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86 MMS December 2017 mmsonline.com FEATURE prevent this damage, with the stock removed in this way very small. Meanwhile, another established potential solu- tion for precision gear machining without coolant is skive hobbing, says Mr. Grass, but the challenge here is that this is not quite precise enough. Skiv- ing alone does not hold the finest tolerances automotive manufacturers require, he says. There- fore, the SG 160 Skygrind machine from Sampu- tensili achieves dry grinding by using these tech- nologies together. Similar to the way hard turning remove s much of the bore's material before grinding, skiving removes much of the gear teeth's remaining material before grinding. To eliminate any imprecision resulting from handling between the two steps, the Skygrind performs dry skiving followed by light, fast, dry grinding within the same cycle on the same machine. Mr. Bagni says that in Europe there is significant regulatory pressure to achieve more environmen- tally friendly manufacturing processes. That pressure alone justif ied the adoption of this technology by a European automotive manufac- turer using it now. By contrast, in North America, he expects the potential cost savings, combined with health and safety improvements resulting from eliminating coolant, to provide ample incen- tive for this system's adoption. The cost savings come in various forms, he says. In addition to doing away with the purchase and handling costs of the coolant itself, there is also the savings in capital equipment investment from eliminating a coolant filtration system. Then there are the floorspace savings. The coolant filtration system for a high-volume grinding pro- cess can easily take up more space than the footprint of the Skygrind machine, meaning dry machining can allow the end user to fit more machine tools into a given unit of space. For these reasons, while converting a new plant to dry machining might be difficult, he sees great promise that new plants built in the years to come might look to this machine to achieve entirely coolant-free gear making. The Skygrind is built on the same platform as Samputensili's G 160 machine, which is a novel de sign in itse lf of fe r ing var ious productiv it y advantages. In place of a rotary table carrying workpiece spindles for two parts, the machine uses two separate, parallel X a xes to quickly move parts into position via linear motors, achiev- ing part-to-part change times that are faster than a rotary table by several seconds. On the Skygrind machine, this feature contributes to dry grinding specifically because the machining cycles for dry grinding of small automotive pinions are liable to be fast. Without fast par t-to-par t time, the changeover between parts would account for a significant share of production time—not the case with this system. Meanwhile, the company notes that another feature of the machine platform also contributes to a small footprint. In place of interpolating with X, Y and Z a xes for the hobbing and grinding heads, the machine realizes the same motion by interpolating with Y, Z and a rotar y A a xis. Eliminating one linear axis allows the machine to be more compact. Star SU, call 847-649-1450 or visit star-su.com The machine performs dry grinding of gears such as these, accommodating parts up to 160 mm diam- eter and up to 300 mm shaft length. A system for chip-to-chip time of less than 2 seconds allows for efficient high-volume processing of parts for which the machining cycle time is short.