Optimization Of Rear Floor Tolerance Allocation And Positioning Hole Layout

The assembly quality of the flexible sheet parts is very important to the production of automobiles.Controlling the assembly deviation and improving the assembly quality of the bodywork is a problem that car companies need to solve urgently.The traditional assembly deviation analysis method is based on the rigid assumption,and does not consider the influence factors such as the clamping deformation of the parts,and is not suitable for the deviation analysis of the flexible sheet parts.In order to improve the assembly quality of the body,this dissertation firstly conducts 3DCS flexible assembly deviation analysis on the rear floor,then considers the impact of clamping deformation to optimize the tolerance distribution of the rear floor,and finally optimizes the positioning hole layout of the rear floor for robustness and multi-objective optimization.The principal research contents and consequences of this dissertation are as follows:(1)The evaluation method of body assembly size was discussed,and the principal factors influencing body assembly deviation were studied,covering the deviation of sheet parts,deviation of welding tools,welding deformation caused by the deviation,deviation caused by different welding assembly structure,and the positioning theories of flexible sheet parts are studied,which lay the theoretical foundation for 3DCS flexible assembly deviation analysis and the optimization of tolerance allocation and positioning hole layout.(2)Based on the 3DCS FEA Compliant Modeler flexible module,the flexible assembly deviation analysis of the rear floor is carried out.Through the process of creating DCS model points,loading FEA data,seting boundary conditions and loads,creating the target size measurements,adding parts tolerance and completing the simulation and other process to obtain the deviation simulation results of the rear floor measuring points and their component ring contribution values.The deviation values of measuring points in the flexible assembly mode were compared with the deviation values of rigid assembly and actual assembly,the validity and accuracy of flexible assembly deviation analysis are verified,which provides a more effective and accurate analysis and verification method for tolerance allocation optimization and positioning hole layout optimization.(3)Tolerance distribution optimization based on the clamping deformation of the rear floor.Since the results of the deviation analysis of the rear floor flexible assembly has not yet reached the assembly requirements,the influence of the clamping deformation was further considered,and the clamping deformation finite element analysis was carried out then added the clamping deformation factors to the tolerance constraint conditions to establish the mathematical model of tolerance allocation optimization based on manufacturing cost and quality loss cost,then used the NSGA-? algorithm to solve the tolerance optimization model,finally,used the 3DCS flexible assembly deviation analysis method to compare and verify the optimization results.The results show that the optimization considering the clamping deformation can greatly improve the assembly quality compared with the optimization before and without considering the clamping deformation and the total cost after optimization is decreased by 12.95% compared with before optimization,the contradiction between quality and cost is resolved.(4)Based on the 6? robustness multi-objective optimization technology,optimize the layout of the rear floor positioning hole.Firstly,the response surface prediction model was established,then set the minimum deviation of the rear floor measurement point as the objective function,the coordinates of the main and auxiliary positioning holes were set as the design variables,and the range of the measuring point deviation was the constraint condition,and carry out the 6? robustness optimization design on the basis of deterministic multi-objective optimization to determine the positioning hole layout scheme which improve the body assembly quality effectively,finally,used the3 DCS flexible assembly deviation analysis method to compare and verify the optimization scheme.The consequences indicate that the robust optimization scheme can decrease the assembly deviation,enhance the assembly quality and ensure the robustness.