Abstract
Mechanical products are composed of two or more parts. The geometric tolerance and dimensional tolerance of each feature in part will affect the assembly performance of the product, which are accumulated and propagated between assembly fit and parts. In this paper, through the secondary development of CAD software, the B-rep model of parts is obtained. The model information is decomposed and simplified based on geometric features to obtain the key information of parts in the assembly process, simplify the operation, and improve the accuracy. Through a directed graph network, the transmission model of assembly error information based on geometrical and dimensional tolerances (GD&T) on the surface of parts is established. Combined with the error transfer characteristics of different geometric surfaces and different error sources, guided by the breadth-first search algorithm and the shortest path theory, the search and establishment of a three-dimensional assembly chain are realized. Finally, the three-dimensional chain is simulated by the Monte Carlo method. The calculation results are compared with the error range obtained by the traditional method to prove the effectiveness of the method.
Highlights
Is an integrative process of joining a complete mechanical product by bringing all individual parts together. ere is a deviation between the nominal size and the actual size of the product. e manufacturing deviation and fitting deviation are propagated and superimposed in the component through the assembly of parts, affecting the assembly quality and expected function of products.rough tolerance analysis and tolerance stack-up, engineers can predict the final assembly accuracy before machining, so it has become a hot research area of automation [1]
We propose a breadth-first algorithm combined with the assembly sequence to search the 3D chain of the required assembly size in the assembly error transfer model to solve this problem
The assembly constraint model and assembly error transfer model are deduced from the assembly information model. e corresponding relationship between the factors affecting the assembly performance and the total weight is established, and the 3D dimension chain search algorithm is constructed. e main contributions of this study are as follows
Summary
Is an integrative process of joining a complete mechanical product by bringing all individual parts together. ere is a deviation between the nominal size and the actual size of the product. e manufacturing deviation and fitting deviation are propagated and superimposed in the component through the assembly of parts, affecting the assembly quality and expected function of products. Under the actual manufacturing conditions, the propagation of geometric, dimensional tolerances (GD&T), the gap between mating parts, and the assembly sequence of parts will cause some mating features to deviate from their nominal positions, affecting the assembly accuracy [3]. Different tolerances on different types of assembly surfaces will have different effects on assembly accuracy, so it is necessary to establish an assembly error transfer model to obtain error transfer and superposition in parts. E key features of part obtained by simplifying the part and determining the influence area of error according to the different contact surfaces. (3) On the premise of obtaining the optimal assembly sequence under multiple constraints, the three-dimensional chain of parts in an assembly accuracy propagation model is searched. The three-dimension chain between the corresponding features of two different parts of the assembly is searched by the graph search algorithm and solving the assembly parts’ assembly error. e basic process is as follows: (1) the hierarchical assembly information model can establish the decomposition of the geometric feature of the part represented by the B-rep model. (2) e assembly information model carries out assembly sequence planning. (3) On the premise of obtaining the optimal assembly sequence under multiple constraints, the three-dimensional chain of parts in an assembly accuracy propagation model is searched. (4) e assembly accuracy of related parts is calculated based on obtaining the dimension chain
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