Research On Key Techniques Of Short Cycle Development Of Automobile Stamping Die

Automobile stamping die is one of the most important equipment in automobile production.The die development cycle is about two-thirds of the car development cycle,and the cost of the die development is directly affected by die development time.Currently,the biggest problem of automobile stamping die is that the development cycle of die is long and the cost is high.Therefore,it is very important to carry out researches on the short cycle development of automobile stamping die.There are many factors that affect the development of stamping dies: die design technology,manufacturing processing technology,tryout machine,production management,workers operating and so on.Several key techniques of shortening the development cycle of stamping die,such as numerical simulation technology,springback control strategy and surface compensation strategy,were investigated in this thesis.According to the state of stamping die development in the enterprise,three aspects which cause long delays to the die development time were found in the investigation in the die manufacturing enterprise: to solve the problem of drawing defects such as cracking and wrinkling cost a long time,to control and improve the size precision of the stamping parts need repeated die tryout,to improve the die surface grind rate spend plenty of working time.In order to achieve the purpose of shortening the die development cycle,the main works of this thesis are as follows:(1)Aiming at the problem that the forming limit diagram cannot be used to quantitatively evaluate the formability of parts,the cracking trend function,the wrinkle trend function and the safety region ratio function were put forward to evaluate the formability of numerical simulation results.Finally,the program written by using Matlab software was used to calculate the proposed functions.(2)In view of the defects such as wrinkling and cracking on the stamping part,the drawing process optimization based on the formability evaluation function and robustness design were put forward to improve the precision and accuracy of numerical simulation.The maximum thinning rate and the proposed fracture trend function,the wrinkle trend function and the safety region ratio were used as the optimization objective in the center composite experiment design,and then the multi-objective optimization method was used to obtain the optimal combination of process parameters.In addition,in order to improve the prediction accuracy of product reliability,the unstable factors and noise factors were considered in the numerical simulation,and the influence of the actual situation fluctuation on the numerical simulation was considered.The effect of the yield strength of the material,the anisotropy index,the friction coefficient and the blank holder force,the thickness of the sheet,the size of the sheet and the position of the sheet were considered in the drawing of the dash board.Process robustness analysis was carried out on the dash board,so as to improve the accuracy and reliability of numerical simulation and to provide the constructive basis for the actual test.It is shown that the proposed method can effectively avoid the cracking and wrinkling of the parts by the production test of the dash board.(3)Aiming at the springback problem in the die development,the multiple-iteration springback compensation method based on the entire process stamping was proposed.Taking a high strength steel automobile part as an example,the concrete implementation process of this method was introduced,and the corresponding experiment was carried out to verify the feasibility of the proposed method.In order to establish an accurate numerical simulation model,the tensile test,the microstructure analysis and the fracture analysis of the base material and tailor welded blanks of high strength steel were carried out.Then,the finite element model of the entire forming processes for the high strength tailor welded blanks was established to calculate the forming process and springback.The drawing die was compensated by using the multiple-iteration springback compensation.The springback part satisfies the allowable tolerance when the iteration springback compensation and entire forming simulation were implemented for the third time.Finally,the compensation results were used to manufacture tools and die tryout.Inspection results show that 24 of the 32 measuring points can satisfy geometrical tolerances,and the maximum deviation of the unqualified test points was 1.16 mm.Experimental results demonstrate that the proposed method is more accurate than traditional empirical method and simple springback compensation.(4)Due to inappropriate tool design or inaccurate CAE analysis,the unqualified formed part which cannot meet the requirements of shape tolerance is inevitable in die tryout.Aiming at the unqualified tryout die,a new method based on three-dimensional(3D)scanning and reverse engineering to compensate for the springback of the formed part was introduced.Taking the rear reinforce plate as an example,a 3D scanner was utilized to scan the formed part.The modeling of the part was built by the reverse software Geomagic,and it was utilized to compare with the design model.The result is shown that the maximum deviations and minimum deviation are +9.51 mm and-4.33 mm,respectively.The accuracy of a 3D scanner is higher than the special fixture.Finally,the die surface was compensated by using the proposed method,and the die tryout was carried out.The inspection results show that 15 of 18 measuring points can satisfy the geometrical tolerances,thus indicating that the qualified rate of this product is 83.33% in the first springback compensation by 3D scanning method.The experimental results show that this method can effectively control the springback of parts and avoid repeated trial.(5)Aiming at the problem that the die surface grind rate is low and the improvement of die surface grind rate is very time-consuming,a surface compensation method which consider the deformation of the dies and the thickness variation of part was put forward to compensate the die surface.The stamping process was analyzed firstly,and then the final load of the forming analysis was mapped to the die for static analysis.Through static analysis of the dash board dies,it is concluded that the hydraulic press platform has a great influence on the die deformation.The maximum displacement of the punch is 1.106 mm with the consideration of the deformation of the hydraulic press platform;the maximum displacement of the punch is 0.278 mm without consideration of the press platform.It is indicating that the results are more accurate when considering the hydraulic press platform.Finally,the punch surface was kept invariant,and the superimposed deformation between punch and die was used to compensate the die surface,and then superimpose the thickness variation of part to obtain the compensated surface for die.The results show that this method can effectively improve die surface grind rate in the first time of die tryout,and shorten the tryout time in the die surface lapping.