Understanding the process to reduce scrap.

Engineers at the General Motors Saginaw (Mich.) division have joined forces with their counterparts at Sandia National Laboratories in Albuquerque, N.M., in a cooperative research and development agreement (CRADA) to define the parameters of induction hardening and thereby reduce waste and scrap

Car manufacturers use induction hardening techniques to extend the life of their driveline components, including axles, gears, and joints, by making them more resistant to wear and fatigue. The process involves placing a steel part into a powerful magnetic coil. A current is induced by the coil that heats the exterior and near-exterior areas of the part from 1800 [degrees] to 2000 [degrees] F. The part is then quenched by a polymer-and-water mixture, water, or oil. This hardens the exterior of the part, imparting superior wear resistance to its surface. Quenching also leaves the interior of the part in a ductile state so that the part can resist fatigue.

The parameters of the induction heating process are not completely understood at present. "As a result, we have no way of knowing how the part will turn out until it comes out," said Dave Hitz, chief process engineer at GM's Saginaw division. General Motors and other automakers lose millions of dollars annually in waste and scrap costs from improperly hardened parts.

The General Motors-Sandia CRADA will focus on four areas: process characterization, material characterization, computer modeling, and controller development. "Understanding the process and materials and developing mathematical models for the computerized controls will enable us to adjust the magnetic field as the part is being heated in order to impart the desired strength and durability," said Hitz.

Engineers at GM's Saginaw division and Sandia are aiming for personal computer-based algorithms to monitor and control the induction-hardening process. "The initial data acquisition and processing and controller development were done using workstations. However, by streamlining the software and developing dedicated hardware, the systems will be able to run on a PC. This will make the technology both more accessible and economically feasible for plant applications," said Russ Skocypec, project manager at Sandia for the GM CRADA.

The GM-Sandia CRADA is also examining nondestructive methods of testing induction-hardened pieces to determine the depth, pattern, and degree of hardness. "Currently, inspection involves cutting the part in half and etching it with acid to visually examine the hardened area, which is darker than the ductile interior. This is both costly and time-consuming," said R. on Hoppe, a process engineer at GM's Saginaw division. Among the nondestructive inspection methods being tested by the GM engineers are eddy current, laser acoustic, and sonic-based techniques.