Study On Optimal Tolerance Allocation Of Auto-Body Based On Clamping Deformation

Auto-body assembly deviation is one of the main factors influencing the quality of automobile. Due to the flexibility of auto-body sheet metal, in welding process the part clamping deformation was easily caused by rigid fixture, affecting the auto-body tolerance allocation and the manufacture quality of automobile. Traditional assembling deviation mainly based on the assumption of the rigid body assembly deviation theory, it was difficult to meet the tolerance allocation optimization requirements of flexible part like auto-body. Therefore, with the left-side of a certain electric vehicle as the object, around the auto-body tolerance allocation optimization, the following several aspects of research work has been done:Firstly, the model of assembly tolerance allocation optimization was studied in this paper. Consider of the manufacturing costs and quality requirements, the auto-body tolerance allocation optimization model was built as minimizing the manufacturing costs, the assembly tolerance-chain and function requirement were given as the restriction conditions. The arithmetic simple, quick convergent speed and better robustness particle swarm algorithm was used to optimize the mathematical model. In view of the contradictory relation between quality and costs, the quality cost theory based on Genichi Taguchi was put forward to evaluate optimization results.Then, In view of the problems of auto-body clamping deformation was easily caused by rigid fixture in the welding process, clamping deformation finite element analysis was presented for the auto-body side, then combined with CAE analysis result, the clamping deformation factor was added to the auto-body tolerance allocation optimization. Finite element model was established in Hypermesh, the clamping deformation produced in welding process was described by displacement constraints, the solve options were set and then imported to NASTRAIN to solve the optimization results. Results show that the clamping deformation has a great effect on assembly deviation, cannot be ignored in tolerance allocation optimization.Finally, Taken left-side of a certain electric vehicle assembly as an example, the auto-body was optimal tolerance allocation based on clamping deformation. Assembly variation analysis was made to the model of an auto-body left side based on 3D tolerance analysis software 3DCS. Combined with CAE analysis result, the clamping deformation factor was added to the assembly tolerance constraints to optimal tolerance allocation of the auto-body side, which was evaluated by the quality cost theory. The results show that after optimization the assembly quality is greatly improved and the total loss reduce down by 7.16%, verifying the rationality of this tolerance optimal allocation method.