Study On Variable Blank Holder Force And Controllable Drawbead In Forming For Box Parts Of Tailor-welded Blanks

With the increasingly serious problems of environment and energy,the development of low-carbon economy has become a major trend.It is particularly important to reduce vehicle weight and carbon emissions for motor industries.The use of TWBs can reduce the weight and increase safety,however,due to the different formability between TWBs and ordinary steel,the traditional forming process is no longer applicable.Many researchers at home and abroad propose to improve the formability of TWBs by setting the initial position of weld line and the thickness ratio of sheet metal reasonably,adopting variable blank holder force,hot forming and hydraulic forming.In this paper,putting forward variable blank holder force and controllable drawbead technology with the change of stroke to control the forming quality of TWBs.The main contents are as follows:1.Optimize the forming quality of box parts of TWBs based on step-type blank holder and variable blank holder force.Firstly,the influence rules of blank holding force loading form on the welding line movement and thinning rate are analyzed,and various schemes are designed for numerical simulation.From the comparison and analysis of the simulation results,it can be concluded that the blank holding force can effectively control the material flow to control weld line movement and thinning rate.It is assumed that F_b is the blank holder force on the thin part,F_h is the blank holder force on the thick part.When F_b>F_h,the pressure on the flange area of the thin part was relatively large,it can control the material flow on the thin part into the die,and the pressure on the thick part is small,which can reduce the movement of the weld from the thin to the thick.Then,considering the welding line movement and thinning rate comprehensively,it is concluded that the forming result is better when the blank holder force is F_b=100~25KN,F_h=25KN.Secondly,on the basis of the better blank holding force obtained above,the forming quality of the box deep drawing is further improved.Set the blank holding force on the thick part to be constant at 25KN,divide the punching stroke on the thin part into 5 stages,and draw a variable blank holding force loading curve.The relevant parameters of the curve are used as input variables,and the index of evaluating the forming quality of the box is used as the output variable.The training samples are obtained by simulation,and a BP neural network prediction model between the variable blank holding force and the forming quality that varies with the stroke is established.Then the genetic algorithm was used to find the optimal solution,and the variable blank holding force loading curve was obtained under the optimal forming condition of the welded blank box,and the numerical simulation was performed to verify it.Finally,comparison with the simulation results of constant blank holding force forming shows that the optimized variable blank holding force can improve the forming quality.2.Research on improving the forming quality of TWBs box parts by controllable drawbead technology.Fristly,using the finite element simulation to study the influence of the structural parameters of the drawbead on the welding line movement of the TWBs drawing,the analysis results show that the height of the drawbead has the greatest effect.At the same time,it is easier to control during the forming process and more convenient to adjust the resistance.Therefore,the research on the height-controllable drawbead is selected.By adjusingt the height in real time to change the drawing resistance in the process,so as to improve the forming performance of TWBs.The finite element model of the deep drawing of TWBs box by controllable drawbead is established,the moving track of drawbead with height change over stroke is designed,the BP neural network prediction model between the moving track and the forming quality of TWBs is established,and then using the genetic algorithm to find the optimal moving track,then the best moving trace is put into Dynaform for verification.Compare the simulation results after optimization with those of fixed height drawbead,and the results show that using of controllable drawbead can do better.3.The application of variable blank holding force and controllable drawbead in the numerical simulation of deep drawing forming of actual automobile panel.The variable blank holder force and the controllable drawbead technology proposed in this paper are applied to the stamping of ato door inner panel made of TWBs.Through the analysis of the simulation results,it is concluded that the optimized blank holder force and the controllable drawbead can improve the forming performance of the door inner panel,which will not occur wrinkling and fracture,and the movement of welding line is the minimum.