Enhanced Distortion Control – ISO Class 8 Gears After Case Hardening

Controlling distortion during the case-hardening process is of key importance when manufacturing gears. By effective control of distortion and the variation of distortion, significant costs in post heat treatment machining processes can be avoided. Especially for E-drive gears such as Internal Ring gears or Final Drive Ring gears significant cost-savings can be achieved.

If distortion is controlled in such manner that ISO class 8 is guaranteed after case hardening, the grinding operation gets obsolete, and parts may be honed only.

The combination of Low-Pressure Carburizing (LPC) and High-Pressure Gas Quenching (HPGQ) offers the potential to provide better control of distortion compared to other process-combinations such as Atmospheric Carburizing with Oil Quenching.

This paper analyses distortion values of gear components from a planetary set of a six-speed automatic transmission over a long period of time. The gears were analyzed in terms of circularity, helix average and helix variation. It is demonstrated that distortion data stays stable and predictable even over a long period of time when applying optimized heat treatment process parameters and if the process-steps in the manufacturing chain before heat treatment are frozen and robust.

When combining this heat treatment technology with appropriate geometrical inspection, this will result in guaranteed ISO class 8 geometry after heat treatment.

The paper gives directions how this goal can be achieved by combining an advanced heat treatment process with advanced gear inspection technology.

Authors: Volker Heuer, David Bolton, Jochen Friedel

ISBN: 978-1-64353-112-0