【作者】 刘少岗； 郑力；

【Author】 LIU Shaogang, ZHENG Li Tsinghua University, Beijing 100084, China

【机构】 清华大学；

【摘要】 为了保证工件加工过程的顺利进行,通常作用在工件上的夹紧力不止一个,当这些夹紧力按照不同的作用顺序施加在工件上时,会对工件的夹紧误差造成不同的影响。本文假定夹具元件与工件之间遵从库仑摩擦定律,则夹具元件与工件之间的相互作用必须满足以下两个条件:夹具元件与工件的作用力只能是压应力,不能是拉应力;夹具元件与工件之间的摩擦力不能大于最大静摩擦力。根据以上两个约束条件,将定位件与工件的接触情况分成以下三种状态:粘着状态、分离状态和滑动状态。粘着状态时夹具元件既没有脱离接触,又没有相对滑动。滑动状态时夹具元件与工件没有脱离接触,但发生相对滑动。分离状态时夹具元件与工件脱离接触。在夹具设计中,夹紧力是主动力,定位反力是被动力,每个定位件与工件的具体接触状态只有通过计算才能得到。本文通过一个迭代过程来确定定位件与工件之间的边界条件。研究发现,夹紧顺序会影响工件的夹紧误差,这是由于定位件与工件之间存在摩擦力。在定位件与工件之间的摩擦系数相同的情况下,工件的夹紧误差随夹紧顺序的改变而改变。在夹紧顺序相同的情况下,夹紧误差也受到定位件与工件之间摩擦系数的影响。最后,用仿真模型对夹紧顺序的影响进行了验证。更多还原

【Abstract】 In order to machine workpiece stably, usually more than one clamping forces are used to clamp workpiece. When these forces act on workpiece according to different sequence, the clamping errors of workpiece are different. In this paper, coulomb law of friction is assumed between fixtures and workpiece. It is known that the normal force between fixtures and workpiece must be compressing forces, and the tangential force is not greater than the maximal friction force. According to these two constraints, the boundary conditions between the locators and workpiece include three states, that is steady state, sliding state and separate state. In steady state, normal force is compressing force and tangential force is less than maximal friction force. In sliding state, normal force is compressing force and tangential force is equal to the maximal friction force. In separate state, normal force is equal to zero. In fixture design, the clamping forces are driving forces and locating response forces are passive forces. In this paper, the boundary condition between locators and workpiece are determined through a numerical iterative process. It is found that because of friction force between locators and workpiece, the clamping sequence influence clamping errors. When the friction coefficient between the locators and workpiece is same, workpiece has different clamping errors at different clamping sequence. At the same clamping sequence, the clamping errors are also influenced by friction coefficient between the locators and workpiece. At last, a simulation model is used to examine the effect of clamping sequence on clamping errors.更多还原