摘要
本文运用上限法分别分析了早期稳定流动阶段及后期非稳定流动阶段的杆杆型轴对称复合挤压过程。在密栅云纹及网格试验的基础上,提出了上述两个阶段的运动学容许速度场,并由此导出变形总功率消耗及平均相对单位压力,同时确定了变形程度和摩擦对单位压力的影响。本文还分析了早期速度场与后期速度场之间的转换关系以及挤压过程中可能出现的三种变形模式。如果正挤变形程度与反挤变形程度相差很大,则可能出现单向流动。在正、反挤压变形程度相等时,正挤部分挤出长度则可能稍大于反挤部分挤出长度。实验表明,理论结果与实验结果相当一致。
The papers using upper-bound approach to analyze the forming processesare fairly numerous [1-5, 7-12], however, bar-bar combined extrusion has al-most not been studied systematically up to the present time. A theoreticalwork on axisymmetric bar-bar combined extrusion was presented by Yang etal. [3], who introduced the arbitrarily inclined triangular elements for velocityfield and derived the upper-bound loads on the punch, but it is only appli-cable to the final stage of the process and the variety of flow patterns duringthe process is not taken into account. Without distinguishing the deformingstage, and without considering the flow pattern, the results obtained from a-nalyzing and computing the deforming process do not agree with experimentalresults in a number of cases. The problems just mentioned are believed to be solved in this paper. Theauthors' contributions are as follows: (1) The new kinematically admissible velocity fields in the early stageand the final stage are advanced. They are very close to the realistic velocityfields, and the calculated force required for deformation is more accurate. (2) Two stages and three possible flow patterns for bar-bar combinedextrusion are put forward. (3) As a result, from the proposed upper-bound formulation in this pa-per the punch pressures and the dimensions of the deformed billet can bedetermined during any process. Good correlation is found between the theoretical and experimental results.The results presented in the paper can be used for process design.
出处
《西北工业大学学报》
EI
CAS
CSCD
北大核心
1990年第1期85-94,共10页
Journal of Northwestern Polytechnical University
基金
国家自然科学基金
关键词
复合挤压
杆杆型
变形
速度场
bar-bar combined extrusion
upper-bound approach
velocity field.
