Analysis of the effect on gear accuracy of workpiece/tool positioning accuracy in the hobbing process

Abstract

Accompanying the improvement of vehicle interior quietness in recent years, there has been a need to manufacture low-noise transmission gears at low cost. In response to this need, we adopted a gear honing process as the finishing method following heat treatment in order to reduce the source of gear noise. Previously, gear manufacturing processes generally proceeded in the order of hobbing, gear shaving, heat treatment and gear honing. For the purpose of reducing manufacturing costs, however, there has been a trend in recent years to eliminate gear shaving, resulting in just the processes of hobbing, heat treatment and gear honing. However, with the manufacturing processes of hobbing, heat treatment and gear honing, there are several factors that make it necessary to improve the machining accuracy of the hobbing process. Therefore, this paper describes a hobbing simulation that has been conceived as a first step toward improving hobbing accuracy. This simulation was devised to make clear the effect of the positional relationship between the workpiece and the tool on gear accuracy, including workpiece pitch error and tooth runout. It has been verified on the basis of machining tests. The following results were confirmed by the simulation and machining tests. (1) Work piece positioning accuracy during hobbing has a large effect on pitch error and tooth runout. (2) Tool positioning accuracy greatly affects the tooth profile and helix undulation and also has a large effect on imparting periodic error to pitch error and tooth runout. These results confirmed the effectiveness of the hobbing simulation in determining hobbing process control values.