关键词: 最大实体要求, 最小实体要求, 公差边界, 装配实效边界, 公差设计

Abstract: Aiming at the problem of how to add Maximum Material Requirement(MMR)modifier and Least Material Requirement(LMR)modifier to a feature of size,a case study demonstrated that the MMR modifier should be added to the toleranced feature to guarantee assemblability or assembly clearance between two parts.And,if the positioning feature of the part was used as datum feature to control the other geometrical features,the MMR modifier should also be added to the datum feature,for the possible Datum Shift(DS)could be compensated to the toleranced feature.New concepts of Actual Assemble Virtual Boundary(AAVB)and Minimum Assemble Virtual Boundary(MAVB)were put forward.It was pointed out that the MAVB should not be exceeded under any working conditions to ensure assembly interchangeability.When the clearance between the positioning features was not allowed for adjusting assembling,MMR modifier should not be added to the datum feature,but the independence principle or the LMR modifier could be used after weighing the qualification rate of parts and the cost of inspection.

Key words: maximum material requirement, least material requirement, tolerance boundary, assemble virtual boundary, tolerance design