Gear Production
Issue link: http://gear.epubxp.com/i/262216
March 2014—23 Dr.-Ing. Hansjörg Geiser, manager of development and design for gear cutting machines at Liebherr, "The main design engineering challenge was to execute the chamfer cut unit at a reasonable cost." So they maintained the size of the machine that would be necessary if the single-tool approach were used, but incorporated a four-station ring-loader concept. Chamfering is done at the 90-degree position in the ring loader. For those who are looking to grind gears, the company has developed the LGG 180 and the LGG 280 machines, with the latter accommodating gear diameters ranging to 280 mm, but both machines having the same exterior dimensions. Explaining this approach, Dr.-Ing. Andreas Mehr, Liebherr grinding and shaping technology development and consultancy, says, "Vehicle manufacturers can thus develop a complete production line, in which all gearing components for a passenger vehicle transmission can be ground: planetary gears, sun gears and bore- type gears, as well as drive and pinion shafts with lengths ranging to 500 mm." It is also worth noting that they've taken a one- table approach. "Choosing a one-table solution means one setting, one geometry," Dr.-Ing. Mehr says. "A key argument in favor of the one-table solution is the statistical capability and reliability in continuously producing controlled micro-range fnish quality." The machine has a grinding head that operates at speeds ranging to 10,000 rpm and has spindle power of 35 kW. These parameters make the LGG machines capable of using 3M's Cubitron II abrasive, which Mr. Yoder says is one of the most signifcant developments in grinding technology in quite some time, in that it provides the means to greatly reduce the costs in gear grinding due to the "precision shaped grains" that are the abrasive of the tool. While the ceramic abrasives in typical grinding worms have undefned shapes, those used in the Cubitron II grinding worms have triangular shapes. What's more, when the triangles wear, they do so in such a way that there are still sharp points. This isn't a matter of plowing through metal with the undefned shapes that tend to load. The triangles are freer cutting, which also means consistent grinding and a reduced chance of burning. In tests, 3M has shown that compared with conventional ceramic abrasives, the Cubitron II abrasive allows a signifcantly higher feed rate, which results in an improvement in cycle time of as much as 50 percent or more in various gear grinding applications. This is a close-up of 3M's Cubitron II abrasive. Note the consistent triangular shape of each of the ceramic abrasive grains. When used in gear grinding, the sharp edges cut more like milling than conventional grinding. When the grains break, they fracture with edges. The abrasive permits the use of high feed rates and can reduce cycle time by some 50 percent. 0314_MMS_Gear_GaryFeature1.indd 23 2/13/2014 2:46:12 PM