Assembly Deviation Analysis Based On Part Feature And Flexible Fixture Optimization

The car body which is an important part of the vehicle is the carrier of other systems in the car.The improvement of dimensional accuracy of car body is an essential work for all car manufacturers in the new product development.Dimensional accuracy of BIW and sub assembly up to standard is the basic requirements of mass production.Aiming at the problem that assembly deviation is not take into consideration in stage of design,but designing tolerance depending on experience,so as to repeat trial and design changes in stage of prototype trial to improve assembly accuracy of car body which results in design development costs can not be reduced,the calculation method of sheet metal assembly deviation is proposed.The following is the main work and research contents of this paper:At first,in the face of complex auto body welding and assembling process,improve welding assembly variation model,using the stiffness matrix of parts and the sensitivity matrix to connect the source of assembly deviation with assembly deviation.The welding assembly deviation model extends from the welding of the two plate to the welding of multiple plates,and extends from the two plate welding to the three plate welding,so it can be applied to more complex welding assembly process.Using the assembly variation model analysis assembly variation of a car body sub assembly.Apply the influence coefficient method to the analysis,and combine finite element method and Monte-Carlo tolerance analysis method.Analysis effect of parts deviation,fixture deviation,welding tool deviation on the body assembly deviation.The influence coefficient matrix of the deviation and the deviation of the source assembly is obtained.Then the model is validated by the measured data,and it shows that the calculation model is consistant with the actual data.assembly the deviation model was validated using the measured data shows that the calculation model and the actual deviation is consistent.Then use the genetic algorithm to optimize the part tolerance and structural,so as to achieve the goal that improve body assembly accuracy with the minimum cost.Reducing the number of body trial to reduce unnecessary costs,and the development cycle of automobile is shorten.Finally,the composition,structure and design method of flexible welding fixture are introduced.A flexible welding platform is designed by using the flexible design method of combination and adjustment.Because the increasing complexity of structure and connection of flexible welding fixture parts,and fixture get counterforce from car body parts,the influence of the deformation of the fixture on the assembly deviation of the flexible sheet metal is considered.The stiffness calculation is carried out according to the location and clamping of the side plate assembly.A calculation formula of assembly deviation considering the welding fixture deformation is deduced...