b'Nice Wheels engineer. The selection process isGrinding wheels were 610 mm (24") often one of trial and error workingin diameter and 508 mm (20") long. to optimize the combination of ma- It took a full shift to remove an old are not used for hand work. chine, cutting fluid, cutting param- wheel and mount a new one. This Super-abrasives like diamond andeters and grinding wheel. majorly disrupted production, so pre-cubic boron nitride are expensive.After the abrasive material andcisely controlling wheel wear was crit-To reduce the amount of abrasivewheel shape, main factors for wheelical to manage costs and meet pro-needed to make a usable wheel, anselection are grit size, bond typeduction requirements. It was a big abrasive is bonded to the periph- and bond hardness. Workpiece ma- blow to us when our wheel manu-ery of a metallic disc. Diamond andterial dictates the abrasive, wheelfacturer discontinued the particu-CBN bonds can be vitrified, resinoidshape and type of bond. Grit sizelar wheel we had used for yearsor metallic. Metallic-bonded wheelsand bond hardness usually are cho- we were the sole company using it use metal powder, such as cobaltsen based on surface finish require-and the lone replacement had a and copper, mixed with an abrasive. Using a process known as sintering, the mixture is formed around the periphery of a wheel. The abrasive and metal powder are baked at a high temperature, causing them to bind together.Super-abrasive wheels have bet-ter performance characteristics but a narrower range of applications as the wheels do not perform well on softer materials. CBN wheels are used most often on hardened fer-rous materials and can be found in machines like tool and cutter grind-ers, camshaft grinders and gearC. Tategrinders.ComparedwithAl 2 O 3 Curvic grinding is performed with a vitrified wheel notmuch differentfrom the wheel found on wheels, CBN wheels run cooler, lasta bench grinder.longer and can function at higher speeds. Diamond is used to grindments and the hardness of material.harder bond. This seemingly minor carbides, glass and other extremelyLow-volume environments gener- change resulted in unpredictable hard nonferrous materials. Super- ally use one type of wheel and ad- wheel wear and unplanned wheel abrasives are more productive butjust grinding parameters to suc- changes.expensive. They frequently costceed as the variation in cycle timesBecausethenewbondwas 10 times more than other types ofand wheel wear is not an issue.harder, the wheel dulled faster and wheels, and their applications areHigh-volume production work likewould cause part geometry to de-typically very specific. that found in automotive manufac- viate from specifications. The only turing requires repeatable perfor- way to recover was to redevelop the Other Factors mance that can be achieved onlygrinding process. Although we had Picking the proper wheel is obvi- with significant development time. many years of experience and sev-ously important for grinding oper- At a previous employer, we haderal experts on centerless grinding, ations and can be challenging forseven centerless grinders, which pro- it required a few weeks to arrive at even an experienced machinist orduced about 2 million parts a year.the ideal set of grinding parameters.Choosing a grinding wheel can seem mysterious, and developing about the authorgrinding parameters is iterative. As Christopher Tate is engineering manager of advancedwith all machining operations, how-manufacturing engineering and machining at the Savannah,ever, experience, knowledge and Georgia, facility of Mitsubishi Hitachi Power Systems Ameri- skilled craftspeople are the key to cas Inc., Lake Mary, Florida. Contact him at chris23tate@ selecting and using the right grind-gmail.com. ing wheel.CTE46SEPTEMBER 2020GrindingWheels.indd 46 8/17/20 11:09 AM'