Conversion of geometric tolerance based on variation of tolerance zone

To solve the problem of geometric tolerance transformation caused by datums' conversion in the process of machining and assembling of parts, a new method of tolerance transformation based on variation of tolerance zone was proposed. According to the types of geometric features, the Degree of Free (DOFs) of functional geometry in different spatial locations constrained by other geometric features were analyzed. By using spatial locations, DOFs of functional geometry constrained by designing datums were obtained. The coordinate system of positioning datums was estabished and checked for its redundancy and completeness. According to the spatial relationship among designing datums, positioning datums and functional geometry, the accumulation equation was used to get the value of geometric tolerance related to the functional geometry after transformation. Based on the proposed method, a software package was developed, and a case study was conducted to prove the feasibility and accuracy of proposed method.