Studies for Highly Qualifing Case-Carburized and Hardened Steel Gear Using Shot Peening and Barrelling Processes

Abstract

Since recently a speed changer in a motor vehicle or a gear reducer in a generalized industrial equipment have been demanded to transmit high torque or to be compact, an improvement of a load carrying capacity of gears used in it will properly be required. Their current gears are almost case-carburized and hardened steels. However, it is often said that these materials have already gotten the limit of endurance. Then, a shot peening process may be expected to improve the fatigue strength of case-carburized and hardened steel. It is very difficult to make the surface roughness of the roller or gear tooth finished smaller than the oil film thickness by a grinding machine. Even if possible, grinding time of the surface will be very long, and it is not economical from the viewpoint of manufacturing process. However, it is thought that the both processes of shot peening and barrelling, which can easily be applied to the gear with complex configuration, are an advantageous for processing time. In the present paper, outlines of pitting strength of rollers finished by these processes are indicated and machining precisions and tooth surface characteristics of gears finished by these ones are discussed. The authors would like to recommend to employ the processes of shot peening and barrelling after grinding the gear tooth of case-carburized and hardened steel from both viewpoints of the improvement of fatigue strength and the economy of attaining a high quality gear.