CHAPTER 13 Methods

Metal Removal Cutting-Tool Materials and Machines Metal Removal Methods Machinability of Metals

Single Point Tools and Operations Turning Methods and Machines 13.1 Introduction grouped into three general classes. Grooving and Threading Modern milling machines look much • Column and Knee Machines Shaping and Planing the same as they did 25 years ago. • Bed Type Milling Machines However, they now must cut super • Special Purpose Machines Hole Making Processes alloys, titanium, and high tensile steels The common subtypes are also iden- and Operations to closer tolerances and at faster rates tified and discussed. Drilling Methods and Machines then previously. To handle these re- Operations and Machines quirements, the new milling machines 13.2.1 Column and Knee Reaming and Tapping provide higher horsepower, greater Machines stiffness, and wider speed and feed Column and knee milling machines Multi Point Machining ranges than before. In addition, more are made in both vertical and horizon- Milling Cutters and Operations accurate lead screws, closer alignment, tal types. The schematic diagrams Milling Methods and Machines (NC) and computer (Fig. 13.2a and Fig.13.2b) show both Broaches and numerical control (CNC) all result in types of machines. Versatility is a ma- and Sawing faster work with better finishes and jor feature of knee and column milling greater accuracy than ever before at- machines. On a basic machine of this Processes tained. A modern CNC vertical mill- type, the table, saddle, and knee can be Grinding Wheels and Operations ing machine is shown in Figure 13.1 moved. Many accessories such as uni- Grinding Methods and Machines versal , rotary tables, and dividing and Honing 13.2 Types of Milling Machines heads, further increase the versatility The many types of milling machines of this type of machine. used in manufacturing have been Regardless of whether the machine is of the vertical or horizontal type, several components on all column and knee milling machines are similar, ex- cept for size and minor variations be- cause of manufacturer’s preference. These similarities are described in terms of general shape, geometric rela- tionship to the rest of the machine, function, and the material from which the components are made. Figure George Schneider, Jr. CMfgE 13.3a shows a standard vertical milling Professor Emeritus machine and Figure 13.3b shows a 3 Engineering Technology axis CNC vertical milling machine Lawrence Technological University A universal Horizontal Column and Former Chairman Knee milling machine is shown in Detroit Chapter ONE Figure 13.4. Society of Manufacturing Engineers Column: The column, which is Former President usually combined with the base as a International Excutive Board Society of Carbide & Tool Engineers single casting, is cast gray iron or ductile iron. The column houses the Lawrence Tech.- www.ltu.edu spindle, bearings, and the necessary Prentice Hall- www.prenhall.com FIGURE 13.1: Modern CNC vertical , clutches, shafts, pumps, and milling machine (Courtesy Ingersoll shifting mechanisms for transmitting Milling Machine Co.) www.toolingandproduction.com Chapter 13/Tooling & Production 1 Chap. 13: Milling Methods & Machines

Motor Arbor Overarm Overarm

Z′ Spindle Outboard bearing Y′ nose and arbor support Column Table Quill X X ( axis) Spindle Saddle Z (Z axis) Table Z Knee Column Y (Y axis) Saddle X Y Elevating screw Knee Z′ Base Elevating screw

Base

(a) (b) FIGURE 13.4: A universal horizontal- spindle column and knee type milling FIGURE 13.2: Schematic illustration of the motions and components (a) of a machine. (Courtesy Summit Machine vertical-spindle column and knee type milling machine and (b) of a horizontal- Tool Manufacturing Corp.) spindle column and knee type of machine. Spindles are hollow so that a drawbar can be used to hold arbors securely in place. The front of the spindle is machined to accept standard arbors. The two keys that fit into corresponding slots in the arbor do the actual driving of the arbor. The internal taper, which is accurately ground so that it is concen- tric with the spindle, locates the arbor. Knee: The knee is a casting that is moved up or down the slide on the front of the column by the elevating screw. Two dovetail or slides are machined at 90 degrees to each other. The vertical slide mates with the slide on the front of the column, and (a) (b) the horizontal slide carries the saddle. It contains the necessary gears, screws, FIGURE 13.3: (a) Stand vertical-spindle column and knee type milling machine. and other mechanisms to provide (Courtesy Bridgeport Machinery, Inc.) (b) Three-axis CNC vertical-spindle column power feeds in all directions. The and knee type milling machine. (Courtesy Chevalier Machinery, Inc.) operator can select various feed rates power from the electric motor to the angle to the face of the column in both with the controls mounted on the knee. spindle at the selected speed. The the lateral and vertical planes. The Saddle: The saddle for a plain gears usually run in oil and are made of tolerances are very close and are usu- milling machine is a casting with two carburized alloy steel for long life. ally expressed in minutes or seconds of slides machined at an exact 90 degree Some of the necessary controls are arc. The large hole in the face of the angle to each other. The lower slide usually mounted on the side of the column casting is for the spindle. The fits the slide on the top of the knee, and column. hole is very accurately bored perpen- the upper slide accepts the slide on the The base is usually hollow, and in dicular to the front slide in two planes bottom of the table. The surfaces of the many cases serves as a sump for the and parallel to the upper slide. slides that make contact with the knee . A pump and filtration Spindle: On a horizontal milling and the table are parallel to each other. system can be installed in the base. machine, the spindle is one of the most Locks for both the cross slide and table The hole in the center of the base critical parts. It is usually machined is fitted to the saddle, along with the houses the support for the screw that from an alloy steel and is heat nuts that engage with the cross feed raises and lowers the knee. treated to resist wear, vibration, thrust, and table feed screws. The machined vertical slide on the and bending loads. The spindle is On a universal milling machine the front of the column may be of the usually supported by a combination of saddle is made in two pieces and is square or dovetail type. The knee ball and straight roller bearings, or by more complex because it must allow moves up and down on this slide. The tapered roller bearings that absorb both the table to swivel through a limited slide must be machined at a 90 degree radial loads and end thrust loads. arc. The lower part has a dovetail slide

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milling machine is often ideal for this kind of work. In this machine the table is supported directly on a heavy bed, while the column is placed behind the bed. A CNC bed-type milling machine is shown in Figure 13.5. and an opera- tional set-up with three spindles is shown in Figure 13.6. There are several advantages of the bed-type machine, particularly for pro- duction runs. Hydraulic table feeds are possible; the hydraulic components be- ing housed in the bed casting. This allows very high feed forces; variable feed rates during any given cut, and FIGURE 13.5: CNC bed type milling machine. (Courtesy WMW Machinery Co., automatic table cycling. The spindle Inc.) may be raised or lowered by a cam and template arrangement to produce spe- Acme thread. cial contours. The basically heavier Milling machines with construction allows more power to be vertical spindles (see Fig. supplied to the spindle, which gives 13.3a), are available in a higher productivity through faster large variety of types and metal removal. Duplex bed-type mill- sizes. The head, which ing machines have two columns and houses the spindle, motor, spindles for milling two surfaces on a and feed controls, is fully part simultaneously. A large 5-axis universal and can be placed CNC bed-type milling machine is at a compound angle to the shown in Figure 13.7. surface of the table. The The chief disadvantage of a bed-type ram, to which the head is milling machine compared to one of attached, can be moved for- the knee and column type is that it is ward and back and locked in less versatile for machining small FIGURE 13.6: Machining operation showing a bed- any position. A turret on top parts. Its advantages lie in its higher type milling machine with three heads (Courtesy: of the column allows the productivity, its adaptability to large Cincinnati Machine) head and ram assembly to sized machines, and its ease of modifi- swing laterally, increasing cation to special applications. that fits the top of the knee and a the reach of the head of the machine. circular slide above it is graduated in Some ram-type milling machines 13.2.3 Special Purpose degrees for a small portion of its pe- can be used for both vertical and hori- Milling Machines riphery. The upper portion of the zontal milling. On ram-type vertical As industrial products have become saddle consists of a circular face that mills that have the motor fits against the lower circular slide, a in the column, power is central pivot point, and a dovetail slide transmitted to the spindle that accepts the table. Locking bolts by gears and splined shafts. moving in a circular T-slot are pro- Some heavy duty vertical vided so that the two parts of the saddle mills have a spindle and can be locked in any position. head assembly that can be Table: Milling machine tables vary moved only vertically by greatly in size, but generally they have either a power feed mecha- the same physical characteristics. The nism or manually. These bottom of the table has a dovetail slide are generally known as that fits in the slide on top of the over arm-type vertical saddle. It also has bearings at each end milling machines. to carry the table feed screw. The top of the table is machined parallel with 13.2.2 Bed-Type Milling the slide on the bottom and has several Machines full length T-slots for mounting vises High production calls for or other work holding fixtures. heavy cuts, and the rigidity A dial graduated in thousandths of of a knee and column type an inch is provided to allow for accu- of milling machine may rate table movement and placement. not be sufficient to take the FIGURE 13.7: Large 5-axis CNC bed type milling The table feed screw usually has an high forces. A bed-type machine. (Courtesy Ingersoll Milling Machine Co.) www.toolingandproduction.com Chapter 13/Tooling & Production 3 Chap. 13: Milling Methods & Machines

the cutter, duplicat- ing the shape of the template. A profile milling operation is shown, using a ball- nosed , in Figure 13.9a. A 5 axis, multi-spindle profile milling ma- chine is shown in Figure 13.9b. (a) Die sinking and other processes in- volving the machin- FIGURE 13.8: (a) Illustration of a - type milling machine. (Courtesy Kennametal ing of cavities can Inc.) (b) Part being machined on a planer- be done on three-di- type milling machine. (Courtesy Ingersoll mensional profilers. Milling Machine Co.) (b) An accurate pattern of the cavity is made more complex, new and unusual varia- planer-type milling machine is shown of wood, plaster, or soft metal. The tions of the more common milling in Figure 13.8b. stylus follows the contour of the pat- machines have been developed. The Planer-type machines are used tern guiding the cutter as it machines objectives are to accommodate larger mostly for machining parts like the out the cavity. Numerically controlled work, make many duplicate parts, lo- bedways for large machine tools, and milling machines are also used for this cate holes and surfaces precisely, or to other long workpieces that require ac- type of work. do other unusual machining jobs. curate flat and angular surfaces or Planer-Type Milling Machines: grooves. 13.3 Computer Controlled The general arrangement of these types Profile Milling Machines: Two Machining Systems of machines is similar to that for plan- dimensional profiling can be done by Several of the standard machines dis- ers (Chapter 7), except that in place of using a template, or with a numerically cussed in previous chapters of this text individual tool bits, milling heads are controlled vertical milling machine. are capable of performing multiple op- installed. The table of the machine Some profilers have several spindles, erations. A for example is ca- carries the work past the rotating cutter and a number of duplicate parts can be pable of turning, , drilling, heads, which are individually powered produced in each cycle. Hydraulic-type threading, etc. A drilling machine is and can be run at different speeds if profilers have a stylus that is brought capable of drilling, reaming, counter- necessary. As many as four cutter into contact with the template to start sinking, tapping, and so on. heads can be used, with two mounted the operation. The operator then However, when increased produc- on the cross rail and two on the vertical moves the stylus along the template, tion rates require the purchase of addi- pillars. An illustration of a planer type causing hydraulic fluid under pressure tional machining capability, it is al- milling machine is shown in Figure to flow to the proper actuating cylin- most always more economical and fea- 13.8a. A part being machined on a ders. The table moves the work past sible to purchase multifunctional ma-

FIGURE 13.9a: Profile milling operation is shown, FIGURE 13.9b: A large 5-axis multispindle profile milling using a ball-nosed end milling cutter. (Courtesy machine. (Courtesy Cincinnati Machine) Ingersoll Milling Machine Co.)

4 Tooling & Production/Chapter 13 www.toolingandproduction.com Chap. 13: Milling Methods & Machines

The relative merits of each will be discussed briefly. Horizontal Machines: Horizontal machines tend to be advantageous for heavy box-shaped parts, such as housings, which have many features that need to be machined on the side faces. The horizontal machine easily supports heavy workpieces of this type. If a rotary worktable is added, four sides of the workpiece can be machined without re-fixturing. Pallet systems used to shuttle pieces in and out of the workstation tend to be easier to design for horizontal ma- chines, where everything in front of the main column is open and accessible. A horizontal machining center with a pallet shuttling system is shown in Figure 13.11. Vertical Machines: Vertical ma- FIGURE 13.10: Preset machining center tools are stored in a toolholder magazine. chining centers are often preferred for (Courtesy Kennametal Inc.) flat parts that must have through holes. Fixtures for these parts are more easily FIGURE 13.11: designed and built for a vertical Horizontal machining spindle. Also, the thrust of the cut center with pallet shuttling developed in drilling or in milling system. (Courtesy pockets can be absorbed directly by the Cincinnati Machine) bed of the machine. The motions of a 3 and 5-axis CNC vertical machining center are shown in Figure 13.12. chines capable of quick The vertical machine is preferred changes, simultaneous where three-axis work is done on a machining, and automatic single face as in mold and die work. processing. The weight of the head of a vertical The term “Automation” machine as it extends away from the was coined in the 1950’s column, particularly on large ma- and applied to devices chines, can be a factor in maintaining that automatically load accuracy, as there may be some ten- and unload parts. The dency for it to drop and lose accuracy term is now accepted to cover, in addi- turret tool holders or provides for auto- and cause chatter. A vertical machin- tion to loading and unloading, func- matic tool change. A tool holder ing center is shown in Figure 13.13 tions such as processing, measuring magazine is shown in Figure 13.10 and a machining center with an adjust- workpiece size, adjusting a machine to Machining centers are built in either able head, tool change magazine and a maintain size, and repeating of horizontal or vertical configuration. pallet system is shown in Figure 13.14 workpiece cycles. Computer Controlled Manufactur- ing Systems discussed here will be Machining Centers and Flexible Ma- chining Systems. 13.3.1 Machining Centers Machining centers are designed and built to provide for flexible manufac- turing. They can be used to machine just a few parts or large production runs. Programming can be relatively simple and the use of ‘canned’ cycles provides a great deal of versatility. An NC machining center by definition is (a) (b) able to perform milling, drilling, and FIGURE 13.12: The motions of (a) a 3-axis CNC vertical machining center and (b) boring cuts and has either indexing a 5-axis CNC vertical machining center. (Courtesy Kennametal Inc.) www.toolingandproduction.com Chapter 13/Tooling & Production 5 Chap. 13: Milling Methods & Machines

FIGURE 13.13: Transparent rendition of a vertical FIGURE 13.14: Machining center with adjustable head, tool machining center. (Courtesy Monarch ) magazine and pallet system (Courtesy Cincinnati Machine)

13.3.2 Flexible Machining systems, monorails, cranes and robots. cycles of individual machines. Systems An FMS material-handling system is Flexible machining systems employ shown in Figure 13.16. 13.4 Milling Machine one or more machining centers, usu- Control Systems: The computer Attachments and ally along with other equipment, to controls of flexible machining systems Accessories produce medium-volume workpieces. have three functional levels Many accessories have been developed A workpiece-handling system is re- Master Control – The master control for milling machines. Some are spe- quired, and a central computer typi- monitors and controls the entire sys- cialized and can be used for only a few cally controls the entire arrangement. tem, including routing workpieces to operations. Others, such as vises, ar- A flexible machining system is shown appropriate machines, scheduling bors, and , are used in almost all in Figure 13.15. work, and monitoring machine func- milling operations. Material Handling: Parts are tions. moved from storage and between ma- – A DNC 13.4.1 Special Milling Heads chine elements by means of one of computer distributes appropriate pro- Several types of special heads have several different types of systems. The grams to individual CNC machines been developed for use on horizontal or material-handling system selected and supervises and monitors their op- vertical milling machines. These ac- must be capable of routing any part to erations. cessories increase the versatility of the any machine in any order and also to Element Control – The third and machine. For example, a vertical head provide a bank of parts ahead of each lowest level of control is can be attached to a conventional hori- machine to realize maximum produc- computer control of the machining zontal column and knee milling ma- tivity. Parts are normally loaded and unloaded manually. The various types of material-han- dling systems used include: automated guided vehicles, towline systems, roller conveyer systems, overhead conveyer

FIGURE 13.15: Flexible machining system. (Courtesy Sandvik Coromant FIGURE 13.16: FMS material-handling system. (Courtesy Giddings + Co.) Lewis LLC)

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mum opening classify vises of this type. Cam-operated plain milling vises are widely used in production work because of the savings in time and effort and the uniform clamping pres- sure that can be achieved. Swivel-Base : A swivel-base vise is more convenient to use than the plain vise, although it is somewhat less rigid in construction. The base, which is graduated in degrees, is slotted for keys that align it with the T-slots in the (a) table. The upper part of the vise is held to the base by T-bolts that engage a FIGURE 13.17: (a) Universal milling circular T-slot. The swivel-base vise, head attachment. (b) A universal milling when used on a milling machine with a head attachment being used on a semi-universal head, makes it possible horizontal milling machine. (Courtesy WMW Machinery Co., Inc.) to mill compound angles on a (b) workpiece. chine, greatly increasing its usefulness, Universal Vise: A universal vise especially in small shops with a limited (Fig. 13.18b) is used mostly in number of machines. toolroom diemaking, and prototype Vertical Heads: Vertical heads are work. The base of the vise is graduated generally attached to the face of the in degrees and held to the table by T- column or to the overarm of a horizon- bolts. The intermediate part of the vise tal milling machine. The head is a has a horizontal pivot upon which the semi-universal type, which pivots only vise itself can rotate 90 degrees. Be- on the axis parallel to the centerline of cause there are several joints and piv- the spindle, or it is fully universal. Fully universal heads can be set to cut compound angles. Both types of heads range of the machine are necessary, are powered by the spindle of the mill- high speed attachments can be placed ing machine and accept standard ar- on both horizontal and vertical milling bors and collets. A universal milling machines. A gear train is generally head attachment is shown in Figure used to step up the speed as much as 6 13.17a.Figure 13.17b shows a univer- to 1, which allows more efficient use of sal milling head attachment being used small cutters. on a horizontal milling machine. Rack-Milling Attachment: The 13.4.2 Vises and Fixtures (a) rack-milling attachment bolts to the In all milling operations, the work is spindle housing of the milling ma- held by fixtures, vises, or clamping chine. Its spindle is at a right angle to arrangements. In most cases the work the main spindle of the machine. Both is held stationary in relation to the spur and helical racks can be milled table while it is being machined, but with this attachment, and it can also be work held in indexing heads and rotary used to mill worms. Some rack-mill- tables can be moved in two planes ing attachments have an outboard sup- while machining operations are in port for the spindle, which makes it progress. possible to take heavier cuts. Plain Vise: Plain milling vises (Fig. Slotting Attachment: This attach- 13.18a) are actuated by an Acme ment that is bolted to the column of a threaded screw, and the movable jaw horizontal milling machine can be moves on either a dovetail or rectangu- swiveled 90 degrees in either direction lar slide. The vises are usually cast of from the vertical position. It is used high grade gray cast iron or ductile primarily in toolmaking and prototype iron and can be heat treated. Steel keys work for cutting keyways, internal are attached in slots machined into the splines, and square or rectangular cavi- bottom of the vise, parallel with and (b) perpendicular to, the fixed jaw to allow ties. The crank that actuates the recip- FIGURE 13.18: (a) A plain vise. (b) A rocating slide is driven directly by the accurate placement on the milling universal vise, which is generally used spindle, and the stroke is adjustable. table. The jaw inserts are usually heat in a toolroom diemaking and protype High Speed Attachment: When treated alloy steel and are attached by work. (Courtesy Palmgren Steel spindle speeds beyond the operating cap screws. The jaw width and maxi- Products, Inc.) www.toolingandproduction.com Chapter 13/Tooling & Production 7 Chap. 13: Milling Methods & Machines

and cannot be held easily in a vise. Holding fixtures, that are a combination of a simple and a , are sometimes used to hold round or hexagonal work for milling. The collet-holding may be manually or FIGURE 13.19: Adjustable-angle tables can be tilted in one or more directions to machine irregularly air operated. Both fixtures (a) shaped parts. (Courtesy Palmgren Steel Products, can be bolted to the milling Inc.) table in the vertical or hori- zontal position or attached to an adjustable angle plate for holding workpieces at simple or compound angles to the table or other reference sur- face. Indexing Heads: The in- dexing head, also known as the dividing head (Fig. (b) 13.20), can be used on verti- cal and horizontal milling FIGURE 13.22: (a) Rotary tables can be used on both vertical and horizontal machines to space the cuts milling machines. (b) A , for such operations as mak- that can also be tilted. (Courtesy ing splines, gears, worm Palmgren Steel Products, Inc.) FIGURE 13.20: Indexing heads, also called dividing wheels, and many other parts heads, can be used on vertical and horizontal requiring accurate division. and wheel reduction ratio of 40:1, re- milling machines. (Courtesy Cincinnati Machine) It can also be geared to the quiring 40 turns of the hand crank to table screw for helical mill- make the spindle revolve once. When ing operations such as cutting the necessary index plates are avail- ots in the vise assembly, the universal flutes in twist drills and making helical able, all divisions up to and including vise is usually the least rigid of the gears. 50 can be achieved by plain indexing. various types of milling machine vises. Indexing heads are of the plain or For some numbers above 50, differen- Angle Plates: Several types of universal type. Plain heads cannot be tial indexing is necessary. angle plates can be used to hold work tilted; universal heads can be tilted to In recent years, programmable pre- or work holding fixtures for milling the vertical or any intermediate posi- cision indexers have become fairly (Fig. 13.19). Plain angle plates are tion. The spindle of the indexing head common in shops doing work that re- available in T-slotted or blank form can be fitted with a , or with quires accurate spacing of complex and are usually strong iron castings. other work holding devices, including hole patterns on surfaces. The indexer Adjustable angle plates may tilt in one collets or a center. A cross-sectional may be mounted with the axis of the direction only or have a swivel base. view of an indexing head is shown in chuck vertical or horizontal, and in They are very useful for milling Figure 13.21. some cases the chuck may be replaced workpieces that are irregular in shape Most indexing heads have a worm with a specially made holding fixture or a faceplate. If necessary, a FIGURE 13.21: may be used to support the end of the Cross-sectional workpiece. The controller is capable of view of indexing head. (Courtesy storing a series of programs, each of Cincinnati which may incorporate as many as 100 Machine) operational steps or positions. Rotary Table: Rotary tables (Fig. 13.22) are available in a wide range of sizes and can be used on both vertical and horizontal milling machines. Most can also be clamped with the face at a 90 degree angle to the surface of the milling machine table. The face of the rotary table has four or more T- slots and an accurately bored hole in the center, which is concentric with the axis about which the table rotates. The base of the rotary table, which

8 Tooling & Production/Chapter 13 www.toolingandproduction.com Chap. 13: Milling Methods & Machines

FIGURE 13.23: Machine frame Schematic drawing of an Spindle arbor mounting Bearings nose with drawbolt used in horizontal milling machines.

Draw bar Arbor

Detail of Arbor Mounting houses the worm drive mechanism, is of the arbor. (a) graduated in degrees, and the Style A arbors consist of the tapered handwheel can be graduated in incre- portion that fits the spindle, the shaft ments as small as 5 minutes or 1/12 of on which the cutter or cutters fit, the 1 degree. On some rotary tables an spacers, and the nut. The shaft has a index plate may be attached to the keyway along its entire length. The base. outboard end of the arbor has a pilot Rotary tables can also be geared to that fits into a bronze bushing in the the table feed screw. When set up in outboard support of the milling ma- this manner, the rotary table can be chine overarm (Fig. 13.2b). One or used to make plate cams and to gener- more cutters can be mounted on the ate a number of other irregular shapes. arbor, either adjacent to each other or separated by spacers and shims. Style 13.4.3 Arbors, Collets, and A arbors are used primarily for light Tool Holders and medium duty milling jobs. Several basic types of arbors and Style B arbors are used for heavy collets are used to hold milling cutters milling operations, especially where it (b) and to transmit power from the spindle is necessary to provide support close to FIGURE 13.25: (a) End milling cutter to the cutter. Regardless of type, they a milling cutter, such as in a straddle toolholders. (b) Shell end milling cutter are usually precisely made of alloy milling operation. One or more bear- toolholders. (Courtesy Lyndex Corp.) steel and heat treated for wear resis- ing sleeves may be placed on the arbor tance and strength. as near to the cutters as possible. An a collet that has a partly straight and Arbors: Arbors for horizontal mill- outboard bearing support is used for partly tapered shank. The collet is ing machines (Fig. 13.23) are available each bearing sleeve on the arbor. secured by a drawbar that is screwed in three basic types: style A, style B, Style C arbors are used to hold and into a tapped hole in the back of the and style C. A draw bolt, that goes drive shell end mills (Fig. 25.25b) and collet and tightened from the top of the through the spindle of the machine, some types of face milling cutters and spindle. Some milling machine manu- screws into the small end of the taper require no outboard support. In some facturers offer collet arrangements that and draws the arbor tightly into the cases, they can also be fitted with do not need a drawbar. Collets of this tapered hole in the milling machine adapters for mounting other types of type can be closed with a lever-oper- spindle. Power is transmitted from the cutters. ated cam or with a large locking nut. spindle to the arbor by two short keys Collets: On some vertical milling Figure 13.24a shows various size that engage with the slots on the flange machines the spindle is bored to accept collets and Figure 13.24b shows a number of tool holders including collets and a set-up fixture. Toolholders: Standard tool holders are available for end mills and shell mills as shown in Figures 13.25a and 13.25b respectively. For some opera- tions that require the use of tools with non-standard shank sizes, chucks can be used to hold the tool. These chucks are available with Morse taper or straight shanks. Either type can be used in milling machines when the (a) (b) proper adapters or collets are available. FIGURE 13.24: (a) Collets of various sizes. (Courtesy Lyndex Corp.) (b) Various toolholders with collets and a setup fixture. (Courtesy Valenite Inc.) Offset boring heads (Fig. 13.26) are www.toolingandproduction.com Chapter 13/Tooling & Production 9 Chap. 13: Milling Methods & Machines

FIGURE 13.28: Conventional or up-milling as compared o climb or down- milling.

FIGURE 13.26: Offset boring heads are often used in milling machines for boring, facing, and chamfering operations. (Courtesy Bridgeport Machine, Inc.) FIGURE 13.29: In gang milling often used in vertical milling machines operations, for boring, facing, chamfering, and horizontal, outside diameter turning operations. vertical, or They are available with straight, Morse angular taper, or standard milling machine surfaces are taper shanks and usually have three machined in mounting holes for boring bars. Two one path. of the holes are usually parallel with (Courtesy the centerline of the tool, and one is Sandvik perpendicular to the centerline. Some Coromant Co.) boring heads have two adjusting cutter that has teeth on the periphery, cuts, the diameter of the two cutters mechanisms, and the movable slide and on one or both sides, is used. must be exactly the same. When cut- can be adjusted accurately in incre- When a single cutter is being used, the ters with helical teeth are used, the ments of 0.0001 inch. teeth on both the periphery and sides helix angles must be opposite. Flycutters can be used for facing may be cutting. The machined sur- Since straddle milled surfaces must operations. The tools in cutters of this faces are usually either perpendicular be parallel to each other and are usu- type are adjusted so that both a rough- or parallel to the spindle. Angle cut- ally held to close tolerances in terms of ing and finishing cut are taken in one ters can be used to produce surfaces width, the condition and size of the pass. that are at an angle to the spindle for collars and shims that separate the such operations as making external cutters are important. The arbor must 13.5 Types of Milling Operations dovetails or flutes in . also turn as true as possible to avoid Milling cutters are used either indi- Straddle Milling: In a typical cutting the workpiece undersize. vidually or in combinations to machine straddle milling set-up (Fig. 13.27) Usually, a combination of collars various surfaces as described below two-side milling cutters are used. A and steel shims can be assembled to and shown in Figure 13.27. straddle milling operation is shown in provide the correct spacing between Plain Milling: Plain milling is the Figure 13.28. The cutters are half-side cutters. For some production opera- process of milling a surface that is or plain side milling cutters, and have tions, a special collar can be made from parallel to the axis of the cutter and straight or helical teeth. Stagger-tooth alloy or medium-carbon steel, heat basically flat. It is done on plain or side milling cutters can also be used. treated, and surface ground to length. universal horizontal milling machines The cutters cut on the inner sides The faces must be perpendicular to the with cutters of varying widths that only, or on the inner sides and the bore and parallel to each other. The have teeth only on the periphery. periphery. If the straddle milling op- cutters should be keyed to the arbor, Side Milling: For side milling, a eration involves side and peripheral and the outboard bearing supports must be placed as close to the cutters as possible. Gang Milling: In gang milling, three or more cutters are mounted on the arbor, and several horizontal, verti- cal, or angular surfaces are machined in one pass (Fig. 13.29). When mak- ing a gang milling set-up, several dif- (a) Straddle milling(b) Form milling(c) Slotting(d) Slitting ferent types of cutters can be used, depending on the job to be done. Cut- FIGURE 13.27: Drawing of a milling cutter showing the difference between advance ters used for producing vertical or an- per revolution (apr) and advance per tooth (apt). gular surfaces must be of the side-

10 Tooling & Production/Chapter 13 www.toolingandproduction.com Chap. 13: Milling Methods & Machines

(a)

FIGURE 13.31: Face milling operation. (Courtesy Valenite Inc.) (a)

(b) FIGURE 13.33: Milling operations: (a) side and face milling cutters used to machine various slots, (b) various indexable milling cutters used to machine an automotive engine block. FIGURE 13.32: End milling operation. (Courtesy Sandvik Coromant Co.) (b) (Courtesy Valenite Inc.) FIGURE 13.30: (a) Slotting operation close tolerances, spacers are usually used in the manufacturing of rotors. that can be machined by peripheral machined and surface ground to pro- (Courtesy Iscar Metals, Inc.) (b) Slitting milling is limited almost only by cutter vide the necessary accuracy. operation to separate cast automotive design. Form cutters are expensive, Face Milling: Face milling (Fig. parts. (Courtesy Sandvik Coromant Co.) but often there is no other satisfactory 13.31) can be done on vertical and means of producing complex contours horizontal milling machines. It pro- cutting type; plain milling cutters of as shown in Figure 13.27. duces a flat surface that is perpendicu- the proper width can be used for hori- Slotting and Slitting Operations: lar to the spindle on which the cutter is zontal surfaces. In some cases face Milling cutters of either the plain or mounted. The cutter ranges in size and mills with the teeth facing inward can side-cutting type are used for slotting complexity from a simple, single-tool be used at one or both ends of the gang and slitting operations (Fig.13.30a and flycutter to an inserted-tooth cutter milling set-up. 13.30b). Slotting and Slitting are usu- with many cutting edges. Large face When only one wide plain helical ally done on horizontal milling ma- mills are usually mounted rigidly to the milling cutter is used as part of a gang chines, but can also be done on vertical nose of the spindle. They are very milling set-up, the side thrust caused mills by using the proper adaptors and effective for removing large amounts of by that cutter should be directed toward accessories. Metal slitting cutters of metal, and the workpiece must be se- the spindle of the machine. If possible, various diameters and widths are also curely held on the milling table. interlocking cutters with opposite helix used to cut slots. A number of identi- End Milling: (Fig. 13.32) End angles should be used to eliminate side cal cutters can also be mounted on the milling is probably the most versatile thrust and reduce the possibility of same arbor for cutting fins. When the milling operation. Many types of end chatter. thickness of the fins must be held to mills can be used on both vertical and Because of the time and effort in- volved in setting up the milling ma- chine for gang milling, the process is used mainly for production work. Since all or almost all of the workpiece is being machined at one time, power and rigidity are very desirable features in the machine being used. Every effort should be made to control vibra- tion, including the use of support bars that are bolted to both the knee and the outboard bearing support. Form Milling: The number of par- (a) (b) allel surfaces and angular relationships FIGURE 13.34: Two turn milling operations. (Courtesy Sandvik Coromant Co.) www.toolingandproduction.com Chapter 13/Tooling & Production 11 Chap. 13: Milling Methods & Machines horizontal milling machines. End different machining methods where a are combined in the machines, single mills are available in sizes ranging milling cutter machines a rotating set-up machining leads to advantages from 1/32 to 6 inches (for shell end workpiece. These methods are prima- of fast through-put times and flexibility mills) and in almost any shape needed. rily used for machining various eccen- of production. Two turn milling opera- Milling cutters can be used individu- trically shaped parts; planes, tapered tions are shown in Figure 13.34a and ally or in pairs to machine various slots and cylindrical surfaces; grooves and Figure 13.34b. (Fig. 13.33a). Many milling cutters inside holes. Advantages associated with turn can also be mounted onto an arbor to Turn milling requires a machine tool milling are: capability of machining perform in a gang milling operation of with certain functions and a number of large and unbalanced parts which can- automotive engine blocks as shown in axes. Machining centers, turning cen- not be rotated at high speeds; complex Figure 25.33b ters, specially adapted , milling surface shapes, eccentric parts and machines, boring mills and special- components with additional elements 13.6 Turn Milling purpose machines are used. When that protrude; log, unstable shafts or Turn milling consists of a number of other operations of turning and milling thin-walled parts.

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