Study on near-net forming technology for bars by axial feed skew rolling based on taper-end billets

Large concavities are formed at both the head and tail of the bar formed by axial feed skew rolling (AFSR), which affect the end face quality and cause material waste. A finite element (FE) model for AFSR process was presented in this work. Based on the simulation results, the forming mechanism of the head end concavity (HEC) and tail end concavity (TEC) was revealed respectively, and the influence of process parameters on the concavity depth was analyzed. Subsequently, a taper-end billet was proposed to compensate for concavity, and the influence of taper-end design on end face-forming quality and biting force was investigated in detail. The results show that the depth of HEC increases with increasing forming angle, and decreases with increasing feeding angle, while that of TEC decreases with increasing the forming angle and feeding angle. The taper-end design can effectively improve the concavity, and the optimal design scheme which can reduce 78% material waste was obtained. The stress evolution trend and stress value at the end center are significantly affected by the taper-end design, which is helpful to reduce the risk of core damage. In addition, the taper-end is conducive to the biting of the billet and greatly reduce the biting force, in particular, the biting force is only 0.2 kN when the cone angle ( θ = 20°) is close to the forming angle ( α = 17°). Moreover, the experiments was presented on a multi-degree rolling mill and verified the effectiveness of taper-end design in improving end concavity.