According to LMT Fette, Gear Runner Internal realizes a pitch accuracy of quality grade 6 on existing machines without additional finishing. Using Gear Runner Internal therefore makes it possible for the first time to achieve the same quality with a dry machining technique as would be case with wet machining – while simultaneously increasing tool life. Furthermore, compared to gear gashing, finishing speed can be increased by up to 40 percent.
What might sound rather simple for users actually presented major challenges for the LMT Fette developers. “When you are hobbing external gears, the tool is structured evenly, and different numbers of teeth can be machined, but for internal gear cutting the tool has to be adapted to the curve of the gear ring. The result is that every single cutting edge on the internal hob is shaped differently,” Thomas Falk, head of gear cutting at LMT Tools, describes the requirements. “We used our design software to analyze the complex processes involved. In a simulation we were able to calculate the tool in such a way that only five different indexable inserts were required to produce the necessary profile,” explains Falk.
The fact that modern high-performance software played a major role in the development of the new tool comes as no surprise to Oliver Winkel. The Head of Gear Machining Technology Development and Application Engineering at Liebherr-Verzahntechnik explains: “Internal hobbing is a traditional process. It disappeared in the early 1970s, partly because the machines back then were not rigid enough to produce large-scale gearing at a high enough quality. Apart from that, tool design was too complex.”
This has now changed. It took engineers at LMT Fette only one and a half years to develop the new tool, which is now ready for the market. Gear Runner Internal has successfully proved itself in a series of arduous tests at Liebherr begun in August 2013. Above all, it is the quality of the gears that has convinced Liebherr, which itself is one of the world’s leading manufacturers and users of gears and large roller bearings. “The gears we produce using Gear Runner Internal demonstrate a much higher pitch accuracy than those produced conventionally. The surface finish is also better,” says Winkel with satisfaction.
LMT Fette has now begun marketing its indexable insert gear hobs under the Gear Runner name. This will include the proven modular external gear cutting range (Gear Runner External) as well as the internal hobs launched in September 2013 (Gear Runner Internal). The cutting materials used are not only the tried and trusted LCP35H, but also LC630XT with Nanotherm, the world’s first thick coating for large gear cutting.