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gear making


Gear manufacturers are increasingly designing asymmetric gears, allowing higher loads with less NVH. Liebherr developed a generating grinding process that solves the complex machine movements needed to grind such gears.


pared to coast-fl ank. “This increases load carrying capacity while reducing NVH,” said Yoders. The challenge, according to him, was developing a gener- ating grinding process that specifi cally addressed dressing of the grinding worm and the complex machine movements to accurately grind asymmetrically. “We believe we are the fi rst to market to do this for asymmetric gears,” he said. Available on the Liebherr LCS- and LGG- platforms, these machines can also provide the completely new develop- ment called generated end-relief (GER), he noted. Until now, end relief in gear grinding was only available with the much slower profi le grinding method, in which each tooth is ground individually. The GER grinding has a similar effect—gears can now be designed with shorter face widths (i.e., lighter weight) but still carry the same loads.


Perhaps the most exciting new technology for addressing NVH is what Yoders describes as Noise Excitation Optimiza- tion, or NEO, developed in a partnership with the Technical University of Munich “This is similar to noise cancellation in that we grind into the teeth a specifi c wavelength and am- plitude of the form error, both in lead and profi le direction on the gear tooth,” he explained. This introduces, on purpose,


a defi ned and engineered “wavi- ness” in the profi le form deviation (commonly defi ned as ffĮ) and lead form deviation (commonly defi ned as ffћ). Yoders presented audio data in an interview with SME that dramatically demonstrated a gear with signifi cantly less gear whine after NEO correction. Other gear manufacturing equipment suppliers have noticed the increasingly stringent technical requirements in automotive. “I think if you were to speak to an automo- tive engineer about transmissions, they would say the difference be- tween the quality of the transmis- sion [today] and one from seven or eight years ago is something like 500%,” said Scott Knoy, vice president of sales for German Ma- chine Tools of America (GMTA; Ann


Arbor, MI). A unique process from GMTA that helps provide that accuracy is their trademark scudding process. What is scudding? “Think of it as a cross between hobbing and shaving,” Knoy said: A continuous generating process using a multi- point tool that eliminates issues such as the spacing error known as drop tooth. “There are no idle strokes on the machine tool, as you get with the gear shaping process,” he said. He said it probably will not completely replace shaving, since it requires a cross-axis angle that prevents the process from getting as close to a shoulder as shaving. “It is especial- ly useful in increasing the quality of the green machining, so that after heat treating you do not have to do as much honing or grinding,” Knoy said. “Presenting a more accurate part after heat treat keeps costs down.” He also hinted that hard scudding might be available in the near future, replacing a grinding or a honing operation after heat treating and further reducing costs while producing higher quality, lighter gears. There are a number of applications where it could be the


process of choice, including ring gears, sliding sleeves, and annulus gearing. Synchronizer parts and hubs are also ideal, according to Knoy. For internal ring gears, he notes that a


56 — Motorized Vehicle Manufacturing 2016


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