A forming technology of spur gear by warm extrusion and the defects control

A forming process of spur gears by warm extrusion is proposed, the forming defects existing in this process such as the insufficient section of gear face and the underfilling of gear tooth which result in the geometrical dimensions of gear tooth are substandard or machining allowance is overlarge are discussed by using the numerical simulation method. The main reason causing the insufficient section of gear face is unbalanced velocity field distribution during the extrusion process; the lubricating condition and the die structure are two decisive factors. The die structure and extrusion speed are optimized by using the Response Surface Method with the goals of defects control and machining allowance optimization. The influence rules of PVR (Profile Variable Ratio of entrance section), PVR′ (Profile Variable Rate of entrance section) and the extrusion speed on forming quality are investigated, the prediction models of the machining allowance of gear face, tooth flank and tip are established. The accuracy of prediction models is verified by implementing numerical simulation and experiment. This work provides one of the feasible ways to manufacture spur gears with the whole gear teeth in the field of plastic forming.