Gear Production

MAR 2014

Gear Production

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22—GEAR Production Supplement F E A T U R E produces continues to be developed to keep up with internal and external customer demand. According to Scott Yoder, vice president of sales for Liebherr Gear Technology, one interesting result of its production of things like hydraulic excavators with service weights ranging to 810 tons is that the company produces the largest gear hobbing machines in the world, equipment capable of handling gears measuring 6,000 mm (almost 20 feet) in diameter. This is certainly germane to people in construction and agricultural equipment manufacturing. That 6,000 mm is longer than a Rolls-Royce Ghost Extended Wheelbase (5,569 mm)—the entire car is smaller than a single gear. But we're interested in learning about developments related to producing gears of a more modest size, such as the LC 180 hobbing machine, which is capable of producing gears ranging to 180 mm in diameter, and the LGG 180, a generating and profle grinding machine with the same capacity. Those familiar with Liebherr will recall that the company has been offering chamfer cut capability since 2005. This process was developed along with German tool manufacturer LMT Fette as an alternative to milling or forming chamfers on the front ends of gear teeth. Chamfering is gaining importance nowadays, particularly for gears used in automotive transmissions. Given that the gears are on the order of 12 mm in diameter, it is important that there is consistency in the size of the chamfer, as a difference between 0.5 and 1 mm is enormous. What's more, throughput time is critical given the production volumes necessary to address the increasing number of gears in automatic transmissions. In the previous approach to chamfer cutting, the hobbing and chamfering tools were mounted on a single arbor. So after the gear was hobbed, it was then addressed by two tools, with the frst deburring and chamfering the top surface and the second doing the same to the bottom surface. While that addressed the issue of precise and reproducible chamfers, there was an issue of cycle time: Given that all of the tools were on one arbor, it was necessary to complete the entire sequence before beginning the hobbing of another gear. "We have solved this by integrating a complete second machining unit for chamfer cut tools—two machines in one, so to speak," says Dr.-Ing. Oliver Winkel, Liebherr- Verzahntecnik director of application technology. "Choosing a one-table solution means one setting, one geometry. A key argument in favor of the one-table solution is the statistical capability and reliability in continuously producing controlled micro-range finish quality." So in the LC 180 hobbing machine, there is a separate area for the chamfering. This means that after part A has been hobbed, it is indexed to the chamfer cut station and part B is loaded into the hobbing station. While part A is undergoing chamfering, part B is being hobbed. "This innovation enables the machine to combine an already undisputed high chamfering quality, provided by the proven chamfer cut procedure, with cycle times that correspond to the demands of the automotive industry," says Dr.-Ing. Winkel. Another beneft of this approach is that because the chamfer tool is separate from the hobbing tool, the length of the hobbing tool can be maximized and the size of the chamfering tool can be reduced to produce the small, precise chamfers necessary in automatic transmissions. However, it wasn't simply a matter of Liebherr's machine designers saying, "Well, we are doing two operations separately, so let's double the size of the machine to do both." Rather, explains 0314_MMS_Gear_GaryFeature1.indd 22 2/13/2014 2:45:49 PM

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