The Dimension Error Analysis And Tolerance Optimization Allocation Of Vehicle Body Components

Vehicle body as an important part of the automobile, its processing quality reflects the automobile enterprise level of design, manufacture and management level. As car competition between enterprises is more and more big, in order to make their products are in a strong position in the market competition, the quality requirements of the various manufacturers for the appearance of the body is becoming more and more high. Domestic and foreign scholars have carried out extensive research on the problem of the control of accuracy and the body of tolerance allocation, and have achieved some results. However, these studies are generally from the functional requirements of body parts, and only to reduce the manufacturing cost of auto makers as the goal, without considering the customer quality loss cost. Therefore it affects the rationality of the body parts of tolerance allocation and these factors on the car body parts of tolerance allocation are extremely important.This paper is supported by the national natural science fund project named "the theory of the body structure of the whole design process and the design method of positive concept research", studied the source of the car body error, and analyzed the influence of the manufacturing process, the locating datum and sheet parts tolerance on the body error, then analyzed the traditional method of tolerance allocation and pointed out the limitations of traditional allocation methods. This article represented the relation between the parts of the car body by using oriented-mating graph based on the graph theory, and then achieved the method of establishing the dimension chain through the Dijkstra algorithm based on the full path search. Introduced the exterior quality loss cost, the model of the tolerance optimize allocation on car body was built that the minimum total cost as the target, the assembly requirement as the constraint conditions and the component loop tolerance of tolerance as the optimization design variables. This model based on the minimum manufacturing cost method of tolerance allocation, and considering the problem of the efficiency of the body parts processing, technical requirements and the loss of quality characteristics fluctuation for the customer.Finally, with the front door and front fender of the BIW (Body in White) as the research object, the assembly dimension chain was established, and achieved the results by using the method of tolerance optimization allocation based on manufacturing cost and quality loss cost and the Lagrange multiplier method. The results were compared with the traditional method of tolerance allocation of tolerance allocation results, and proved that the tolerance of car body meet the demand of automobile body assembly, better than that of the traditional method, can provide reference for tolerance design of car body.