Transfer method of geometric tolerance items based on assembly joints

In order to reduce the uncertainty in the selection of geometric tolerance items, a qualitative method for top-down transfer of geometric tolerance items is proposed. The assembly joint which is composed of two mating surfaces with functional requirements or structural constraints is acted as the basis of geometric tolerance items transmission. According to the structural characteristics, the assembly joints are divided into meta-assembly joints and composite assembly joints, and the priority rules for assembly joints are proposed. The transfer path of part-level geometric tolerance items is established according to the functional requirements and structural constraints among parts. On this basis, by adding information about the composition and constraint types of assembly joints between parts and the position constraint relationship of the general structure surface in the part, the transfer path of part-level geometric tolerance items is extended to the transfer path of geometric feature surface-level. With the development of product design, the initial functional requirements will be transformed into structural constraints between parts and geometric feature surfaces, and the structural transformation model of functional requirements is constructed. The generation specifications of geometric tolerance items based on structural constraints and the transfer specifications of datums are established. And based on the above specifications, the mapping relationship between functional requirements, structural constraints, and geometric tolerance items is defined. The synchronous transmission of geometric tolerance items along with the product design process are realized which provides an effective analysis tool for the top-down design of geometric tolerance items. Finally, the effectiveness of the method is verified by taking the transmission parts and connection parts in the crankshaft-piston mechanism as an example.