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Reprinted from , February 1994 Issue Don’t let initial cost and perceived risk scare you CBN GRINDING A TEMPTING TECHNOLOGY

or years, CBN grinding This material also offers was on the fringes of the potential for improved F technolo- production through better gy. Manufacturing engi- finish, greater part consis- neers used it only when tency, and tighter toler- they had to, usually because ances. CBN can offer a sig- a was too difficult to nificant time saving in high cut or finish any other way. speed production because The picture is changing wheel dressing is less fre- today with about 25% of all quent. CBN grinding is not industrial grinding in Japan limited to traditional fin- done with CBN, 15% in ishing operations. Its Europe, and 10% in the US. potential for fast material Although CBN use in the US removal means it can is statistically low, interest is sometimes eliminate quite high. Predictions are machining steps. In some that its use will expand dra- cases, grinding can do in matically for three reasons: one setup what would oth- conversion from other erwise require , abrasives, chiefly alum- grinding, heat treating, and inum oxide; introduction of . Grinding CBN compatible grinders; bits from bar stock is one and new applications as such application. harder, more complex work ‘Today, high-speed materials are introduced. Landis CBN machines, shown doing pin journal grinding, are grinding (16,000-40,000 According to data from gaining acceptance in the US automotive . sfm, 80-200 m/s) accounts GE Superabrasives (Worthington OH), total use. Aerospace and gear manufac- for about 3% of all CBN grinding. Some global sales of CBN wheels was $145 turing follow with 9% and 8%, respec- experimental systems claim 100,000 million in 1988, reaching $300 million tively. As to grinding techniques, CBN rpm. But “high speed” is not well last year. The company estimates use has made its greatest inroads with ID defined. According to Mike Brooks, a can grow another 4.5 times to reach grinding because wheels are smaller Borozon CBN engineer with GE Super- $1.6 billion. and, therefore, less costly. abrasives, most work with CBN is done In the US, CBN wheel sales for 1992 at speeds between 8000 and 12,000 sfm were an estimated $63 million, only a Why It’s Better (40 and 60 m/s), although cam - 13% penetration of the potential $480 CBN has many advantages over con- ing, a major CBN application, is done million market. Currently, the automo- ventional abrasives. It is twice as hard at 16,000 sfm (80 mps). These speeds tive industry is the largest user of CBN as aluminum oxide, so a CBN wheel are also typical of most aluminum wheels with 30% of the market, says lasts longer, often 100 times or more. oxide grinding. “But,” says Brooks, GE. production (both production ■ “because CBN grinding is cooler, there and resharpening) is the second largest is less tendency to burn. The bottom market with about 20% of sales. Robert B. Aronson line is higher speeds mean lower wheel Bearing manufacturing is a growing Senior Editor cost because of longer life and application now representing 12% of improved quality. “

Society of Manufacturing Engineers Another unique feature of CBN, resid- and it can’t be treated like a $10 wheel. (Wixom, MI) has specialized in automo- ual compressive stress, leads to higher The first step in exploring CBN is to tive applications such as camshaft quality parts. Evidence indicates metal know your costs and production needs grinding and made major sales to Ford. surfaces contract during CBN grinding, intimately. In trying to sell CBN grinding Conventional cylindrical grinders eliminating the microscopic surface wheels and machines, suppliers com- operate at 6500-12,000 sfm (32-60 m/s). cracks that typically exist in steel. This plain that manufacturing engineers The most recently introduced Toyoda makes the metal stronger in machine, the GZ32P operates at many applications. On the other 40,000 sfm (200 m/s) using a thin hand, when grinding burns vitrified CBN wheel for slot metal, the heat generated grinding. European based expands the surface and opens grinder manufacturers, such as the microcracks and encourages Junker (West Springfield, MA), early failure. Guehring (Sussex, WI), and Some CBN users say residual Maegerle (Schaumburg, IL) are compressive stress allows reduc- known for specialized app- ing component size because the lications such as high-speed individual elements can take cylindrical, surface, and greater loads. One example is an creep-feed grinding. automotive transmission where In the US, some grinder man- smaller, but stronger, ufacturers are just their CBN-ground gears allowed a attention to grinders designed size reduction. for CBN. According to Pat Harrington, vice president, engi- Cost Problems neering, Bryant Grinder Corp. The major negative is initial (Springfield, VT), his company cost. First, there is the cost of the has designed machines around wheel. A 10” (254 mm) alu- the CBN process for six years, minum oxide wheel might cost but the company only recently $150; whereas a comparable designed one from the ground CBN wheel might sell for $1500. up for CBN, their UL2. Bryant This “sticker shock” keeps many specializes in ID grinding with first-time buyers away. CBN most wheels in the 1. 5” Remanufactured machines, such as this thread prices have dropped 50% (38-mm) diam. range. “We over the last 10 years, according machine from Drake Manufacturing, is one way around the high cost of new CBN grinders took on this design because to data from GE Superabrasives, the effectiveness of CBN was and continue to fall as sales volume usually don’t have a clear understanding becoming obvious,” he says. Bryant increases. This trend encourages users of their own grinding costs. They usually to look at CBN as a viable production have data available on the cost of the is also working with the University technology, but total cost, performance, work material and expendable supplies of Connecticut to develop a super and part quality are still the deciding such as wheel and costs, but lit- high-speed OD CBN grinder. factors. tle beyond that. You need a more com- Huffman (Clover, SC), another Another major cost consideration is plete analysis, both up and downstream. old-timer in the US grinding industry, the . It isn’t always This includes an in-depth analysis of the recently offered a six-axis grinder with practical to just bolt a high cost CBN less obvious items that increase operat- CBN capability. The company has had wheel onto a conventional grinder. ing costs such as scrap, coolant mainte- Absence of a truing and dressing system significant success in tool manufac- nance, waste disposal (both and ture and maintenance with CBN. or lack of machine rigidity won’t give the coolant), production downtime due to user the full benefits of using CBN. Top wheel changes and other maintenance, One of the newer entries with a of the line machines sell for around truer cost, and wheel break- machine specifically designed for $100,000 to $500,000. If those costs are age. Then it’s important to get numbers CBN is Edgetek, (Middlefield, CT), a too great, a user might upgrade or for the benefits of increased production company that offers a plated-wheel rebuild an older machine to use CBN cycle, lower scrap rates, and higher part system selling for about $225,000. wheels. quality. With those figures in hand, They refer to the type of grinding A difficult-to-predict cost is loss from CBN’s benefits may become more obvi- their machine does as high-efficien- operator error. One crash of a large CBN ous. cy deep grinding (HEDG), a form of wheel can instantly wipe out any eco- nomic advantages, so operator training What Machine? high-speed creep-feed grinding. is essential. CBN wheel makers say that Many of the grinders using CBN in HEDG is said to have the advantages working with CBN is not difficult, it’s just the US are imported. The Japanese have of material removal rates as high as different. Operators must understand broad experience and have done well in those of conventional machining the CBN wheel takes careful handling grinding production parts. Toyoda and ability to cut hardened parts with no damage due to heat. any major redesign of our machines speed was unnecessary. Nelson Campbell Grinding Co. (Muskegon because we have always had a rigid Beaulieu, an engineer for Blohm MI), a company with an aerospace design. We did have to add the precise Grinding Systems, says their company industry niche, makes rotary vertical dressing and positioning systems CBN feels they can do most CBN grinding grinders using all types of CBN wheels. requires, however.” tasks adequately at speeds around The company’s major market is in the The company now offers surface 9000 sfm (45 m/s). jet-engine part manufacture, chiefly grinders with both plated and vitreous shafts and vanes. But it is What’s Required? expanding into other aero- For a grinder to use CBN suc- space and automotive applica- cessfully, it must have the nec- tions. Campbell recently intro- essary stability, conditioning duced a model with a turret devices, positioning, gauging, changer and automatic part speed, and cooling sys- inspection. This design allows tem. using both CBN and conven- Stability. The machine must tional abrasive wheels on the be strong and stiff to resist the same part, but needs a wide dynamic loads and minimize speed range to accommodate vibration. Grinding machine both types of wheels. builders frequently use an arti- Weldon , Inc. ficial granite from suppliers (York, PA), has offered CBN such as Anorad I Hauppauge, compatible grinding machines NJ), which, company spokes- for more than five years. man say, has 45 times the vibra- According to company presi- tion damping capability of dent Jim Flinchbaugh, they steel. This material both have specialized in cylindrical increases machine mass and grinding with an emphasis on has low transmissibility. Both punch applications. “In devel- features reduce vibration oping our CBN capability, we resulting in a better surface fin- stress customer ready’ mach- ish, tighter tolerances, and ines. We want to make the cus- longer tool life. The composite tomer’s transition to CBN easy, bases also reduce thermal dis- so we pay close attention to tortion. According to Anorad, those aspects of the process about 60% of domestic grinder that are somewhat different, Feasibility study by LeBlond Makino combined a plated CBN manufactures use some form of wheel with conventional in the MC98 machining center. composite in their designs. such as dressing cycle, wheel The wheel finish ground a diesel block and the “machining/ speed, and coolant applica- ginding” center performed all the functions of a 26-station Heat generated by opera- tion.“ transfer line. tions and transmitted to the Landis Grinding Machines (Waynes- bonded wheels. The largest wheel, a machine from the environment boro, Pa.) is successful in the automo- 24” (600-mm) diam. vitrified bond can distort a grinding machine signifi- tive industry with significant sales of unit, runs at nearly 22,000 sfm (110 cantly. Considering certain critical fea- CBN grinders to both Ford and GM for m/s). “We have run wheels experimen- tures minimizes this distortion such as engine component manufacturing. tally at 26,000 sfm (130 m/s),” says spindle shaft size, fixtures, and dis- According to Bill Pflager, manager of Mattison. The company also offers tance between the grinding-wheel R&D, the company is making a major double-disc grinders for CBN operat- shaft and workpiece. push into CBN grinding. Their OD ing at 6000-8000 sfm (30-40 m/s). Conditioning. Special care or condi- grinders were redesigned to have the Mattison says about half their output is tioning of a CBN wheel is essential. capabilities CBN requires. “Right now, currently sold overseas. Although definitions vary, condition- it is a break-even situation in some Late in 1993, GE Industrial Power ing is usually considered the truing and applications because of the high and Systems Div. (Greenville, SC) made dressing of the wheel. Truing refers to up-front wheel cost,” says Pflager. “But a major move toward CBN by bringing the wheel’s roundness and balance; we are confident that long-term results in five German-made Blohm (Rich- dressing is the condition of the abra- will show the merits of CBN.” mond, VA) RT-HSGE grinding centers. sive on the wheel’s surface. Mattison Surface Grinders (Rock- The machines are dedicated CBN Conditioning methods depend on ford, IL) has offered CBN, “Since some- machines operating at 9000 sfm (45 the type of CBN wheel, bond system, one first thought of the material,” m/s) and doing general surface grind- and application requirements. according to company president, Phil ing jobs on a number of gas turbine and metal-bonded wheels need separate Mattison. “Moving to CBN didn’t take components. This is a case where high truing and dressing operations because tion without conditioning. Some systems, however, use “touch dressing,” which removes a small fraction of the grit to maintain the desired ability and surface finish. Because of CBN’s hardness, dressing most wheels with a single point diamond, as is done with many other abrasives, is impractical. Diamond caused by the CBN is so great that it cannot maintain a consistent dress across the wheel’s sur- face. New vitreous bonds now under development may make single-point tru- ing possible in the future, however. To dress properly, the operator must know where the wheel is so the dressing wheel can make the required depth of cut, particularly when dealing with micron measurements. One develop- ment that has made accurate dressing possible is an acoustic touch sensor. The instrument, used with the dressing sys- tem, tells the operator when the dressing Huffman six-axis design shows versatility of new grinding centers. wheel and CBN wheel are about to touch. This establishes a reference point from the bond material is not porous. Truing be trued and dressed in one pass. The dia- which to make the dressing pass. requires a wheel brake mond wheel rotates at about 0.4 to 0.6 Positioning. Positioning accuracy in device or a powered rotary diamond disc. times the speed of the CBN wheel and the millionths of an inch is necessary to Dressing uses a stick of aluminum oxide. essentially “machines” off some of the exploit the finish CBN can provide. A ser- Both operations can be manual or auto- wheel’s surface. In grinders designed for vomotor and ballscrew feed system pro- mated. higher speed production, this operation vides the submicron accuracies. The porous structure of vitreous bond- is automatic and triggered by the wheel’s Gauging. The success of CBN grinding ed wheels responds well to rotary dia- condition. Electroplated wheels, or depends heavily on precise gauging. The mond conditioning so these wheels can metal-brazed single-layer wheels func- operator needs to know not only where the (the wheel) is but how much the wheel is wearing. Three types of America First? gauging cover these requirements. High-precision work requires all three. Stung by the need to go offshore for Grinding R&D. These projects • In-process gauging checks the part for the latest grinding technology, are currently underway: and indicates when a specific cut is com- Pratt & Whitney (Hartford, CT) Precision spindle. It will have pleted. joined forces with the National interchangeable bearings (aerosta- • Post-processing gauging feeds back Center for Manufacturing Sciences tic, rolling element, magnetic, and trends on part dimension shifts so the (Ann Arbor, MI) to try a project hydrostatic). control system can adjust for changes in called, “US Grinding Partnership Slideway. It combines both stiff- machinery or wheel wear. 2000. “ It’s goal is to define and carry ness and precision. • Wheel gauging, the acoustic signal out a number of programs that will Infinite stiffness aerostatic bear- mentioned earlier, locates the position of make the US a world leader in grind- ing. It will work with piezoelectric the wheel before dressing so it makes the ing technology by the year 2000. restrictors to control stiffness and dressing cut precisely. These efforts would link equipment withstand an applied load of 250 N. Spindle. The higher wheel speeds and suppliers and users. The NCMS has High-speed CBN grinding stiffness requirements are causing completed initial research on defin- machine. It will operate at 50,000 sfm grinder builders to go to special electric ing programs, and if approved, could (250 m/s) and have a water-based drives and hydrostatic bearings. They are have projects underway soon. lubrication. Bryant Grinder Corp. also developing adaptive control for the In another attempt to boost the and Torrington Co. (Torrington, CT) grinding process based on power or force quality of US grinding technology, are collaborating. monitoring. the University of Connecticut (Storrs) High-speed wheel. A flexible rim Coolant. Controlling heat is essential has several programs at its Advanced will filter out high-frequency vibra- both to maintain accuracy and to prevent Technology Center for Precision tion to reduce chatter. wheel failure. CBN has a much higher Manufacturing and Center heat transfer rate, about 40 times that of aluminum oxide, so the material itself helps inhibit heat build up. High-speed New Isn’t Necessary less than half the cost of a new machine cutting can be relatively cool, but it If the application allows, you can get we can put today’s technology into an requires high pressure coolant flow and into CBN grinding for just a few thou- old unit by adding a diamond roll dress- specially designed nozzles or wheels to dollars: the wheel plus some ing, servos, ballscrews, and stiffer spin- get the coolant into the work zone. reworking of an existing grinder. The dles. Many older machines were overde- There is currently a lot of effort to find main thing is to increase rigidity which signed, so rigidity is not a problem in a the most efficient coolant for CBN oper- can be done by getting a more rigid rework. But that doesn’t mean every ations. Oil lubricates better and leads to spindle, improving the fixturing, and machine can be refitted. Some are only longer wheel life. The down side is the possibly adding truing and dressing sys- worth their scrap price. environmental issue. Disposing of oils is tems. “With our rework, we can dress to I difficult, particularly when they are con- Although a reworked machine pro- micron and position to 0.1 micron,” taminated. They also have some in- viding the same benefits as a new CBN Drake continues. “But thermal problems plant disadvantages. Blohm, for exam- grinder is unlikely, you might get can be a big headache. It’s difficult to ple, recommends staying with oil as a enough to meet your specific job correct after a machine is built. You coolant. “Will what you save on wheel requirements. The key is preparing an can’t bring a bad machine back with life pay for the clean up gauging. cost? You have to look at each job.” says Blohm Wheel Types engineer Beaulieu. There are two broad categories of Water-based are CBN wheels: bonded and plated. With widely used, however, bonded wheels, the manufacturer with somewhat de- blends abrasive of various grit with a creased performance. resin, , or metal matrix bonding CBN product manager material. Resin is the most compliant Joe Eramo of Abrasive and used for applications such as tool- Technology (Westerville, making. Metal is the stiffest and used OH) says his company for rough and form grinding. For exam- has developed, through a ple, the German manufacturer Junker USAF contract, a system uses a narrow steel-bonded wheel for to enhance CBN wheel -like grinding applications. The life in a watersoluble vitreous bond is the most versatile and coolant. According to currently most frequently used for Eramo, “The system can automated, high-productivity grinding. be optimized for water to The manufacturing process shapes achieve wheel life that the mixture of grit and bonding materi- meets or exceeds current al around a core. Because CBN performance in oil. It in- slowly and is costly, the amount of volves CBN grit size, bonded CBN material is typically bond type, as well as 3-5-mm thick. The core can be alu- coolant velocity, flow minum, steel, or, in the most recent rate, and other critical developments, a composite. Composite variables.” Toyoda’s latest grinder, the GZ32 CNC/CBN, features a spindle core wheels, such as the experimental Whatever the fluid bearing with a rotational accuracy of 0.1μm. fiber version offered by Noritake used, most experts rec- Co. (Cincinnati), can handle speeds up ommend coolant temperature control accurate analysis of what you want done to 40,000 sfm (200 m/s). The wheel core to minimize heat buildup and thermal and what a reworked machine can do. or hub material is critical because of shock to the workpiece and wheel. Industry experts, however, caution, high centrifugal forces. Cores made of Filtering is also essential because grind- “CBN novices should not try this on high strength, ductile materials such as ing generates micron size debris. their own.” steel and aluminum absorb these stress- Control. Last but not least is control. Used machines may also meet your es. To deliver the precision CBN grinding needs. According to Mike Drake, presi- To reduce costs and minimize the requires the controller needs software dent of Drake Manufacturing (Warren, hazards if a wheel crashes, some large that works with all variables. For exam- OH), a company that remanufactures CBN wheels have solid cores and vitri- ple, Bryant’s Harrington says that an machine tools, “There are many old fied-bond CBN segments. This design important consideration is dress pro- machines out there from the ‘40s on, so allows for some thermal expansion and gramming: “The software should deter- reworking those old units offers an alter- also limits the amount of CBN lost in a mine dress time based on a power native to a new half million dollar crash. A segmented wheel cuts better in analysis.” machine. Grinding is a fairly mature some applications because it reduces industry so profits are not great and not burn and loading of chips and grit. too many can afford new machines. For According to Dr. Mike Research Abrasives (Willoughby, Hitchner, Universal Super- OH) claims their plastic-bonded abrasives (Romulus, MI), wheel with aluminum oxide grit “Conventional vitrified-core has taken a number of jobs from wheels have burst speeds of CBN operations. The downside 24,000 sfm (120 m/s); to plastic is it wears faster than metal-cored segmented vit- CBN. rified wheels have burst Meanwhile, 3M and others are speeds of 50,000-52,000 sfm moving ahead with a variety of (250260 m/s). And we are belt abrasives. J.D. Phillips Corp. working on Kevlarbased (Alpena, MI) is applying abrasive cores, which may have burst belt technology on a grinder that speeds as high as 90,000 sfm can do multiple pins for the (450 m/s). These high wheel and GM is speeds are not possible for reportedly using belt grinders for all CBN operations. ID and some of their camshaft applica- double-disc grinding, for tions. Although Ford has a strong Work area of a Bryant’s new “Ultraline” UL2 grinder example, are still limited to commitment to grinding, Jim the same speeds as convention- ating speeds, and ability to be replat- DeVerena, manufacturing engi- al vitrified wheels. ID grinding can ed and reused. LeBlond-Makino neer, engine division, says, “There’s have some problems with quill whip (Mason, OH) and GE Superabrasives no clear cut preference for CBN. We and hydroplaning at speeds much Application Development Lab are do a lot of pin and cam lobe grinding, above 10,000 sfm (50 m/s).” working on plated wheels to use in but we analyze each new job and The plated wheel has a steel core LeBlond’s machining centers. These decide on a cost basis. Right now, it’s and one layer of CBN grit. The benefit grinding tools are included in the tool between aluminum oxide and CBN of this design is the wheel can have magazine and used as needed. wheels. If the price of CBN comes any machinable contour. There are down, we might do more jobs with it.” two types: conventional electroplated Maybe Not CBN ■ and metal single layer (MSL). The Some have compared a move to MSL configuration exposes about CBN to buying a Mercedes and sug- 60% of the grain to give more cutting gest that maybe you don’t need that action. In a conventional plated kind of quality to get the job done. wheel, about 40% of the CBN crystal is Maybe a Geo will do as well. The exposed. MSL does not achieve as answer is in knowing which system tight a tolerance in some instances, works best for your product. however. For example, both Norton (Wor- Abrasive Technologies’ Eramo cester, MA) and 3M (Minneapolis) makes a strong case for plated wheels offer non-superabrasive grits that over bonded wheels. Some advan- cover a multitude of applications. In tages he lists are manufacturing to wheel design, plastic bonded wheels tight tolerances on complex shapes, are said to offer many of the advan- eliminating dressing, increasing oper- tages of CBN, but at one fifth the cost.

Society of Manufacturing Engineers

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