椭球形制件复合成形规律的研究

采用理论分析、数值模拟与实验验证相结合的方法,对椭球形制件的复合成形规律进行了研究。建立了应力分界圆半径的数学表达式,理论分析表明,应力分界圆半径的大小与板料的初始尺寸、厚度、摩擦系数、压边力大小和凹模圆角半径等因素有关。当压边力、坯料尺寸以及摩擦系数加大,而相对圆角半径减小时,应力分界圆半径变大,复合成形中胀形成分加大;反之,应力分界圆半径减小,拉深成分增加,揭示了复合成形的阶段性特征。数值模拟结果表明,应力分界圆半径是动态变化的,椭球形制件复合成形具有明显的阶段性特征,没有直线段的椭球形制件的成形可分为纯胀形、以胀形为主的胀形-拉深复合成形和以拉深为主的拉深-胀形复合成形3个阶段;在成形的第Ⅰ、Ⅱ阶段初期,坯料尺寸和压边力的大小对应力分界圆半径影响不大;在第Ⅱ阶段后期和第Ⅲ阶段,随毛坯尺寸和压边力的增大,应力分界圆增大。在变形过程中存在两个可能发生失稳起皱时刻,即第Ⅱ阶段初期和第Ⅲ阶段初期。试验验证了理论分析和数值模拟所得的结果。

The research on compound forming law of elliptic hemispheroid part

The compound forming law of elliptical hemispheroid part is researched by the way of theory analysis and numerical simulation combined with experimental validate.The math expression of the stress boundary circularity radius is established.The theory analysis shows that the size of stress boundary circularity radius is related with the original dimension of the sheet blank,thickness,friction coefficient,the magnitude of blank holder pressure and the die corner radius etc.The size of stress boundary circularity radius and the stretching component are increased in the compound forming process when the blank holder pressure,blank size and friction coefficient are increased,and the relative die radius is reduced.On the contrary,the size of stress boundary circularity radius is reduced and the drawing component is increased.The stage characteristic is revealed and numerical simulation results show that the stress boundary circularity radius is dynamically changed and the stage characteristic appears in the compound forming process.The forming process of the hemispheroid part without line section can be divided into three stages.The first stage is pure stretching process;the second is stretching-drawing compound forming process,and the main forming is stretching;the third is drawing-stretching compound forming process,and the main forming is drawing.The size of stress boundary circularity radius is little affected by the blank size and the magnitude of blank holding pressure in the first forming stage and the beginning of the second forming stage.In the last of the second stage and the whole third stage,the size of stress boundary circularity radius is increased with the increases of original blank size and the blank holding pressure.There are two possible moments for making wrinkle in the forming process:The beginning of the second stage and the beginning of the third stage.The results of theory analysis and numerical simulation are validated by the experiments.