Research On Accurate Surface Construction And Processing Method Of Panel Drawing Die

The contacting ratio is one of the important indicators for the evaluation of the drawing die of the automotive panel,which has an important impact on the mold development process and cycle.However,the automotive panel dies have a relatively high requirement on the contacting ratio,making the workload in grinding die is heavy and its manufacturing cycle is long.Therefore,taking the contacting ratio into consideration in the die design by making a study on the generative mechanism of the grinding surface,is of great significance to ease the workload of the fitter grinding die in the later stage,shorten the manufacturing cycle of the die and improve the die’s quality.Based on the numerical simulation of sheet metal forming,in this thesis,a virtual sheet metal which contained information of sheet metal forming results and its forming process was constructed in the entire griding area of the die.Next,the entire grid nodes of the die were adjusted to conform to the thickness distribution of the formed parts based on the virtual sheet metal,and the virtual sheet metal with the thickness value convergence was obtained through iterative calculation.Then,the original machining tool path of the die was offset based on it and the accurate surface machining tool path of the die could be directly obtained.In this paper,the drawing die accurate surface machining tool path offset method based on virtual sheet metal mesh model was studied.The major works were as follows:Firstly,considering the cavity surface of the die,the sheet metal flow area surface of the blank holder,and the coordinated area surface of the blank holder were different in functions and grinding ways in the drawing forming,the grinding area of the entire die was divided,the grinding of above three surfaces was respectively explored,and then the basic idea of optimizing the whole surface of the die based on the virtual sheet metal mesh model was further proposed.Secondly,based on the numerical simulation of sheet metal forming,a virtual sheet metal was constructed according to the thickness distribution of the formed sheet.And then,the accurate surface mesh model of the entire die was constructed based on the virtual sheet metal through grid mapping and the calculation of the shape function interpolation.Next,the constructed accurate surface mesh model was iteratively optimized to obtain the mesh model of virtual sheet metal that the sheet thickness value was converging to a certain threshold value.Then,the cutter location points were offset based on the virtual sheet metal mesh model so that the processed die clearance could not only adapt to the thickness distribution of the sheet after stamping,but also could achieve the strong pressure effect which was adjustable on the wrinkled area of the sheet.Thirdly,the accurate surface construction and machining system of automotive panel was written by using C++ language to realize the functions of the construction and optimization of virtual sheet metal,the reconstruction of accurate surface mesh,and the offsetting of machining tool path.Fourthly,taking the actual machining of a stepped box die as an example,the die machining tool path was offset by using the method proposed in this thesis,and then a comparative test on the two dies respectively processed by offset tool path and original tool path was made.By comparing the deviation between the offset tool path and the original tool path,the actual stamping coloring transfer of the original die and the new die machined by offset tool path,and the actual die clearance,it can be clearly observed that the method proposed in this thesis can effectively improve the contacting ratio of the drawing die.