Specific grinding energy causing thermal damage in precision gear steels

Abstract

This project is aimed at developing a better understanding of thermal damage caused by grinding of precision gear materials and also a model to predict the onset of burn in AISI 9310 gear steel. This study is concerned with the thermal aspects of grinding, which is mainly directed towards controlling thermal grinding damage. On the basis of a relatively simple heat transfer analysis, a relation has been derived for the grinding zone temperature for grinding processes in terms of the power consumption and the grinding parameters. By inverting the heat transfer solution, the allowable power corresponding to a critical surface temperature can be specified in terms of the grinding parameters. This concept has been applied to predict the onset of thermal damage for surface grinding of AISI 9310 gear steel using two different grinding wheels and two different coolants. The grinding wheels used for this research are plain alumina wheel-32A80-JVBE and Seeded Gel alumina abrasive-5SG80-JVS. The coolants used are water based coolant (FUCH PT 95 with water in the ratio 1:20) and straight oil coolant (Castrol 41-129A). Thermal damage results for AISI 9310 using straight oil based coolant and 32A80-JVBE has already been established. This result is compared to that obtained using different combinations of alumina wheel, Seeded Gel (SG) abrasive, water based coolant and straight oil coolant. The motivation of the project came from a prior research project on identification of R&D needs in precision gear manufacturing. The main focus was gear production by a production partner. In addition to the thermal damage the project also touches upon the amount of residual stress in the specimen after the grinding operation. Residual stress is determined by a coefficient C, which correlates the effect of power density and wheel/workpiece contact time.