However as a side-effect the components get distorted. This distortion has a significant cost-impact, because distorted components need to be hard-machined after heat treatment. Therefore the proper control of distortion is an important measure to minimize production costs.

By applying the technology of Low Pressure Carburizing (LPC) and High Pressure Gas Quenching (HPGQ) heat treat distortion can be significantly reduced.

HPGQ provides a very uniform heat transfer coefficient. The predictability of movement during quenching is more certain and uniform throughout the load. Further improvements can be achieved by “Dynamic Quenching” processes where the quenching severity is varied during the quench sequence by step control of the gas velocity. Proper fixturing is another factor for distortion control. Modern CFC-materials (carbon reinforced carbon) are well suited as fixture-material for gas quenching. When compared to traditional alloy CFC demonstrates no deflection or distortion after many subsequent years of use.

The paper presents how LPC and HPGQ processes are successfully applied on Internal ring gears for a 6 speed automatic transmission. The specific challenge in the heat treat process was to reduce distortion in such a way that subsequent machining operations are entirely eliminated. As a result of extensive development in the quenching process and the use of specialized CFC- fixtures it was possible to meet the design intent.

The internal ring gears have been in continuous production since 2006. By utilizing the special CFC-fixtures and quench methodology of "Dynamic Quenching," the customer was able to achieve the design intent, while eliminating all machining operations of the ring gears following LPC/HPGQ.

Subsequent testing and monitoring over a two year period progressively demonstrated that conformance and quality inspection was reduced accordingly.