Research On Accurate Forming Theory Of Multi-step Shaft Without Stub Bar In Cross Wedge Rolling

The multi-step shaft is an important load-bearing part in the transmission system of transportation tools.It not only bears the effect of torque,but also bears the effects of vertical force,lateral force,traction force and braking force.Therefore,the forming quality and mechanical properties of the multi-step shaft are required to be high.when multi-step shaft parts are formed by Cross Wedge Rolling(CWR),end concave and microstructure inhomogeneity are easy to appear,resulting in the decline of mechanical properties and low utilization of materials.Therefore,the end quality and microstructural homogeneity of multi-step shaft parts were studied in order to improve the material utilization rate and mechanical properties of products in cross wedge rolling process.In this paper,numerical simulation and rolling experiments are combined to carry out the research on process parameters optimization,forming mechanism,end quality and microstructure uniformity.In order to improve the microstructural homogeneity and end quality,a multi-objective optimization orthogonal experiment about process parameters of cross wedge rolling was designed,and the primary and secondary relationship between the process parameters and the comprehensive quality of the shaft was obtained.The forming mechanism of multi-step shafts was analyzed,and the distribution of stress field and strain field and the variation of core damage during cross wedge rolling were obtained.According to the characteristics of metal flow at the end of multi-step shaft in the forming process,this paper breaks through the limitation of traditional flat-end billet,innovates multi-step shaft rolling with variable cone billet,and obtains the influence law of variable cone angle billet parameters on the end quality.On this basis,the change law of temperature field and microstructure in multi-step shaft forming process based on variable cone angle billet are analyzed and studied.Finally,rolling experiments and metallographic experiments were carried out to verify the finite element simulation results.The results show that the use of variable cone angle billet can effectively solve the end concave problem of multi-step shaft in cross wedge rolling.The research results in this paper provides theoretical guidance for improving the forming accuracy and mechanical properties of multi-step shafts in cross wedge rolling,provide reliable experimental basis for solving the problem of end concave and microstructure inhomogeneity of multi-step shafts,improve the competitiveness and the theoretical development of cross wedge rolling technology.