杯外径不相等的杯杯型轴对称复合挤压凸模单位压力

RAM PRESSURE OF AXISYMMETRIC CUP CUP WITH DIFFERENT OUTER RADIUS COMBINED EXTRUSION

本文建立了杯外径不相等的杯杯型轴对称复合挤压的运动学容许速度场.在此基础上,用上限法分析了此类复合挤压的变形过程,确定了此类复合挤压变形不同阶段所需的上凸模平均单位压力.研究结果表明:作用于上凸模上的平均单位压力随着反挤变形程度的变化呈近似抛物线型;随着正挤变形程度的变化呈单调增函数.在挤压过程中,随着上凸模的逐渐压入,变形体的变形模式发生改变,即由早期阶段的稳态流动进入晚期阶段的非稳态流动.而正挤、反挤部分的变形程度组合是除剩余坯料相对厚度以外影响变形模式转换的主要因素.本文的理论分析结果可较为方便地运用于实际生产中的工艺设计.实验表明:理论分析结果与实际结果颇为一致.

In this paper, the kinematically admissible velocity fields for the axisymmetric cup-cup with different outer radius combined extrusion are put forward. On the basis of these velocity fields, the deforming processes are analyzed and the average pressures acting on the upper ram in the different deformation stages are determined by upper-bound approach. Analytical results show that the average pressure acting on the upper ram varies with that the reduction in area of the backward-extrusion part in a manner somewhat similar to a parabolic function, and that it varies monotonically with the reduction in area of the forward-extrusion part. During the extrusion process, with progressive penetration of the upper ram, the deforming pattern in the deformed body may change from steady flow in the early stage into non-steady flow in the final stage. Besides the thickness of bottom, the combination of the reduction in area of backward-extrusion part and that of forward-extrusion part is a primary factor affecting the transformation of deforming patterns. The results presented in the paper can be used for process design. Good correlation is found between the theoretical and experimental results.