Reliability Modeling And Parameters Optimization For Process System Of Sheet Metal Assembly

Sheet metal parts are widely used in automobiles, aircrafts and other large industrial manufacturing field, sheet metal assembly is a typical feature of modern equipment manufacturing industry. Assembly process system reliability is important factor that ensure the assembling quality and production efficiency. Taking the sheet metal assembly process as the research object, the reliability model for process system of sheet metal assembly is established, and the process parameters optimization design method based on reliability is proposed. It provides a new way for process system reliability assessment and parameter optimization of sheet metal assembly, the main research contents are as follows:Firstly, the reliability model of single station assembly process system is carried out. The failure mechanism of the assembly process system is described. The relationship between the locating deviation and the assembly deviation is analyzed;the digital statistic characteristic model of assembly deviation is established. Then,wear mechanism of the pin is analyzed, and the wear model of the pin is deduced, the digital statistical characteristic of the cumulative wear of the locating pin is obtained.The relationships among locating pin failure, assembly deviation and assembly process system reliability are discussed. The process system reliability model for single station assembly of sheet metal is established, which considers positioning pin tolerances, part hole(slot) tolerances, fixture layout and locating pin wear. Then, it takes simple automotive side panel as an example to analyze the pin-hole(slot)tolerances, fixture layout, and positioning pin wear impact on the process system reliability.Secondly, the reliability modeling research for process system of multi-station assembly is carried out. The relationship between the positioning deviation and the state variables is investigated, based on state space model of variation propagation;the relationship between assembly deviation and state variables is obtained, an evaluation model of multi-station assembly quality is set up. Then, the effect of parts assembly deviation on locating pin failure is analyzed, locating pin failure rate model is obtained, and then the multi-station assembly process system reliability model which consider locating pin failure and assembly quality is established. Combined with automobile body side wall assembly example, the process system reliabilities of three different conditions are obtained and the effect of assembly sequence on processsystem reliability is discussed.Thirdly, the optimization design of process parameters for automotive body side wall assembly is studied based on reliability. Taking automotive body side wall assembly as research object, the effects of each pin-holes(slots) size tolerances on process system reliability are discussed by single factor analysis, and the main factors are obtained, then, the response surface model of process system reliability and main factors. Using the assembly cost which contains processing costs of the positioning pin and part hole(slot) minimization as optimization objective, the process system reliability as constraints, and the optimization design model of process parameters is established for automotive body side wall assembly. The optimal solutions are obtained, it ensure process system reliability and lower assembly cost.