筒形件液压拉深过程最优压边力的研究

结合筒形件液压拉深新装置的基本工作原理，提出了筒形件拉深法兰部分切向应变更为精确的简化计算公式，进一步获得了该法兰区域板料径向及切向应力的新的数学表达式。应用能量法重新建立了筒形件拉深时法兰区板料不起皱的最小压边力的数学表达式。明确指出液压拉深时拉深中的危险断面在板料凹模圆角区和筒壁区相交处，建立了相应的拉深力的计算公式，并获得了拉深破裂临界状态时极限拉深力及径向应力表达式。推导出了拉深破裂最大压边力的公式．指出实际拉深时最佳压边力应在防皱最小压边力和拉破最大压边力之间选取，同时根据该结果也能计算液体压力与最小拉深系数的关系。计算结果表明，该液压拉深方法可大幅度提高拉深变形程度，值得在工业实际中推广应用。

Optimal Blank Holding Force in Hydraulic Drawing Process of Cylindrical Cup

The basic principle and advantages of a new hydraulic drawing mechanism for cylindrical cup are simply described and the necessity of analytical researching on optimal blank holding force(BHF)is pointed out in this paper. Firstly, a new reasonably simplified strain formula of flange of cylindrical cup is presented to approach the real stain by exponent x. Based on the strain formula, accurate expressions of tangential stress and radial stress of the cup flange are deduced. Secondly, the expression of minimum BHF avoiding flange wrinkle is rebuilt by using energy method, in which the surface integral method, more suitable for hydraulic drawing, is firstly used for calculating the energy consumed of BHF. According to analysis of the hydraulic drawing process, it is pointed out that the fractural section lies in the tangential area between rounded corner and straight wall of the die in hydraulic drawing. Finally, the maximum drawing force is acquired and the maximum BHF to avoid fracture is deduced, so the practical BHF curve should be chosen between minimum BHF avoiding wrinkle and maximum BHF to prevente from fracture, which depends on practical conditions. The relationship between hydraulic pressure and drawing ratio also can be drawn by numerical computation. The result of calculation shows that the new type of hydraulic drawing can greatly improve drawing ratio.