moon defect (0.050-0.125) (1000) (0.012--0.020) associated with spar milling deficiencies in Source" Ref 5 an area adjacent to a change in section thickness. Figure 7 shows a circular indica- tion that is associated with vertical plunge cut pocketing operations using an end mill. The 25 mm (1 in.) diameter of the soft spot dition, because the less ductile structure is ly, no variations in dimensions are encoun- is a function of the end mill diameter. Figure more machinable. tered. However, when low cutting forces 8 shows a similar example of a milling The distortion resulting from machining (typical of those required for machining problem that occurred in a numerically con- stress can often be minimized by purchasing aluminum) are combined with a small feed trolled (NC) machining application using a the alloy in a stress-relieved condition, nor- and light cut, the total force may be insuf- 75 mm (3 in.) diam cutter. mally designated by T451, T651, or T851 if ficient to overcome tool-slide friction. A different type of problem is illustrated the metal has been stress relieved by Then, some movement may still occur, and in Fig. 9. Two silver-white defective areas stretching. The code Tx52 denotes stress the tool may float. are clearly visible on the tee section part relief by compression; Tx53, stress relief by machined from an extrusion. All 36 parts in heat treating. Soft Spots in Machined the batch were similarly affected. The de- A major source of dimensional variation Aluminum Parts (Ref 3) fects are attributed to a lack of full-support arises from the presence of movement, or tooling backup that did not provide an ade- play, in the feed mechanism of the machine. Machining practices that are less than quate heat sink. The milling cutter was When the tool or the machining conditions optimum may cause localized overheating allowed to dwell at the start of the rebate cause forces that take up the play complete- in aluminum alloys. In alloys being ma- cut, thus introducing frictional heating. The Machining of Aluminum and Aluminum Alloys / 773

Table 11 Nominal speeds and feeds for the planing of aluminum alloys with high-speed tool steels and carbide tools I High-speed steel tool I I Carbide tool Tool Tool Depth of Speed, Feed, material Speed, Feed, material Hardness, cut, mm m/min mm/stroke grade,ISO m/min mm/stroke grade, ISO Material HB (500 kg) Condition (in.) (sfm) (in./stroke) (AISI) (sfm) (in./stroke) (C grade) Wrought EC 2218 5252 6253 30--80 Cold drawn 0.25 90 (a) $4, $5 90 (a) KI0, MI0 1060 2219 5254 6262 (0.010) (300) (a) (M2, M3) (300) (a) (C-2) 1100 2618 5454 6463 2.5 90 3.20 $4, $5 90 3.20 K20, M20 1145 3003 5456 6951 (0.100) (300) (0.125) (M2, M3) (300) (0.125) (C-2) 1175 3004 5457 7001 12 90 2.30 $4, $5 90 2.30 K30, M30 1235 3005 5652 7004 (0.500) (300) (0.090) (M2, M3) (300) (0.090) (C-2) 2011 4032 5657 7005 75-150 Solution treated and aged 0.25 90 (a) $4, $5 90 (a) K10, MI0 2014 5005 6053 7039 (0.010) (300) (a) (M2, M3) (300) (a) (C-2) 2017 5050 6061 7049 2.5 90 3.20 $4, $5 90 3.20 K20, M20 2018 5052 6063 7050 (0.100) (300) (0.125) (M2, M3) (300) (0.125) (C-2) 2021 5056 6066 7075 12 90 2.30 $4, $5 90 2.30 K30, M30 2024 5083 6070 7079 (0.500) (300) (0.090) (M2, M3) (300) (0.090) (C-2) 2025 5086 6101 7175 2117 5154 6151 7178 Cast Sand and permanent mold AI40 319.0 357.0 A712.0 40--100 As-cast 0.25 90 (a) $4, $5 90 (a) KI0, MI0 201.0 328.0 359.0 D712.0 (0.010) (300) (a) (M2, M3) (300) (a) (C-2) 208.0 A332.0 B443.0 713.0 2.5 90 3.20 $4, $5 90 3.20 K20, M20 213.0 F332.0 514.0 771.0 (0.100) (300) (0.125) (M2, M3) (300) (0.125) (C-2) 222.0 333.0 A514.0 850.0 12 90 2.30 $4, $5 90 2.30 K30, M30 224.0 354.0 B514.0 A850.0 (0.500) (300) (0.040) (M2, M3) (300) (0.090) (C-2) 242.0 355.0 520.0 B850.0 70-125 Solution treated and aged 0.25 90 (a) $4, $5 90 (a) KI0, MI0 295.0 C355.0 535.0 (0.010) (300) (a) (M2, M3) (300) (a) (C-2) B295.0 356.0 705.0 2.5 90 3.20 $4, $5 90 3.20 K20, M20 308.0 A356.0 707.0 (0.100) (300) (0.125) (M2, M3) (300) (0.125) (C-2) Hiduminium RR-350 12 90 2.30 $4, $5 90 2.30 K30, M30 (0.500) (300) (0.090) (M2, M3) (300) (0.090) (C-2) (a) Feed : 3/4 the width of square nose finishing tool. Source: Ref 5

part was then turned over, and the opera- niques, tooling, and so on, is always desir- Cutting Fluids. An adequate and contin- tion was repeated, thus producing an oppo- able. uous flow of cutting fluid (flood or mist) site soft spot. The milling sequence is out- Cutters. All tools should be kept sharp directed at the cutting edges is essential. lined in Fig. 10. This illustrates clearly the and in good condition at all times. Tool The flow of cutting fluid should begin before phenomenon of soft spot location repeat- geometry must be maintained within the cutting and must continue until the cutter ability. established requirements for aluminum al- has been removed from the part. Fluid Another example of soft spot indications loys. circulation must be continuous because is shown in Fig. 11. Of the 19 parts pro- Cutters must have the optimum number even a momentary reduction in flow, such duced in this batch, 13 were affected. The of flutes and the optimum spiral configura- as could be caused by an air lock, may defects are attributed to vibration or distortion for each application. For most applica- result in local overheating. tion at an inadequately clamped edge of the tions, the minimum number of flutes and a Support Fixtures and Clamping Meth- parts during milling on a vacuum chuck. As coarse spiral are more desirable. Clogging ods. Machining backup fixtures must be a result, heat dissipation was restricted. results in rubbing and frictional heating; it rigid and must have sufficient contact area All soft spots have a lower hardness and a can be minimized by maintaining a good and mass to provide an adequate heat ab- higher electrical conductivity than the adja- surface finish in the flutes. sorption capacity. Gaps in modular fixtures cent normal material. The strength reduc- Feeds and speeds must be correct for the should not be excessive. This is especially tion can be significant. operation being performed. In particular, a true in areas adjacent to section changes. In slow feed rate (dwelling) combined with addition, it is vital that clamping methods Sources of high spindle speeds is especially trouble- maintain continuous contact between part Machining Problems some. Great care must be taken not to and fixtures because even a minute air gap reduce feeds any more than is absolutely due to part distortion or vibration, together Some of the more common machining necessary when the cutter is approaching or with the resultant deeper cutting action, problems are outlined in this section. It is actually machining areas requiring sec- may produce overheated areas. On fiat should be kept in mind that the basic cause tion changes. On multispindle equipment, it parts that are being machined on a vacuum of the defects under discussion is always is vital that sufficient net horsepower be chuck, it is important that the edge seal be excessive heat. This may arise directly by available to each spindle during heavy located as close to the periphery as practical frictional heating and/or indirectly by insuf- roughing cuts. Where practical, when using in order to eliminate vibration and conse- ficient cooling. Because the cause(s) of end mills, deep plunge cuts should ramp in quent gapping around the outer edges. In some problems may be obscure, on-site or start from a predrilled hole and should general, all thin edges are susceptible to analysis of the hardware, machining tech- progress on a multipass basis. heat buildup. Similarly, thin-section vertical 774 / Machining of Specific Metals and Alloys

Table 12 Nominal speeds and feeds per tooth (chip load) for the Wor k piece 2017-T4 broaching of aluminum alloys with high-speed tool steels Chip load, Tool material Hardness, Speed, mm/tooth grade, lSO 0.555 Material HB (500 kg) Condition m/min (st'm) (in./tooth) (AISi or C) Wrought EC 2218 5252 6253 30--80 Cold drawn 12 (40) 0.15 (0.006) $4, $2 (M2, MT) 1060 2219 5254 6262 75-150 Solution treated 12 (40) 0.15 (0.006) $4, $2 (M2, MT) 1100 2618 5454 6463 and aged O. 1145 3003 5456 6951 0:2,9~ spline ID I------I.155------I~ 1175 3004 5457 7001 1235 3005 5652 7004 This surfoce _L to spline ID within 0.0005 "fir ~ 2011 4032 5657 7005 [--- 2014 5005 6053 7039

2017 5050 6061 7049 i o 2018 5052 6063 7050 'R \L_,-~ F'--~ ~- finishing teeth 2021 5056 6066 7075 2 ° semifinishing teeth 2024 5083 6070 7079 I ° roughing teeth 2025 5086 6101 7175 2117 5154 6151 7178 Broach profile Speed, m/min (sfm) ...... 9.1 (30) Cast Feed, mm/tooth (in./tooth) .... 0.05 (0.002) Sand and permanent mold Length of stroke, mm (in.) ... 152 (6) AI40 319.0 357.0 A712.0 40-100 As-cast 12 (40) 0.15 (0.006) $4, $2 (M2, MT) Cutting fluid ...... Soluble oil:water (1:25) 201.0 328.0 359.0 D712.0 70-125 Solution treated 12 (40) 0.15 (0.006) $4, $2 (M2, M7) Setup time, min ...... 30 208.0 A332.0 B443.0 713.0 and aged Production rate, pieces/h ..... 180 213.0 F332.0 514.0 771.0 Tool life/grind ...... 2000 pieces 222.0 333.0 A514.0 850.0 Total tool life ...... 40 000 pieces 224.0 354.0 B514.0 A850.0 242.0 355.0 520.0 B850.0 295.0 C355.0 535.0 Fig 16 Clutch housing and details of broach used • for producing the internal splines. Dimen- B295.0 356.0 705.0 sions in figure given in inches 308.0 A356.0 707.0 Hiduminium RR-350 Source: Ref 5 reason, a fine cutting edge is desirable, and higher clearance angles are generally recommendedm8 to 15 ° for high-speed steel tools, 6 to 10° for carbides, and somewhat webs of pocketed or stiffened parts, for parts is acceptable. Wholesale rejections less for diamonds. which no backup support is practical, are can be avoided by close monitoring of ma- Traditional practice in the machining of also prone to these problems. Figure 12 terial conductivity values in critical areas aluminum has specified high, positive rake illustrates this latter problem on a small during machining, particularly on new angles, both back and side, for high-speed pocketed end fitting in which the effect is parts. As a result, the impact of down- steel and carbide tools, especially for the noticeable on the vertical flanges. stream economic losses and potential major gummier alloys rated D and E in machin- Numerically Controlled Machining Op- operations difficulties (cost of replacement ability. Although these recommendations erations. All of the foregoing consider- parts plus the associated disruptive factors) are specifically for single-point turning op- ations regarding sources of machining prob- can be minimized. erations, they are also generally applicable lems also apply to NC operations. In to other types of tools. In addition, as the addition, however, there is generally less Turning alloy in question increases in Brinell hard- operator involvement or awareness of the ness, in alloying complexity, and in machin- actual machining operation in NC pro- As indicated in Fig. 2 and 3, the cutting ability rating, lower rake angles can be cesses. For example, in some plants, one force, and therefore the power, required to used. operator may attend several machines. turn aluminum is considerably less than that One of the major reasons for using high- Futhermore, the programmer may be less needed to turn low-carbon steel of approx- rake tooling is to prevent, or at least delay, aware of possible pitfalls, and the optimum imately the same hardness and tensile prop- the formation of a built-up edge on the mathematical cutter path may create local erties. cutter. For the same reason and to facilitate potential problems. Dwelling at corners or Tool Design. The recommended angles chip flow, it is universally recommended between subroutines must be strictly avoid- for a single-point lathe tool are given in that all tool surfaces that contact either the ed. Table 7. Cutting angles should be on the workpiece or the chip be given a high pol- Quality Control. The causes of overheat- high end of the ranges for alloys that are not ish. Any grinding marks on the rake face or ing during machining are well recognized heat treatable or that are more ductile than flank of the tool should be parallel to the (Fig. 13). However, the safety margin be- the free-cutting alloys. direction of the chip-flow or the cut, which- tween acceptable and unacceptable practic- Low modulus of elasticity, high ductility, ever is applicable. Grinding marks should es is not wide; therefore, the utmost care and the tendency to stick to tool materials be removed by stoning or polishing. and attention to detail is warranted at all are the principal factors dictating differ- Because carbide tools are more brittle times. ences in the cutting tools used on alumi- than high-speed steel tools, they will chip or The maximum impact of these problems num. Because of its low modulus of elastic- break when the cutting angles are too large. obviously occurs over the short term. The ity, aluminum has a greater tendency to In turning free-cutting alloys, increasing the tendency of these defects to be repetitive in yield, or spring, under the pressure of a side relief or side rake angle, or both, will one batch of parts can raise havoc with a cutting tool. It deforms more than steel reduce the power required. Because the tight production schedule if none of the before the cutter can start to bite. For this power needed for turning aluminum alloys Machining of Aluminum and Aluminum Alloys / 775

Cut, in. x 105 Uncut chip thickness, in. 0 1 2 0.001 0.004 0.007 0.010 0.35 0.014 7.6 I I 300 Rake angle 0 -5 ° 0.30 i i= 0.012 6.3 250 • 5 ° E /k 15 ° :::::L :::L /," - 0.010 0.25 5.0 200 ...: E Cast iron/ oo (D E E E v J v ,,,.- - r" ,-- 0.20 0.008 "" t- r.~ (I.} E 3.80 0 150 ._u~ ,.e ( ) .E ,¢, ,,-. r- 0.15 0.006 (D J m o ii ii /f "-,_ 2.50 ) () 100 0.10 0.004 g~ U') / 390-T5 alloy / 1.25 50 0.05 / ' 0.002

o/----~ 0 0 0 0 1.25 2.5 3.75 5.1 0.025 0.100 0.175 0.255 Cut, mm x 10 6 Uncut chip thickness, mm

Typical tool wear when broaching with a carbide cutting tool at 45 m/min Fig. 18 Surface finish at various depths of cut when broaching 390 aluminum F ig. 17 (~ ~0 s~.) Source: Ref 2 alloy of 100 HB at 45 m/min (150 sfm) with a carbide tool. Although the rake angle varied, the shear angle of the tool was 0 ° in all three cases. Source: Ref 2

is small (about one-third that needed for optimum results (see the section "Ma- For cutoff tools, a feed rate of 0.05 mm/ machining soft low-carbon steel), a turning chining of High-Silicon Aluminum Alloy rev (0.002 in./rev) is usually satisfactory, tool ground with angles that are too large is 390" in this article). regardless of the alloy being turned, the tool likely to hog the work metal. Because the The speed used in turning aluminum al- material, or the width of the cutoff tool. tool floats in operation, any backlash or loys depends to some extent on the alloy Depth of cut in turning aluminum often play in the spindle or machine ways causes and condition, but far more on tool material depends on the power available. The speeds difficulty in holding tolerances. Tool life and type of tool (single-point, form, or given in Table 7 are based on a 3.81 mm and surface finish also suffer. Surface finish cutoff). The effect of alloy composition and (0.150 in.) depth of cut for roughing and 0.64 can be improved by grinding a large nose condition is small in selecting a turning mm (0.025 in.) for finishing. When power is radius on the turning tool. However, the speed, except for the nonheat-treated cast available, roughing cuts of 6.35 mm (0.250 maximum nose radius depends partly on the alloys. in.) are common. Finishing cuts of less than allowable fillet on the workpiece when turn- Nominal speeds for turning aluminum 0.64 mm (0.025 in.) often result in better ing to a shoulder. As the nose radius is with high-speed steel and carbide tools are surface finish. made larger, cutting force and horsepower given in Table 8. These speeds are based on Cutting fluid is recommended for turning requirements increase. On small-diameter feeds and depths of cut that are typical for all aluminum alloys (see the section "Cut- stock, increased cutting force may cause turning aluminum alloys and on the assump- ting Fluids" in this article). the work metal to bend away from the tool; tions that the setup is rigid, that a cutting The procedures and equipment for therefore, stock supports or rests are re- fluid is used, and that the workpiece can be turning that are the same for all metals are quired. A nose radius that is too large also rotated to attain these surface speeds with- discussed in the article "Turning" in this causes chatter, which results in poor sur- out causing excessive vibration. When con- Volume (special considerations for high- face finish and possibly tool breakage. ditions are below normal, speeds must be silicon content alloys are given below). Be- Another way to improve surface finish is scaled down from those given in Table 8. cause aluminum alloys are far less sensitive to grind the end cutting edge of the tool Similarly, under nearly ideal conditions, to abrupt changes in speed, feed, and depth parallel to the work for a width equal to 11/2 higher speeds are often used successfully. to 2 times the feed rate in millimeters per Feed. For rough turning with single-point revolution. This flat edge will cut behind the tools, regardless of tool material, a feed of Table 13 Tool angles for drilling nose of the tool to smooth out the ridges 0.38 mm/rev (0.015 in./rev) is common for aluminum alloys with high-speed caused by the feed. Too wide a fiat will all aluminum alloys. For finish turning, a steel drills in drill presses cause chatter, and a negative angle will feed of 0.18 mm/rev (0.007 in./rev) is rec- leave a taper equal in length to the width of ommended; this feed will usually result in a Point angle (0), degrees the fiat, on the work at the end of the turn. surface finish of 1.60 to 3.20 i~m (63 to 125 Thin stock ...... 118.--I 50 Tool Honing. Honing a carbide tool with ixin.). Lighter feeds are sometimes used to Thinned point ...... (a) a diamond-impregnated stone will improve provide a better finish. General work ...... 118-140 the surface finish on the workpiece and will In form turning, the width of the form tool Aluminum-silicon alloys ...... >90 extend the life of the tool. Disposable car- is the major variable that affects the rate of Helix angle, degrees bide inserts have a honed edge when pur- feed. For all alloys and tool materials, a Thin stock ...... 24 chased, and no additional honing is neces- feed rate of 0.089 mm/rev (0.0035 in./rev) is Medium depth(b) ...... 28 sary. generally satisfactory for form tools no wid- Deep holes(c) ...... 40-48 Tool Material. Carbide tools, either er than 12.7 mm (0.500 in.). Rate of feed Lip clearance, degrees brazed-insert or disposable-insert, last far should be decreased as the width of the Soft alloys ...... 17 longer than high-speed steel tools for turn- form tool increases. Feed rates of 0.08 and Strong alloys ...... 15 ing any aluminum alloy. For turning the 0.05 mm/rev (0.003 and 0.002 in./rev) are Aluminum-silicon alloys ...... 12 recommended for form tool widths of 25 (a) Diameter + 1.8 stock thickness = tan 0/2. (b) Up to six times high-silicon alloys, the use of carbide tools drill diameter. (c) Over six times drill diameter or polycrystalline diamond is mandatory for and 50 mm (1 and 2 in.), respectively. 776 / Machining of Specific Metals and Alloys

Table 14 Nominal speeds and feeds for the drilling of aluminum alloys with high-speed tool steel tool

Speed, I Feed, mm/rev (ln./rev)(a) at a nominal hole diameter of: I Tool material Hardness, m/rain I.$ mm 3 mm 6 mm 12 nun 18 mm 25 mm 35 mm 50 mm grade, ISO Material HB (500 kg) Condition (sfm) (~6 in.) (~ in.) 0/4 in.) (~ in.) (~/4 in.) (1 in.) (1~ in.) (2 in.) (AISI or C)

Wrought EC 3005 6066 30--80 Cold drawn 43 0.025 ...... $2, $3 1060 4032 6070 (140) (0.001) ...... (MI0, M7, MI) 1100 5005 6101 105 • • • 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3 I 145 5050 615 l (350) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, M1) 1175 5052 6253 75-150 Solution treated 43 0.025 ...... $2, $3 1235 5056 6262 and aged (140) (0.001) ...... (M10, M7, MI) 2011 5083 6463 84 • • • 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3 2014 5086 695 I (275) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, M1) 2017 5154 7001 2018 5252 7004 2021 5254 7005 2024 5454 7039 2025 5456 7049 2117 5457 7050 2218 5652 7075 2219 5657 7079 2618 6053 7175 3003 6061 7178 3004 6063

Cast Sand and permanent mold A410 F332.0 520.0 40-100 As-cast 43 0.025 ...... $2, $3 201.0 333.0 535.0 (140) (0.001) ...... (MI0, M7, MI) 208.0 354.0 705.0 105 • • • 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3 213.0 355.0 707.0 (350) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, MI) 222.0 C355.0 A712.0 70-125 Solution treated 43 0.025 ...... $2, $3 224.0 356.0 D712.0 and aged (140) (0.001) ...... (MI0, M7, MI) 242.0 A356.0 713.0 84 • • • 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3 295.0 357.0 771.0 (275) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, MI) B295.0 359.0 850.0 308.0 B443.0 A850.0 319.0 514.0 B850.0 328.0 A514.0 A332.0 B514.0 Hiduminium RR-350

Die castings 360.0 A380.0 40-100 As-cast 46 0.025 ...... $2, $3 A360.0 C443.0 (150) (0.001) ...... (MI0, M7, MI) 380.0 5 i 8.0 115 • • • 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3 (375) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, MI) 70--125 Solution treated 46 0.025 ...... $2, $3 and aged (150) (0.001) ...... (MI0, M7, MI)

90 • • • 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3 (300) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, MI)

383.0 413.0 40-100 As-cast 30 0.025 ...... $2, $3 A384.0 A413.0 (100) (0.001) ...... (MI0, M7, MI) 43 ... 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3 (140) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, MI) 70-125 Solution treated 27 0.025 ...... $2, $3 and aged (90) (0.001) ...... (MI0, M7, MI) 37 ... 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3 (120) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, MI)

390.0 40-100 As-cast 8 0.025 ...... $2, $3 392.0 (25) (0.001) ...... (MI0, M7, MI) 15 ... 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3

(50) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, M1) 70-I 25 Solutiontreated 8 0.025 ...... $2, $3 and aged (25) (0.001) ...... (MI0, M7, MI) 14 -.. 0.075 0.18 0.30 0.40 0.50 0.65 0.75 $2, $3

(45) • • • (0.003) (0.007) (0.012) (0.016) (0.019) (0.025) (0.030) (MI0, M7, MI) (a) For holes more than two diameters deep, reduce speed and feed. Source: Ref 5

of cut than many other metals, they are tools at speeds up to 900 m/min (3000 sfm). always improve tool life; however, alloy 390 especially well adapted to turning in auto- Carbide tools are satisfactory for speeds up can be turned dry, if required, but with matic equipment. to 150 m/min (500 sfm). Carbide tools somewhat reduced tool life. Dry turning The turning of high-silicon aluminum should be polished for best results. Either speeds should be limited to 300 m/min (1000 alloys (gef 2) such as alloy 390 is best tool material should have at least a slight sfm) for diamond and 30 m/min (100 sfm) for accomplished with polycrystalline diamond positive rake. The use of a coolant will carbide tools. Machining of Aluminum and Aluminum Alloys / 777

Table 15 Nominal speeds and feeds for the spade drilling of aluminum alloys with high-speed tool steels and carbide tools Speed, / Feed, mndrev (ln./rev), at a nominal hole diameter of: / Hardness, m/mln '18-25mm 35 mm 50 mm 75 mm 100 mm 150 mm 200 mm 200 mm and Ul~ Tool material grade, Material HB (500 kg) Condition (sfm) (~/4--Iin.) (IV4 in.) (2 in.) (3 in.) (4 in.) (6 in.) (8 in.) (8 in. and up) ISO (AIS! or C)

Wrought EC 3005 6066 30--80 Cold drawn 90 0.40 0.45 0.65 0.90 1.10 1.65 1.90 2.30 $3, $4, $5, $2 1060 4032 6070 (300) (0.015) (0.018) (0.026) (0.035) (0.042) (0.065) (0.075) (0.090) (MI, M2, M3, MI0) 1100 5005 6101 185 0.13 0.15 0.20 0.30 0.36 0.55 0.65 0.75 K20 1145 5050 6151 (600) (0.005) (0.006) (0.008) (0.012) (0.014) (0.022) (0.025) (0.030) (C-2) 1175 5052 6253 75-150 Solution treated 84 0.40 0.45 0.65 0.90 1.10 1.65 1.90 2.30 $3, $4, $5, $2 1235 5056 6262 and aged (275) (0.015) (0.018) (0.026) (0.035) (0.042) (0.065) (0.075) (0.090) (MI, M2, M3, MI0) 2011 5083 6463 185 0.13 0.15 0.20 0.30 0.36 0.55 0.65 0.75 K20 2014 5086 6951 (600) (0.005) (0.006) (0.008) (0.012) (0.014) (0.022) (0.025) (0.030) (C-2) 2017 5154 7001 2018 5252 7004 2021 5254 7005 2024 5454 7039 2025 5456 7049 2117 5457 7050 2218 5652 7075 2219 5657 7079 2618 6053 7175 3003 6061 7178 3004 6063 Cast Sand and permanent mold A 140 F332.0 520.0 40-100 As-cast 90 0.40 0.45 0.65 0.90 1.10 1.65 1.90 2.30 $3, $4, $5, $2 201.0 333.0 535.0 (300) (0.015) (0.018) (0.026) (0.035) (0.042) (0.065) (0.075) (0.090) (MI, M2, M3, MI0) 208.0 354.0 705.0 185 0.13 0.15 0.20 0.30 0.36 0.55 0.65 0.75 K20 213.0 355.0 707.0 (600) (0.005) (0.006) (0.008) (0.012) (0.014) (0.022) (0.025) (0.030) (C-2) 222.0 C355.0 A712.0 70-125 Solution treated 84 0.40 0.45 0.65 0.90 1.10 1.65 1.90 2.30 $3, $4, $5, $2 224.0 356.0 D712.0 and aged (275) (0.015) (0.018) (0.026) (0.035) (0.042) (0.065) (0.075) (0.090) (M l, M2, M3, M I0) 242.0 A356.0 713.0 185 0.13 0.15 0.20 0.30 0.36 0.55 0.65 0.75 K20 295.0 357.0 771.0 (600) (0.005) (0.006) (0.008) (0.012) (0.014) (0.022) (0.025) (0.030) (C-2) B295.0 359.0 850.0 308.0 B443.0 A850.0 319.0 514.0 B850.0 328.0 A514.0 A332.0 B514.0 Hiduminium RR-350 Source: Ref 5

High-speed steel tools yield consistently Tools ...... Tungsten carbide, C-3, SPG422 insert tool life would be even greater, to the right poor results. Tool wear is rapid, and work- with J polish in Fig. 14). All of the turning tests, except piece buildup on the cutting tool is rapid and Polycrystalline diamond, SPG422 insert for sand cast alloy 390, were conducted Geometry ..... 0 ° Back rake angle inconsistent, resulting in poor surface finish 5* Side rake angle using soluble-oil emulsion coolant at the and diffficult-to-control dimensions. 5 ° Side rake angle ratio of 20:1. The dashed lines in Fig. 14 Ceramic tools exhibit rapid tool edge 5 ° End clearance angle (relief) represent extrapolations of actual data buildup at high speeds with consequent loss 5 ° Side clearance angle (relief) (solid lines). 15° Minor cutting edge angle (end) of finish and geometry. At lower speeds, 15° Lead angle (side) these conditions improve, but excessive 0.76 mm (0.030 in.) corner radius Boring heat transmitted to the ceramic material results in premature failure due to fracture The boring of aluminum alloys, particu- of the tool insert. Polycrystalline diamond is destined to larly the alloys with high silicon content, The best overall carbide grade has been become the most cost-effective tool materi- requires the use of tools with acute rake and found to be C-3, with C-2 as next best. Both al for machining harder and more abrasive clearance angles. In general, rake angles are are typical grades used for machining gray casting alloys such as 390. It can ensure a increased as silicon content is decreased. iron. It is desirable to have a good polish on potential improvement in transfer line pro- The same tool geometry and cutting tools the top rake face of the tool to minimize tool ductivity. used to turn high-silicon aluminum alloys edge buildup. Any good natural or synthetic Tool lives for the machining of alloys 380 such as 390 apply to boring operations of soluble-oil emulsion is recommended in or- and 390 are shown in Fig. 14. The data this same alloy (see the section "Turning of der to prolong tool life. Generally, positive represent the cutting times required to High-Silicon Aluminum Alloys" in this ar- rake and relief angles and a sharp nose achieve a 0.38 mm (0.015 in.) uniform wear ticle). radius promote good surface finish and min- land on the flank face of the cutting tool Tool Material. Although high-speed steel imize tool edge buildup for both carbide and (except for the die cast alloy 390 machined tools are used to some extent for boring polycrystalline diamond tools. Tool grades with diamond; in this case, cutting was aluminum, carbide tools permit higher sur- and geometry for turning 390 aluminum stopped at a uniform wear land of 0.25 mm, face speeds (up to 300 m/min, or 1000 sfm, alloy are: or 0.010 in.; and the 0.38 mm, or 0.015 in., or more), with markedly longer tool life. 778 / Machining of Specific Metals and Alloys

Table 16 Maximum depths per drill entry for drilling in automatic bar Table 18 Relation of drill diameter and chucking machines to approximate maximum depth of I Depth, in drill diameters hole in gun drilling First drill Second drill Depth of hole, I First Second Third I I First Second Third Subsequent [ Drill diameter ] number of drill Drill type entry entry entry entry entry entry entries mm in. diameters

Standard twist drill ...... 4 1 '/2 3/4 ...... -<13 ---I/2 ...... 12 High or low helix, or straight flute ...... 5 2 1 11/2 3/4 I/2 ½ 13-25 ½-1 ...... 7 25-38 1-172 ...... 6 38--50 I !/2-2 ...... 5 50-64 2-21/2 ...... 4 Table 17 Feeds for drilling aluminum alloys in automatic bar and 64-75 2½-3 ...... 3 chucking machines I Feed I Drill diameter.-----] I Tolerance - I I 2011-T3 ] [---- Other alloys is higher than can be obtained with most mm m. mm in. mm in. mm m. planers. 1.59 0.0625 ...... __.0.038 _+_0.0015 0.102 0.0040 0.10 0.004 Roughing feeds are about 2.3 mm (0.090 3.18 0.125 ...... __.0.05 __+0.002 0.305 0.0120 0.25 0.010 in.) per stroke when depth of cut is near the 4.75 0.187 ...... _+0.05 _+0.002 0.366 0.0144 0.30 0.012 recommended maximum of 13 mm (I/2 in.). 6.35 0.250 ...... _+0.05 _+0.002 0.426 0.0168 0.36 0.014 When shallow cuts are necessary (for lack 9.53 0.375 ...... _+0.064 _+0.0025 0.518 0.0204 0.43 0.017 12.70 0.500 ...... _+0.064 _+0.0025 0.518 0.0204 0.43 0.017 of power or other reasons), a heavier feed 19.05 0.750 ...... _+0.08 _+0.003 0.518 0.0204 0.43 0.017 can be used. For a 2.5 mm (0.10 in.) depth of cut, feed can be increased to about 3.18 mm (0.125 in.) per stroke. The finish planing Carbide cutters readily yield surface finish- accuracy, or surface finish when aluminum of aluminum alloys is usually done with a es of 0.25 to 0.50 ~m (10 to 20 ixin.). is bored without a cutting fluid. A mixture cut no deeper than 0.25 to 0.38 mm (0.010 to When used in conjuction with precision of one part soluble oil to 20 to 30 parts water 0.015 in.) and a feed equal to three-fourths boring machines, diamond tools can pro- is most commonly used. In addition, miner- the width of the broad-nose finishing tool. duce surface finishes of 0.025 ixm (1 ixin.). al oil, or mineral oil mixed with up to 50% Aluminum alloys are often planed with- They are also capable of holding size over a lard oil, is often used, especially when the out a cutting fluid. A cutting fluid is helpful long production run. If the cut is continuous best possible surface finish is desired. Mix- in producing a better surface finish, but and the work metal contains no hard spots, tures of kerosenes and lubricating oil are flooding with cutting fluid is seldom feasi- diamond tools are most effective in boring sometimes used. ble. When surface finish is a primary objec- the abrasive high-silicon alloys. Procedures and equipment common to tive, application of a mixture of kerosene Tool Sharpening. For optimum tool life, the boring of all metals are covered in detail and lubricating oil, or of kerosene and lard cutting edges and adjacent surfaces must be in the article "Boring" in this Volume. oil, by means of a swab is common practice. free of burrs and scratches. The hand ston- Specific procedures for boring an aluminum Sprayed cutting fluid is effective. Soluble- ing of cutting edges with an oil stone is alloy are described in the example that oil mixtures are ordinarily used in cutting recommended. When a carbide boring tool follows. fluid spray systems. Table 11 lists nominal is sharpened with a 400- or 500-grit diamond Example 2: The Boring of Concentric speeds and feeds for the planing of wrought wheel, surface finishes of 0.075 to 0.10 Ixm Holes. Two small and two large holes were and cast aluminum. (3 to 4 i~in.) can be obtained. rough and finish bored from opposite sides Shaping. Tool forms, tool materials, and Speed and Feed. The optimum speed for of a heat-treated aluminum forging, as cutting fluids for shaping aluminum are the boring aluminum alloys depends somewhat shown in Fig. 15. It was required that the same as those for planing. Maximum speed on alloy and temper, but largely on tool large and small holes be concentric within in shaping is usually the maximum ram material and whether the operation is 0.010 mm (0.0004 in.) total indicator reading speed of the machine. Feed and depth of cut roughing or finishing. Selection of feed de- (TIR), parallel within 0.008 mm (0.0003 in.), also depend to some extent on machine pends largely on tool material and whether and square with the surface within 0.008 capabilities. A feed of 0.51 to 0.76 mm/ the operation is roughing or finishing. mm (0.0003 in.). The operation was done in stroke (0.020 to 0.030 in./stroke) for rough- Nominal speeds and feeds for boring with a double-end precision boring mill, and car- ing and about 0.25 mm/stroke (0.010 in./ high-speed steel and carbide tools are given bide tools were used. Details are given with stroke) for finishing are common. Depth of in Table 9; speeds and feeds for boring Fig. 15. cut is often as much as 0.25 mm (0.10 in.) aluminum alloys with polycrystalline dia- for roughing and 0.51 mm (0.020 in.) or less mond tools are given in Table 10. Speed is for finishing. increased for a shallower depth of cut and Planing and Shaping lighter feed, regardless of the alloy or tool Broaching material. The techniques and equipment used for Depth of Cut. The speeds and feeds given the planing and shaping of other metals are All aluminum alloys can be broached in Tables 9 and 10 are based on a 2.5 mm generally applicable to aluminum alloys. successfully with standard broaching equip- (0.10 in.) depth of cut for roughing and 0.25 Planing methods are discussed in the article ment and with the same general procedures mm (0.010 in.) for finishing. Depth of cut is "Planing" in this Volume. Similar informa- as for other metals. However, better sur- sometimes greater than 2.5 mm (0.10 in.) for tion for shaping appears in the article face finish and dimensional accuracy are rough boring if power is available and the "Shaping and Slotting" in this Volume. obtained with heat-treated alloys. Details of setup can be made sufficiently rigid. Finish- Planing. Either high-speed or carbide equipment and procedures that are common ing cuts significantly less than 0.25 mm tools for planing aluminum usually have a to the broaching of all metals are covered in (0.010 in.) in depth are seldom used. back rake angle of 30 ° or more (sometimes the article "Broaching" in this Volume. Cutting fluid is recommended, but bor- as much as 60 °) and a 0 ° side rake. A speed The principal limitation in broaching alumi- ing has been done dry. There is usually of 90 m/min (300 sfm) is generally recom- num is the difficulty in maintaining an accu- some sacrifice of productivity, dimensional mended as maximum; however, this speed rate relation between the broached hole and Machining of Aluminum and Aluminum Alloys / 779

Table 19 Nominal speeds and feeds for the gun drilling of aluminum alloys with carbide tools Carbide [ Feed, mm/rev (in./rev)(a), at a nominal hole diameter of: ] tool Hardness, Speed, material HB m/rain 2-4 mm 4--6 mm 6-12 mm 12-18 mm 18-25 mm 25-50 mm grade, Material (500 kg) Condition (sfm) (0.078-0.156 in.) (0.156-0.250 in.) 0/4--~ in.) (~/~/4 in.) (3/4--1 in.) (1-2 in.) ISO (C)

Wrought EC 3005 6066 30--80 Cold drawn 215 0.004-0.006 0.008--0.013 0.025--0.063 0.038--0.075 0.050-0.102 0.075--0.13 K20 1060 4032 6070 (700) (0.00015--0.00025) (0.0003-0.0005) (0.001-0.0025) (0.0015--0.003) (0.002-0.004) (0.003-0.005) (C-2) 110O 5005 6101 75-150 Solution treated 200 0.004--0.006 0.008--0.013 0.025-0.063 0.038--0.075 0.050--0.102 0.075--0.13 K20 1145 5050 6151 and aged (650) (0.00015--0.00025) (0.0003--0.0005) (0.001-0.0025) (0.0015-0.003) (0.0O2-0.004) (0.003-0.005) (C-2) 1175 5052 6253 1235 5056 6262 2011 5083 6463 2014 5086 6951 2017 5154 7001 2018 5252 7004 2021 5254 7005 2024 5454 7039 2025 5456 7049 2117 5457 7050 2218 5652 7075 2219 5657 7079 2618 6053 7175 30O3 6061 7178 3004 6063 Cast Sand and permanent mold Al40 F332.0 520.0 40-10O As-cast 200 0.004-0.006 0.008--0.013 0.025-0.063 0.038-0.075 0.050--0.102 0.075-0.13 K20 201.0 333.0 535.0 (650) (0.00015-0.00025) (0.0003-0.0005) (0.001-0.0025) (0.0015--0.003) (0.002-0.004) (0.003-0.005) (C-2) 208.0 354.0 705.0 70-125 Solution treated 200 0.0(04).006 0.008-0.013 0.025-0.063 0.038--0.075 0.050-0.102 0.075-0.13 K20 213.0 355.0 707.0 and aged (650) (0.0o015-0.00025) (0.0003-0.0005) (0.001-0.0025) (0.0015-0.003) (0.002-0.004) (0.0O3-0.0O5) (C-2) 222.0 C355.0 A712.0 224.0 356.0 D712.0 242.0 A356.0 713.0 295.0 357.0 771.0 B295.0 359.0 850.0 308.0 B443.0 A850.0 319.0 514.0 B850.0 328.0 A514.0 A332.0 B514.0 Hiduminium RR-350

Die castings 360.0 A380.0 40-100 As-cast 200 0.(1(144).006 0.008--0.013 0.025--0.063 0.038-0.075 0.050--0.102 0.075-0.13 K20 A360.0 C443.0 (650) (0.00015-0.00025) (0.0003-0.0005) (0.001-0.0025) (0.0015--0.003) (0.002-0.004) (0.003-0.005) (C-2) 380.0 518.0 70-125 Solution treated 200 0.t)044).006 0.008--0.013 0.025-0.063 0.038-0.075 0.050-0.102 0.075-0.13 K20 and aged (650) (0.00015-0.00025) (0.0003-0.0005) (0.001-0.0025) (0.0015--0.003) (0.002-0.004) (0.003-0.005) (C-2)

383.0 40-100 As-cast 200 0.0044).006 0.008-0.013 0.025-0.063 0.038--0.075 0.050--0.102 0.075-0.13 K20 A384.0 (650) (0.00015-0.00025) (0.0003-0.0005) (0.001-0.0025) (0.0015--0.003) (0.002-0.004) (0.0O3-0.0O5) (C-2) 413.0 70-125 Solution treated 200 0.0(0-0.006 0.008--0.013 0.025-0.063 0.038--0.075 0.050--0.102 0.075--0.13 K20 A413.0 and aged (650) (0.00015--0.00025) (0.0003--0.0005) (0.001-0.0025) (0.0015--0.003) (0.002-0.004) (0.003-0.005) (C-2)

390.0 40-10o As-cast 150 0.004-0.006 0.008-0.013 0.020--0.050 0.025-0.063 0.038-0.075 0.050-0.102 K20 392.0 (500) (0.00015--0.00025) (0.0003-0.0005) (0.0008-0.002) (0.001--0.0025) (0.0015--0.003) (0.002-0.004) (C-2) 70-125 Solution treated 135 0.004-0.006 0.008-0.013 0.020--0.050 0.025-0.063 0.038--0.075 0.050-0.102 K20 and aged (450) (0.00015--0.00025) (0.0003--0.0005) (0.0008--0.002) (0.001-0.0025) (0.0015--0.003) (0.002-0.004) (C-2) (a) Feeds are specified for single-flute gun drills. Source: Ref 5

other surfaces of the workpiece, even when steel broach was increased from 2000 to 31/2°; for internal broaching, 2 °. Although a the starting hole is accurately located. 7400 pieces when the cutting edges were large clearance angle provides better cutting Tool Material. The general-purpose high- wet blasted with a superfine abrasive. action, it markedly reduces broach life. speed steels, such as M2, are used for most Broach Design. In rough broaching, a Therefore, clearance angles should be kept tools for broaching aluminum. In some coarse tooth pitch is desirable, with only to a minimum to reduce loss of size when high-production operations, especially two or three teeth in contact and cutting at the broach is sharpened. when broaching high-silicon alloys, broach- any one time. For internal finish broaching, Speed and Feed. A speed range of 9.1 to es made of the more highly alloyed high- the best results are obtained if only two 15 m/min (30 to 50 sfm) is generally recom- speed steels or of carbide have proved teeth are cutting; in external finish broach- mended for broaching aluminum alloys. economical. Surface treatments such as ing, it is often best to have only one tooth When rigidity, supply of cutting fluid, and chromium plating or oxidizing help to pro- engaging at a time. hardness of the work metal are nearly ideal, long the life of high-speed steel broaches. Broaches used for aluminum should have the upper portion of the range can be used. A fine finish on the tool can be important. a face angle of l0 °. For external surface When one or more of these conditions is In one application, the life of a high-speed broaching, the clearance angle should be less than ideal, the speed can be reduced. 780 / Machining of Specific Metals and Alloys

Lifting sling Gun 7075-T6 high stock removal rates, and machine Table 20 Reamer design and used as clemp-~ drill--\ /-tie-bolt hole, l~diem, downtime is typically low. operating conditions for reaming Because of their low hardness, modulus, aluminum alloys and strength, aluminum casting alloys have traditionally been considered unlikely can- Reamer design didates for this type of broaching. The cut- Reamer size Hand reaming, number //...]...... ~0 ting speed capability typical of a broach designed to machine cast iron is slow (7.6 to times drill diameter ...... 1.01 Machine reaming, number 46 m/min, or 25 to 150 sfm). Most aluminum times drill diameter ...... 1.02 ..... alloys are gummy at such speeds; because Flute type ...... Straight to 10° spiral of relatively low hardness, chips clog the Tooth spacing cutting teeth of the broach, and the surface Straight flute ...... Uneven(a) Spiral flute ...... Even of the resulting broached casting is torn and Tooth style rough. The unit tool forces, characteristic of Roughing ...... Solid or nicked such a broach, result in breakage of thinner Finishing ...... Solid casting sections and edge breakout on other Top rake, degrees ...... 5-8 (36 diom, 36 long) Clearance angles, degrees sections (chipping of the trailing edge of the Primary ...... 4-7 workpiece as the tool exits). The low mod- Secondary ...... 15-20 Clamp block Mechine toble ulus of most aluminum castings, when com- Cutting angle, degrees ...... 85-91 Fig. 19 Setup for deep-hole drilling an explosive pared to that of iron, also results in addi- Land width, mm (in.) ...... 0.51-1.52 forming die in a boring mill. Dimensions (0.020-0.060)(b) given in inches tional fixturing and clamping requirements. One study concluded that alloy 390 could Operating conditions be broached at cutting speeds and tool Speed, roughing, m/min (sfm) geometries typical of existing iron cutting Hard alloys ...... -<60 (200) Greater feed per tooth (chip load) is rec- Soft alloys ...... 18-30 (60-100) ommended for broaching aluminum alloys broaches with carbide tooling. Tool life was Speed, finishing, m/min (sfm) than for steel. A feed of 0.15 mm/tooth much better than that achieved for cast iron Straight reamers ...... <-120 (400) (0.006 in./tooth) is usually optimum for (Fig. 17). It also becomes evident that sur- Taper reamers ...... -<90 (300) face finishes better than 2.50 mm (100 txin.) Feed, mm/rev (in./rev) spline broaching and about 0.08 mm/tooth Roughing ...... 0.33--0.89 (0.013-0.035) (0.003 in./tooth) for broaching round holes. could be obtained as long as the uncut chip Finishing ...... 0.08-0.25 (0.003-0.010) Table 12 lists nominal speeds and feeds for thickness of each cutting edge was kept (a) To avoid chatter. (b) Land width is approximately V25 of machining both wrought and cast aluminum below 0.10 ~m (0.004 in.) (Fig. 18). Such reamer diameter. alloys. chip loads are typical of finishing cuts when Cutting fluid is required for best results. broaching cast iron, and the surface finishes A copious supply of soluble oil mixed with obtained are comparable to or better than water is satisfactory for most applications. those obtained with cast iron. The use of For drilling in drill presses, the helix However, mineral oil, or mineral oil mixed coolant had little effect on tool life or sur- angle of the drill should be increased with with lard oil, will usually improve surface face finish; however, coolant would tend to the depth of the hole to be drilled, ranging finish (see the section "Cutting Fluids" in aid in chip disposal. from a low-helix 24 ° angle for very shallow this article). Tests have shown that varying the rake holes in thin stock to a high-helix (40 to 48 °) Production Practice. The following exam- angles, shear angles, and chip loads can be angle for deep holes, for which freer cutting ple provides details of typical practice in effective in reducing cutting forces during is important (Table 13). The high-helix drill broaching aluminum. For the workpiece broaching. This approach to low-force tool- has a more acute cutting angle, resulting in described in this example, broaching was ing may not be needed for alloy 390, be- more rapid penetration and freer and clean- the most feasible and least costly method of cause the cutting forces are less than one- er cutting. Lands and margin are narrower obtaining the required results. half the forces for cast iron in comparable than on the low-helix drill, resulting in re- Example 3: The Broaching of Internal roughing cuts using negative-rake tooling. duced friction and increased chip space in Splines. Internal splines were broached in a However, these concepts have proved suc- the flutes. The slightly greater resistance to 2017-T4 aluminum clutch housing (Fig. 16). cessful in reducing breakage while broach- chip movement can be overcome by polish- The splined hole contained eight teeth with ing lighter-weight, thin-wall gray iron parts ing the flutes and supplying ample cutting 32 diametral pitch, 20 ° pressure angle, and and will also perform successfully when fluid. This type of drill is recommended for partial dedendum; the internal diameter was broaching alloy 390. deep holes, but is unsuitable for drilling thin 5.550 mm (0.2185 in.). The length of the stock because of its tendency to hog in. broaching cut was 7.49 mm (0.295 in.). The Drilling in Drill Presses A twist drill with a 28 ° helix is suitable for pull broach (details in Fig. 16) was made of holes of medium depth up to about six drill high-speed steel, and broaching was done in Although the standard twist drills and diameters. A drill with a 24 ° (or less) helix is a 9 kN (1 tonf) vertical machine. Processing drilling equipment used for steel can be recommended for thin stock because it has data are given in the table accompanying employed in drilling aluminum alloys, opti- less tendency to overfeed. Fig. 18. mum results require drills of special design The point angle supplied on standard Broaching of 390 High-Silicon Alumi- as well as higher rotational speeds and twist drills is 116 to l l8 °. The angle should num Alloy (Ref 2). Horizontal broaching heavier feeds. Drills for aluminum are usu- be about 130 to 140° for drilling most alumi- has long been the preferred method for ally made with deep, well-polished flutes, num alloys to facilitate chip removal and to rough and finish machining for such com- narrow margins, and large helix angles. minimize burring. However, drills for high- plex cast iron castings as cylinder heads and Proper drill design and drilling practice will silicon alloys should have a less obtuse engine blocks. Broaching permits several frequently permit the removal of three to point, down to about 90 ° , for ease of pene- surfaces on such parts to be machined in four times as much aluminum as steel per tration. For drilling thin sheet, the point exact relationship to each other because unit of power. The article "Drilling" in this angle should be very obtuse to permit the this relationship can be build into the Volume discusses general equipment and drill to cut to its full diameter before the broach tooling. Broaching also permits very practice. point breaks through. With this type of drill, Machining of Aluminum and Aluminum Alloys / 781

Table 21 Nominal speeds and feeds for the reaming of aluminum alloys with high-speed tool steel and carbide tools

S Roughing material ~ IS Finishing J Hardness, peed, Feed, mm/rev (in./rev)(a), at a reamer Tool peed, Feed, mm/rev (in./rev)(a), at a reamer Tool material HB m/rain ,13 diameter, mm (in.), of: (2)1 grade, ISO m/mln .13 diameter, mm (in.), of: (2)j grade, ISO Material (500 kg) Condition (sfm) (Vs) 6 (V4) 12 (½) 25 (I) 35 (1.5) 50 (AlSi or C) (sfm) (Vs) 6 (V4) 12 (½) 25 (I) 35 (1.5) 50 (AIS! or C)

Wrought EC 3005 6066 30-80 Cold drawn 150 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 55 0.102 0.15 0.25 0.40 0.45 0.50 $3, $4, $2 1060 4032 6070 (500) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (180) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (MI, M2, M7) ! 100 5005 6101 305 0.13 0.18 0.25 0.40 0.50 0.65 K20 76 0.102 0.15 0.25 0.40 0.45 0.50 K20 1145 5050 6151 (1000) (0.005) (0.007) (0.010) (0.015) (0.020) (0.025) (C-2) (250) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (C-2) 1175 5052 6253 75-150 Solution 150 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 55 0.102 0.15 0.25 0.40 0.45 0.50 $3, $4, $2 1235 5056 6262 treated (500) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (180) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (MI, M2, M7) 2011 5083 6463 and aged 305 0.13 0.18 0.25 0.40 0.50 0.65 K20 76 0.102 0.15 0.25 0.40 0.45 0.50 K20 2014 5086 6951 (I000) (0.005) (0.007) (0.010) (0.015) (0.020) (0.025) (C-2) (250) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (C-2) 2017 5154 7001 2018 5252 7004 2021 5254 7005 2024 5454 7039 2025 5456 7049 2117 5457 7050 2218 5652 7075 2219 5657 7079 2618 6053 7175 3003 6061 7178 3004 6063 Cast Sand and permanent mold AI40 F332.0 520.0 40-100 As-cast 150 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 49 0.102 0.15 0.25 0.40 0.45 0.50 $3, $4, $2 201.0 333.0 535.0 (500) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (160) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (MI, M2, M7) 208.0 354.0 705.0 305 0.13 0.18 0.25 0.40 0.50 0.65 K20 76 0.102 0.15 0.25 0.40 0.45 0.50 K20 213.0 355.0 707.0 (1000) (0.005) (0.007) (0.010) (0.015) (0.020) (0.025) (C-2) (250) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (C-2) 222.0 C335.0 A712.0 70-125 Solution 120 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 49 0.102 0.15 0.25 0.40 0.45 0.50 $3, $4, $2 224.0 356.0 D712.0 treated (400) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (160) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (MI, M2, M7) 242.0 A356.0 713.0 and aged 260 0.13 0.18 0.25 0.40 0.50 0.65 K20 76 0.102 0.15 0.25 0.40 0.45 0.50 K20 295.0 357.0 771.0 (850) (0.005) (0.007) (0.010) (0.015) (0.020) (0.025) (C-2) (250) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (C-2) B295.0 359.0 850.0 308.0 B443.0 A850.0 319.0 514.0 B850.0 328.0 A514.0 A332.0 B514.0 Hiduminium RR-350

Die castings 360.0 A380.0 40-100 As-cast 150 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 37 0.102 0.15 0.25 0.40 0.45 0.50 $3, $4, $2 A360.0 C443.0 (500) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (120) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (MI, M2, M7) 380.0 518.0 305 0.13 0.18 0.25 0.40 0.50 0.65 K20 60 0.102 0.15 0.25 0.40 0.45 0.50 K20 (1000) (0.005) (0.007) (0.010) (0.015) (0.020) (0.025) (C-2) (200) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (C-2) 70-125 Solution 120 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 37 .0.102 0.15 0.25 0.40 0.45 0.50 $3, $4, $2 treated (400) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (120) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (MI, M2, M7) and aged 260 0.13 0.18 0.25 0.40 0.50 0.65 K20 60 0.102 0.15 0.25 0.40 0.45 0.50 K20 (850) (0.005) (0.007) (0.010) (0.015) (0.020) (0.025) (C-2) (200) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (C-2)

383.0 40-100 As-cast 105 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 30 0.102 0.15 0.25 0.40 0.45 0.50 $3, $4, $2 A384.0 (350) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (100) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (MI, M2, M7) 413.0 215 0.13 0.18 0.25 0.40 0.50 0.65 K20 53 0.102 0.15 0.25 0.40 0.45 0.50 K20 A413.0 (700) (0.005) (0.007) (0.010) (0.015) (0.020) (0.025) (C-2) (175) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (C-2) 70-125 Solution 105 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 30 0.102 0.15 0.25 0.40 0.45 0.50 $3, $4, $2 treated (350) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (100) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (Ml, M2, M7) and aged 215 0.13 0.18 0.25 0.40 0.50 0.65 K20 53 0.102 0.15 0.25 0.40 0.45 0.50 K20 (700) (0.005) (0.007) (0.010) (0.015) (0.020) (0.025) (C-2) (175) (0.004) (0.006) (0.010) (0.015) (0.018) (0.020) (C-2)

390.0 40-100 As-cast 30 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 24 0.13 0.20 0.30 0.45 0.50 0.65 $3, $4, $2 392.0 (100) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (80) (0.005) (0.008) (0.012) (0.018) (0.020) (0.025) (MI, M2, M7) 60 0.18 0.25 0.40 0.50 0.65 0.75 K20 30 0.13 0.20 0.30 0.45 0.50 0.65 K20 (200) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (C-2) (100) (0.005) (0.008) (0.012) (0.018) (0.020) (0.025) (C-2) 70-125 Solution 30 0.18 0.25 0.40 0.50 0.65 0.75 $3, $4, $2 24 0.13 0.20 0.30 0.45 0.50 0.65 $3, $4, $2 treated (100) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (MI, M2, M7) (80) (0.005) (0.008) (0.012) (0.018) (0.020) (0.025) (MI, M2, M7) and aged 60 0.18 0.25 0.40 0.50 0.65 0.75 K20 30 0.13 0.20 0.30 0.45 0.50 0.65 K20 (200) (0.007) (0.010) (0.015) (0.020) (0.025) (0.030) (C-2) (100) (0.005) (0.008) (0.012) (0.018) (0.020) (0.025) (C-2) (a) Based on four flutes for 3 and 6 mm (Vs and V4 in.) reamers, six flutes for 12 mm (½ in.) reamers, and eight flutes for 25 mm (1 in.) and larger reamers. Source: Ref 5 a spur point may be necessary to assist in Drill Material. Most drills for aluminum high-speed tool steel drills can be oper- centering, are made of high-speed tool steels; Ml, M7, ated at a maximum of about 180 m/min The standard lip clearance of 12 to 13 ° and M10 are the most common grades. Only (600 sfm). When variable speed is available, should be increased to about 17 ° for heavy rarely can the additional cost for drills made drill life can be increased in drilling deeper feeds and for softer alloys. Insufficient lip of a more highly alloyed grade of high-speed holes by bringing the drill up to speed grad- clearance will cause excessive drill break- tool steel or of carbide be justified for ually. age. The drill cutting lips must be keen and conventional drilling in drill presses. Because of the ease of penetrating most smooth, and all surfaces over which the Speed and Feed. With most drill presses, aluminum alloys, feeds up to twice those chip passes must be polished to minimize the peripheral speed of small-diameter drills used for drilling steel can be employed. friction and chip buildup. Recommended is relatively low; therefore, such drills can Feed varies with drill diameter; the larger- point angles, helix angles, and lip clearanc- be operated at the maximum efficient rota- diameter drills permit heavier feeds, as in- es are summarized in Table 13. tional speed of the machine. In general, dicated below: 782 / Machining of Specific Metals and Alloys

mm/rev Feed I Drill diameter depth to diameter, half-round or gun drills Table 22 Nominal speeds for the in./rev mm in. are sometimes used. tapping of aluminum alloys 0.025 0.001 ...... 1.6 !/16 When standard twist drills are used for 0.08 0.003 ...... 3.2 !/8 drilling deeper than three diameters, it may 0.18 0.007 ...... 6.4 !/4 be necessary to enlarge the flutes. This can 0.30 0.012 ...... 13 V2 Nonheat-treated cast alloys ...... 35 115 0.41 0.016 ...... 19 3/4 be done with a thin grinding wheel that has Heat-treated cast alloys, solution 0.48 0.019 ...... 25 1 been dressed to a radius. The flute is held at treated and aged ...... 27 90 0.64 0.025 ...... 38 1I/2 an angle to the wheel to ensure the proper Cold-drawn wrought alloys ...... 38 125 0.76 0.030 ...... 50 2 curvature in the flute. All flutes on a drill Heat-treated wrought alloys, solution should be ground alike. treated and aged ...... 30 100 Drill Margin. Margins along the edges of Nominal speeds and feeds for wrought and flutes support the drill in the hole and keep cast aluminum alloys are listed in Table 14. the drill cutting the correct diameter. When Web Thickness. For drilling aluminum Table 15 provides speed and feed data using drilling aluminum alloys, standard drill mar- alloys, web thickness at the point should be spade drills. gins can often be reduced in width without reduced as the drill is ground back. This will Cutting Fluid. Drilling of thin sections loss of necessary support. The narrower reduce the end pressure on the drill because does not require a cutting fluid, but it is margin reduces friction between the drill the chisel point does not cut but compresses essential to both drill life and hole quality and the hole, thus reducing the amount of the metal ahead of it. Generally, the web that a copious supply of cutting fluid be heat generated. In many production jobs, a can be somewhat thinner at the point with- provided for all deep-hole drilling. Soluble- narrower margin greatly increases drill life. out making the drill susceptible to breakage oil emulsions or kerosene and lard oil mixtures are satisfactory for general drilling. In drilling to a depth greater than six times the Table 23 Nominal speeds for the tapping of aluminum alloys with drill diameter, the workpiece should be kept high-speed tool steels cool by spraying. In addition, the drill should be withdrawn several times during Speed, m/min (sfm) at a pitch, [ mm (threads/in.), of: I High-speed steel drilling to ensure that the cutting fluid Hardness, >3 1.5-3 I-I.5 -< I tool material floods the hole completely. Material HB (500 kg) Condition (-<7) (8-15) (16-24) (>24) grade, ISO (AISi) Drilling Operations in Wrought Automatic Bar and EC 2218 5252 6253 30--80 Cold drawn 17 29 37 38 $2, $3 1060 2219 5254 6262 (55) (95) (120) (125) (MI0, M7, MI) Chucking Machines 1100 2618 5454 6463 75-150 Solution treated 14 23 29 30 $2, $3 1145 3003 5456 6951 and aged (45) (75) (95) (100) (MI0, M7, MI) When drilling is done in multiple-opera- 1175 3004 5457 7001 tion machines, it is especially important that 1235 3005 5652 7004 the tool be correctly ground and set (see the 2011 4032 5657 7005 2014 5005 6053 7039 section "Automatic Lathes" in the article 2017 5050 6061 7049 "Multiple-Operation Machining" in this 2018 5052 6063 7050 Volume). Standard twist drills are generally 2021 5056 6066 7075 used for drilling holes up to six diameters 2024 5083 6070 7079 2025 5086 6101 7175 deep. For drilling deeper holes, drills that 2117 5154 6151 7178 pass the chips up the flutes more readily are recommended. When machining 2017-T4, Cast 2024-T4, and 2011-T3, straight-flute drills Sand and permanent mold are generally used for drilling holes deeper AI40 319.0 357.0 A712.0 40-100 As-cast 15 26 34 35 $2, $3 than six diameters. Either high-helix or low- 201.0 328.0 359.0 D712.0 (50) (85) (110) (115) (MI0, M7, MI) 208.0 A332.0 B443.0 713.0 70-125 Solution treated 12 20 26 27 $2, $3 helix drills can be used for drilling deep 213.0 F332.0 514.0 771.0 and aged (40) (65) (85) (90) (MI0, M7, MI) holes. The web of the high-helix drill is 222.0 333.0 A514.0 850.0 uniform in thickness along the entire length 224.0 354.0 B514.0 A850.0 of the body, providing large flutes for the 242.0 355.0 520.0 B850.0 295.0 C355.0 535.0 chips. Wide flutes also characterize the B295.0 356.0 705.0 low-helix drill. Both types give good re- 308.0 A356.0 707.0 sults, particularly in the drilling of soft or Hiduminium RR-350 gummy alloys. For holes with a high ratio of Die castings 360.0 A380.0 40-100 As-cast 20 34 43 46 $2, $3 Cutting -Radial margin (0.005 to 0.010 in.) A360.0 C443.0 (65) (110) (140) (150) (MI0, M7, MI) edge~ End cutting margin 380.0 518.0 70-125 Solution treated 14 23 29 30 $2, $3 (0.005 to 0.005 in.) and aged (45) (75) (95) (100) (MI0, M7, Mi) 91 ° 88 383.0 40-100 As-cast 20 34 43 46 $2, $3 A384.0 (65) (ll0) (140) (150) (MI0, M7, MI) 413.0 70-125 Solution treated 14 23 29 30 $2, $3 A413.0 and aged (45) (75) (95) (100) (MI0, M7, MI)

390.0 40-100 As-cast 17 30 34 37 $2, $3 relief (6 lo I0 °) --,,,,J Radial ~-~ ---,,,_ 392.0 (55) (100) (110) (120) (MI0, M7, MI) rake (7°)-- Radial relief (8 to 12% 70-125 Solution treated 12 21 27 29 $2, $3 and aged (40) (70) (90) (95) (MI0, M7, MI) -'uc"'. 20 Design of a finishing reamer used for (a) These speeds are for tapping 65 to 75% threads in shallow through holes. Reduce the speed when tapping deep holes, blind holes, reaming aluminum in automatic bar and or a higher percentage of thread. Source: Ref 5 chucking machines. Dimensions given in inches Machining of Aluminum and Aluminum Alloys / 783

Cutting speed, sfm Table 24 Geometry and cutting conditions for the drilling and tapping 0 100 200 300 400 500 600 of alloy 390 2000 I I I 1 I o High-speed steel, parabolic flute Type ~r~-miSnpeed ~ Feed Coolant 1750 • High-speed steel, coolant fed Carbide tip, coolant fed Drl~s 1500 Tungsten carbide tipped, coolant fed .... 90 300 508 mm/min (20 in./min) 34 L/min (9 gal./min) at 3.5 MPa (500 psi), soluble oil (20:1) 1250 High-speed steel, high helix, O t- 380 mm/min 510 mm/min parabolic flute, noncoolant fed ...... 20 70 381 mm/min (15 in./min) 19 L/min (5 gal./min), O at 170 kPa (25 psi) soluble oil (20:1) ,- 1000 High-speed steel, regular helix, t~ E coolant fed ...... 20 70 4.6 m/min (15 sfm) 34 L/min (9 gal./min) at 3.5 z 750 MPa (500 psi), soluble oil ~~80mm/min \ X (20: l) Taw 500 Thread forming, high-speed steel, I ~n~ 510 mm/min four lubricant grooves ...... 20 70 Determined by pitch 19 L/min (5 gal./min), 510 mm/mi K. soluble oil (20: l) 250 510 mm/min- 510 mm/min Source: Ref 2

0 30 60 90 120 150 180 Cutting speed, m/min rake for the new cutting edge, which is Center Drills. When a drill starts against a ground to the center of the point of the drill. flat surface, it may skid sideways before "'u©". 21 Drill life at various penetration rates for several types of drills when drilling perma- When the entire flute at the point is cutting, particularly if it is small or pro- nent mold 390 aluminum alloy. Source: Ref 2 thinned by grinding, a thin wheel that has trudes considerably from the holder. This been dressed to a radius is used. The drill is may cause the drill to break or to cut held so that the flute is at an angle to the off-center. Therefore, except with large, 0.18 7-'- ~ A wheel, as when widening the flute. Most of rigidly held drills, a center drill is recom- the metal should be ground off the back of mended to provide an accurate start. the land, and care must be taken not to For maximum rigidity, center drills grind the rake formed by the helix angle should be of relatively large diameter and from the cutting edge or to destroy the short length. Unless a countersink of a shape of the cutting edge. Thinning of the special angle is to be left in the workpiece, web must be done uniformly in each flute to an included cutting-lip angle of 90 ° should ensure that the cut remains balanced on be used. In general, for proper centering, both sides of the centerline of the drill. the outside of the cutting lips of the drill that Cutting-Lip Angle. In general drilling follows the center drill should strike the Section A-A 1~--18 NEF--2B 380 alloy practice, if holes are not too deep, a stan- stock first, ensuring adequate support. dard included cutting-lip angle of 118 ° will Depth of Hole. In multiple-operation ma- Details of single-point threading tool give a satisfactory performance. However, chines, to prevent chips from jamming in Material ...... Carbide if deeper holes are drilled with this cutting- the flutes and causing drill breakage when Cutting edge angle, degrees ...... 60 Top rake angle, degrees ...... 20 lip angle, the chip produced does not come deep holes are being drilled, a limit must be Clearance angle, degrees ...... 7 out easily. For drilling deeper holes, larger set on the depth drilled with each entry of Operating conditions included cutting-lip angles are used, form- the tool. The maximum depths, in terms of ing a narrower chip that readily passes up drill diameter, that can be drilled per entry Speed, m/min (sfm) ...... 145 (475) Diameter of bore, mm (in.) ...... 43 (l~l/16) the flutes. under normal production conditions are giv- Length of threads, mm (in.) ...... 4.75 (0.187) Occasionally, smaller cutting-lip angles en in Table 16. Before reentry, the drill Cutting fluid ...... Soluble oil:water can be used because the transverse forces at should be completely backed out of the hole (1:25) the cutting edges are greater and the tool so that the chips can be washed away. Setup time, h ...... I Cycle time, s ...... 40 can drill without runout. However, a broad- The type of workpiece, the number of Production rate, pieces/h ...... 75 er chip is produced. When several drills are positions on the machine available for drill- used in the same hole, each succeeding tool ing, and the type of machine determine the Fig. 22 Die casting threaded in a single-spindle should have a slightly more blunt cutting-lip practice for drilling deep holes. It is some- chucking machine with a threading attach- angle than that of the preceding one, so that times economical to use several drills for ment. Dimensions in figure given in inches it can center at the outside of the cutting drilling deep holes. edges. For holes more than eight diameters The clearance angle behind the cutting deep, half-round or gun drills are often when drilling aluminum alloys than when edges should be 12 to 20 °. Larger clearances used. To ensure adequate support for the drilling steel. are used for straight-flute drills and for drills half-round drill when it starts cutting, an- For small-diameter drills, notched-point ground with large cutting-lip angles. Clear- other type of drill should be used to drill a thinning is common. On larger drills, this ance should extend from periphery to cen- starting hole three diameters or more deep. type of point may produce a poor chip; ter so that the chisel point is at an angle of The half-round drill can drill four diameters therefore, the entire flute is ground at the 130 to 145 ° with the cutting edges. deeper in the first entry of the started hole. point. The notched point is obtained by Rake angles are set by the helix angle of Drill Speed. Generally, small-diameter, using the sharp corner of an abrasive wheel the drill. For standard twist drills, this is high-speed tool steel drills can be operated with the side of the wheel following the usually 20 to 25°; for high-helix drills, 40 to at speeds up to 180 m/min (600 sfm). How- angle of the chisel point. The drill should be 43°; for low-helix drills, 7 to 15°; and for ever, when larger drills are used to remove held at an angle to the wheel to form a slight straight-flute and half-round drills, 0 °. large quantities of metal at a rapid rate, 784 / Machining of Specific Metals and Alloys

Polished Polished Secondary Primary Circular land primary primary land land (0.08-0.13mm) land land marre,,e* F1 Primary relief / / ,, ,,,/ __... ~ /t, P / / / T ~~~i~:.ii~it ~ Polished ; (~Snhed ~/ ~~ Secondary ~ J~ii!i~]i~:...iiiii~iiiiiiiiii~ \ land | I" ~/~:] clearance ~ j~.....y x Chip Secondary __~ ~~!!1 ~~ \ path clearance ~~~!~ ~ ~ii| ~ ~ ._

face ~ ~i~i~ ~ Secondary /¢'~~ t~li~~ tooth ~!i;ili!ii!iiii iiiii]!iiiiiiiiii!]iiiiiiiiiiii!i~iiiiii~!i!i~!i~.L.~ I~]i ii'iiiiiii'!i'ii~ii~!'ii~i'iii!]iiiiiii]iiiiiiiiiiiiii!iii!ii~ilii ii'i'i!'~ surface

(a) (b) (c)

Fig. 23 Three end mill geometries designed for the cutting of aluminum alloys. (a) Conventional milling. (b) Heavy metal removal. (c) Finishing operations. Source: Ref 1 lower speeds will give more economical Drill Size Versus Hole Size. Drills, when having much greater length-to-diameter ra- drill life. A guide for choosing proper properly ground and set, will cut aluminum tios are often used. Table 19 lists nominal speeds for most conditions is: alloys to size or not more than 0.05 mm speeds and feeds for the gun drilling of (0.002 in.) oversize. However, any condi- wrought and cast aluminum alloys. Lm-- Drill diameter~ i m/min Spt~ sfml tion that causes overheating is likely to Gun drills, with a single-flute cutting head decrease the size of the hole when it is and grooved shank, must have a sufficient <25 < 1 ...... 180 600 measured after the workpiece has cooled. flow of cutting fluid under high pressure at 25-38 I- 1 tA ...... 170 550 This is especially noticeable when drilling the point where the cutting edge contacts >38 > 1 I/2 ...... 140 450 large holes. The drilling of deep holes at a the work; this keeps the cutting edge cool high feed rate will decrease hole size in and ensures that the chips will be forced out Feed for drilling in multiple-operation ma- relation to drill size. Other tools working through the chip groove. Cutting fluid is chines depends on the size and strength of simultaneously will sometimes generate normally applied at a pressure of 3.4 to 4. l the drill; finish, tolerance, and concentricity enough heat to cause the production of MPa (500 to 600 psi) for drills 9.5 mm (3/8 in.) desired; and power available. As feed is holes close to or even smaller than drill size, in diameter or smaller and at 2.1 to 2.8 MPa increased, torque on the drill increases, as measured after the workpiece has cooled (300 to 400 psi) for larger drills. A pump of until the breaking point may be reached. On to room temperature. 3.7 kW (5 hp) capacity is usually required the other hand, lower feed produces thinner for average applications. A paraffin-base oil chips, which are more likely to clog the Deep-Hole Drilling with a viscosity of 100 to 125 SUS at 40 °C flutes than thicker chips. Clogging is likely (100 °F) has been used satisfactorily in gun to break the drill or mar the finish of the Gun drills, tipped with either carbide or drilling aluminum with a 9.5 mm (3/8 in.) workpiece. high-speed tool steel, have replaced twist diam drill at a speed of 90 m/min (300 sfm) Recommended drill feeds are given in drills for many deep-hole drilling applica- for high-speed tool steel or 180 m/min (600 Table 17 for drill sizes up to 19.05 mm tions, regardless of the metal being drilled. sfm) for carbide and at feeds of 0.025 to 0.08 (0.750 in.) in diameter. Feeds for larger In gun drilling, the maximum depth of hole mm/rev (0.001 to 0.003 in./rev). drills usually depend on the power available that can be drilled successfully is generally Although deep-drilling problems have in the machine. related to drill size (Table 18). The length- been alleviated to some extent by the devel- For greater accuracy and better finish, to-diameter relationships shown in Table 18 opment of gun drills and special gun drilling lower feed may be necessary. For deep are generally standard, although gun drills equipment, this equipment is expensive and holes, machined with several entries, feed should be decreased 15% for each succes- D~rect0on of rotation sive entry. Lower feed should be used to drill thin-wall parts. Power Requirements. When large quantities of metal are removed, lower feed may be necessary to keep the power within the limits available in the machine. When drilling with standard drills (ground to 118° included cutting-lip angle and 15° clearance) to four diameters deep in 2017-T4 and 2024- T4, the metal removal rate is 18 000 to 24 000 mm3/min/kW (1.5 to 2 in.3/min/hp). For 2011-T3, the rate is 31 000 to 37 000 Sintered mm3/min/kW (2.5 to 3.0 in.3/min/hp). These carbide tip .~.------64 ~ figures are based on a feed of 0.43 mm/rev (0.017 in./min). With lower feed, the rate of metal removal decreases. Fig. 24 Special two-cut tooth end mill with sintered carbide cutters. Dimensions given in millimeters. Source: Ref 4 Machining of Aluminum and Aluminum Alloys / 785

,~ /~,=,..~ Direction of rotation vent the reamer from feeding itself into the hole. Flutes should be large enough to pass the chips readily, and there should be enough flutes to provide adequate support --t.._-~\\ /, 900- /.~ I I \ \ " to the tool. The margins of straight-flute reamers should be as narrow as possible to reduce friction between tool and work. Straight-flute reamers are designed with an "~20 ° / even number of blades arranged opposite each other in pairs, but with flute spacing varied slightly to prevent chatter and mark- ing. Spiral flutes (right-hand cut, left-hand spiral) are frequently more effective than angular spacing in reducing chatter. However, a spiral-flute reamer must have sufficient spiral so that two or more flutes overlap in the length of the reamed hole. The spiral angle must be held to a minimum because the steeper the angle, the more end pressure e Sintered /? I'~""-- 78"5~][~~ 80-'~ is required to feed the reamer through the hole. Additional reamer design data are given in Table 20. When the hole has close tolerances and rigid surface finish requirements, the ream- 10° I - ing procedure must sometimes be altered. If the design of the workpiece permits, spiral- flute reamers with 7 ° hook will produce fine finishes, especially on angular surfaces. When reaming diameters of 19.05 mm (0.750 in.) or larger, a carbide-tip expandable reamer will produce good finish and provide extended tool life. Speed and Feed. The nominal speed for reaming the nonheat-treated cast alloys Fig. 25 Toolgeometry for specialtwo-tooth sinteredcarbide-tip milling cutter usedto cut aluminumalloys. with high-speed tool steel (M l, M2, or M7) Dimensionsgiven in millimeters.Source: Ref 4 reamers is 150 m/min (500 sfm). For all other cast and wrought alloys (excluding high-silicon alloys), speed should be about cannot always be justified. The following and doweled to one another to maintain 120 m/min (400 sfm). example describes a deep-hole drilling ap- alignment. The assembly was then set up in When reaming the nonheat-treated cast plication that utilized available equipment a boring mill as shown in Fig. 19. Each of alloys with carbide tools, nominal speed is (in this case, a boring mill). the 41 mm (15/8 in.) diam tie-bolt holes was 300 m/min (1000 sfm). For other cast and Example 4: Deep-Hole Drilling in a drilled in one pass using a standard gun wrought alloys (excluding high-silicon Boring Mill. The 914 mm (36 in.) diam, 914 drill. Drilling time was reduced from 7 h by alloys), nominal reaming speed is 260 m/min mm (36 in.) long explosive forming die the original method to I/2 h by the improved (850 sfm). illustrated in Fig. 19 was originally made up method. Feed rate in reaming aluminum alloys is from nine 102 mm (4 in.) thick aluminum The boring mill was modified by adding a generally the same for all alloys and tool alloy plates. Because no plate stock obtain- hydraulic pump with a capacity of 154 L/ materials; hole size, however, does affect able was wide enough to make a 914 mm (36 min (40.6 gal./min) to supply cutting fluid to optimum feed, as indicated below: in.) diam one-piece plate, each round plate the drill point at 2.1 MPa (300 psi). A baffle was made by doweling together two 102 mm plate and filter system were installed to mm/rev Feed Hole diameter in./rev I mm in. (4 in.) thick half-sections. As each 102 mm handle the flow of oil. (4 in.) plate section was completed by ma- 0.13 0.005 ...... 3.2 chining the die cavity hole through its cen- 0.18 0.007 ...... 6.4 1/4 Reaming 0.30 0.012 ...... 13 V2 ter and drilling 12 tie-bolt holes, it was 0.38 0.015 ...... 25 1 mated to the next 102 mm (4 in.) thick plate The machines, basic designs of reamers, 0.51 0.020 ...... 38 11/2 until the die was completed. Each individ- and techniques discussed in the article 0.76 0.030 ...... 50 2 ual plate was placed on the preceding plate "Reaming" in this Volume are generally so that the half-section cut lines were 90 ° applicable to aluminum alloys. Table 21 lists nominal speeds and feeds for from those in the preceding plate. Then Reamer Design. Because it is less likely the rough and finish reaming of aluminum each section was doweled with two pins to to cause chatter, a spiral-flute reamer (solid, alloys. the next, completing the die. expandable, or adjustable) is generally pref- Cutting Fluid. At high reaming speed, a By the improved method of producing erable to a straight-flute reamer for finishing cutting fluid is required for reducing the these dies, four 914 mm (36 in.) diam, 229 holes in aluminum alloys. In most applica- temperature in the workpiece, minimizing mm (9 in.) thick forgings were obtained. tions, it is advantageous to use a reamer distortion, and preventing undersize ream- These forgings were machined (as were the with a negative spiral (this is, one spiraled in ing. For reaming with high-speed tool steel 102 mm, or 4 in., thick plates) individually the direction opposite to rotation) to pre- reamers, mixtures of lard oil and paraffin oil 786 / Machining of Specific Metals and Alloys

Table 25 Nominal speeds and feeds for the peripheral end milling of aluminum alloys with high-speed tool steel and carbide tools I High-speed steel tool ] [ Carbide tool I Radial [ Feed, mm/tooth (in./tooth) [ 1~ Feed, mm/tooth (in./tooth) [ Hardness, depth of Speed, with a cutter diameter of: Tool material Speed, with a cutter diameter of: Tool material HB cut(a) m/min 10 mm 12 mm 18 mm 25-50 mm grade, ISO m/rain 10 mm 12 mm 18 mm 25-50 mm grade, ISO Material (500 kg) Condition mm (in.) (sfm) (3/s in.) (½ in.) (¥4 in.) (1-2 in.) (AISI) (sfm) (~ in.) (~ in.) (3/4 in.) (1-2 in.) (C)

Wrought EC 3005 6066 30-80 Cold drawn 0.5 245 0.075 0.102 0.13 0.18 $4, $5, $2 395 0.075 0.102 0.13 0.18 K20, M20 1060 4032 6070 (0.020) (800) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (1300) (0.OO3) (0.0O4) (O.0O5) (0.OO7) (C-2) 1100 5005 6101 1.5 185 0.102 0.15 0.20 0.25 305 0.102 0.15 0.20 0.25 1145 5050 6151 (0.060) (600) (0.OO4) (0.006) (0.008) (0.010) (1000) (0.004) (0.006) (0.008) (0.010) 1175 5052 6253 diarrff4 150 0.075 0.102 0.15 0.20 275 0.075 0.13 0.15 0.20 1235 5056 6262 (diam/4) (500) (0.003) (0.004) (0.006) (0.008) (900) (0.003) (0.005) (0.006) (0.008) 2011 5083 6463 diarrff2 120 0.050 0.075 0.13 0.15 245 0.050 0.102 0.13 0.15 2014 5086 6951 (diam/2) (400) (0.002) (0.003) (0.005) (0.006) (800) (0.002) (0.004) (0.005) (0.006) 2017 5154 7001 75-150 Solution treated 0.5 245 0.075 0.102 0.13 0.18 $4, $5, $2 395 0.075 0.102 0.13 0.18 K20, M20 2018 5252 7004 and aged (0.020) (800) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (1300) (0.003) (0.004) (0.005) (0.007) (C-2) 2021 5254 7005 1.5 185 0.102 0.15 0.20 0.25 305 0.102 0.15 0.20 0.25 2024 5454 7039 (0.060) (600) (0.0O4) (0.006) (0.008) (0.010) (1000) (0.004) (0.006) (0.008) (0.010) 2025 5456 7049 diam/4 150 0.075 0.102 0.15 0.20 275 0.075 0.13 0.15 0.20 2117 5457 7050 (diam/4) (500) (0.003) (0.004) (0.006) (0.008) (900) (0.003) (0.005) (0.006) (0.008) 2218 5652 7075 diand2 120 0.050 0.075 0.13 0.15 245 0.050 0.102 0.13 0.15 2219 5657 7079 (diam/2) (400) (0.002) (0.003) (0.005) (0.006) (800) (0.002) (0.004) (0.005) (0.006) 2618 6053 7175 3003 6061 7178 3004 6063 Cast Sand and permanent mold AI40 F332.0 520.0 40-100 As-cast 0.5 305 0.075 0.102 0.13 0.18 $4, $5, $2 395 0.075 0.102 0.15 0.18 K20, M20 201.0 333.0 535.0 (0.020) (1000) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (1300) (0.003) (0.004) (0.005) (0.007) (C-2) 208.0 354.0 705.0 1.5 245 0.102 0.15 0.20 0.25 305 0.102 0.15 0.20 0.25 213.0 355.0 707.0 (0.O6O) (80O) (0.004) (0.006) (0.008) (0.010) (1000) (0.004) (0.006) (0.008) (0.010) 222.0 C355.0 A712.0 diam/4 185 0.075 0.102 0.15 0.20 275 0.075 0.13 0.15 0.20 224.0 356.0 D712.0 (diam/4) (600) (0.003) (0.004) (0.006) (0.008) (900) (0.003) (0.005) (0.006) (0.008) 242.0 A356.0 713.0 diam/2 150 0.050 0.075 0.13 0.15 245 0.050 0.102 0.13 0.15 295.0 357.0 771.0 (diam/2) (500) (0.002) (0.003) (0.005) (0.006) (800) (0.002) (0.004) (0.005) (0.006) B295.0 359.0 850.0 70-125 Solution treated 0.5 245 0.075 0.102 0.13 0.18 $4, $5, $2 395 0.075 0.102 0.13 0.18 K20, M20 308.0 B443.0 A850.0 and aged (0.020) (80O) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (1300) (0.003) (0.004) (0.005) (0.007) (C-2) 319.0 514.0 B850.0 !.5 185 0.102 0.15 0.20 0.25 305 0.102 0.15 0.20 0.25 328.0 A514.0 (0.O60) (6OO) (0.004) (0.006) (0.008) (0.010) (1000) (0.004) (0.006) (0.008) (0.010) A332.0 B514.0 diam/4 150 0.075 0.102 0.15 0.20 275 0.075 0.13 0.15 0.20 Hiduminium RR-350 (diam/4) (500) (0.003) (0.004) (0.006) (0.008) (900) (0.003) (0.005) (0.006) (0.008) diam/2 120 0.050 0.075 0.13 0.15 245 0.050 0.102 0.13 0.15 (diam/2) (400) (0.002) (0.003) (0.005) (0.006) (800) (0.002) (0.004) (0.005) (0.006)

Die castings 360.0 40-100 As-cast 0.5 305 0.075 0.102 0.13 0.18 $4, $5, $2 395 0.075 0.102 0.13 0.18 K20, M20 A360.0 (0.020) (1000) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (1300) (0.003) (0.004) (0.005) (0.007) (C-2) 380.0 1.5 245 0.102 0.15 0.20 0.25 305 0.102 0.15 0.20 0.25 A380.0 (0.060) (800) (0.004) (0.006) (0.008) (0.010) (1000) (0.004) (0.006) (0.008) (0.010) C443.0 diam/4 185 0.075 0.102 0.15 0.20 275 0.075 0.13 0.15 0.20 518.0 (diam/4) (6OO) (0.003) (0.004) (0.006) (0.008) (900) (0.003) (0.005) (0.006) (0.008) cliam/2 150 0.050 0.075 0.13 0.15 245 0.050 0.102 0.13 0.15 (diam/2) (5OO) (0.002) (0.003) (0.005) (0.006) (800) (0.002) (0.004) (0.005) (0.006) 70-125 Solution treated 0.5 275 0.075 0.102 0.13 0.18 $4, $5, $2 395 0.075 0.102 0.13 0.18 K20, M20 and aged (0.020) (9OO) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (1300) (0.003) (0.004) (0.005) (0.007) (C-2) 1.5 215 0.102 0.15 0.20 0.25 305 0.102 0.15 0.20 0.25 (0.060) (700) (0.004) (0.006) (0.008) (0.010) (1000) (0.004) (0.006) (0.008) (0.010) diam/4 150 0.075 0.102 0.15 0.20 275 0.075 0.13 0.15 0.20 (diam/4) (5OO) (0.003) (0.004) (0.006) (0.008) (900) (0.003) (0.005) (0.006) (0.008) diam/2 120 0.050 0.075 0.13 0.15 245 0.050 0.102 0.13 0.15 (diam/2) (400) (0.002) (0.003) (0.005) (0.006) (800) (0.002) (0.004) (0.005) (0.006)

383.0 40-100 As-cast 0.5 275 0.075 0.102 0.13 0.18 $4, $5, $2 395 0.075 0.102 0.13 0.18 K20, M20 A384.0 (O.O20) (900) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (1300) (0.003) (0.004) (0.005) (0.007) (C-2) 413.0 1.5 215 0.102 0.15 0.20 0.25 305 0.102 0.15 0.20 0.25 A413.0 (0.060) (700) (0.004) (0.006) (0.008) (0.010) (1000) (0.004) (0.006) (0.008) (0.010) diam/4 150 0.075 0.102 0.15 0.20 275 0.075 0.13 0.15 0.20 (diam/4) (500) (0.003) (0.004) (0.006) (0.008) (900) (0.003) (0.005) (0.006) (0.008) diam/2 120 0.050 0.075 0.13 0.15 245 0.050 0.102 0.13 0.15 (diam/2) (400) (0.002) (0.003) (0.005) (0.006) (800) (0.002) (0.004) (0.005) (0.006) 70-125 Solution treated 0.5 245 0.075 0.102 0.13 0.18 $4, $5, $2 305 0.075 0.102 0.13 0.18 K20, M20 and aged (0.020) (800) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (1000) (0.003) (0.004) (0.005) (0.007) (C-2) 1.5 185 0.102 0.15 0.20 0.25 275 0.102 0.15 0.20 0.25 (0.060) (600) (0.004) (0.006) (0.008) (0.010) (900) (0.004) (0.006) (0.008) (0.010) diam/4 120 0.075 0.102 0.15 0.20 245 0.075 0.13 0.15 0.20 (diam/4) (400) (0.003) (0.004) (0.006) (0.008) (800) (0.003) (0.005) (0.006) (0.008) diam/2 90 0.050 0.075 0.13 0.15 215 0.050 0.102 0.13 0.20 (diam/2) (300) (0.002) (0.003) (0.005) (0.006) (700) (0.002) (0.004) (0.005) (0.008) Machining of Aluminum and Aluminum Alloys / 787

Table 25 (continued) I High~peeds~el tool I ] Carbide tool I Radial [ Feed, mm/tooth (in./tooth)--1 [ Feed, mm/tooth (in./tooth) [ Hardness, depth of Speed, with a cutter diameter of: Tool material Speed, with a cutter diameter of: Tool material HB cut(a) m/min 10 mm 12 mm 18 mm 25-50 mm grade, ISO m/min 10 mm 12 mm 18 mm 25-50 mm grade, iSO Material (500 kg) Condition mm (in.) (sfm) (~ in.) (I/zin.) (3/4in.) (1-2 in.) (AISI) (din) (3/8 in.) (½ in.) (¥4 in.) (1-2 in.) (C) 390.0 40-100 As-cast 0.5 90 0.075 0.102 0.13 0.18 $4, $5, $2 185 0.075 0.102 0.13 0.18 K20, M20 392.0 (0.020) (300) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (600) (0.003) (0.004) (0.005) (0.007) (C-2) 1.5 60 0.102 0.15 0.20 0.25 150 0.102 0.15 0.20 0.25 (0.060) (200) (0.004) (0.006) (0.008) (0.010) (500) (0.004) (0.006) (0.008) (0.010) diam/4 53 0.075 0.102 0.13 0.18 120 0.075 0.13 0.15 0.20 (diam/4) (175) (0.003) (0.004) (0.005) (0.007) (400) (0.003) (0.005) (0.006) (0.008) diam/2 46 0.050 0.075 O. 102 O. 13 90 0.050 O. 102 O. 13 O. 15 (diam/2) (150) (0.002) (0.003) (0.004) (0.005) (300) (0.002) (0.004) (0.005) (0.006) 70-125 Solution treated 0.5 76 0.075 0.102 0.13 0.18 $4, $5, $2 150 0.075 0.102 0.13 0.18 K20, M20 and aged (0.020) (250) (0.003) (0.004) (0.005) (0.007) (M2, M3, M7) (500) (0.003) (0.004) (0.005) (0.007) (C-2) 1.5 60 0.102 0.15 0.20 0.25 120 0.102 0.15 0.20 0.25 (0.060) (200) (0.004) (0.006) (0.008) (0.010) (400) (0.004) (0.006) (0.008) (0.010) diam/4 46 0.075 O. 102 O. 13 O. 18 90 0.075 O. 13 O. 15 0.20 (diam/4) (150) (0.003) (0.004) (0.005) (0.007) (300) (0.003) (0.005) (0.006) (0.008) diam/2 38 0.050 0.075 O. 102 O. 13 60 0.050 O. 102 O. 13 O. 15 (diam/2) (125) (0.002) (0.003) (0.004) (0.005) (200) (0.002) (0.004) (0.005) (0.006)

(a) For standard-length end mills, maximum axial depth can be up to 1.5 times the cutter diameter. Source: Ref 5 or kerosene, or of petroleum and turpen- the land to prevent the pickup of work metal For tapping blind holes less than 3.2 mm tine, are especially recommended. Sulfur- when the tap is withdrawn. Pitch diameters (I/8 in.) in diameter, spiral flutes should be ized and chlorinated oils are often used, but should be one thread class higher than those avoided. For best size control, it is prefer- they are likely to stain the work. With normally used for steel to compensate for able not to bring the chip up the flute but to carbide reamers, emulsions of soluble oil elastic deformation during the tapping pro- push it ahead of the tap with a spiral point. and water are the most widely used cutting cess. The efficiency of tapping may be greatly fluids. Taps with a diameter less than 9.5 mm (3/8 improved by a change in tooling or method-- Reaming and Burnishing. When diffi- in.) should have no more than two flutes. for example, a change from a solid tap to a culty is encountered in obtaining the desired Larger taps should have the maximum num- collapsible tap. tolerance and surface finish, it may be nec- ber of flutes that will give the relationships The tapping speed recommended for essary to employ two-stage finishing--for of land width to circumference shown be- aluminum is considerably higher than the example, to ream the hole 0.013 mm (0.0005 low: speeds used for steel. Alloy composition in.) under the specified dimension and then and condition, thread pitch, and method of to burnish it to size and finish requirements i--Tapcircumference---] tapping are major factors affecting tapping (see the article "Roller Burnishing" in this am in. Optimum land, % speed. Volume.) 13--25 !/2-1 ...... 33 Assuming that the thread pitch is fine (18 Reaming in Automatic Machines. A 25--44 I-I 3/4 ...... 25 to 24) and that the operation can be closely finishing reamer for use in automatic bar >44 >13/4 ...... 20 controlled (as in leadscrew tapping), the and chucking machines is shown in Fig. 20. nominal speeds given in Table 22 are gener- This reamer finishes three diameters and The straight-flute tap is satisfactory for ally suitable. faces the part to length. A radial rake angle use with many aluminum alloys. The spiral- For coarser pitches, such as 8 to 12, any of approximately 7 ° helps improve surface flute tap can be used for any of the alloys; of the speeds given in Table 22 will be finish, particularly in reaming angular sur- this is better than the straight-flute type, decreased because of the difficulty in con- faces. The varied angular spacing of the especially for tapping soft material. A spi- trolling the machine. For short thread flutes is intended to minimize slip, deflec- ral-flute tap for cutting right-hand threads lengths, speeds for tapping a coarse thread tion, and chatter. should have a right-hand spiral of about the should be about one-half the speeds given in same angle as that found on an ordinary Table 22. For long threads of the same twist drill; it should have a generous taper, pitch, the speed can be faster than for short Burnishing and this taper should be backed off. The top threads because of the longer time between rake on the front face should be approxi- starting and stopping. The use of lead con- In the roller burnishing of aluminum, mately 25 to 45 °. The rake on the back face trol devices permits higher tapping speeds tools of hardened and polished steel are enables the tap to cut rather than bind when than when no control is used. For example, normally employed to finish a surface by it is reversed, and it provides a clean thread. a speed of 35 m/min (115 sfm) was used to compressing the surface while either the The spiral-flute tap will bridge a keyway or tap 10-24 UNC threads in 2024-T4. The tool or the work is rotating. Holes in alumi- slot in a hole and aid in the movement of holes were blind and approximately 13 mm num are also sometimes burnished in pro- chips from the hole. (1/2 in.) deep. However, leadscrew control duction by pressing a beating-grade steel Taps for through holes and the harder was used. Under the same conditions but ball through the bore to improve the finish. aluminum alloys should be provided with a without leadscrew control, speed would hook angle of l0 to 20 °, a spiral point, 3 to 4 have been 18 m/min (60 sfm) maximum. threads chamfer, and a pitch diameter of Table 23 is a more detailed listing of tapping Tapping GH2 (basic plus 0.013 to 0.025 mm, or speeds and tooling used. Taps for producing threads in aluminum 0.0005 to 0.001 in.) or GH3 (basic plus 0.025 Cutting Fluid. Lard oil diluted with ker- are usually made of one of the general- to 0.038 mm, or 0.001 to 0.0015 in.). Taps osene or other low-viscosity mineral oil is purpose grades of high-speed tool steel such for blind holes and soft alloys should have usually preferred for tapping aluminum. as Ml, M7, or Ml0. Taps should have l0 to 15° hook and 40 ° fight-hand spiral Low-viscosity commercial cutting oils are polished flutes and ample backoff behind flutes. also used successfully. Soluble-oil emul- 788 / Machining of Specific Metals and Alloys

Table 26 Nominal speeds and feeds for the face milling of aluminum alloys with high-speed tool steel and carbide tools .... Carbide tool, uncoated I I n~h-speed steer tooJ I I Speed / Hardness, I Speed, Feed, Tool material Brazed, lndex~bk; Feed, Tool material HB Depth of cut(a), m/rain ram/tooth grade,ISO m/rain m/rain ram/tooth grade, ISO Material (500 kg) Condition nun (in.) (stm) (in./tooth) (AISI) (sfm) (sfm) (in./tooth) (C)

Wrought EC 3005 6066 30-80 Cold drawn 1 365 0.25 $4, $2 610 Max 0.25 KI0, M20 1060 4032 6070 (0.040) (1200) (0.010) (M2, M7) (2000) (Max) (0.010) (C-2) 1100 5005 6101 4 245 0.40 $4, $2 550 Max 0.50 KI0, M20 I 145 5050 615 I (0.150) (800) (0.015) (M2, M7) (1800) (Max) (0.020) (C-2) 1175 5052 6253 8 200 0.50 $4, $2 365 Max 0.65 K20, M30 1235 5056 6262 (0.300) (650) (0.020) (M2, M7) (1200) (Max) (0.025) (C-2) 2011 5083 6463 75-150 Solution treated 1 365 0.25 $4, $2 610 Max 0.25 KI0, M20 2014 5086 695 I and aged (0.040) (1200) (0.010) (M2, M7) (2000) (Max) (0.010) (C-2) 2017 5154 7001 4 245 0.40 $4, $2 550 Max 0.50 KI0, M20 2018 5252 7004 (0.150) (800) (0.015) (M2, M7) (1800) (Max) (0.020) (C-2) 2021 5254 7005 8 200 0.50 $4, $2 365 Max 0.65 K20, M30 2024 5454 7039 (0.300) (650) (0.020) (M2, M7) (1200) (Max) (0.025) (C-2) 2025 5456 7049 2117 5457 7050 2218 5652 7075 2219 5657 7079 2618 6053 7175 3003 6061 7178 3004 6063

Cast Sand and permanent mold AI40 F332.0 520.0 40- 100 As-cast 1 365 0.20 $4, $2 610 760 0.25 KI0 M20 201.0 333.0 535.0 (0.040) (1200) (0.008) (M2, M7) (2000) (2500) (0.010) (C-2) 208.0 354.0 705.0 4 245 0.30 $4, $2 550 610 0.40 K20 M30 213.0 355.0 707.0 (0.150) (800) (0.012) (M2, M7) (1800) (2000) (0.015) (C-2) 222.0 C355.0 A712.0 8 200 0.40 $4, $2 365 460 0.50 K30, M40 224.0 356.0 D712.0 (0.300) (650) (0.016) (M2, M7) (1200) (1500) (0.020) (C-2) 242.0 A356.0 713.0 70-125 Solution treated I 305 0.20 $4, $2 550 760 0.25 KI0, M20 295.0 357.0 771.0 and aged (0.040) (1000) (0.008) (M2, M7) (1800) (2500) (0.010) (C-2) B295.0 359.0 850.0 4 215 0.30 $4, $2 425 550 0.40 K20 M30 308.0 B443.0 A850.0 (0.150) (700) (0.012) (M2, M7) (1400) (1800) (0.015) (C-2) 319.0 514.0 B850.0 8 170 0.40 $4, $2 305 395 0.50 K30, M40 328.0 A514.0 (0.300) (550) (0.016) (M2, M7) (1000) (1300) (0.020) (C-2) A332.0 B514.0 Hiduminium RR-350

Die castings 360.0 A380.0 40-100 As-cast I 365 0.20 $4, $2 425 550 0.13 KI0, M20 A360.0 C443.0 (0.040) (1200) (0.008) (M2, M7) (1400) (1800) (0.005) (C-2) 380.0 518.0 4 245 0.30 $4, $2 350 460 0.25 KI0, M20 (0.150) (800) (0.012) (M2, M7) (1150) (1500) (0.010) (C-2) 70-125 Solution treated I 305 0.20 $4, $2 380 490 0.13 KI0, M20 and aged (0.040) (1000) (0.008) (M2, M7) (1250) (1600) (0.005) (C-2) 4 215 0.30 $4, $2 305 395 0.25 KI0, M20 (0.150) (700) (0.012) (M2, M7) (1000) (1300) (0.010) (C-2)

383.0 40-100 As-cast I 305 0.20 $4, $2 350 460 0.13 KI0, M20 A384.0 (0.040) (1000) (0.008) (M2, M7) (1150) (1500) (0.005) (C-2) 413.0 4 215 0.30 $4, $2 290 365 0.25 KI0, M20 A413.0 (0.150) (700) (0.012) (M2, M7) (950) (1200) (0.010) (C-2) 70-125 Solution treated 1 215 0.15 $4, $2 350 425 0.13 KI0, M20 and aged (0.040) (700) (0.006) (M2, M7) (1150) (1400) (0.005) (C-2) 4 185 0.25 $4, $2 275 335 0.25 KI0, M20 (0.150) (600) (0.010) (M2, M7) (900) (1100) (0.010) (C-2)

390.0 40-100 As-cast I 50 0.15 $4, $2 130 150 0.13 KI0, M20 392.0 (0.040) (165) (0.006) (M2, M7) (425) (500) (0.005) (C-2) 4 43 0.23 $4, $2 115 135 0.25 KI0, M20 (0.150) (140) (0.009) (M2, M7) (370) (450) (0.010) (C-2) 70-125 Solution treated I 47 0.15 $4, $2 115 145 0.13 KI0, M20 and aged (0.040) (155) (0.006) (M2, M7) (375) (475) (0.005) (C-2) 4 40 0.23 $4, $2 105 130 0.25 KI0, M20 (0.150) (130) (0.009) (M2, M7) (350) (425) (0.010) (C-2)

(a) Depth of cut is measured parallel to axis of cutter. Source: Ref 5 Machining of Aluminum and Aluminum Alloys / 789

Table 27 Nominal speeds and feeds for the face milling of aluminum alloys with diamond tools

Hardness, I Depth of cut(a) I I Speed I I Feed I Material HB (500 kg) Condition mm in. m/min sfm mm/tooth in./tooth Wrought EC 2218 5252 6253 30--150 All 0.25--0.75 0.010--0.030 610 2000 0.13 0.005 1060 2219 5254 6262 0.75-1.25 0.030--0.050 425 1400 0.25 0.010 1100 2618 5454 6463 1.25-2.50 0.050-0.100 305 1000 0.40 0.015 1145 3003 5456 6951 1175 3004 5457 7001 1235 3005 5652 7004 2011 4032 5657 7005 2014 5005 6053 7039 2017 5050 6061 7049 2018 5052 6063 7050 2021 5056 6066 7075 2024 5083 6070 7079 2025 5086 6101 7175 2117 5154 6151 7178 Cast Sand and permanent mold AI40 319.0 357.0 A712.0 40-100 As-cast 0.25--0.75 0.010--0.030 1005 3300 0.13 0.005 201.0 328.0 359.0 D712.0 0.75-1.25 0.030--0.050 840 2750 0.25 0.010 208.0 A332.0 B443.0 713.0 1.25-2.50 0.050--0.100 550 1800 0.40 0.015 213.0 F332.0 514.0 771.0 70-- 125 Solution treated and aged 0.25--0.75 0.010--0.030 915 3000 0.13 0.005 222.0 333.0 A514.0 850.0 0.75-1.25 0.030--0.050 760 2500 0.25 0.010 224.0 354.0 B514.0 A850.0 1.25-2.50 0.050-0.100 550 1800 0.40 0.015 242.0 355.0 520.0 B850.0 295.0 C355.0 535.0 B295.0 356.0 705.0 308.0 A356.0 707.0 Hiduminium RR-350

Die castings 360.0 A380.0 40-100 As-cast 0.25-0.75 0.010--0.030 1100 3600 0.13 0.005 A360.0 C443.0 0.75-1.25 0.030--0.050 975 3200 0.25 0.010 380.0 518.0 1.25-2.50 0.050--0.100 840 2750 0.40 0.015

383.0 40-100 As-cast 0.25-0.75 0.010-O.030 1005 3300 0.13 0.005 A384.0 0.75-1.25 0.030--0.050 840 2750 0.25 0,010 413.0 1.25-2.50 0.050--0.100 550 1800 0.40 0.015 A413.0

390.0 40-100 As-cast 0.25--0.75 0.010--0.030 855 2800 0.13 0.005 392.0 0.75-1.25 0.030--0.050 670 2200 0.25 0.010 1.25-2.50 0.050--0.100 470 1550 0.40 0.015 (a) Depth of cut is measured perpendicular to the axis of the cutter. Source" Ref 5 sions are sometimes used, but they will not by substituting soluble oil (in a 1:20 mixture as fast as those used for their cutter-type provide as good a finish as the other cutting with water) for mineral oil as the cutting counterparts. Limitations are the same for fluids mentioned. However, the following fluid, thread finish became acceptable, and form tapping as for cutting tapping, and the example describes an application in which a productivity and tap life were increased: same cutting fluids are used. The following soluble oil was more effective than a miner- example compares performance of cutting al oil, probably because of the lower viscos- Mineral oil Soluble oil taps and form taps. ity of the soluble-oil emulsion, which al- Holes tapped/h ...... 1480 1520 Example 6: Tapping: Cutting Venus lowed it to penetrate more readily to the Total tap life, holes ...... 6250 8900 Forming. The performance of No. 4-40 cutting edges of the tap and also allowed it cutting taps was compared with that of form to flow in greater volume for flushing away Optimum results are obtained when the (chipless) taps in tapping a through hole in chips. cutting fluid is applied with pressure, espe- a 6.4 mm (1/4 in.) section of alloy 380 Example 5: Mineral Oil Versus Soluble cially when tapping blind holes. die castings. Both taps were used in a Oil for Tapping. An automatic tapping Form Tapping. If chips are a serious leadscrew machine at 3000 rev/min. The machine was used for cutting 6-32 UNC-2B problem and if the hole wall is thick enough cutting fluid was a high-grade cutting oil threads in through holes (6.4 mm, or I/4 in., to support the pressure of the tool, a form with low sulfur content. Although the pro- deep) in alloy 2024-T4. Taps were straight- (chipless) tap can be used (see the article duction rate for both taps was 400 pieces flute, spiral-point, with 15 ° chamfer angle "Tapping" in this Volume). Although a per hour, the production rate per setup with and 18° hook, and they were operated at 75% thread is generally recommended for the form tap (1200 pieces) was double the 4150 rev/min (37 m/min, or 122 sfm). Cut- cut threads, tap drilling for 55 to 65% thread rate obtained when the cutting tap was ting fluid was mineral oil. is practical for threads produced with a used. Chip congestion, together with buildup of form tap. All aluminum alloys except the In tapping these die castings, a form tap work metal on the cutting edges of the tap, high-silicon (12%) die casting alloys can be was superior to a cutting tap in all sizes resulted in rough threads and tap breakage. tapped with form taps. from No. 2 through No. 8, provided the hole Variations in tapping speed were tried but In some applications, form taps have wall was thick enough to support the pres- did not alleviate these problems. However, been successfully operated at speeds twice sure of the form tap. 790 / Machining of Specific Metals and Alloys

Table 28 Nominal speeds and feeds for the end milling and slotting of aluminum alloys with high-speed tool steel tools

Feed, mm/tooth (in./tooth), at a width of slot of: High-speed tool Speed, steel material Hardness, Axial depth of m/min 10 mm 12 mm 18 mm 25-50 mm grade, LSO Material HB (500 kg) Condition cut, mm (in.) (sfm) (~ in.) (½ in.) (~/4 in.) (1-2 in.) (AISI)

Wrought EC 2218 5254 6463 30--80 Cold drawn 0.75 150 0.075 0.13 0.15 0.25 $4, $5, $2 1060 2219 5454 6951 (0.030) (500) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) 1100 2618 5456 7001 3 135 0.102 0.15 0.20 0.30 1145 3003 5457 7004 (0.125) (450) (0.004) (0.006) (0.008) (0.012) 1175 3004 5652 7005 diam/2 120 0.075 0.13 0.15 0.20 1235 3005 5657 7039 (diam/2) (400) (0.003) (0.005) (0.006) (0.008) 2011 4032 6053 7049 diam/1 105 0.050 0.075 0.13 0.15 2014 5005 6061 7050 (diam/l) (350) (0.002) (0.003) (0.005) (0.006) 2014 5050 6063 7075 75-150 Solution treated and aged 0.75 145 0.075 0.13 0.15 0.25 $4, $5, $2 2017 5052 6066 7079 (0.030) (475) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) 2018 5056 6070 7175 3 130 0.102 0.15 0.20 0.30 2021 5083 6101 7178 (0.125) (425) (0.004) (0.006) (0.008) (0.012) 2024 5086 6151 diam/2 115 0.075 0.13 0.15 0.20 2025 5154 6253 (diam/2) (375) (0.003) (0.005) (0.006) (0.008) 2117 5252 6262 diam/1 100 0.050 0.075 0.13 0.15 (diam/l) (325) (0.002) (0.003) (0.005) (0.006) Cast Sand and permanent mold AI40 319.0 357.0 A712.0 40-100 As-cast 0.75 120 0.075 0.13 0.15 0.25 $4, $5, $2 201.0 328.0 359.0 D712.0 (0.030) (400) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) 208.0 A332.0 B443.0 713.0 3 105 0.102 0.15 0.20 0.30 213.0 F332.0 514.0 771.0 (0.125) (350) (0.004) (0.006) (0.008) (0.012) 222.0 333.0 A514.0 850.0 diam/2 90 0.075 0.13 0.15 0.20 224.0 354.0 B514.0 A850.0 (diam/2) (300) (0.003) (0.005) (0.006) (0.008) 242.0 355.0 520.0 B850.0 diam/l 76 0.050 0.075 0.13 0.15 295.0 C355.0 535.0 (diam/I) (250) (0.002) (0.003) (0.005) (0.006) B295.0 356.0 705.0 70-125 Solution treated and aged 0.75 115 0.075 0.13 0.15 0.25 $4, $5, $2 308.0 A356.0 707.0 (0.030) (375) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) Hiduminium RR-350 3 100 0.102 0.15 0.20 0.30 (0.125) (325) (0.004) (0.006) (0.008) (0.012) diam/2 84 0.075 0. ! 3 0.15 0.20 (diam/2) (275) (0.003) (0.005) (0.006) (0.008) diam/I 69 0.050 0.075 0.13 0.15 (diam/l) (225) (0.002) (0.003) (0.005) (0.006)

Die castings 360.0 40-100 As-cast 0.75 150 0.075 0.13 0.15 0.25 $4, $5, $2 A360.0 (0.030) (500) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) 380.0 3 135 0.102 0.15 0.20 0.30 A380.0 (0.125) (450) (0.004) (0.006) (0.008) (0.012) C443.0 70-125 Solution treated and aged 0.75 145 0.075 0.13 0.15 0.25 $4, $5, $2 518.0 (0.030) (475) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) 3 130 0.102 0.15 0.20 0.30 (0.125) (425) (0.004) (0.006) (0.008) (0.012)

383.0 40-100 As-cast 0.75 135 0.075 0. ! 3 0.15 0.25 $4, $5, $2 A384.0 (0.030) (450) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) 413.0 3 130 0.102 0.15 0.20 0.30 A413.0 (0.125) (425) (0.004) (0.006) (0.008) (0.012) 70-125 Solution treated and aged 0.75 130 0.075 0.13 0.15 0.25 $4, $5, $2 (0.030) (425) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) 3 120 0.102 0.15 0.20 0.30 (0.125) (400) (0.004) (0.006) (0.008) (0.012)

390.0 40-100 As-cast 0.75 53 0.075 0.13 0.15 0.25 $4, $5, $2 392.0 (0.030) (175) (0.003 ) (0.005) (0.006) (0.010) (M2, M3, M7) 3 46 0.102 0.15 0.20 0.30 (0.125) (150) (0.004) (0.006) (0.008) (0.012) 70-125 Solution treated and aged 0.75 46 0.075 0.13 0.15 0.25 $4, $5, $2 (0.030) (150) (0.003) (0.005) (0.006) (0.010) (M2, M3, M7) 3 38 0.102 0.15 0.20 0.30 (0.125) (125) (0.004) (0.006) (0.008) (0.012) Source: Ref 5

Drilling and tapping of high-silicon best tool material and geometry becomes with a volume and pressure sufficient to alloy 390 (Ref 2) can be successfully ac- more significant as the hole-depth-to-diam- reach the cutting lips of the tool and to flush complished with the same tool materials eter ratio increases. the chips out of the hole. Inadequate cool- and geometries used for other aluminum The use of natural or synthetic soluble-oil ant can result in chips packing in the flutes casting alloys; however, cutting must be cutting fluids is strongly recommended. of a drill or the teeth of a tap, a condition performed at lower speeds. Selection of the Coolant should be directed into the hole that can cause rapid wear, poor hole finish, Machining of Aluminum and Aluminum Alloys / 791

,cCIomp /-Workp~ece AI- 7% Mg coolant and by moving the tool through the ~/ ~ casting ,, ~..-~"~- work in as few revolutions as possible. This creates an easier-to-remove, substantial chip. Coolant-fed drills were also evaluated, but with mixed results. Carbide-tip, cool- fill ant-fed drills produced 1000 holes at a speed i of 90 m/min (300 sfm) and a feed rate of 508 t 3 I mm/min (20 in./min) (Fig. 21). Not only did this accomplish a much higher production Operating conditions(a) rate, but hole size control, roundness, Form milling (one pass), mm/min (in./min) .... 75 (3) straightness, and finish were much im- Standard milling (five passes), mm/min (in./min) proved over noncoolant-fed drills. Drilling 1 Side mill slot ...... 203 (8) 2 Side mill center slot ...... 203 (8) Cutter details with coolant-fed, high-speed tool steel, on 3 Straddle mill reliefs ...... 127 (5) Type ...... Face mill, inserted blade the other hand, resulted in no productivity 4 Straddle mill two 6.4 mm (I//4 in.) x 45 ° Size, mm (in.) ...... 152 (6) diameter or hole quality improvement over the best chamfers ...... 203 (8) Number of teeth ...... 12 solid drills. 5 Straddle mill two 3.2 mm (I/8 in.) radii ..... 203 (8) Material ...... Carbide-tip blades Far better tool life results have been Time analysis Operating conditions reported using diamond-tip gun drills in Time/piece, min Speed, at 2345 rev/min, similar-size holes (10.79 mm, or 0.425 in.) at Form milling ...... 2.54 m/min (sfm) ...... 1120 (3680) a hole depth of eight diameters when boring Standard milling ...... 7.79 Feed, mm/tooth (in./tooth) .. 0.14 (0.0055) Time saved by using form milling ...... 5.25 Depth of cut, mm (in.) ...... 3.2 (I/8) max through solid material. When used in the (a) For all operations, cutter speed was 23 m/min (75 sfm), and Cutting fluid ...... None mass production of automobile engine cyl- sulfurized oil was used as the cutting fluid. Setup time, h ...... 1.5 inders, these diamond-tip gun drills give a Downtime for changing service life 60 times that of customary twist tools, min ...... 15 Fig. 27 Contour that could be milled in a single Production rate, pieces/h .... 31 drills. pass using a form cutter or in five opera- Cutter life, pieces/grind ..... - 100 Tapping tests were conducted with vari- tions using standard milling cutters. Dimensions in figure Tolerances, mm (in.) ous types of thread cutting and thread form- given in inches Flatness ...... Within 0.025 (0.001) ing tools. No thread cutting taps threaded Width ...... -+0.08 (-+0.003) Parallelism error ...... 0.13 (0.005) max more than 360 holes before they would no 35 ° for 11/2 threads. This chamfer will ensure Finish, I~m (win.) ...... 1.60 (63) longer gage to size. The best performance, a smooth, even start. more than 1000 holes, was achieved with a Speeds up to 40 m/min (130 sfm) for the Simultaneous face milling of parallel sur- standard form tap having four lobes. It has nonheat-treated cast alloys and about 30 m/ Fig. 26 faces on opposite sides of a casting. also been shown that form taps produce the min (100 sfm) for the other alloys can be Dimensions in figure given in inches strongest threads. The conditions that were used, if the length and pitch of the thread most successful for both the drilling and and the equipment used permit control at tapping experiments are given in Table 24. these speeds. Speeds no more than half of and blowout fracturing of the exit surface the above are more often used because at upon emergence of a through hole drill. the higher speeds control is more difficult, Even more important with respect to alloy Single-Point Threading especially when threading short lengths or 390 is that the chips are exceptionally abra- close to a shoulder. Single-point threading tools of conven- sive and can wear on the lip and margin of a tional design are used to cut both internal drill if not quickly flushed from the hole. and external threads on aluminum alloys. Milling In a recent study, several drill and tap Speeds of 150 m/min (500 sfm) are common, materials and geometries were evaluated, The characteristics of chip formation although higher speeds have been used. and cutting conditions were optimized for sometimes cause difficulty in the milling of Typical practice is represented by the fol- the most promising combinations. Chip aluminum alloys. In some applications, chip lowing example. packing became a problem at a depth of Example 7: Single-Point Threading of ejection in the milling of deep slots or heavy approximately three diameters (13 mm, or cuts can be improved by changing from an Die Castings. A fine-pitch thread (pitch I/2 in., holes), with slow and regular helix alloy in the O or F temper to one in the T4 diameter: 42.113/41.946 mm, or 1.6580/ drills (24 to 33 °) causing breakthrough blow- or T6 temper. In the T tempers, the chip is 1.6514 in.) was machined in an alloy 380 die outs and rapid drill wear. Solid high-speed much less likely to clog the cutter. Howev- casting (Fig. 22) with a single-point carbide tool steel drills with a high helix angle (38 °) er, when aluminum is milled in the heat- tool. This alloy was susceptible to chipping and a parabolic flute shape showed less treated condition, the production rate may and tearing if high cutting pressure was wear under all cutting conditions than high- be lower because a lighter feed rate may be applied, particularly if the die casting was helix (40 °) drills that had a standard flute necessary. porous in the area being threaded. design. Power Requirements. Metal removal A speed of 20 m/min (70 sfm) and a feed rates greater than 2600 mm3/min/kW (3.0 rate of 381 mm/min (15 in./min) worked well Die Threading in.3/min/hp) can be readily attained in the with a high-helix, parabolic flute shaped production milling of aluminum alloys. drill (Fig. 21). A tool life of over 1000 holes Circular chasers for die threading alumi- Some rules applicable to milling aluminum was achieved when drilling 13 mm (1/2 in.) num alloys should have a hook angle of 20 ° are: holes to a depth of five to six diameters. and a face angle of 2 °. When threading with Heavy feed rate (in terms of inches per tangential chasers, a combination of nomi- • If feed per tooth is doubled, the horse- revolution) produced a better tool life than nal back rake angle of 20° and side rake power at the cutter must be increased in light feed rate. angle of 0 ° is generally best. the ratio of 3:2, or 50% The best method of drilling alloy 390 is to To avoid damage to the first few threads, • If the width of cut is doubled, the horse- move the chips quickly by flushing with chasers should have a lead chamfer of 25 to power at the cutter must be doubled 792 / Machining of Specific Metals and Alloys

7075 alloy forging .~ Best results can be obtained with a cutter 0.20 0.008 that has fewer teeth and larger positive-rake [--~ A-A angles than cutters for milling steel. Fewer E 0.15 0.006 .t5 teeth permit more chip space, which is =._" especially important in milling aluminum 0.10 ---" 0.004 ~ 13 ~ o because speeds are usually much greater o 0.05 0.002 o than those used in milling steel. To prevent I- chatter, however, the cutter should have o o enough teeth so that at least two teeth are 0 100 200 300 400 engaged at all times. Number of blocks Because of the high speeds used in milling Fig. 29 Tool wear curves for the single-tooth mill- aluminum, careful consideration must be ing of alloy 390 engine blocks (wet) at given to the effect of centrifugal force on the 0.30 mm/rev (0.012 in./rev), A, carbide, 150 m/rain (492 sfm); B, diamond, 1500 m/min (4920 sfm); C, cutter. This is more important with cutters diamond, 150 m/rain (492 sfm). Source- Ref 2 of large diameter. Cutter bodies in which teeth are wedge locked and from which some of the teeth have been removed to Some cutters for general routing purposes provide greater chip space should not be may have two flutes with a helix angle of operated at high speed. All cutters for high- 25 ° . The best overall performance in routing } speed milling that have inserted teeth accurate slots or grooves is with a two-flute 66 (brazed or mechanically secured) should be cutter having a 45 ° helix angle, with the dynamically balanced. Careful attention direction of helix and of cut the same. Machine ...... Three-axis profile milling machine, should be given to cutter adapters, cutter Cutters for routing stacked sheet stock numerically holders, arbors, spacers, and other compo- should be designed with a single flute and a controlled, 4370 x nents that rotate with the cutter. helix angle of 25 to 45 °. An integral pilot 1320 x 457 mm (172 End mills for aluminum should have running in an outboard bearing is used on x52x 18in.) Cutter sharp rake angles with sufficient clearance some of these cutters to help control deflec- Material ...... Modified M2 to prevent heeling. Neither rake nor clear- tion. high-speed tool steel ance angles should be excessive, or digging- All cutters should have a 15 ° hook angle Number of cutters ...... 27 in will result. The cutter should contact the Size of cutters, mm (in.) ... 19. l (0.75) diameter x on the cutting lip. The flute should be of 2.3 95 (33/4) long to 76.2 workpiece in such a manner that any tor- mm (0.09 in.) uniform depth, with a smooth (3.00) diameter x 203 sional, or lateral, deflection will decrease gullet extending 3.2 mm (1/8 in.) inward from (8) long the depth of cut. the lip. The lips should be radially relieved Rake angles ...... l0 ° radial, 30 ° axial Flute form and surface finish in the flute on the periphery to 0.08 to 0.18 mm (0.003 Operating conditions are important. Consequently, many of these to 0.007 in.) per 1.6 mm (IA6 in.) width of Speed, m/rain (sfm) ...... 60-135 (200--450) cutters are made by grinding from the solid land behind the cutting edge. Feed, mm/tooth (in./tooth) ... 0.1.%0.33 (0.006--0.013) after heat treatment. The lips of an end mill Special-Geometry End Mills for Alumi- Depth of cut, axial (of either the plain two-flute or ball-nose num dimension, mm (in.) ...... 3.0-178 (0.12-7.00) (Ref 1, 4). An interesting example of Width of cut, radial type) that is to be used for making plunge fluted cutters designed specifically for ma- dimension, mm (in.) ...... 9.40 (0.37) to cutter cuts directly into solid aluminum should chining aluminum is provided by the end diameter have slightly greater clearances than is nor- mills shown in Fig. 23. The first departure Machining time, each part, h .. 91(a) mal for these cutters in order to prevent Cutting fluid ...... Soluble oil: water (1 "25) from standard end-mill design is an increase Tolerance on critical heeling. Preferably, the faces of the cutting to 45 ° in the helix angle from the standard dimensions, mm (in.) ...... _+0.05 (_+0.002) edges should have a surface finish of 0.038 30°--the equivalent of high, positive side Surface finish, I~m (l~in.) ..... 1.50-3.05 (60--120) i~m (1.5 I~in.) and should never be rougher rake. The second departure is in the form of (a) Roughing, 29 h; finishing, 62 h than 0.088 I~m (3.5 i~in.). the tooth, the face of which provides a In making plunge cuts directly into alumi- curved, positive-rake, polished primary sur- "'u=='- 28 Part that was machined from a large num, the problem of chip ejection becomes face followed by a secondary undercut that blocker forging by NC profile milling. acute. For this reason, it is best to feed the blends into the web (Fig. 23). The polished Dimensions in figure given in inches cutter into the material in such a way that, primary face surface and the discontinuity for each axial advance of the cutter (equal provide smooth chip flow and minimize the to about half the cutter diameter), the cutter • If the depth of cut is doubled, the horse- adherence of chips that invariably leads to is fed laterally about one diameter in an power at the cutter must be increased in clogging. oscillating pattern until the desired depth of the ratio of 1.9:l, or 90% Two versions of these aluminum cutting cut is reached, rather than making a purely • If the depth of cut is halved and horse- end mills are available---one for heavy met- axial cut. power at the cutter remains the same, the al removal applications (such as pocketing For milling slots, or pockets, where the feed may be increased by a factor of 2.5 and rough profiling) and one for finishing end of the cutter is in contact with the operations in which the radial depth of cut • If the speed of the cutter is doubled and workpiece, it is usually best to have the the feed per tooth is halved, the horse- approximates 5% of tool diameter. The lat- same direction for the cut and the helix. power at the cutter must be increased by ter type incorporates an unrelieved circular However, when profiling with the periphery about 30% land of 0.08 to 0.13 mm (0.003 to 0.005 in.) of the cutter, where the end of the cutter is width on the periphery to minimize any Cutter Design. For efficiency in milling not in contact with the workpiece, a combi- tendency toward chatter, vibration, or aluminum, the cutter should have a radial nation of fight-hand cut, left-hand helix squealing. rake angle of l0 to 20 °, an axial rake angle of gives the best results. Somewhat similar to this concept is the 15 to 45 °, and end or peripheral clearance of Router bits are a special type of end mill use of a molded chip-breaker style of car- l0 to 12°. Form-relieved cutters should have that is modified to ensure chip ejection at bide insert. This type of insert increases the a relief of l0 ° on the profile. the speeds normally used for these cutters. positive rake (nominally 5 ° rake, with 5 ° Machining of Aluminum and Aluminum Alloys / 793

Cutting speed, sfm milling cartridge (I 2) 300 500 1000 2000 3000 1000

500

I 200 I ! Diamond :l-tip boring insert (I) I 100 I L t.) _o ~ 50 .c_

E I O I_ ~ 20: .ID E z / ~--'-'-''-''~ffng oo.,oe

5 -, Diamond-lip chamfering insert (1. roughing culler only) r

1 90 150 300 610 910 Cutting speed, m/min Fig. 31 Schematic of a combination boring-milling cutter with diamond-tip cutters machining a 380 aluminum Fig. 30 Tool life of carbide and diamond tools alloy transmission extension housing at 3840 m/min (12 600 sfm) when milling alloy 390 engine blocks (dry). Source: Ref 2

cut, and the type of cut (rough or finishing (2000 to 4000 sfm) are frequently used, as cut). Various formulas have been developed illustrated in the following example. clearance in the matching toolholder) while by cutter manufacturers to determine the Example 8: Face Milling Parallel Sides maintaining stronger edge geometry. optimum number of teeth for all types and Simultaneously in a Duplex Machine. Although the most common geometry for sizes of milling cutters for milling alumi- Face milling two opposite sides was the first positive-rake inserts provides a relief of 10 num. For good cutter performance, as a machining operation performed on the cast- to I l °, which is decreased by the top rake general rule, not more than two of the teeth ing shown in Fig. 26. Maintaining required angle at which it is held, it is also possible to should engage the cut at the same time. The dimensions in subsequent operations de- specify carbide inserts with higher relief teeth should have a strong cross section but pended greatly on the accuracy obtained in angles. One supplier of these inserts recom- ample chip space. milling the sides. Parallelism was easily mends a 20 ° relief insert for turning applica- Speed. Nominal speeds for peripheral, maintained by milling the two sides simul- tions and 26° for millingmand without any face (high-speed, carbide, and diamond), taneously because the workpiece did not chip control groove, especially for the gum- and end milling are given in Tables 25 to 28. have to be moved and reclamped. mier alloys. This allows the top surface of Factors affecting speed are the alloy being A 7.5 kW (10 hp) duplex machine was the insert to be lapped or polished to the milled, tool material, and depth of cut used for this operation. This type of ma- high finish desirable for improved chip flow. (roughing or finishing). A major variable chine afforded two advantages in addition Special end mills and face mills designed that is not reflected in Tables 25 to 28 is chip to good dimensional control. First, after the with two carbide inserts for high milling disposal. If the chips can be adequately initial cut, the spindles were advanced speeds can be used to reduce milling time. ejected from the cutting zone, speeds for slightly to take a skim (finish) cut as the Cutters for operations at high speeds should carbide cutters are limited mainly by the table returned to the start position. Second, be statically and dynamically balanced. capabilities of the machine. However, when milling both sides at one time increased The carbide inserts in the cutter shown in the speed is too high for a particular setup, productivity, compared to milling each side Fig. 24 can be adjusted for the depth of cut the cutter teeth may not have sufficient time separately. Details of the milling cutters and and the most effective rake angle. The radi- to remove stock at the proper rate because operation are tabulated below Fig. 26. al and axial rake angles of the end milling of erratic feeding; the cutter teeth may dig Feed. Nominal feeds for peripheral, face, cutter shown in Fig. 25 result from the and fide, or cut and skip. Optimum speed and end milling are given in Tables 25 to 28. position of the insert in the body of the depends on the machine, work metal, depth For wheel-type cutters (peripheral and cutter. This cutter removed a large amount of cut, and power. face), the alloy being milled has little effect of aluminum and incorporates adequate Under certain conditions, milling speeds on feed. Depth of cut has some effect, chip space. as high as 4600 m/min (15 000 sfm) have although usually this is not large. Some The number of teeth in a cutter is largely been used. However, speeds this high are reduction in feed is usually made when determined by its diameter, the depth of the rarely feasible. Speeds of 600 to 1200 m/min high-speed tool steel cutters are replaced by 794 / Machining of Specific Metals and Alloys

Table 29 Nominal speeds and feeds for circular sawing of aluminum alloys with high-speed tool steel blades Soad stock HJO-qa~'d t,~ Hardness, HB diunteter or Pitch, mm/tooth Cutting speed, Feed, mm/tooth steel material Material (500 kg) Condition thickness, mm (in.) (in./tooth) m/rain (sfm) (in./tooth) grade, ISO (AISI)

Wrought EC 2218 5252 6253 30--80 Cold drawn 6--80 5-30 305 0.25 $4, $2 1060 2219 5254 6262 (1/4,--3) (0.20-1.10) (1000) (0.010) (M2, M7) 1100 2618 5454 6463 80-160 18--40 245 0.25 1145 3003 5456 6951 (3-6) (0.70-1.50) (800) (0.010) 1175 3004 5457 7001 160--250 25-45 185 0.30 1235 3005 5652 7004 (6--9) (1.00-I.80) (600) (0.012) 2011 4032 5657 7005 250--400 30--60 150 0.30 2014 5005 6053 7039 (9-15) (1.20-2.40) (500) (0.012) 2017 5050 6061 7049 75-150 Solution treated and aged 6--80 5-30 305 0.25 $4, $2 2018 5052 6063 7050 (I/,-3) (0.20-1.10) (1000) (0.010) (M2, M7) 2021 5056 6066 7075 80--160 18--40 245 0.25 2024 5083 6070 7079 (3--6) (0.70-1.50) (800) (0.010) 2025 5086 6101 7175 160-250 25-45 185 0.30 2117 5154 6151 7178 (6--9) (1.00-1.80) (600) (0.012) 250--400 30--60 150 0.30 (9-15) (1.20-2.40) (500) (0.012) Cast Sand and permanent mold AI40 319.0 357.0 A712.0 40-100 As-cast 6-80 5-30 380 0.25 $4, $2 201.0 328.0 359.0 D712.0 (I/,--3) (0.20-1.10) (1250) (0.010) (M2, M7) 208.0 A332.0 B443.0 713.0 80-160 18-40 305 0.25 213.0 F332.0 514.0 771.0 (3-6) (0.70-1.50) (1000) (0.010) 222.0 333.0 A514.0 850.0 160-250 25--45 230 0.30 224.0 354.0 B514.0 A850.0 (6-9) (1.00-1.80) (750) (0.012) 242.0 355.0 520.0 B850.0 250-400 30--60 185 0.30 295.0 C355.0 535.0 (9-15) (1.20-2.40) (600) (0.012) B295.0 356.0 705.0 70-125 Solution treated and aged 6-80 5-30 305 0.25 $4, $2 308.0 A356.0 707.0 (!/~3) (0.20-1.10) (1000) (0.010) (M2, M7) Hiduminium RR-350 80-160 18-40 245 0.25 (3-6) (0.70-1.50) (800) (0.0 I0) 160-250 25-45 185 0.30 (6-9) (1.00-1.80) (600) (0.012) 250--400 30--60 150 0.30 (9-15) (1.20-2.40) (500) (0.012)

Die castings 360.0 A380.0 40-100 As-cast 6--80 5-30 380 0.25 S4, $2 A360.0 C443.0 (i/4-3) (0.20-1.10) (1250) (0.010) (M2, M7) 380.0 518.0 70-125 Solution treated and aged 6--80 5-30 305 0.25 $4, $2 (I/,--3) (0.20-1. I0) (1000) (0.0 I0) (M2, M7)

383.0 40-100 As-cast 6--80 5-30 380 0.25 $4, $2 A384.0 (!14.--3) (0.20-1.10) (1250) (0.010) (M2, M7) 413.0 70-125 Solution treated and aged 6--80 5-30 305 0.25 $4, $2 A413.0 (i/4,--3) (0.20-1.10) ( i 000) (0.010) (M2, M7)

390.0 40-100 As-cast 6--80 5-30 150 0.25 $4, $2 392.0 (V4-3) (0.20- I. 10) (500) (0.0 ! 0) (M2, M7) 70-125 Solution treated and aged 6--80 5--30 150 0.25 $4, $2 (!/~3) (0.20-1.10) (500) (0.010) (M2, M7) Source: Ref 5

Table 30 Nominal speeds and feeds for the circular sawing of aluminum alloys with carbide-tip tools Quantity of available data was limited. Performance data are presented instead of the general recommendations given in other machining operations in this Volume. Hardness, Solid stock diameter or Carbide tool HB thickness [ Pitch I I Feed I F Cutting speed ----7 material grade (500 kg) Condition mm in. mm/tooth in./tooth mm/tooth in./tooth m/min sfm ISO C <60 ...... Cold drawn 6-25 0.25-1 15-25 0.60-1.00 0.25 0.010 4575 15 000 K30 C-2 25-50 I-2 23-35 0.90-1.40 0.25 0.010 4575 15 000 50-100 2-4 25-50 1.00-2.00 0.13 0.005 3650 12 000 100-150 4--6 40--65 1.50-2.50 0.13 0.005 3650 12 000 60-150 ...... Solution treated 6-25 0.25-1 15-25 0.60-1.00 0.18 0.007 3650 12 000 K30 C-2 and aged 25-50 1-2 23-35 0.90-1.40 0.18 0.007 3650 12 000 50-100 2-4 25-50 1.00--2.00 0.075 0.003 3050 10 000 100-150 4--6 40--65 1.50-2.50 0.075 0.003 3050 10 000 > 150 ...... Solution treated 6-25 0.25-1 15-25 0.60-1.00 0.13 0.005 3050 10 000 K30 C-2 and aged 25-50 1-2 23-35 0.90-1.40 0.13 0.005 3050 10 000 50-100 2--4 25-50 1.00-2.00 0.050 0.002 2750 9 000 100-150 4--6 40--65 1.50-2.50 0.050 0.002 2750 9 000 Source: Ref 5 Machining of Aluminum and Aluminum Alloys / 795

Table 31 Nominal speeds for the power band sawing of aluminum alloys with high-speed tool steel blades Material Hardness, thickness ~ Thread designation --7 ~ Band speed Material HB (500 kg) Condition nun in. Tooth form(a) Pitch, mm Teeth/in. m/min sfm

Wrought EC 2218 5252 6253 30-80 Cold drawn <12 <1/2 P 1.8-1.4 14-18 305(b) 1000(b) 1060 2219 5254 6262 12-25 !/2-1 P 2.5-1.8 10-14 275(b) 900(b) 1100 2618 5454 6463 25-75 1-3 P 4-2.5 6-10 230(b) 750(b) 1145 3003 5456 6951 >75 >3 C 8.5 3 200(b) 650(b) 1175 3004 5457 7001 75-150 Solution treated and aged <12 <1/2 P 1.8-1.4 14-18 275(b) 900(b) 1235 3005 5652 7004 12-25 1/2-1 P 2.5-1.8 10-14 245(b) 800(b) 2011 4032 5657 7005 25-75 1-3 P 4-2.5 6-10 200(b) 650(b) 2014 5005 6053 7039 >75 >3 C 8.5 3 170(b) 550(b) 2017 5050 6061 7049 2018 5052 6063 7050 2021 5056 6066 7075 2024 5083 6070 7079 2025 5086 6101 7175 2117 5154 6151 7178 Cast Sand and permanent mold Al40 319.0 357.0 A712.0 40-100 As-cast < 12 < V2 P 1.8-1.4 14-18 305(b) 1000(b) 201.0 328.0 359.0 D712.0 12-25 I/2-1 P 2.5-1.8 10-14 275(b) 900(b) 208.0 A332.0 B443.0 713.0 25-75 1-3 P 4-2.5 6-10 230(b) 750(b) 213.0 F332.0 514.0 771.0 >75 >3 C 8.5 3 200(b) 650(b) 222.0 333.0 A514.0 850.0 70-125 Solution treated and aged <12 <1/2 P 1.8-1.4 14--18 275(b) 900(b) 224.0 354.0 B514.0 A850.0 12-25 V2-1 P 2.5-1.8 10-14 245(b) 800(b) 242.0 355.0 520.0 B850.0 25-75 1-3 P 4-2.5 6-10 200(b) 650(b) 295.0 C355.0 535.0 >75 >3 C 8.5 3 170(b) 550(b) B295.0 356.0 705.0 308.0 A356.0 707.0 Hiduminium RR-350

Die castings 360.0 40-100 As-cast <12 <1/2 P 1.8--1.4 14-18 200(b) 650(b) A360.0 12-25 !/2-1 P 2.5-1.8 10-14 185(b) 600(b) 380.0 25-75 I-3 P 4-2.5 6-10 150(b) 500(b) A380.0 >75 >3 ...... C443.0 70-125 Solution treated and aged 75 >3 ......

383.0 40-100 As-cast <12 <1/2 P 1.8-1.4 14-18 170(b) 550(b) A384.0 12-25 I/2-1 P 2.5-1.8 10-14 150(b) 500(b) 413.0 25-75 1-3 P 4-2.5 6--10 120(b) 400(b) A413.0 >75 >3 ...... 70-125 Solution treated and aged <12 <1/2 P 1.8-1.4 14-18 150(b) 500(b) 12-25 I/2-1 P 2.5-1.8 10-14 135(b) 450(b) 25-75 1-3 P 4-2.5 6--10 105(b) 350(b) >75 >3 ......

390.0 40-100 As-cast <12 75 >3 ...... 70-125 Solution treated and aged <12 75 >3 ...... (a) P, precision; C, claw; B, buttress. (b) Recommended speed for high-carbon-steel blade. Source: Ref 5 carbide cutters, mainly because the speeds In machining aircraft components, skin heating and sudden chilling of the carbide are usually greater for carbide cutters. milling, which involves deep cuts (some- tips. Rapid heating and cooling is extremely Depth of cut (roughing or finishing), partic- times 50 mm, or 2 in., or more), is common detrimental to the life of carbide cutters. ularly in face milling, has some effect on the practice. Machines used for skin milling are For high-speed milling, emulsions of sol- rate of feed selected. For end milling, the basically planer mills that have evolved into uble oil and water at a 1:15 ratio are recom- principal factor affecting rate of feed is elaborate tracer-controlled machines. The mended. For low-speed milling, a ratio of cutter diameter (Table 28) because small milling is ordinarily done by means of large 1:30 is recommended. end milling cutters lack rigidity. peripheral-type (slabbing) cutters. Kerosene is effective with form cutters. Depth of cut is commonly about 6.35 mm Cutting fluid should be supplied copi- When modified T-slot cutters were used to (0.250 in.) for roughing and 0.64 (0.025 in.) ously and under pressure to the tool and mill a blade-root slot in aluminum wheels or less for finishing. If power is available, workpiece. It is important, particularly with for axial-flow compressors to a tolerance of depth of cut can be several times greater carbide cutters, that the cutting fluid be less than 0.025 mm (0.001 in.), no cutting than the above when large amounts of metal supplied uniformly and consistently to all fluid except kerosene could produce the are to be removed. parts of the cutter in order to prevent over- required accuracy and surface finish. 796 / Machining of Specific Metals and Alloys

Table 32 Nominal speeds and feeds for the power hacksawing of aluminum alloys with high-speed tool steel blades Material Hardness, thickness ~ Thread designation --7 Sp~tl, / Feed Material HB (500 kg) Condition nun in. Pitch, nun Teeth/in.(a)' strokes/rain ~nndstroke in./stroke Pressure(b)j Wrought EC 2218 5252 6253 30-80 Cold drawn <6 <1/4 4 6 160 0.15 0.006 M 1060 2219 5254 6262 6-18 I/4--3/4 4 6 160 0.23 0.009 H 1100 2618 5454 6463 18-50 ¥4-2 6.3 4 160 0.30 0.012 H 1145 3003 5456 6951 >50 >2 6.3 4 160 0.30 0.012 H 1175 3004 5457 7001 75-150 Solution treated and aged <6 50 >2 6.3 4 140 0.30 0.012 H 2017 5050 6061 7049 2018 5052 6063 7050 2021 5056 6066 7075 2024 5083 6070 7079 2025 5086 6101 7175 2117 5154 6151 7178 Cast Sand and permanent mold AI40 319.0 357.0 A712.0 40-100 As-cast <6 50 >2 6.3 4 140 0.30 0.012 H 222.0 333.0 A514.0 850.0 70-125 Solution treated and aged <6 50 >2 6.3 4 130 0.30 0.012 H B295.0 356.0 705.0 308.0 A356.0 707.0 Hiduminium RR-350

Die castings 360.0 A380.0 40-100 As-cast <6 50 >2 6.3 4 140 0.30 0.012 H 70-125 Solution treated and aged <6 50 >2 6.3 4 130 0.30 0.012 H

383.0 40-100 As-cast <6 50 >2 6.3 4 130 0.30 0.012 H 70-125 Solution treated and aged <6 50 >2 6.3 4 130 0.23 0.009 H

390.0 40-- ! 00 As-cast <6 <1/4 2.5 10 125 0.15 0.006 M 392.0 6-18 V4,-3/4 4 6 125 0.15 0.006 M 18--50 3/4-2 6.3 4 115 0.15 0.006 M >50 >2 6.3 4 115 0.15 0.006 M 70--125 Solution treated and aged <6 <1/4 2.5 10 120 0.075 0.003 L 6-18 I/4-¥4 4 6 120 0. i 5 0.006 M 18-50 3/4---2 4 6 110 0.15 0.006 M >50 >2 6.3 4 110 0.15 0.006 M (a) Conversions per ISO 2336. (b) L, light; M, medium; H, heavy. Source: Ref 5

Form milling is often an economical tooth faces without changing the form. If relieved cutters, but they require more method for machining complicated shapes surface finish is a secondary consideration, equipment and more skill in grinding. in aluminum. The complexity of form that straight-tooth cutters are used because they The feasibility of form milling depends on can be built into the design of a cutter are easier to sharpen. However, if surface several variables, including cutter cost, vol- is limited, as when the tangent of the cur- finish is important, helical cutters must be ume of production, design of workpiece, vature approaches 90 ° to the horizontal used. Although helical cutters can be oper- and type of milling machine available. Thus, plane. As a result, secondary operations are ated at higher speeds and greater feeds than for small production lots, the cost of a single sometimes required to complete a complex straight-tooth cutters, they require consid- form cutter must be compared with the cost form. erably greater care when being sharpened. of several cutters of less complex shape. Basic types of form cutters have cam- Shape form cutters are made either with For form milling, the workpiece must be relieved teeth or shaped teeth. Cam- integral teeth or blade inserts. These cutters relatively large, must have no thin sections, relieved teeth are sharpened by grinding the are less expensive than integral-tooth, cam- and must be capable of being well secured. Machining of Aluminum and Aluminum Alloys / 797

Finally, form milling requires high-power achieved using HI0 grade cemented car- equipment that is rugged and in good oper- bide. The tool life when dry milling with ating condition. The following example de- polycrystalline diamond at speeds ranging scribes an application of form milling and from 400 to 800 m/min (1312 to 2625 sfm) shows the production quantity required to was approximately 1000 engine blocks at justify a high-cost form cutter. the lower speed. Surface finish was also Example 9: Cost of Standard Versus greatly improved, indicating that polycrys- Form Milling. The contour of the work- talline diamond is much less sensitive than piece shown in Fig. 27 could be milled carbide to the effect of coolant when milling Fig. 32 Shape that wos contour band sawed from equally well by using five standard cutters aluminum plate. Dimensions given in inches alloy 390. These results do not indicate that for five separate operations or by using one the application of coolant is not desirable to specially designed form cutter that could prolong tool life, but it does mean that mill the contour in a single operation. The shear angles should be used. Optimum tool milling with polycrystalline diamond with- operations performed by both methods are life will be achieved if a coolant is used, but out coolant, if desired, can be a commercial listed in the table accompanying Fig. 27. alloy 390 can be machined dry with good reality. Although the cost of the cutters was the tool life and with little built-up edge prob- Milling of Alloy 380 With Polycrystal- same for form and standard milling, the time lem. line Cutting Tools (Ref 1). An interesting required for form milling was only about Compared to other aluminum alloys, al- application of diamond tooling is the ma- one-third that for standard milling. loy 390 has traditionally been milled at chining of an aluminum automotive exten- Automatic Control. The generally good rather slow speeds (90 to 175 m/min, or 300 sion housing made of die cast 380 aluminum machining characteristics of aluminum al- to 575 sfm) using C-2 grade tungsten carbide alloy, which contains approximately 8% Si. loys make them especially well adapted to inserts with a liberal application of flood The component is about 330 mm (13 in.) automatic control, by which extremely coolant. Feed rates of 0.10 to 0.30 mm/tooth long, tapering from about 203 x 254 mm ( 8 complex shapes can be milled efficiently. (0.004 to 0.012 in./tooth) and cutting depths x 10 in.) at one end to a diameter of about The following example gives details of an ranging from 0.13 to 5.1 mm (0.005 to 0.20 75 mm (3 in.) at the other. The overall shape application in which automatic control was in.) are common practice. of the casting is relatively complex, and the used. Cutter geometry is important for ensuring nominal wall thickness over most of its area Example 10: Milling a 758 kg (1670 adequate surface finish of the machined is about 4.0 mm (5/32 in.). A 14-station Ib) Forging With Numerical Control. The casting and a long tool life for the cutting pallet-type transfer machine performs a part shown in Fig. 28 was made from an inserts. The entering angle should be 45 ° to number of drilling, tapping, reaming, cham- alloy 7075 blocker forging that weighed 758 minimize vibration and workpiece fritter- fering, boring, and facing operations on the kg (1670 lb). Overall measurements of the ing. A large positive-rake angle, from 5 to transmission part. forging were 3380 × 1730 × 406 mm (133 x 20 ° , extends tool life and reduces the ten- The large end of the casting requires the 68 x 16 in.), and those of the finished part dency toward built-up edge. Clearance an- machining of a shallow, interruped bore of were 3330 x 1680 x 356 mm (131 x 66 x 14 gles from 5 to 15 ° reduce buildup on the about 140 mm (51/2 in.) in diameter and 9.5 in.). The weight of the finished part was 178 edge clearance flank. Pitch depends largely mm (3/8 in.) deep and the facing (milling) of kg (393 Ib), with 579 kg (1277 lb) of metal on the diameter of the cutter, depth of cut, the entire end. To maintain perpendiculari- having been removed in machining. and type of cut (roughing or finishing). As ty, the boring and the milling tools are With the part held in a special milling with turning, the productivity and tool life combined into a single cutter body. Two of fixture, rough profile machining was per- performance of the milling operation can be these are used----one for roughing (which formed in a tape-controlled three-axis pro- greatly improved through substitution of also incorporates a tool for chamfering the file milling machine. A special boring fix- polycrystaUine diamond for carbide. bore inside diameter), and one for finishing. ture was used for rough line boring the 140 The first large-volume alloy 390 engine The overall configuration of the cutter is and 222 mm (5.50 and 8.75 in.) diam trun- manufactured in the United States was ma- essentially a hollow mill with a central bor- nion holes. After roughing cuts were com- chined on a transfer line designed for gray ing bar. Tool and workpiece are both shown pleted, approximately 3.05 mm (0.120 in.) of iron. Instead of broaching, face milling was in Fig. 31. This is fed axially into the part to metal remained to be removed by finish employed, with an average production tool produce the bore and the chamfer, while the machining after the forging was heat treated life of 130 engine blocks per carbide tool. milling teeth rotate beyond the periphery of to the T6 temper. Special fixtures prevented When compared experimentally with the part. The cutter is then withdrawn from warpage during heat treating and in finish polycrystalline diamond (Fig. 29), the per- the bore and fed radially across the surface milling. Machining was completed using the formance of the milling operation was great- to be face milled. The milling teeth are same NC machine. Details of the process, ly enhanced. At ten times the speed and positioned farther out axially than the bor- machine, and cutter are given with Fig. 28. metal removal rate, tool life would be pro- ing and chamfering teeth so that there is no Dimensional accuracy is affected by re- jected to be in excess of 1000 engine blocks. interference. sidual stress in the workpiece, induced At the same speed and production rate used All cutting edges are polycrystalline dia- stress caused by milling, built-up edge on for carbide, the diamond tool life would be mond. The boring tool is a special diamond- cutters, and dull cutters. Workpieces with practically infinite. tip 9.5 mm (3/8 in.) inscribed circle triangular complex shapes or variable section thick- This performance improvement was also insert clamped in place with 2 ° radial rake ness, especially in the aged condition, are experienced in a study in which alloy 390 and 5 ° axial rake. The chamfering tool is a more difficult to mill to close tolerances. To engine blocks were face milled without 9.5 mm (3/8 in.) square insert with a brazed achieve dimensional stability and to main- coolant (Fig. 30). The best tool life achieved diamond cutting edge. This insert is pre- tain close tolerances, residual stress must when milling with carbide from 100 to 175 sented to the cut with 0 ° radial and 5 ° axial be avoided. m/min (328 to 574 sfm) was approximately rake. Although chamfering is done only at Milling of high-silicon alloy 390 (Ref 2) 50 engine blocks at lower speed. The feed the roughing station, a dummy cartridge is is accomplished with carbide tools at speeds rate was 0.18 mm/tooth (0.007 in./tooth), used to maintain balance of the finishing up to 175 m/min (575 sfm) or with polycrys- and the depth of cut was 1.02 mm (0.040 in.) cutterna necessity at these speeds. talline diamond tools at speeds up to 790 m/ for roughing and 0.51 mm (0.020 in.) for Twelve milling teeth are set on an effec- min (2600 sfm). Moderate positive-rake and finishing cuts. The best tool life was tive diameter of 356 mm (14 in.). These are 798 / Machining of Specific Metals and Alloys

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Grinding wheel 3 FI32-T5 casting Table 34 Abrasive cutoff wheels for cutting aluminum alloys I Wheel identification ,, _.~ 0.020 to I..-- Hardness, Dry curing Wet cutting 0.050 50 to 90 Material HB (500 kg) Condition ISO ANSI iSO ANSI Wrought I 0.0007 EC 2218 5252 6253 30-150 Cold drawn or A36--RB A36--RB A46--PR A46--PR ''---- Work pi ec e 0.0003 1060 2219 5254 6262 solution treated 1100 2618 5454 6463 aged Surfoce pottern prior and i i i! to tin plotinq 1145 3003 5456 6951 1175 3004 5457 7001 1235 3005 5652 7004 Machine ...... Cylindrical grinder, 152 x 2011 4032 5657 7005 457 mm (6 x 18 in.), with automatic infeed 2014 5005 6053 7039 2017 5050 6061 7049 electric-cycle control 5052 7050 and semiautomatic 2018 6063 2021 5056 6066 7075 prof'de dresser 2024 5083 6070 7079 Wheel 2025 5086 6101 7175 Type ...... A-46-K5-V 2117 5154 6151 7178 Size, mm (in.) ...... 508 x 60 x 305 (20 x 23/s x 12) Life per dressing ...... 100 pieces Cast Sand and permanent mold Operating conditions AI40 295.0 514.0 A712.0 40-125 As-cast or A36--RB A36--RB A46--PR A46--PR Wheel speed, at 1300 201.0 B295.0 A514.0 D712.0 solution treated rev/min, m/min (sfm) ..... 2100 (6800) 208.0 308.0 B514.0 713.0 and aged Work speed, rev/min ...... 96 213.0 319.0 520.0 771.0 Feed/pass, mm (in.) ...... 0.41-0.46 (0.016-0.018) 222.0 355.0 535.0 850.0 Grinding fluid ...... Soluble oil: water (!:25) 224.0 C355.0 705.0 A850.0 Production rate, pieces/h ... 106 242.0 B443.0 707.0 B850.0 Time/pass, s(a) ...... 20 Hiduminium RR-350 Surface finish, o.m (l~in.) .... 1.25-2.25 (50-90) Die castings (a) lnfeed set with automatic timer C443.0 518.0 Sand and permanent mold Fig. 33 Permanent mold cast piston (90 to 120 328.0 333.0 A356.0 40-125 As-cast or A36--RB A36--RB A46--PR A46--PR HB) that was ground in a single pass, A332.0 354.0 357.0 solution treated removing 0.41 to 0.46 mm (0.016 to 0.018 in.) of stock. F332.0 356.0 359.0 and aged Dimensions in figure given in inches Die castings 360.0 383.0 413.0 A360.0 A384.0 A413.0 380.0 390.0 cartridge-type cutters with brazed diamond A380.0 392.0 tips having the following geometry: 15 ° lead Source: Ref 5 angle (the inner edge), 5 ° radial rake, 5 ° axial rake, 6 ° clearance, and 1.52 mm (0.060 in.) nose radius. On the finishing cutter, one of these is ground with a 0.76 mm (0.030 in.) to 8 in.) thick, for cutting rates of 0.032 to Example 11: Contour Sawing of a wiper flat instead of the radius, which was 0.16 m2/min (50 to 250 in.2/min). Recom- Large Plate. An aluminum alloy plate found to improve significantly the surface mended tooth angles and contours for the weighing 653 kg (1440 lb) and measuring finish produced on the part. three types of saws are given in Tables 29 to 1220 x 1525 x 127 mm (48 x 60 x 5 in.)was These combination cutters are run at 3450 32. rough machined in a milling machine to rev/min for both roughing and finishing, Circular Sawing. Peripheral speeds are obtain the contour shown in Fig. 32. Milling yielding a cutting speed of 1514 m/min (4967 45 to 4600 m/min (150 to 15 000 sfm) for required about 41/2 h. The same part was sfm) for the boring and chamfering opera- high-speed steel and carbide-tip circular produced in 67 min in a contour band saw, tions and 3854 m/min (12 645 sfm) for the saws, depending on the saw material, the cutting at a rate of 9700 mmE/min (15 in.E/ face milling operations. In roughing, mate- type of cut, and the ability of the machine to min). rial removal is approximately 2.03 mm withstand high speeds (Tables 29 and 30). Sawing was done with a high-speed steel (0.080 in.) in the bore and 1.65 mm (0.065 The limiting factor is usually the maximum blade (hook tooth; taker set; 6 pitch; 25 in.) on the face. In finishing, 0.38 mm (0.015 safe operating speed of the machine and mm, or l in., wide; 0.89 mm, or 0.035 in., in.) is removed from both surfaces. blade. thick), using a heavy-duty chemical solution The feed rate for circular sawing ranges as a cutting fluid. A dimensional tolerance from 0.05 to 7.6 mm/tooth (0.002 to 0.30 in./ of +-0.38 mm (+-0.015 in.) was maintained. Sawing tooth), depending mainly on the alloy being Power hacksawing is done at 110 to 160 The contour cutting of aluminum alloys is sawed. The width of the section being strokes per min with a feed of 0.15 to 0.30 usually done by band sawing; straight cut- sawed and the speed of the saw have some mm/stroke (0.006 to 0.012 in./stroke) (Table ting is done on a circular saw, band saw, beating on the rate of feed. 32). The higher speed is recommended for power hacksaw, or abrasive cutoff wheel. Band Sawing. Hard-tooth, flexible-back sawing nonheat-treated cast aluminum al- Circular saws or band saws are preferred carbon steel bands are used at 46 to 305 m/ loys, and the lower speed (1 l0 strokes per for the rapid cutoff of rod and bar stock; min (150 to 1000 sfm) on cast and wrought min) for abrasive materials such as 390 and either can be readily adapted for high- aluminum alloys (Table 31). The following 392 solution-treated and aged die cast al- speed, automatic work handling. example compares milling and contour band loys. Linear feed rates as high as 762 to 2030 sawing for producing a shape from an alu- Cutting Fluid. Although circular saws mm/min (30 to 80 in./min) are sometimes minum alloy plate. In this application, band can be operated satisfactorily on aluminum used in the cutoff of stock 50 to 203 mm (2 sawing was faster and less expensive. alloys at moderate speeds and medium cuts Machining of Aluminum and Aluminum Alloys / 801

Table 35 Nominal speeds for the abrasive belt grinding of aluminum alloys

Hardness, Abrasive Grain i Belt spced(a) ------7 I Contact wheeIHardness, I Material HB (500 kg) Condition Operation type size m/s sfm Type(b) Durometer Wrought and cast ...... 30-150 Cold drawn, Roughing A1203, SiC 24-80 25-33 5000-6500 SR, SFR 70-95 as-cast, or Polishing Ai20 3, SiC 100-240 25-40 5000--8000 SR, SFR, B 20--60 solution treated and aged (a) Use lower values of belt speed when good surface integrity is required. (b) SR, serrated rubber; SFR, smooth face rubber; B, buff type. Serrations are usually at a 45* angle, although some heavy stock removal operations use a 60° angle. Widths of lands and grooves vary from narrow lands and wide grooves for fast aggressive cuts to wide lands and narrow grooves for intermediate and finishing operations, depending on workpiece shape and operating conditions. Source: Ref 5

Table 36 Honing recommendations for aluminum alloys Hardness, J Honing stone material ~ [--- Grain size at a surface roughness, R,, pm (pin.), of: .---1. Spindle motion, m/min (stm) Working

Grade, ,-,,.,,,. "0.025-0.125 0.15-0.25 0.30-0.50 0.53--0.75 >0.75 Rotating Reciprocating pressure, Material HB (500 kg) Type or ISO (I-$) (6-10) (11-20) (21-30) (>30) speed speed kPa (psi) Cutting fluid Wrought and cast ...... 30--450 Silicon carbide or L(a) 600 500 400 280 220 15.2--64 2,7-22.9 276 70--30 kerosene/ diamond (600) (500) (400) (280) (220) (50-210) (9-75) (40) oil (sulfurized (metal bonded) or chlorinated) (a) L, a medium grade. Source: Ref 5

without a cutting fluid, it is advisable to ment and Processes" and "Superabra- sides of the wheel. To eliminate this prob- supply copious amounts of soluble-oil:wa- sives" in this Volume). The following ex- lem and to provide for safe operation, spe- ter emulsion (1:20) for all high-speed cut- ample describes specific grinding practice cial reinforced, flexible, abrasive wheels ting. The cutting fluid should flood the blade for pistons. have been developed. These wheels are and workpiece under slight pressure and it Example 12: Grinding of Pistons. After manufactured from laminated sheets of cot- should be filtered or settled before recy- extensive testing, an A-46-K5-V wheel was ton fiber filled with abrasive grain and are cling. In some applications, the addition of a selected for grinding the skirt of permanent used for operations ranging from heavy little kerosene or lard oil to the emulsion has mold cast FI32-T5 pistons (Fig. 33). Re- grinding to light sanding: cutting off, sharp- been beneficial. Soap solutions can be sub- quirements for the wheel were: ening, deburring, and finishing. Such stituted for oil emulsions. wheels used for aluminum are C-24-O14-B • Satisfactory performance without fre- For band saws, some cutting fluid is to C-24-U 14-B. quent redressing essential for all but the lightest cuts. A wide Speed. Typical wheel speeds for several • Ability to hold the required profile selection of compounds is available, ranging types of grinding are given in Table 33. • Production of a 1.25 to 2.25 I~m (50 to 90 from tallow or grease sticks to kerosene- Sometimes, by adjusting the speed, a wheel ~in.) finish thinned mineral-base lubricating oil or that was previously unsuited for a particular emulsions of soluble oil and water. It is The A-46-K5-V wheel was capable of grind- operation can be made to grind satisfactori- often more convenient to use a fluid lubri- ing 100 parts between redressings and met ly. For example, if a wheel is too soft, cant, supplied generously through a recy- the other requirements. increasing the speed will give a harder ac- cling system. For hacksawing, procedures A special hydraulic dresser, equipped tion. are similar to those for band sawing. with a profile bar, was used to dress the Using the recommended speed for a wheel. The dressing tool was a 3/4-carat wheel is important, not only from the stand- Grinding diamond that was turned in its holder after point of grinding results but also to ensure eight dressings to maintain a sharp point. safety. Stress from centrifugal force in- The harder, free-cutting aluminum alloys Details of this grinding operation are given creases greatly as wheel velocity increases. are comparatively easy to grind. The non- in the table accompanying Fig. 33. The force tending to pull a wheel apart will free-cutting alloys, particularly in their soft- Cutoff Wheels. Abrasive cutoff wheels be four times greater at 3600 rev/min than at er tempers, are likely to clog grinding for aluminum are usually of aluminum ox- 1800 rev/min. wheels, and they do not finish to as bright ide, as indicated in Table 34. For wet grind- Grinding Fluid. Neutral soluble-oil emul- and smooth a surface as the harder alloys. ing, which is generally recommended, the sions are satisfactory for grinding alumi- Abrasive Wheels. For grinding alumi- bond is usually rubber. For dry grinding, num. The addition of a wetting agent (deter- num alloys, a silicon carbide abrasive in a either rubber or resinoid bond can be used. gent) is sometimes helpful. Although an flexible base is generally preferred. Alumi- Typical specifications are A-20-U6-R (alu- emulsion of 1 part soluble oil to 35 parts num oxide is seldom recommended, except minum oxide, 20 grain size, U grade, 6 water is commonly used, a better cushion- for piston grinding and in cutoff wheels. structure, rubber bond) and A-24-S7-B (alu- ing effect, which also prevents clogging of Wheels of medium hardness, about 46-grit minum oxide, 24 grain size, S grade, 7 the wheel, is obtained by using more oil and size, and with a synthetic resin bond work structure, resinoid bond). The width of the less water. One manufacturer, in grinding best for roughing. For finishing, wheels of wheels ranges from 0.08 to 3.96 mm (0.003 soft aluminum alloy castings, went progres- finer grit size (to about 60) and with a to 0.156 in.); diameter varies from 25 to 762 sively from a mixture of I part oil to 20 parts vitrified bond are generally used. Recom- mm (1 to 30 in.). These wheels cut to an water to a mixture of 1 part oil to 6 parts mendations for wheels for several different accuracy of a few thousandths of an inch. water before obtaining satisfactory results. types of grinding operations are given in Reinforced (Flexible) Wheels. In cutting In rough grinding, where stock removal is Table 33 (the ANSI system for identifying off gates and sprues from castings of irreg- the primary objective, a generous applica- the characteristics of grinding wheels is ular shape, excessive wheel breakage can tion of wax or stick grease is often satisfac- explained in the articles "Grinding Equip- occur because of very high pressure on the tory. This type of lubricant is often used 802 / Machining of Specific Metals and Alloys

metal being ground. For a good finish, a heavy grease should be used. Some operations use two types of grease, side by side, on the same abrasive belt. One side is used for a high rate of stock removal, J and the other for a finer finish. If the belt F- 24~~ =i becomes loaded despite the use of grease, an application of kerosene will free the belt 6061 alloy of embedded particles. Liquid lubricants are primarily used to -.ug:"- 35 Part from which 0.005 mm (0.0002 in.)of prevent belt glazing. When water is used, a metal was removed by lapping to smooth the surface to 0.02,5 I~m (1 I~in.). Dimensions given in rust inhibitor should be added. inches Soluble oil mixed with water is effective in grinding aluminum if stock removal is the primary objective. Table 35 lists data for Speed, at 900 rev/min, m/min (sfm) ...... 190 (620) abrasive belt grinding. Fig. 34. The blocks were fixtured for honing Spindle reciprocation rate, and were held in position by a light clamp- strokes/min ...... 60 Honing ing force on the head faces. Each block was Hone speed, m/min (sfm)... 21 (70) held securely so that it could resist torsional Stock removed, mm (in.)... 0.038--0.51 (0.0015--0.020) Honing time, s ...... 25 Aluminum alloys are honed by methods forces from the honing tool, but adjustment Cutting fluid ...... Mineral seal oil similar to those used for other metals (see of clamping force was critical because ex- Size control method ...... Air gage the article "Honing" in this Volume). Resin cessive force would distort the block. Hy- Stone life, per set (average).. 300 assemblies bond abrasives are preferred; sulfurized draulic cone expanders automatically fed Production rate, pieces/h ... 75 Bore alignment before mineral-base oil or lard oil mixed with ker- out the single bank of six carbon-bonded honing, mm (in.) ...... 0.05 (0.002) osene is used to flush the abrasive sticks silicon carbide stones (50 x 6.4 mm, or 2 x Bore alignment after clean and to carry away heat. Table 36 lists I/4 in., 120 grit). Fifteen fiber guides, each 75 honing, mm (in.) ...... 0.018 (0.0007) honing specifications for aluminum alloys. x 6.4 mm (3 x I/4 in.), were incorporated in Specified tolerance, mm (in.) ...... _+0.008 (_+0.0003) Honing is used to finish anodized alumi- the honing tool. Processing details are given Specified finish, ~m (o.in.)... 0.50-0.63 (20-25) num surfaces (primarily the bores of some in the table with Fig. 34. small aluminum engine blocks) and most Fig. 34 Die cast engine block that was honed with aircraft hydraulic cylinders. Long anodized gray iron bearing caps in place, and aluminum tubes that are components of Lapping honing tool that was used (bottom). Dimensions in figure in-flight refueling apparatuses are finished The methods used for lapping aluminum given in inches by manual honing. The tubes are chucked in are the same as those used for other metals a lathe, and the honing tool is moved man- (see the article "Lapping" in this Volume). when the application of liquids is not feasi- ually. The oil supply is attached to the However, because similar finishes often can ble. honing tool in such a manner that the flow be produced by other methods at less cost, Bell Lubricant. Grinding fluids or stick of oil is directed where most needed. This lapping is seldom used. In the following lubricants improve the finish produced by a method of honing is also used for finishing example, an extremely smooth finish of coated abrasive belt and prevent glazing of connecting-rod journals or crankshafts in 0.025 ~m (l win.) on an anodized part was the belt. Lubricants used range from water aircraft overhaul shops. produced by two methods of lapping. to stick waxes; standard cutting oils and The following example describes the Example 14: Lapping Hard-Anodized soluble-oil mixtures are often used in high- technique and conditions employed in the Alloy 6061. The hard-anodized aluminum production belt machines. honing of main bearing bores in aluminum part (surface hardness equivalent to 65 Greases cushion the penetrating action of engine blocks. The aluminum blocks and HRC) shown in Fig. 35 required removal of the abrasive into the work and produce finer the gray iron beating caps were honed si- 0.005 mm (0.0002 in.) from the three lands finishes than are obtained in dry grinding. multaneously with a silicon carbide abra- to produce a finish of 0.025 Ixm (1 ~in.). Although the crest of each grain is free to sive, even though, if honed separately, gray Diamond abrasive (8000 mesh) in a paste cut, the grease prevents deep scratches. iron and aluminum would be honed with vehicle was used for both centerless roll Greases are used for the offhand grinding different abrasives. lapping and lapping in a two-plate machine. of aluminum die castings. When stock re- Example 13: Simultaneous Honing of The roll lapper, at a rotation speed of 100 moval is the primary objective, a light Aluminum and Gray Iron. Main-bearing rev/min (large roll) and a stroke speed of 50 grease should be used, preventing the belt bores in six-cylinder, die cast aluminum ram/rain (2 in./min), produced ten parts per from loading but permitting a maximum engine blocks were honed with gray iron hour. The two-plate machine, which had amount of abrasive penetration into the beating caps bolted in place, as shown in upper and lower cast iron laps 406 mm (16 Table 37 Comparison of data and characteristics of systems for the chemical milling of titanium, steel, aluminum, and nickel- and cobalt-base alloys

Optimum Average surface [ Etch rate ] etch depth Etchant temperature roughness, R a Metal Principal etchant mm/min in./min mm in. °C °F am Ixin. Titanium alloys ...... Hydrofluoric acid 0.015-0.030 0.00064).0012 3.2 0.125 46_+2.7 115_+5 0.4-2.5 16-100 Steels ...... Hydrochloric acid-nitric acid 0.015--0.030 0.(X)064).0012 3.2 0.125 63-+2.7 145-+5 0.8-3.2 30-120 Aluminum alloys ...... Sodium hydroxide 0.020--0.030 0.0008-0.0012 3.2 0.125 90_+2.7 195_+5 2.0-3.2 80-120 Nickel- and cobalt-base alloys ...... Nitric acid-hydrochloric 0.010-0.038 0.0(0)O).0015 3.2 0.125 60_+2.7 140_+5 1.0-3.8 40--150 acid-ferric chloride Source: Ref 5 Machining of Aluminum and Aluminum Alloys / 803

Table 38 Properties of maskant materials exposed to acids or alkalies Table 39 Surface roughness that are widely used in the chemical milling of aluminum alloys achieved by the chemical milling of Maskant material aluminum alloys I I Property Butyl robber Acrylonitrile rubber Neoprene rubber' Surface roughness, R., after 0.25-0.40 mm Ease of manufacture ...... Fair Fair Good (0.010-0.015 in.) removed Shelf life, months ...... 4-6 3-6 6--8 Form Ixm pin. Solids, % ...... 20-25 15-25 25-35 Ease of application Sheet ...... 2.00-3.8 80-150 Dipping ...... Good Good Good Casting ...... 3.8-7.6 150-300 Flow coating ...... Good Good Good Forging ...... 2.50-6.3 100-250 Air spraying ...... Poor Poor Fair Source: Ref 5 Type of cure ...... Heat Air or heat Air or heat Tensile strength, MPa (ksi) Air-dried, 24 h ...... - • • 7 (1.0) max 14 (2.0) max Heat cured ...... 6-11 (0.87-1.6) 11-17.5 (1.6-2.5) 11-21 (1.6-3.0) Resistance to etchant Depth of cut, in. Deterioration ...... Very good Very good Very good E 0 0.004 0.008 0.012 0.016 0.020 .~ Permeability ...... Excellent Very good Very good - 3.0 120 m Heat limit, °C (°F)(a) ...... 150 (300) 120 (250) 95 (200) ..._.. eo (a) Maximum useful temperature for intermittent exposure and for curing temperature. Source: Ref 5 2.0 80 ffl'~ ¢--0 1-- c-

o 1.0 40 0~

in.) in diameter and 75 mm (3 in.) thick, surfaces. The maskant material is removed o lapped 1000 parts per hour. from the workpiece by hand or with the aid -c 0 0 -c of a demasking solution. if)~ 0 0.1 0.2 0.3 0.4 0.5 c~ Chemical Milling When scribe-and-peel maskants are used, Depth of cut, mm cuts as deep as 13 mm (0.5 in.) can be made. -'ucz". 36 Relationship between surface finish and Parts can be chemically milled over their With the thinner and less chemical-resistant depth of cut for the chemical milling of entire surface, or the surface can be selec- silk-screened masks, the depth of cut is 7075 aluminum sheet. Source: Ref 5 tively machined by masking areas that do limited to 1.5 mm (0.060 in.), but a more not require machining. The process is main- accurate and detailed cavity is possible. ly used for parts having large surface areas Photoresists provide still more detail and 0.225 in. deep (typ requiring small amounts of metal removal accuracy, but the cut is limited to a depth of (see the article "Chemical Milling" in this 1.3 mm (0.050 in.). Sheets and plates are Volume). tapered in thickness by immersing and with- Chemical milling is primarily used for drawing the workpiece from the etching parts having shallow cavities or pockets or bath at a controlled rate. Steps are pro- requiring overall weight reduction. The duced by repeated cycles of etching with main application has been in the aerospace different areas masked. The depth of cut is 4'0" industry to obtain maximum strength-to- limited to about 13 mm (I/2 in.) in plate weight ratios, but the process has also been materials and to less than this with forgings, receiving attention from other industries. castings, and extrusions. Extremely large parts such as aircraft skin Table 39 lists data for the surface rough- ~ .....I-- 7072 aluminum alloy and fuselage sections and airframe extru- ness of three forms of aluminum alloys that .- ~ 0.250 in. thick sions are chemically milled. were subjected to the chemical milling pro- Fig. 37 Preformed aircraft skin section chemically Table 37 compares the chemical milling of cess. The effect of depth of cut on the contoured to reduce weight. Dimensions aluminum to that of other metals typically surface finish of 7075 aluminum sheet is given in inches machined by this process. In contrast to shown in Fig. 36. Typical tolerances of titanium alloys, steels, and nickel- and co- various depths of cut are: bait-base alloys, which use acid as an Metal removed, in. 0 0tl 0.2 0.3 etchant, caustic soda is the usual etchant for Depthof cut I I-- Tden.~ ----1 aluminum alloys. mm in. mm in. When selective machining is involved and 0-1.25 0-0.050 ...... 0.025 0.001 !it! I the scribe-and-peel method is used, mask- 1.25-2.50 0.051-0.100 ...... 0.038 0.0015 ing material is applied to the workpiece by 2.5-6.4 O. 101-0.250 ...... 0.05 0.002 6.4-12.7 0.251-0.500 ...... 0.075 0.003 ...... I spraying, dipping, or brushing. The dry maskant is scribed from a pattern and peeled from the workpiece to expose the Additional information is availableiiiiiiiiiiiiiiiii! in the iii areas that are to be chemically milled. Mask- article "Chemical Milling" in this Volume. ant can also be selectively applied by the The following example illustrates the use of silk-screening process or by photographic chemical milling to reduce the weight of a methods. Properties of maskants used to 7072 aluminum aircraft part. 0 iii5271i);iiiilil;ii)iiiil;iiiiliiiii!i!iSii~i~i:.iiii~i~isF;;;,:::::: ...... ~ chemically mill aluminum alloys are listed Example 15: Fuselage Section Made 0 1.25 2.5 3.75 5.0 6.25 7.5 in Table 38. From Preformed 7072 Aluminum Alloy Metal removed, mm Machining takes place when the work- Plate. The fuselage skin section shown in piece, contained in a work basket or held by Fig. 37 was chemically milled after stretch total length of fillet (ft) Fillet ratio - a rack, is immersed in the chemical solu- forming. The web areas comprising about total area of part (ft 2) tion. Agitation of the work or circulation of 80% of the surface area (one side) of the Fig. 38 Breakeven between chemical and mechan- the solution is necessary to ensure uniform originally 6.4 mm (1/4 in.) thick section were ical milling. Choice between them depends rates of metal removal from all exposed etched to a thickness of 0.64 mm (0.025 in.), on fillet ratio and depth of cut. 804 / Machining of Specific Metals and Alloys

reducing the weight of the part from 27 to metal thicknesses greater than 6.35 mm REFERENCES 6.8 kg (60 to 15 lb). (0.250 in.) should be removed mechanically; Before the development of chemical mill- thicknesses less than 3.18 mm (0.125 in.), 1. Machining Aluminum, Special Report ing, parts of this type were made by welding chemically. Between these two values, the 702, Am. Mach., March 1978 or riveting reinforcing sheet sections to a choice depends on fillet ratio, which gov- 2. J.C. Miller, "Machining High Silicon formed 0.64 mm (0.025 in.) thick skin; there erns the weight penalty. Aluminum," Paper G-T81-035, present- was no practical method of forming such a ed at the 1 l th International Die Casting panel after machining or of machining such ACKNOWLEDGMENT Congress and Exposition, Cleveland, a panel after forming. Chemical milling low- OH, Society of Die Casting Engineers, ered manufacturing cost by greatly reducing ASM INTERNATIONAL would like to June 1981 the number of parts and eliminating assem- thank Alan McMechan, McDonnell Dou- 3. A. McMechan, "Soft Spots in Machined bly time. glas Canada; Eli Levy, The de Havilland Aluminum Parts," Paper presented at Chemical Versus Mechanical Milling. Aircraft Company of Canada; and R.A. the Western Metal & Tool Exposition Figure 38 presents a typical curve for Morley, Reynolds Aluminum, for their as- & Conference, Los Angeles, CA, Mc- choosing the most economical of these two sistance in updating this article. Mr. Mc- Donnell Douglas Corporation, March methods for removing metal from fiat parts Mechan prepared the section "Soft Spots in 1982 on which large areas having complex or Machined Aluminum Parts," Mr. Morley 4. Machining Alcoa Aluminum, Aluminum wavy peripheral outlines are to be reduced supplied data on the machining of high- Company of America, 1967 in thickness. Fillet ratio and thickness of silicon aluminum alloys, and Mr. Levy pro- 5. Machining Data Handbook, Vol 1 and 2, metal to be removed are used as the basis vided information on machining practices in 3rd ed., Metcut Research Associates, for evaluation. For this specific application, the aerospace industry. Inc., 1980