Improvement of axial forging process for spline shaft by die design

Abstract

As an effective method of forming spline shaft, the axial cold forging process is appropriate for long shaft and exhibits high efficiency. The two defects of folds and accumulation were found to result in large forming force and low quality of products in the experiments. To analyse the cause the defects, a finite element model was built with a strain rate-dependent material model, in which the parameters were determined by material test. Metal flow was divided into three different parts, and relevant parameters were proposed to quantify them. An assembling method of three dies and a new die with a variable tooth shape were designed by the fast simulated annealing optimization method using the quantification parameters to improve metal flow and decrease forming force. The differences in metal flow, tooth profile and axial force were compared amongst conventional axial forging, the assembling dies and the new die. The assembling method of three dies decreased the force by 31.2% compared with the conventional axial forging. However, fold defects were significant which might lead to stress concentration. On the basis of the optimisation of the assembling method, the die with a variable tooth shape decreased the load by 55% compared with the conventional axial forging. The shape quality of the product formed by the new die with a variable tooth width was also improved owing to the avoidance of defects.