最大实体要求应用解析与实例研究

Study on Application Interpretation of Maximum Material Requirement and Its Case Study

针对在被测要素和基准要素上使用最大实体要求(MMR)的问题进行了解析,首先分析了最大实体要求应用于被测要素产生"公差补偿",使得几何公差带动态增大;其次,分析了最大实体要求应用于基准要素产生"基准偏移",使得几何公差带相对于基准可平移或旋转。指出公差补偿和基准偏移均放松了零件公差要求,但基准偏移不等于公差补偿,基准偏移带来的"补偿"与基准所能约束几何公差带的自由度有关,当基准要素远离其最大实体状态时,基准偏移才能在其所限制的自由度上作相应的偏移补偿;最后,以铰链组件装配为例进行了实例研究,其结果可为最大实体要求在几何公差设计中应用以及公差控制和分析提供参考。

Aim at the problem of how to use the Maximum Material Requirement (MMR)on the toleranced feature and datum feature.Firstly,tolerance compensation (bonus tolerance)is incurred when MMR is applied to the toleranced feature.It makes the geometric tolerance zone increase dynamically.Secondly,datum shiftis incurred when MMR is applied to the datum feature.It makes the geometric tolerance zone translation or rotation relative to the datum.It is pointed out that bonus tolerance and datum shift all relax the part's tolerance,but the datum shift is not the same as bonus tolerance for tolerance compensation.The "compensation"caused by the datum shift is related to the degree of freedom of the geometric tolerance zone which can be restrained by the datum.When the datum feature is far away from its Maximum Material Condition(MMC),the datum shift can just be used as tolerance compensation in the degree of freedom it constrained.Finally, the case of a hinge assembly is taken as an example to study the application of MMR on toleranced feature and datum feature,the results can provide reference for the MMR application in tolerance design,control and analysis.