SkiveFinishing is a new method for efficiently hard machining high quality internal gears. It combines the flexibility of gear skiving with the surface quality of CBN grinding technology. An innovative CBN tool by Liebherr-Verzahntechnik ensures a long tool life and even enables profile modification.

A more efficient method

Up to now, two methods have been used in hard-fine machining internal gears. Firstly, Hard skiving with a geometrically defined cutting edge, which – while economical – comes up against its limits when maximum quality is required. Secondly, profile grinding with a geometrically undefined cutting edge, which offers maximum precision, but is time and cost intensive and therefore only suitable for series production under certain limited conditions, for example in e-mobility or commercial vehicles. SkiveFinishing fills this gap: it uses the kinematics of gear skiving in combination with a non-dressable electro-plated skiving tool. This achieves higher quality than in hard skiving, but is also faster and more efficient than profile grinding.

SkiveFinishing is based on the same kinematics as gear skiving

Innovative tool, tested technology

The CBN tool used offers a crowned geometry and multiple usable shift positions. It machines with an axial feed along the contact line. If a position is worn, the tool shifts to the next position. The tool design and the extremely tough CBN coating (the second hardest cutting material after diamond) combine to ensure a long tool life and high process stability. SkiveFinishing combines the flexibility of skiving with the advantages of CBN grinding. This means optimal roughness values and efficient processes can be implemented by specific selection of CBN grain sizes.

Component modifications possible

SkiveFinishing increases the tooth flank load capacity thanks to the higher residual compressive stresses. Modifications like tip reliefs, profile crowning or tooth trace modifications can also be made directly to the component – even on challenging geometries like internal gears. Previously this was only possible using the costly profile grinding process or a special dressing kinematic process.

If the tool is completely worn, it will be treated at the Ettlingen site. Liebherr’s CBN expertise goes back more than 30 years and so guarantees consistently high quality. This opens up new options for users to optimally adapt manufacturing process to components and economic efficiency.

Non-dressable, electro-plated skiving tool with multiple shift positions
AIMED AT E-MOBILITY AND AEROSPACE
SkiveFinishing is aimed at applications which have to combine very high quality requirements with economically efficient processes. In aerospace, where cost pressures are constantly rising, precision and load capacity matter. In e-mobility, new gearbox designs require lower noise levels and longer service life.

SkiveFinishing provides a greater power density for planetary gears in trucks and tractors: reducing the amount of heat treat distortion means smaller and lighter and yet more powerful gearboxes can be designed.