Investigation of manufacturing bilayer gears using flow forming process to enhance the strength of gears

Due to the widespread industrial use of gears, a mass production method with high economic efficiency is essential. Flow forming is a novel manufacturing technique that not only forms the gear but also performs hardening by adding a thin layer of desired metal simultaneously. In this process, a copper tube is placed concentrically inside a steel tube, and the assembly is inserted into a mandrel with an internal gear profile. Both the tube assembly and mandrel rotate simultaneously during internal flow forming. A roller induces plastic deformation in the copper tube, reducing its wall thickness and forming gear-like teeth matching the mandrel's geometry. The geometry of the teeth and required forming forces were analyzed and compared between forward and backward flow forming methods. Crush forces needed to deform the teeth were also evaluated. Results showed that flow-formed copper gears have double the crush resistance compared to non-flow formed ones. Additionally, a hardened steel 304 L layer on the gear further doubles the strength against crushing. This study demonstrates a simple process to effectively form and strengthen gears.