内高压成形合模力对变径管尺寸精度的影响

Influence of Clamping Force on Dimensional Accuracy of Variable-diameter Tubular Part in Hydroforming

目的在内高压成形过程中,合模力加载不合理不仅会导致模具寿命降低,而且容易引起管件截面精度超差,需探究合模力对管件截面尺寸的影响以改善这一缺陷。方法以低碳钢和铝合金变径管为例,采用内高压成形实验与数值模拟的方法,在两种不同的加载条件下分析合模力对管件截面尺寸精度的影响规律。结果变径管内高压成形时,模腔上、下侧的等效应力高于左、右侧,模腔顶部的径向位移最小,分型面附近的径向位移最大。模腔在合模力的作用下被压扁,导致卸载内压和合模力后管件截面竖直方向的直径始终小于水平方向,存在一定的不圆度。SAPH440低碳钢和6063铝合金变径管的截面最大不圆度分别为0.27%和0.26%。结论在内高压成形过程中,合模力对截面精度的影响不可避免,需通过增大模具尺寸或采用可变合模力的加载方式以减小其影响。

During the hydroforming process,an unreasonable loading of clamping force will not only reduce the life of form-ing die,but also easily cause the sectional dimension accuracy of tubular parts to be out of tolerance.It is necessary to investigate the influence of clamping force on the sectional dimension of tubular parts to improve this defect.Experiment of hydroforming and numerical simulation of variable-diameter tubular parts with low carbon steel and aluminum alloy were carried out,the influence law of clamping force on sectional dimension accuracy under two different loading conditions was analyzed.The results show that the equivalent stress on the upper and lower sides of the die cavity is higher than that on the left and right sides in the hydroforming process of the variable-diameter tubular parts.The radial displacement at the top of the die cavity is the smallest,while near the parting surface is the largest.The die cavity is pressed to be oblate by clamping force,leading to the fact that the vertical diameter of the tubular part's section is always smaller than the horizontal diameter after unloading the internal pressure and clamping force,re-sulting in a certain degree of out-of-roundness.The maximum out-of-roundness of variable-diameter tubular parts with SAPH440 low carbon steel and 6063 aluminum alloy are 0.27%and 0.26%,respectively.It shows that in the hydroforming process,the in-fluence of clamping force on the section accuracy is inevitable.It is necessary to reduce its influence by increasing the size of the die or using a loading method with variable clamping force.