Distortion minimization of disks for gear manufacture

In order to minimize shape deviations in hardening of gear wheels, all production steps in the manufacture of disks made of SAE 5120 prior to heat-treatment were analyzed by means of design of experiments (DoE). The influence of hardenability, pre-heat treatment, forging temperature, and feed rate and partition of material removal in cutting on the distortion of disks were investigated. Standard case hardening of the disks led to a characteristic shape change called “dishing”. The statistical analysis of the test results has proven that dishing of disks is mainly affected by the partition of the material removal in the considered case. In additional experiments dishing could be eliminated (on average) by an optimized partition of the material removal. However, results from experiments with spray-formed disks and with disks using a different forming strategy imply that the material flow combined with material inhomogeneities are the physical causes for dishing rather than the partition of material removal.