基于偏差传递的二维多工位装配夹具系统公差可行稳健设计

Feasible Robust Tolerance Design for Fixture System in Two-dimensional Multi-station Assembly Processes Based on Variation Propagation

提出一种基于偏差传递的二维多工位装配夹具系统公差可行稳健设计方法。分析二维多工位装配尺寸偏差传递关系,建立由定位销和零件定位孔(槽)公差引起夹具定位偏差的偏差流状态空间模型。采用数论网格方法对定位销和零件定位孔(槽)公差进行采样,将得到的公差样本代入夹具定位偏差模型,求得夹具定位偏差样本空间,将夹具定位偏差作为状态空间模型的输入偏差,提出基于状态空间模型的二维多工位装配成功率计算方法。继而应用Taguchi正交试验直观分析方法,分析得到影响装配成功率的主要因素即夹具系统定位销副关键公差,运用回归正交组合设计拟合得到二维多工位装配成功率与夹具系统定位销副关键公差的响应面模型。以定位销、零件定位孔(槽)制造成本所构成的装配成本最小化为目标,二维多工位装配成功率为约束,建立二维多工位装配夹具系统定位销和零件定位孔(槽)公差可行稳健设计模型。以汽车车身地板二维三工位装配为例,建立其公差可行稳健设计模型并对该模型进行计算与分析,结果表明在装配成本增幅较小的情况下,采用稳健约束后可显著提高公差设计的可行稳健性。该方法为二维多工位装配夹具系统公差稳健设计提供了一种新途径。

Based on variation propagation,a method of feasible robust design tolerance is developed for fixture system in two-dimensional multi-station assembly processes.The relationship of dimensional variation propagation for two-dimensional multi-station assembly processes is analyzed,and the state space model of variations stream is built,in which the fixture locating variations are caused by the tolerances of pin and part hole/slot.By means of number-theoretical net method,the tolerances sample of pin and part hole/slot is presented which is used to substitute into the variations model of fixture locating to obtain the sample space of fixture locating variations.Based on state space model,taking fixture locating variations for input vectors,an evaluation method of assembly yield is proposed for two-dimensional multi-station assembly processes.Furthermore,Taguchi orthogonal experiment method is adopted to analyze the main factors that influence the assembly yield and the design of regression-orthogonal combination is applied to fit the response surface model of assembly yield.With the objective to satisfy the lowest manufacturing cost of pin and part hole/slot,taking the assembly yield for constraint,the model of feasible robust tolerance design for fixture system in two-dimensional multi-station assembly processes is established.Automotive body floor assembly process with three-station is given as an example to build the model which is calculated and analyzed.The results show that the robustness of tolerance design is improved significantly with robust constraint while assembly cost increases slightly.It provides a new way of feasible robust tolerance design for fixture system in two-dimensional multi-station assembly processes.