AUTOMOTIVE GEARMAKING
Competitive pressures require all these gears to be quiet and robust over a long time. That puts pressure on machine tool makers to deliver machines that cut gears faster to an almost unbelievable tolerance level.
A gear that has just been hobbed (cut) on the Kashifuji KE201 Gear Hobber, available through Involute Gear & Machine.
A good example are automatic trans- missions. These often use planetary gear sets, composed of a set of ring, sun, and pinion gears. “We’re produc- ing some of these pinion gears in four or fi ve seconds today,” he said. “Ten years ago, they were being produced in a minute or two.” That translates into ob- vious savings for the customer, requiring fewer machines. Faster cutting means a much more rigid machine tool combined with effi cient automation and associ- ated gaging. “Robust, noise-free gears
mean cutting them to a very tight tolerance,” he said. Where even just a few years ago the industry spoke of tolerances in the thousandths of an inch, today it is expected to be 3–5 μm, according to Goodfellow. “That is a pretty dramatic change in the fundamentals of gearcutting,” he said.
Process Changes, Quality Gears Made Cleaner Another dramatic change in the process itself is the move
away from fi rst hobbing a gear, then shaving it and then heat treating it. Hobbing is a multipoint cutting process that rotates both tool and workpiece in precise relations to each other. It is used to rough cut multiple gear teeth at once. “Today, automakers are hobbing gears, heat treating them and then grinding them post-heat treat. This provides a harder, more robust gear. Post-heat treat fi nishing of these gears eliminates distortion or changes of geometry in that gear set. The toler- ance requirement after grinding is pretty critical,” he said. The push for environmentally friendly factories is adding yet another challenge for machine tool builders—eliminating poten- tially toxic coolants. “Nowadays, everybody wants to machine dry to get rid of oil, contamination, smoke, and the potential harm to operators as well as simply keeping a clean shop fl oor,” Goodfellow said. Towards that end, Star SU partner Sampu- tensili (Bentivoglio, Italy) introduced a new dry grinding machine in October, 2015, in response to the pressure to eliminate the mess and bother of coolants while grinding after heat treating. Called the SG160 Sky Grind, it features two spindles, one for
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AdvancedManufacturing.org | May 2016
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