Researches On Some Key Techniques For CAE-Oriented Die-face Design System Of Automobile Panels

During the automobile design and manufacture cycle, the design level ofpanel die is the core element to restrict the rate and quality of productdevelopment. In fact, it has become the main bottleneck to further shorten therenewal cycle and improve the quality. The application of CAD technology forauto panel at home is still on the level that the alternant plotting and modeling isdone on the popular CAD software system with the designer's experience, whichmakes CAD software become a drawing board barely. At the same time, trial andrepair is repeated much times because the design results are lack of evaluation indesign process. The job is inefficiency, costly and time consuming.Along with the development and application of CAE technique, the CAEanalysis is more and more widely used to test the quality of die-face design. Thedesigns of die addendum need amending frequently when they fail to pass theexamination of CAE analysis. Usually, we must send the model back to CADsystem to modify it, and then transfer the new design to do CAE analysis again.Some complex and time-consuming processes must be operated once more, suchas the finite element mesh generation, flanging, holes filling etc. So theCAE-oriented die-face design system for automobile panels is needed.Supported by the National Outstanding Youth Foundation (No. 10125208),the Key Project of the National Natural Science Foundation of China (No.19832020) and the Project 985-Automotive Engineering of Jilin University, Howto construct the "CAE-oriented die-face design system for automobile panels" isa few keys technique that investigative core contents. In this paper, we make thethorough research on the system.As a consequence of diverse precision adopted by different data format,approximation changes with the conversion in different data format will bringapertures or overlaps among the curve surface which generated by auto bodyCAD modeling or mesh generation, a method based on finite element mesh forCAD surface data repair is presented in this paper. To any degree, the approachalso can repair some defects of the mesh on curve surface. The amelioration canexpand the range of the acceptable finite element mesh and is helpful to reducethe difficulty in high quality mesh generation of auto body CAD.An adaptive method to transform finite element mesh on die face ofautomobile panels is implemented in this paper. The initial mesh may beconstructed of entirely triangular elements or may consist of a mixture oftriangular and quadrilateral elements. It ameliorates an approach of triangulartransformation on plane. The validity is conformed by the results of the complexindustry-forming product. In order to approximate the original curve surface,bring forward the rule and the way for optimization to deal with the includedangle among elements is the key point of the algorithm.In contrast with the process of CAD-driving die-face design, there are somespecial steps for the CAE-driving die-face design. The most obvious difference isthat the auto-body part contour needs smoothing earlier than the design ofaddendum surfaces does. It is helpful to improve the design quality of addendumsurface. In spite of extensive researches on smoothing technique, there is stilldearth of the published solutions about smoothing the part contour withadditional surface. The additional surfaces, which are created by the contour ofautomobile panel and the smoothing curve, have the C 1 continuity with the partsurfaces at the boundary. The smoothing curve is used to smooth the part contourand created by the algorithm presented in the paper. The aim of smoothing thepart contour is to close the open regions on the original part, to change thedifferent drawing depth into an even one, to decrease the quantity and the depthof the concave regions on part contour. This paper attempts to analyze thedifficulties and provide practical solutions. Main results include the algorithm tocalculate the segments needing to be smoothed on boundary, the strategy tocreate the smoothing curve and the procedure of surface generation. The relevantfunction modules for parametric design are developed.Parametric modeling method can reduce the time consume of design andmodification greatly. It can change the model design by modifying the sizeparameter. the repeat jobs of engineers can be reduced and the design efficiencycan be increased enormously by means of introducing the parametric designthinking into the modeling process of addendum and binder surface。Therefore,comparing with the traditional CAD system adopting the method of manualentirely for creating the addendum surface and the binder surface, the parametricdesign of the addendum surface and the binder surface has become the trend forits high efficiency and convenience of modification. The design result of theaddendum surface and the binder surface has great effects on the forming qualityof automotive panel. The method of CAE-oriented design for drawing die hasbeen the development direction for its high efficiency and convenientmodification. The paper presents a method to generate the addendum surface andthe binder surface by section curves after smoothed the stamping part withadditional surface. The feasibility of the technique is proved by the numericalsimulation which creates the addendum surface and the binder surface of thefront fender successfully.The spread method of product part by inverse FEM neglected the blank areaexcept for the part itself. The blank mesh of product part needs to be extended tomake sure of the right size of the final blank. A method for extending the blankboundary based on the mesh is presented. The algorithm execute the procedure asfollows: Firstly, fitting all discrete data points on the boundary into NURBScurves, and extending these curves to get the new blank boundary;secondly,generating the surface by skinning all the boundary curves;finally, partitioningthe surface into finite element mesh. The algorithm can provide the intact size ofa blank. At the same time, an optimized algorithm for complex boundary isprovided to reduce the complexity of industry production.