Integration of Case Hardening Into the Manufacturing-Line: "One Piece Flow"


For decades the gear industry has addressed the challenge to produce high performance components in a cost-efficient manner. To meet quality-specifications the components need to be heat treated, which traditionally takes place in a central hardening shop. However this separation between machining and heat treatment results in high costs for transportation and logistics within the production-plant. Therefore for many years it has been being discussed how to integrate heat treatment into the manufacturing line.
For about 10 years it has been possible to integrate heat treatment into the machining facility by applying the technology of Low Pressure Carburizing (LPC) and High Pressure Gas Quenching (HPGQ). The components are collected after soft-machining into big batches and treated with LPC- and HPGQ-technology. This means however that the heat treatment is not synchronized with soft- and hard-machining since the components must be collected in buffers before heat treatment and must be singularized again after heat treatment.
In order to totally integrate heat treatment into the manufacturing line and in order to synchronize heat-treatment with machining, a new heat treatment cell has been developed. Following the philosophy of "One Piece Flow" the parts are: taken one by one from the soft machining unit; then heat treated in time with the cycle-time of soft machining ("synchronized heat treatment") and then passed down one-by-one to the hard machining unit. To allow for rapid case hardening, the components are low pressure carburized at high temperatures (1050°C) followed by gas quenching.
In addition to the cost-savings for logistics, the new concept in equipment offers the following advantages: individual processes customized for each gear-component; homogenous and quick heating of the components and therefore low spread of distortion; homogenous and controllable gas quenching and therefore low spread of distortion; environmentally friendly carburizing and quenching; and compact and space-saving heat treat unit.
The paper shows first results achieved with the new process technology applied in the new heat treatment cell.
ISBN: 1-978-61481-023-0 Pages: 12
Authors: V. Heuer, K. Löser, G. Schmitt and K. Ritter
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