组装公差分析..doc

组装公差分析 公差分析主要是探讨一个描述工件组合后，其公差变动模式，一个好的公差分析模式可以预测组件公差能吻合实际组件公差界限有多少，其预测之机率愈大愈好。组装公差分析可分成三种模式：最坏状况模式(Worst-case model)、统计模式(Statistical model)和蒙地卡罗模式(Monte Carlo model). 概念 Dimension chain (sometimes called tolerance chain) is a closed loop of interrelated dimensions. It consists of increasing, decreasing links and a single concluding link. In figures 2-4 and 2-5, link i is the increasing link, d is a decreasing link and c is the concluding link.Apparently, the concluding link c is the one whose tolerance is of interest and which is produced indirectly. Increasing and decreasing links (both called contributing links) are the ones that by increasing them, concluding link increases and decreases; respectively. Figure 1. Dimension Chain of c, 2 links, 1D Figure 2.: Dimension Chain of c, 4 links, 1D The equation for evaluating the concluding link dimension is [Lin and Zhang (2001)]: ---------(1) Where: Σi: The summation of the increasing link dimensions. Σd: The summation of the decreasing link dimensions. j: increasing links index. k: decreasing links index. l: number of increasing links. m: number of decreasing links. For figure 1 ,c can be found as: c = i - d ------(2) As for chain in figure 2, c can be found as: c = (i1 + i2)-( d1 + d2) ------(3) 1. 最坏状况模式(Worst-case model) 最坏状况模式又称上下偏差模式、极限模式、完全互换模式，此模式是以工件的最大及最小状况组合，可以满足完全互换性、组件公差最大. In worst-case method, the concluding dimension’s tolerance Δc can be found as following: ------(4) Referring to figure 2 and equations (3 and 4), the deviation of the concluding link is: Δc = Δi1 + Δi2 + Δd1 + Δd2------(5) T0: 总公差 m: 零件之数目 Ti: 各零件之公差 2. 统计模式(Statistical model) 大量生产的产品，其零组件因为生产过程的变异所造成的公差呈统计分布，统计公差分析虽然可以估算结果尺寸公差的特性，但实际的分布情形还是无法掌握，统计模拟即是透过随机取样的原理 统计模式又称均方根和模式(Root sum squared model)，假设各零件公差都依据本身的特征或加工条件会符合常态之钟型曲线分布，且分布中心与公差带中心值相同,分布范围与公差范围也相同,组合公差为 --------(6) m: 零件个数 , Ti :各零件之尺寸公差 另一种堆栈统计公差观念如下 In statistical method, the concluding dimension’s tolerance Δc can be found as following: --------(7) Referring to figure 2