Study And Sotfware Secondary Development Of Autobody Compliant Sheet Metal Single-station Assembly Variation Analysis

The product quality of the autobody, which is one of the three major components of avehicle, directly affects various aspects of the vehicle, such as the appearance andperformance. The autobody is composed of various parts, which are hierarchicallyassembled in multiple stations. During the assembly process, the quality of the assemblytransfers through the downstream stations, eventually affecting the quality of the generalassembly. Therefore, controlling the assembly quality of every station is an indispensableportion of autobody quality control.As one of the aspects measuring autobody quality, the dimensional variation of autobodyassembly affects various performances of a vehicle directly, such as sealing, noise andappearance. Using assembly variation analysis to quantitatively assess the quality ofautobody sheet metal assembly is the primary means of autobody assembly dimensionalvariation control. Improving the accuracy and efficiency of assembly variation analysis canhelp reduce the difficulty and time of dimensional variation control. And the single-stationassembly dimensional variation analysis is the basis of autobody general assembly variationanalysis, thus improving the accuracy and efficiency of single-station assembly variationanalysis is of great significance to autobody assembly dimensional variation control.In order to improve the accuracy and efficiency of single-station assembly variationanalysis, this paper first introduces how to establish an analysis model for autobody sheetmetal single-station assembly variation using the finite element method and the method ofinfluence coefficients, and then on this basis the methods of handling assembly interferenceare studied, followed by the development of a variation analysis plugin in ABAQUS basedon the aforementioned contents. At last, a number of assembly variation analyses areconducted on a rear lamp bracket assembly using the variation analysis plugin and VisVSAseparately. The main studies of this paper are as described below:(1) Modeling of autobody compliant sheet metal assembly variation The “N-2-1” positioning and general assembly process of compliant sheet metalassembly are studied, followed by a detailed analysis on how to establish a linearrelationship between input variation of parts and output variation of the assembly, with theadjunction of fixture variation modeling and the unification of both part and fixture variation.In the end, an assembly variation analysis using the method of influence coefficients isconducted on a simple lap-joint compliant sheet metal assembly, and with the usage ofMonte Carlo simulation method, the distribution characteristics of the assembly measuringpoints are obtained.(2) Handling the assembly interference in compliant sheet metal assembly variationanalysisTwo ways of handling assembly interference in assembly variation analysis arediscussed in detail, including a method that simulates the mechanics between parts and themethod of defining contact interactions in ABAQUS. A detailed analysis and certainimprovements are made on the three steps of the first method at first, which are combinedwith the method of influence coefficients, giving the method of influence coefficients theability to handle assembly interference. Then the important steps of the second method arediscussed, namely, property definition of contact interactions, contact interactions definitionand interference fits definition, whose theory is discussed as well.(3) Development of an assembly variation analysis pluginThe basis of secondary development in ABAQUS is introduced at first, includingworking principle of ABAQUS, script execution, interface programming, communicationbetween user interface process and kernel process and kernel scripting. Then thedevelopment of the variation analysis plugin is discussed in detail, including the overallstructure, the user interface and the workflows of functions. The overall workflow of theplugin and the detailed workflows of the modules are discussed in the section of therealization of plugin functions, and the functions in the plugin are progressively programmedbased on these workflows.(4) Case study on autobody assembly variation analysisA number of assembly variation analyses are conducted on a finite model of a rear lamp bracket and the results are compared. Three of these analyses are conducted using thevariation analysis plugin, where one of these analyses ignores the assembly interference,while the other two handle the assembly interference in two different approaches,respectively. Then a direct Monte Carlo simulation is carried out on the model using VisVSA.Previous three analyses require a short period of time and little manual operation, whichindicates that the variation analysis plugin is able to improve the efficiency of assemblyvariation analysis. And the comparison between the results of previous three analyses andMonte Carlo simulation verifies that the method of influence coefficients applies to variationanalysis of compliant assembly and that the impact assembly interference has on assemblyvariation analysis is not negligible, which can be taken into consideration properly by twospecific approaches. But each of these two methods has its own pros and cons, thus it shouldbe chosen discreetly depending on the details of the model.