薄壁钢筒温挤件背压式冷精整技术

Backpressure cold finishing technology for warm extrusion thin-walled steel cylinder part

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。

For the inner cavity bulges on the top of warm extrusion thin-walled steel cylinder part,the whole forming process and the causes of product defects were analyzed by velocity field,stress field and point tracking methods. In the beginning of the cold finishing process,the stress of upper metal on the top of deformation zone is less than that of the bottom,so the metal has a trendency to flow upward. Besides,the surrounding metal moves slowly than the central metal due to friction,with the downward movement of the top die,bulges emerges at the inner cavity. The backpressure cold finishing technology was put forward by analyzing the force from the top of extrusion part. And the material flow on the top of workpiece was controlled again by the pressure from the top of workpiece to restrain material from flowing upwards. Furthermore,the feasibility of the new technology was analyzed based on theories of plastic mechanics,and the backward force was optimized by numerical simulation. The result shows that the appropriate backward forces of two cold finishing processes are 3460 N and 7500 N respectively. The experiment was done on the self-developed backpressure cold finishing molding machine.The results show that the defects can be completely eliminated.