SkiveFinishing is a new process for economical hard machining of internal gears with high quality. It combines the flexibility of hobbing with the surface quality of CBN grinding technology. An innovative CBN tool developed by Liebherr-Verzahntechnik GmbH ensures long tool life and even allows for profile corrections.
Until now, two processes were available for the hard finishing of internal gears: the economical hard hobbing with a geometrically defined cutting edge, which, however, encounters limits with maximum quality requirements, and profile grinding with a geometrically undefined cutting edge, which offers the highest precision but is time- and cost-intensive – and thus only partially suitable for series production, such as in e-mobility or commercial vehicles. SkiveFinishing fills this gap: It utilizes the kinematics of hobbing in conjunction with a dress-free, galvanically coated hobbing wheel. This achieves a higher quality than hard hobbing, while being faster and more economical than profile grinding.
Innovative tool, proven technology
The CBN tool used has a convex geometry and several usable shift positions. The machining is done with axial feed along a contact line. When one position is worn, it simply shifts to the next. The combination of tool design and the extremely hard CBN coating (the second hardest cutting material after diamond) ensures long tool life and high process stability. 'SkiveFinishing combines the flexibility of hobbing with the advantages of CBN grinding,' explains Haider Arroum, Head of Tools Division and Location. 'By selectively choosing the CBN grain sizes, optimal roughness values and economical processes can be realized.'
Modifications in the component are feasible
Thanks to the higher pressure residual stresses, SkiveFinishing improves the load-bearing capacity of the tooth flanks. Modifications such as head reductions, profile roundness, or flank line modifications can also be directly integrated into the component – even with complex geometries like hollow gears. This was previously only possible through elaborate profile grinding or a special dressing kinematics.
When the tool is completely worn out, it is refurbished at the Ettlingen location. Liebherr's more than 30 years of CBN expertise ensures consistently high quality. 'This opens up new options for users to optimally align manufacturing processes with components and economic efficiency,' says Haider Arroum.
High quality with economical manufacturing
SkiveFinishing addresses applications that must combine very high quality requirements with economical processes. In aviation, precision and load-bearing capacity are critical amid constantly rising cost pressures. In e-mobility, new transmission concepts require lower noise development and higher durability. For planetary gears in trucks and tractors, SkiveFinishing offers a higher power density: Due to reduced hardening distortions, smaller, lighter, and yet more powerful transmissions can be constructed. The process and tool were first presented to the world public at EMO in September 2025.
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