MARCH 1997

WESTEC ‘97 Preview

Society of Manufacturing Engineers 1 AreAre TheyThey forfor Experts differ on GrindingGrinding oror ?Milling? what to call a process that uses a CBN grinding wheel that removes metal at milling speeds and produces tiny milling chips

Free-cutting, single-layer, plat- hen a process uses a CBN with increased wheel speed it is possible to plated grinding wheel yet increase removal rate (productivity).” ed CBN form wheels, like these produces a chip that looks from Abrasive Technology, have W like a miniature milling tight tolerances and cover a wide chip under a microscope we ask: is it Call it Superabrasive grinding or milling? It uses high wheel range of forms. rotation speeds and traverse rates and rel- Machining atively deep depths of cut to remove hard Wes Lee president of Edgetek The basic Edgetek machine has a 35- aerospace alloy materials at speeds Corp (Meriden CT) which has sold over 55 hp (26-kW) spindle and runs at speeds to approximately equal to the speeds that CNC machine tools using plated single- 14,000 rpm. Its extremely rigid cast-poly- milling cuts soft steels. It is definitely not layer CBN form wheels formerly referred mer base and column absorbs vibration grinding in the usual way we think of to the process as HEDG grinding. The from heavy cutting forces more effectively grinding. Nor is it creep-feed grinding company’s first two were than cast iron. At the top spindle speed of since the machine table does not creep but shipped in 1991; today Lee insists that the 14,000 rpm. a 6" (152 mm) diameter wheel traverses in the 30-100 ipm (760-2540 mm process is not grinding at all. He calls it runs at 22,000 sfm (6706 m/min) and an 8" min) range. This process has been gradual- “superabrasive machining.” The word (203 mm) wheel at about 30,000 sfm (9144 ly catching on in American industry in the ‘grinding” does not appear in company lit- m/min). These speeds and rigidity let the last two years. erature. One brochure says: “The super- machine remove metal fast especially in University professors call this process abrasive machining process has been slotting or form-grinding operations. The high-efficiency deep grinding (HEDG) but compared to grinding but it is more accu- motor’s power and the wheel diameters that term has not caught on generally. rately described as a milling process. The and widths are typically smaller than on Milton C. Shaw professor emeritus of engi- preformed steel core wheels are electro- the big creep-feed grinders, so the forms neering at Arizona State University plated with CBN and mounted on the and grooves suited to it are not as wide as (Tempe AZ) described HEDG grinding in spindle. The wheels act more like a milling those tackled by the creep-feed grinders. his 1996 book Principles of Abrasive cutter than a grinding wheel. At high rpms. The price, however, is about a third to Processing this way: “When CBN is used at and relatively high feed rates the CBN a half the cost of the big creep-feed high wheel speed and at an increased wheels provide surface finishes equal to grinders. The Edgetek machine has three, removal rate in creep-feed grinding with a grinding.” four, and five-axis versions, and all come copious supply of fluid a new grinding with a large coolant tank and powerful concept called high-efficiency deep grind- FREDERICK MASON high-pressure coolant system. Oil is the ing (HEDG) emerges. When CBN is used SENIOR EDITOR, SPECIAL PROJECTS coolant used most frequently; nozzle

REPRINTED FROM MARCH 1997-MANUFACTURING ENGINEERING 2 and wheel form closely so that, when plat- ed with a given grit size, the wheel will conform precisely to the form to be machined. About 40-50% of the CBN crys- tal is exposed above the bond, providing ample room for chip formation. The wheels act like a very sharp wheel and, so, cut aggressively and with less power than aluminum oxide wheels. Plated CBN form wheels have several advantages over bonded conventional or superabrasive wheels, according to Joe Eramo of Abrasive Technology Inc. (Lewis Center, OH). “Plated wheels have higher material removal rate capabilities, but are freer cutting, which reduces thermal met- allurgical damage to the work’s surface. Plated wheels grind virtually the same pro- file from the first cut to the last, grinding hundreds or thousands of workpieces. The times associated with set ups, wheel changing, and wheel dressing are signifi- cantly reduced or eliminated.” “We can turn the wheel’s steel core to precision complex forms.” According to Eramo, “Plated technology has improved to the point that profile tolerances of ± 0.0006" [0.015 mml may be held today, an improvement over the ± 0.002" [0.05 mm] of five years ago. The steel core provides for safety at high operating speeds [>20,000 sfm or 6100 m/min]. The wheels may be stripped of worn CBN and replated several times, resulting in a greatly reduced average wheel price.” design and placement need optimization. Corp.” He called the Edgetek “a true HEDG “Although plated wheels cost less than

This process can eliminate manufac- machine [with] huge Q'w [cubic inches per vitrified and metal-bonded wheels, it is turing steps. It can machine hardened minute of metal removal per inch of width] not the cost that is driving the trend parts–those formerly milled in their soft values.” He reported high metal removal toward plated CBN but the productivity,” condition, then heat-treated, and finally rates at high wheel speed on both materi- reports Eramo. Smaller production runs ground–in their hardened condition, elim- als, without burning with a clean wheel and more setups, he says, means that inating milling. Other benefits from face. Working with two 8" (203 mm) diam- many companies no longer have the luxu- machining with plated CBN include high eter wheels and with water-soluble oil at a ry to amortize the cost of diamond rolls productivity, good surface integrity and 22% concentration, he ground Inconel 718 and the long nonproductive setup times size control, consistent finish, and usually at speeds from 10,480 fpm to 31,440 fpm associated with bonded wheels, over long a burr-free part. Less thermal stress, (3195 to 9583 m/ min) without leaving production runs. Plated technology fills enhances part quality. Surface quality on burn marks. “The huge Q'w values on the need for high metal removal rates with groove walls is close to that of convention- Inconel 718 [reaching about Q'w = 7] are short setup times and eliminates the need al grinding, about a 32 µin. AA finish. quite impressive” compared with metal for dressing.” Groove or slot bottoms look more like a removal rates achieved in the better- American Pfauter offers a similar view, finely machined finish, around 90 µin. AA known process of creep feed grinding with reporting that CBN is free cutting. “It does finish. The CBN grains do not wear, so aluminum-oxide wheels. not cause burning because the heat goes there is no burnishing effect. Radii on into the chip. The thermal conductivity of forms can be reliably held to about 0.020" Why Plated CBN Wheels? CBN, compared to aluminum-oxide, is 46 (0.51 mm), although wheels have been to 1. Using CBN, about 4% of the heat gen- plated with radii down to 0.005" (0.13 mm). From Edgetek’s general-purpose erated goes into the work. With aluminum Well-known grinding expert Dr. Superabrasive machining technology, to oxide wheels, about 63% of the heat gener- Richard P. Lindsay, Lindsay Consulting, American Pfauter’s CBN micromachining ated goes into the work.” (Marlborough, MA) tested the Edgetek technology for parallel-axis , (See machine for two days with plated-CBN sidebar) the process commonly relies on Vitrified CBN is an wheels in late 1995 and issued a report nondressable but replatable single-layer Alternative entitled “Grinding Chrome Vanadium plated CBN wheels. Wheel suppliers con- Steel and Inco 718 at Edgetek Machine trol CBN crystal sizes, the plating process, Another company, Campbell Grinder

REPRINTED FROM MARCH 1997-MANUFACTURING ENGINEERING 3 (Muskegon Heights, Ml), entered the mar- ket for aerospace grinding with CBN a few Cutting Machine Builder Calls it years ago, when they shipped three machines equipped with plated wheels to ingle-layer plated-CBN Pratt & Whitney. General Electric is also S machining with formed buying a number of these machines. Their wheels, developed in the 1980s, is basic CBN machine, which, incidentally, probably the most significant they call a HEDG grinder, grinds vanes, development in gear manufactur- blades, shrouds, and shafts, one at a time. ing in recent decades. It has The machine is similar in size and power replaced, in some applications to Edgetek’s. Bruce Hammond, mechani- cal design engineer at Campbell, says, within the industry, “Our machines are built extremely stiff. pregrind gear hobbers and They move through the part like milling. In shapers that cut gears from the one straight test cut we took a 0.400" [10 solid. Users change wheels to suit mm] depth of cut, 4" [100 mm] wide at a the gear size and form. Typically, feed of 3 ipm [76 mm/min] The widest root but depending on stock form we have ground is a 3" wide form for allowances, two-double passes, a land-based generator. We have found each double pass consisting of a that in some cases our process can grind at down stroke and an up stroke as CBN-plated dual wheel set grinding gear a dramatically lower cost-per-part than on a milling machine, perform the with roughing and finishing wheel on Pfauter P400G vertical gear and form creep-feed grinding.” The company is rough cut and the finish cut on shipping about one machine per month at grinder. heat-treated gears. this time. “As applied by Kapp, [cutting with threads, the process replaced such Campbell’s preference is to use vitrified slow and expensive processes as sin- CBN wheels, rather than plated ones. plated] CBN is a micromachining gle-index milling. “Dressable vitrified wheels,” says Ham- process more akin to milling than mond, “last longer and can run many more grinding” says Brian Cluff vice presi- At American Pfauter, these parallel parts than a plated wheel. They cost more, dent, American Pfauter. “The nickel axis gear-grinders start at about but that cost can be amortized over the bonded particles on the Kapp form $750,000 on the low end, for gears up larger volume of parts. We largely gave up wheel are like the cutting edges of to 400 mm, and cost over $5 million for on plated wheels two or three years ago, for microscopic milling cutter inserts. the top-of-the-line systems for large two reasons. Many of the wheels we exam- Furthermore the chips look when mag- gears. The more sophisticated ined had unacceptable runout between the nified, like milling cutter chips, with a machines combine several cutting wheel bore and the plated OD. And second, characteristic comma shape. These operations and complete gear inspec- the plated wheels required the machine to chips differ dramatically from those tion before removing the gear from the run with oil, whereas with a vitrified wheel, produced by aluminum-oxide wheels machine. the machine runs with a waterbased where the chips are not uniform.” American Pfauter has just intro- coolant, minimizing coolant disposal duced two new, small, vertical CNC costs” Although the German grinder builder gear and from grinders. One, the One of their preferred suppliers of vitri- Kapp, and now its former US partner, fied CBN wheels is the Precision Grinding American Pfauter, refer to their P200G serves the high-production Systems Div. of Universal Superabrasives machines as grinders, because that is small ground-gear gearbox manufac- (Romulus, Ml). The company also makes what people understand, they too won- turers. The other, the P400G serves plated wheels. CBN applications expert der about the correct name for the the truck and tractor transmission Mike Hitchiner says, “We match the wheel process. gearbox manufacturers and job shops. to the application. For lower part volumes, Kapp and American Pfauter were The P400G is a 400-mm diameter tolerances around ± (0.0005" (0.013 mm), using single-layer plated-CBN wheels capacity vertical gear-and-form grinder and moderate surface finishes, the plated to grind parallel-axis gears on a Kapp that uses roughing and finishing sin- wheel is ideal. But aerospace companies developed grinder in 1992. Since then, gle-layer plated-CBN wheels mounted are demanding closer tolerances and finer Kapp has sold several hundred CBN side-by-side on the spindle, for high finishes to maintain high process reliabili- efficiencies in production gear grinding, ty. For high volumes, tolerances around ± form grinders worldwide and American says American Pfauter. The machine 0.0002-0.0001" (0.005-0.0025 mm), and fin- Pfauter has an installed base of more can use any single-layer plated-CBN ishes typically around 32 µin. all around a than 100 Kapp and Pfauter gear ground form, the vitrified wheel will do the grinders in North America. American wheel, or the buyer can buy CBN job. One reason vitrified wheels can hold Pfauter says that in single-index gen- Pfauter-Winter grinding wheels from closer tolerances is because they are erating gear grinding, the CBN grind- Pfauter Maag Cutting Tools (Loves dressed with a form diamond roll, so the ing process is ten times faster than tra- Park IL). Options include an inductive precision is not dependent on the plating ditional gear grinding in the 500-5000 sensor for workpiece alignment, and process.” mm size range. In some other applica- an automated arbor-loader for high There are some limitations to vitrified tions, such as slots, splines, and production. wheels too. Hitchiner says, “You can’t run a

REPRINTED FROM MARCH 1997-MANUFACTURING ENGINEERING 4 milling slots on a machin- interrupt is Roger Pinard, operation man- ing center. At Doncasters ager, New Tech Replacement Parts Turbo Products Div. Company. His company makes a splined

(Photo: Edgetek) (Ivoryton, CT) it makes spindle shaft for a major machine tool previously broached root manufacturer, from heat treated Rc 28 4140 forms on certain blades. steel. The former process was rough Metalworking hand- milling, heat treating, and then finish books do not suggest milling six spline teeth just over 8" (205 grinding as an alternative mm) long. Milling sometimes had difficul- to milling because grind- ty holding the ± 0.0005" (0.013 mm) toler- ing is ten times slower ance on spline tooth thickness, forcing the and more expensive. shop to hand-lap the splines to fit in the Highspeed metal removal spindle assembly. with single-layer CBN “Today,” he says “we rough and finish wheels, however, under- mill the splines in two operations on an mines the handbook wis- Edgetek. The 6" (152 mm) plated form wheel from Cape Abrasives [Erie, Ml] with 60 or 80 grit CBN typically runs at 12,000 Blade and vane slots and forms have rpm, 18,000-19,000 sfm [5490-5790 m/min], been a major application for the at a table feed of 10-12 ipm [250-300 superabrasive machining process mm/min] The roughing operation cuts a groove 0.110 deep by about 3/16" wide [2.8 vitrified wheel as fast as a plated wheel. In x 4.75 mm]. The finishing operation takes the smaller wheel diameters, up to 8" [203 0.015-0.020" [0.38-0.51 mm] on the two mm], the fastest the vitrified wheel runs sides and bottom of each spline tooth to safely is about 12,000 sfm [3660 m/min] finish each groove But we can get such high speeds as 150 to Each pass takes 30-40 sec. Now the 200 meters/sec with 14-16" [356-406 mm] parts are fully interchangeable at assem- wheels.” bly, with a 32 µin. or better finish. We have seen a 500% improvement in throughput in the roughing operation and a 300% improvement in the finishing operation.” He estimates it takes four or five wheels for a lot of 600 parts. dom, wisdom that now obstructs grasping “Those who say this new technology. In fact, shops getting up the learning curve on the technology Replace Vertical Mill it cannot be find they must put aside what they know Gary Leever of Leever’s Grinding, a done should not about grinding, to reach the level of metal grinding and milling job shop, said he removal the machine is capable of. If you bought his superabrasive machine with a interrupt the cling to thinking its grinding, you may fourth axis rotary table a year ago to han- never “get it.” dle a variety of work, including aerospace person doing it” Perhaps when the experts at the job shop work, mold work, and especially University of Connecticut’s Center for can tooling. For a can tooling job, he cut Chinese Proverb Grinding Research and Development D2 Rc 60-62 hardened material for the can (Storrs, CT) get some experience with the tooling directly and eliminated a vertical machine Edgetek has contributed to their mill as an intermediate step. research program for a year, they will coin a “CBN grinding lends itself well to good name for the process, as well as Inconel,” he says. ‘We machined the roots reduce the skepticism around it. of 25,000 cast Inconel 718 jet engine tur- Replace Milling or Skepticism is an issue. At Fortune 500 bine blade blanks. The roots are 3/4" [19 companies, traditional grinding people mm] square. In a roughing operation, we and manufacturing managers often say take off 1/8" [3.18 mm] per side and do Shops usually call the process grind- “You can’t do that,” when told of this chamfers all around the root form in about ing, but they often use it to replace milling process. As the Chinese proverb says, three minutes per part. The CBN cuts well, or broaching. At New Tech Replacement “Those who say it cannot be done should and wheel life from Abrasive Technology’s Parts Co. (Forestville, CT), the Edgetek not interrupt the person doing it.” What wheels is decent.” machine replaces a spline machining follows are stories of the people doing it, He also appreciated the way a plated process of rough milling, heat treat, and even if they can’t decide what to call it. CBN wheel 0.060" (1.52 mm) wide, with finish milling. The new process eliminated 0.015" (0.38 mm) radii at the corners did a vertical milling operation in making can not break down when cutting about 1500 tooling at Leever’s Grinding (Dayton). At Replace Spline Milling slots 1/4" deep by 3" long (6.35 x 76.2 mm) Westfield Gage (Westfield, MA), it replaces One person the naysayers should not in heat-treated Rc 42 4340. “We cut five

REPRINTED FROM MARCH 1997-MANUFACTURING ENGINEERING 5 slots per rotor in three minutes; a smooth- The superabrasive machining process, rather than a machining cutting operation.” center, slotted these aerospace rings at Westfield Gage. Replace Machining Centers The owner of Westfield Gage, Louis almost a year ago, does complete Filios, a 92-year old gentleman, had a turbine vane grinding, according vision: Milling with CBN wheels would to Gary Griessmann, vice presi- help his shop, since its many machining dent and manager of engineer- centers put slots in many rings and span- ing. “We consider it grinding,” he ner nuts. Worn milling inserts fill large says, “because it is similar to cans near most of the mills. The materials continuous-dress creep-feed. they slot–aerospace metals such as grinding, except there is no inconels, nitraloy, nimonic, and stainless dressing.” steels–eat up carbide inserts. “The process has one advan- James Frisbie, production manager, tage for doing odd quantities. We and Michael Sabadosa, milling supervisor, can run one vane at a time and report that, with form CBN wheels from do not need the multistation Abrasive Technology Inc., they cut slots in complex tooling, typically a 2-5" one or two passes on their superabrasive [0.6-1.5 m] diameter fixture to machine and save about 50%-80% of the hold 20 to 30 vanes. The big tool- milling time. Depending on the finish gas turbines for power plants. The estab- ing takes 4-5 hr to change. Instead, with requirements, a slot may require one or lished processes for generating slots and the five-axis machine, we can swing a sin- two passes. Process parameters are about root forms in the blades were either gle vane around a theoretical centerline as 10,500-rpm spindle speed and 35-ipm broaching or creep-feed grinding. if it were on a large radius. So it’s a good (889 mm/min) table feed rate, using 6 and Although those methods still dominate the machine for development and multiple 8" (152.4 and 203.2 mm) diameter wheels. plant. machining with plated CBN is mak- changeovers.” The shop turns its own wheel blanks and ing inroads. A small lot that Hi-Tek runs across the sends them to the CBN plater. In a machining cell for low-volume Edgetek, rather than the company’s stan- “We run hundreds of parts on a wheel; blades, an Edgetek machine works with dard radial vane grinders, is 50 pieces/- whereas a set of milling inserts lasts only a two CNC vertical mills and a hand-polish- month of a cobalt-nickel superalloy vane few dozen parts with some of the materi- ing station. “Many hours went into process for a new engine program. “We cut a als,” says Sabadosa. There is less heat and development, much of it in new territory. groove about 0.100” wide by 0.200" deep less distortion than with milling. Another The result is a reliable machining process by 8" long [2.5 x 5 x 203 mm] in a little over benefit is that we eliminate manual debur- for close-tolerance root forms that keeps a minute. We run them one at a time and ring, which could take up to an hour on a pace with. other cell operations. Impr,pve- do not have the investment in a big fix- milled ring or spanner nut.” ments are ongoing,” says Tedeschi. ture.” One typical job, cutting 12 equalIy Keeping a half-dozen CBN wheels in spaced rectangular slots 0.255" wide by stock is much less costly and is more time- On the Horizon 0.160" deep (6.48x4.06 mm) in a 3.250 ly than broach maintenance, and, besides, (82.55-mm) diameter nickel alloy) ring, says Tedeschi, “Broach setup is so long that Ed Elie, co-founder and co-owner of ran two parts at a time in under 4 min. we can not always ship blades within 24 Edgetek with Wes Lee, says that there are Another slotting job, requiring six equally hours. With the Edgetek and a supply of two new machine designs in the works. spaced 90° V-slots with a 0.125" (3.18 mm) wheels, we can often build one order and One is a downsized machine, so that will radius at the bottom in M2 tool steel, went from the old milling time of 30 min to a start a different design within 24 hours. let the technology diffuse more widely to new time of 4 min. A hydraulic spool is Setup time has been reduced by as much smaller shops. “The present base price of another case in point. Rather than mill, as 90% over broaching.” That is important $250,000 for a three-axis machine is a little heat treat, and finish grind three slots in in the land-turbine industry. where a utili- high for many of the shops we want to each of three rings, as the old process did, ties power generator off-line awaiting reach,” he says, “so we are trying to take the Edgetek cuts the slots in the heat-treat- parts is very costly. $100,000 out of the machine to offer the “It is unusual to use CBN to grind soft same capability in a smaller package.” ed Rc 55 material, leaving no burrs or only a feather burr, and saving time in milling stainless steel, such as the Rc 28 403 stain- The other new project is to develop a and deburring. less on one of the blades run in the cell,” machine like a cylindrical grinder, that says Tedeschi, “But the cut is fast, and it holds the work between centers, for slot- will produce a distortion-free long root ting rotational parts of aerospace alloys Blade and Vane Machining form, a difficult task with broaching.” and other hard materials. Since Edgetek is Mark Tedeschi, a manufacturing engi- Already a process innovator, Tedeschi revolutionizing thinking around grinding neer at Doncasters Turbo Products Div. plans to go further. We plan to raise the versus milling, it hopes to repeat this cre- was hired to be the company’s broaching coolant pressure to reduce the amount of ative engineering with grinding versus engineer, but played an active role in mov- material adhering to the wheel. “ turning. A prototype is under construc- ing some of the low-volume parts from Vane grinding is a related niche. At Hi- tion. broaching to grinding with plated CBN Tek Manufacturing (Mason, OH), a five- Lee says that the company is also wheels. TPD makes blades for land-based axis Superabrasive machine, installed developing the process to generate airfoils

REPRINTED FROM MARCH 1997-MANUFACTURING ENGINEERING with its five-axis machine and thus com- pete with blade milling. They are testing the feasibility of holding the forged blade by the dovetail in a precision Erowa (Arlington Heights IL) pallet in order to machine the airfoil and similarly to hold the airfoil in the Erowa a pallet to machine the dovetail. As with blade milling the challenge will be to get good quality blends of surfaces around the leading and trailing edges of the blades.

For more information, contact:

abrasive technology, inc.  8400 Green Meadows Dr. • PO Box 545 Lewis Center, OH 43035 USA (740) 548-4100 Fax: (740) 548-7509 http://www.abrasive-tech.com (800) 964-8324

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