Original Date: 03/08/1999
Revision Date: 01/18/2007
Best Practice : Ausform Finishing
Ausforming is a hardening process that produces very high strength steel. The process converts metastable austenite to martensite by quenching, and increases material strength up to 50% without any loss in ductility. The strengthening is proportional to the degree of deformation, and higher strength persists after the tempering operation. Ausform strengthening is also a result of fine structural changes rather than macroscopic grain and shape effects. Ausform finishing integrates three commonly used gear manufacturing processes: induction heating, martemping (or marquenching), and gear roll finishing. The Applied Research Laboratory at the Pennsylvania State University’s (ARL Penn State) Drivetrain Center (DTC) consolidated these processes into a single, in-line automated manufacturing operation that is capable of finishing spur and helical gears to a quality rating of 12 or higher per the American Gear Manufacturers Association.
Conventional gear processing consists of carburizing and slow cooling. Gears are reheated, quenched to martensite, and case-hardened to a Rockwell hardness of over 60. However, residual stress caused by these processes distorts the dimensional accuracy that is needed for useable gears. In response, the ARL Penn State developed a machine that integrates ausform strengthening with precision gear-roll finishing. Two power-driven, master precision gear- rolling dies made of hot, high-hardness tool steel are used to produce precision-finish gears. The process involves contour austenization of the case-hardened gear teeth and quenching to metastable austenite, followed by plastic deformation of the gear-tooth surface layers to final dimensions and quenching to martensite. Ausrolling integrates the heat treatment and hard-finishing processes into a single, in-line automated manufacturing operation, which eliminates grinding and refrigeration requirements.
The ARL Penn State consistently produces ausformed gears with a surface finish of four to six micrometers compared to eight to ten micrometers using traditional honing methods. Ausforming also improves the bending strength of critical sections on spur and helical gear teeth.
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