Variable contour two-step warm extrusion forming of spur gear and the deformation behavior of 20Cr2Ni4A steel

Abstract

The warm deformation behavior of 20Cr2Ni4A steel and the relative constitutive equation are ascertained to support the technical study. Factors that influence the warm extrusion of spur gear are analyzed by using the numerical simulation method. Among the various influencing factors, the lubricating condition, entrance angle, and initial blank size are the crucial factors. Spur gears with a good quality can be one-step formed by warm extrusion under a good lubricating condition (friction factor less than 0.3). Nevertheless, this kind of lubricating condition is very hard to be achieved in a real production environment. “Variable contour two-step warm extrusion” is proposed, in order to obtain a good forming result in a poor lubricating condition. Pre-extrusion is firstly implemented by a die which contour is enlarged from the final-toothed contour for the tooth forming, and then the workpiece is turned around to implement the finish extrusion by a die with the final-toothed contour for insufficient section compensation and tooth sizing. Accuracy of the finished gear obtained through this process is tested; the maximum mean error of single tooth is 15.5 μm.