The Research On Springback Of Auto-body Panel Based On RE

Crack and wrinkle and springback are three kinds basic defects during forming,there is no appropriate method to eliminate springback for shallow forming parts especial like auto-body outer panel so far. Springback causes the surface and sideline of forming part deformation. Mending forming technics can not eliminate springback completely notwithstanding it can shrink springback of forming part in certain degree,mould compensation can eliminate springback in theory however how to get the accurate compensation surface is the choke point for its application and at present mould compensation surface is acquired by CAE iterative calculation, however the compensation surface acquired by CAE iterative calculation is not right because springback of forming part has not been calculated accurately by springback simulation calculation so far, therefore there is difference between actual forming part and its design model. The paper puts forth the method to study springback based on RE,this article main work is as follows:1.3-D complex forming part's springback evaluationFirstly the actual forming part's surface is reconstructed by RE, then the reconstructed surface is imported into CAD model that design model is in, the relative position of two models is kept basic alignment through the manual regulation, then two aligned models are imported into CAE software to carry on the grid division, and mapping relationship of elements and nodes between the CAD model and reconstructed model is acquired by forcible deformation simulation and the model's geometry center coordinate value is calculated and corresponding element and node is found according to geometry center coordinate value and the models are aligned by coordinate transformation, then the best revolving position is acquired by GA, the nodes' normal deviation values are calculated and they are treated as the springback value of the actual forming parts. For the better expressing springback distribution, the final result will be expressed through the cloud figure on the model. On the one hand the method can instruct the mould's mend, on the other hand it can be used for calculating the springback simulation error.2. The establishment of simulation error compensation model for forming part's springback and the second compensation of mouldThe mould design compensation may fundamentally eliminate the springback, however it is difficult to acquire accurate compensation surface due to springback simulation error. So the paper puts forth the idea to deal with the problem by establishing springback simulation error compensation model and the second compensation of mould is realized based on the model. The concrete method is: firstly numerical model of the actual forming part is reconstructed by RE, and then it is compared with the springback simulation result through the method of 3-D complex forming part's springback evaluation. Because this comparison is carried on between the actual forming part and the springback simulation result, therefore the normal deviation of the nodes can be regarded as the springback simulation error. Considering springback does not change the surface's complex degree, so the surface's deformation caused by springback is called as small deformation, meanwhile the paper puts forward the hypothesis that the small deformation does not change the springback simulation error. The simulation error compensation model can be established through reverse normal deviation of corresponding nodes of design model, and the second mould's compensation is realized by CAE iterative calculation based on the error compensation model and the new surface of mould can be acquired, the forming experiment shows that the method can enhance forming precision greatly for considering springback simulation error.3. The calculation of trimming line based on the method of FEM grid mappingAscertaining trimming line is the important job in working out forming process and it is difficult for the flanging part, the traditional graphical solution and analytical method of mathematics have their respective defects. In the thesis, flanging process is simulated by FEM and the contour line is scattered into points and they are projected on the elements, the coordinate values before flanging are acquired according to the elements and nodes mapping relationship established by simulation and trimming line is reconstructed based on the new coordinate value. The method can keep high calculation accuracy for trimming line because FEM can accurately calculate forming of the forming part.4. The calculation of actual trimming line after springback based on RETrimming is the last process for some forming part and generally the design trimming line is the contour line of forming parts, the forming springback and trimming springback can make the trimming line deformation, therefore it is eager to acquire the deformation of trimming line so that it can be controlled by adjusting the position of trimming tool in advance. The paper puts forth that the numerical model of actual forming part is reconstructed by RE and the surface is regarded as actual trimmed surface, then grids and nodes mapping relationship between design model and actual forming part is acquired through compelling deformation simulation, and the design trimming line is dispersed into points according to a certain precision and the projective points and the coordinate values of the intersection points of projective line on the grids formed by discrete points are calculated along trimming direction, the new coordinate values of projective points and intersection points of projective line after deformation are calculated based on the mapping relationship of grids and nodes, the deformed trimming line can be acquired through fitting the points into curve.5. The estimation of forming part's sidelineThe estimation of forming part's sideline is significant in weld and assembly process, the paper puts forth two kinds of method to realize quantitative analysis for the deformed sideline, one is using line contour error to estimate deformed sideline combined with GA and taking the value of line contour error as target to check whether it is in the range of precision; The other is comparing curvature and torsion of design model with curvature and torsion of deformed model to check the sideline's precision. The first method estimates sideline on the whole and the second method estimates sideline on the part.