Tolerance Robust Design For Multi-station Assembly Processes Based On Assembly Yield

Propagation, accumulation and coupling of dimensional variation in multi-stationassembly processes are vital factors that effect products assembly yield. Takingmulti-station assembly processes for research object, and automotive body floorassembly for a real case, state space model of dimension variation propagation areinvestigated. Evaluation method of assembly yield based on state space model isproposed. Then, taking the minimum manufacturing cost of pin and part hole asassembly cost for objective, and assembly yield for constraint, the model oftolerance robust design for multi-station assembly system is established.Firstly, fixture variations, part variations, part variations caused by fixturevariations and reorientation variations are described in details. The modeling methodof state space model is studied. Moreover, the relationship between pin/part holetolerance and fixture variations is analyzed. Then, state space model of dimensionvariation propagation for automotive body floor three-station assembly is built.Secondly, assembly yield evaluation model in multi-station assembly processesbased on state space model of dimension variation propagation is built, and itsresponse surface model is established as well. Calculation samples are created byusing Number theoretical net method. Evaluation method of assembly yield based onstate space model is proposed. Visual analysis of Taguchi orthogonal experiment isused to analyze the main factor which influencing on assembly yield. After that,regression orthogonal combination design is applied to fit response surface model ofassembly yield. It can solve the difficult problem that modeling assembly yield inmulti parameters and stations assembly processes.Finally, the model of fixture pin and part hole tolerance robust design formulti-station assembly processes is explored, which taking into account assemblyyield. The minimum manufacturing cost of fixture pin and part hole is taken asobjective, and assembly yield as constraint. The assembly yield robustness isevaluated by using extreme method and the probability method comprehensively.Afterwards, the model of tolerance robust design in multi-station assembly processesis established. A real case in automotive body floor assembly is given as an example,tolerance robust design for pin and part hole is carried out based on assembly yield.The tolerance robust design results show that assembly cost increase slightly whereas robustness of tolerance design is improved when robust constraint isinvestigated.