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针对薄壁钢筒温挤件在冷精整过程中出现的内腔顶部凸起现象,应用速度场、应力场和点追踪法分析了薄壁钢筒温挤件的成形过程和缺陷形成的原因。在精整过程的初始阶段,顶部变形区上部金属所受应力小于下部金属所受应力,金属有向上流动的趋势,由于摩擦力的作用,周边层金属的流动滞后于中心层金属,因此,随着上模的向下移动,内腔顶部逐渐向上凸起。根据挤压件顶部受力分析,提出了背压式冷精整技术,通过对工件顶部施加反向压力,实现了对工件顶部材料流动的再控制,即抑制金属的向上流动。基于塑性力学理论分析了新技术的可行性,通过数值模拟优化了背压力,结果表明:两次精整的背压力分别为3460和7450 N时最为合适。在自主研发的背压式精整装置上,进行了实验验证,发现完全可以消除顶部缺陷,从而达到改善顶部缺陷的目的。
Aiming at the phenomenon of bulge at the top of cavity during the cold finishing of the thin-wall steel cylinder temperature extrusion, the forming process and the reason of the formation of the thin-wall steel cylinder temperature extrusion are analyzed using the velocity field, stress field and point tracking method. In the initial stage of the finishing process, the stress on the upper metal in the top deformation zone is less than the stress on the lower metal, and the metal tends to flow upwards. Due to the frictional force, the flow of the metal in the periphery lags behind the center metal. Therefore, With the die moving down, the top of the lumen gradually protrudes upward. According to the analysis of the top of the extrusion, a back pressure cold finishing technology is proposed. By applying the reverse pressure on the top of the workpiece, the material flow at the top of the workpiece is re-controlled, that is, the upward flow of the metal is suppressed. Based on the theory of plasticity mechanics, the feasibility of the new technology was analyzed. The back pressure was optimized by numerical simulation. The results showed that the back pressure of the two times of finishing was the most suitable for 3460 and 7450 N respectively. In the independent research and development of back pressure finishing device, the experimental verification, we can completely eliminate the top defects, so as to achieve the purpose of improving the top of the defect.