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以运动学许可速度场为基础的上限法是分析非稳态过程问题的有效工具。本文在建立杯杆型轴对称复合挤压运动学许可速度场的基础上,用上限法对复合挤压的早期和晚期阶段的变形进行了分析研究,确定了复合挤压变形不同阶段所需的凸模平均单位压力。研究结果表明,复合挤压正挤部分变形程度的增大,总是使凸模单位压力增大;而反挤部分变形程度增大,则可能使凸模单位压力增大,也可能使之减小。挤压过程中,随凸模逐渐压入变形体,其塑性变形区的大小和形状,不断发生变化。当毛坯剩余厚度小于某值以后,复合挤压发生变形流动模式的转换,即由早期变形流动模式进入晚期变形流动模式,而变形程度的大小是影响变形流动模式转换的主要因素。利用分析得到的复合挤压力上限解的表达式,用电子计算机计算并绘制的复合挤压凸模平均相对单位压力曲线,可用于复合挤压的工艺设计。实验表明,理论分析结果与实测结果较为一致。
The upper limit method based on the kinematic permitting speed field is an effective tool for analyzing unsteady process problems. Based on the establishment of cup-rod axisymmetric kinematic permitting speed field, the upper limit method was used to analyze the deformation of the early and late stage of compound extrusion. Punches average unit pressure. The results show that the increase of the deformation degree of the positive extrusion part of the composite extrusion always increases the unit pressure of the punch and the increase of the deformation degree of the reverse extrusion may increase the pressure of the punch unit, small. During the extrusion process, the size and shape of the plastic deformation zone are constantly changing as the male mold is gradually pressed into the deformed body. When the residual thickness of the blank is less than a certain value, the transformation of the deformation flow pattern occurs during the composite extrusion, that is, from the early deformation flow pattern to the late deformation flow pattern. The deformation degree is the main factor that affects the deformation flow pattern conversion. Using the expression of the upper limit solution of the composite extrusion pressure obtained by analysis, the average relative unit pressure curve of the composite extrusion punch calculated and drawn by the computer can be used in the process design of the composite extrusion. Experiments show that the theoretical analysis and the measured results are more consistent.