Modern Machine Shop

DEC 2017

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Page 87 of 140 December 2017 MMS 85 FEATURE H ans Grass, vice president of the machine tool group with Star SU, and Rober to Bagni, machine tool product manager with the company, say that a recently developed option for dry grind- ing the external tooth forms of automotive gears resulted from the widespread adoption of hard turning for machining a very different feature of the gear, the bore. The connection between the two features is this: For the bore, performing much of the stock removal through turning, with grind- ing then removing only a small amount of remain- ing stock, enables bore machining to run dry. That is, a heavy amount of grinding requires coolant, but hard turning plus slight grinding can do with- out it. This change, removing coolant from bore machining, left grinding the teeth as the last gear- machining operation still in need of a cutting fluid. If coolant could be eliminated from this step as well, then the result could be an entirely coolant- free process for high-volume gear production. Gear manufacturing equipment supplier Sampu- tensili, which is represented in the U.S. by Star SU, decided that the pressure was on to develop and introduce a coolant-free gear finishing machine. Dry grinding of gear teeth is not new. However, How Dry Grinding Permits Coolant-Free Gear Making Grinding the external forms of automotive gears came to be the last step still needing coolant. This machine eliminates cutting fluid by combining gear grinding with dry skiving in the same cycle. BY PE TE R Z E LI N S K I (Facing Page) The Skygrind achieves dry grinding by combining skive hobbing and grinding within the same cycle. The hob (top), grinding wheel (bottom) and gear workpiece can all be seen in this view inside the machine. (All three are spinning.) The engineering of the machine's axes helps to realize a compact footprint, but even more space savings results from eliminating coolant. In a production facil- ity, the coolant system itself is liable to occupy at least the space of a machine. (This photo and all the images in this article were taken at the most recent EMO show in Hannover, Germany.) the problem it has faced—and the issue that makes dry grinding challenging for volume production— is the risk of heat-related damage to the teeth. The dry grinding pass must be quick in order to

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