| The auto body, which is composed of stamped metal sheet by spot welding assembly, is the largest assembly of the whole car. Its weight and manufacturing costs account for about 40%-60% of the whole car. Usually the typical auto body assembly process is a complex multi-level process. In this process, the dimensional variation, which is inevitable, will affect the auto body manufacturing quality and production process. The customers’ valuation on product and subjective understanding of the vehicle performance are influenced by the auto body assembly quality, and that is inflected in the market competition of automotive products.The accuracy of auto body is a direct representation of its quality, and the dimensional variation is digital reflection of the accuracy of it. One of the effective ways to improve the auto body dimensional precision is quality control of the auto body. In recent years, the variation predictive analysis of sheet metal of the auto boy and the position design of fixture, which is researched by scholars, are mostly considered on a single station or multi-station that is based on rigid hypothesis. But, the flexible characteristics and the process of multi-station are not considered in the above studies therefore, it has a great significance to establish an analysis model to predict assembly variation of sheet metal on multi-station and optimize the layout of fixture pointing position, which is based on the model.Firstly, this paper studies the influence of spring-back variation to lap of the elastic part, which provides evidence to choose a reasonable contact type of the single-station assembly variation analysis model. The analysis model of single-station assembly variation is established that combined with the analysis model based on Euler transformation, unit displacement response and unit force response method. Then, based on the single-station model and the transfer model of relocation variation, the variation analysis model of flexible sheet multi-station assembly is established. After that, three theoretical model proposed in this paper is verified by 3DCS software and physical experiments. Finally, based on statistical evaluation types of auto body and analytic hierarchy process, auto body comprehensive quality evaluation objective function is proposed. Combined with improved discrete binary particle swarm optimization and secondary development technology of computer, a process approach about multi-station assembly fixture location layout optimization of the auto body flexible sheet is studied out, and an assembly instance of body floor is used by this method. The main work is as follows:(1) Establishment of flexible sheet single-station assembly variation analysis modelFirstly, the 1-D spring structure, 2-D cantilever structure and 3-D flexible sheet structure are applied to study the influence of spring-back variation to lap of the elastic part, which provides evidence for choosing a reasonable contact type of the analysis model of single-station assembly variation. Then, based on analysis of the actual auto body assembly process, the analysis model, which is based on Euler transformation, unit displacement response and unit force response method, is researched. Finally, flexible sheet single-station assembly variation analysis model is proposed.(2) Establishment of multi-station assembly variation analysis model of flexible sheetSheet metal parts are easily deformed in the assembly process and the parts conversing between stations will produce relocation variation. Therefore, the transfer model of relocation variation is deduced based on 3-D variation analysis model and Euler transformation firstly. Then, combined with the single-station model, which is proposed previously, the variation analysis model of flexible sheet multi-station assembly is established. Finally, the flexible sheet single-station assembly variation analysis model, multi-station assembly variation analysis model of flexible sheet and transfer model of relocation variation, which are proposed previously, are verified by 3DCS software and physical experiments to indicate the accuracy and validity of the models in this paper.(3) optimization of multi-station assembly fixture location points layout of flexible sheetMulti-station assembly quality control needs to balance indicators and targets of global stations and partial stations. Firstly, based on statistical evaluation types of auto body and analytic hierarchy process, the auto body comprehensive quality evaluation objective function is proposed. Then, according to the discrete field optimization searching characteristics of sheet, the filter strategy is proposed, and the discrete binary particle swarm optimization is improved. Taking the efficiency of optimization into account, based on the interface relationship between ABAQUS and MATLAB, a secondary development method using computer cluster parallel computing to achieve optimization is proposed. Finally, it demonstrated that the optimization process and the improvement of efficiency are effective through the application and analysis of a multi-station assembly instance of body floor. |
PDF Full Text Request