Study on the material characteristic and process parameters of the open-die warm extrusion process of spline shaft with 42CrMo steel

The principle and deformation characteristic of the traditional open-die extrusion process of spline shaft are analyzed firstly, and then a novel open-die warm extrusion process of spline shaft with 42CrMo steel is proposed to solve the process problems such as high forming loads, poor material plasticity and tooth filled quality. Next, the material characteristic of 42CrMo steel during the warm forming process is investigated through the isothermal compression tests, the microstructure with tempered sorbite and high accuracy constitutive equations of 42CrMo steel are obtained. Besides, the effects of the main process parameters on the forming loads and tooth filled quality during the open-die warm extrusion process are studied, the optimum die angle of entrance section and warm forming temperature are established as 20 °C and 650 °C, respectively. Finally, the relevant improvement of tooth divided flow method (TDFM) is employed to eliminate the negative effects of the large blank diameter on this novel process.