| As the application of high-strength steel in automotive processing and manufacturing increases,the processing method for high-strength steel has become a hot research topic in the field of material processing and manufacturing.Due to the limitations of processing high-strength steel materials in low and medium temperature conditions,the forming effect is relatively poor.In addition,the size of the crimping force is also one of the key factors affecting the forming effect of high strength steel.In this paper,the effect of variable crimping force on the forming effect of high strength steel under high temperature stamping is studied.In this paper,two kinds of high-strength steel plates,Ductibor450 and Usibor1500 P,are used as the main objects in this test(coded as 20200401115GX).The failure evaluation of the forming limit diagram is also presented.Secondly,the thermomechanical properties of the two materials are obtained by high temperature tensile tests and the corresponding stress-strain curves are plotted.The stress-strain curves obtained from the tests are imported into Dynaform software for numerical simulation.The molding effects of the two materials under different combinations of process parameters are obtained and evaluated.In this paper,the effect of the combination of forming temperature,crimping force,friction coefficient and tensile rate on the forming effect of high-strength steel square box-shaped parts is investigated.The minimum thinning rate of 18.783% and the minimum thickening rate of 15.223% were obtained for Ductibor450 at a forming temperature of 700°C,a constant crimping force of15 KN,a friction coefficient of 0.15,and a stamping rate of 500mm/s;and for Usibor1500 P at a forming temperature of 700°C,a constant crimping force of 20 KN,a friction coefficient of 0.15,and a stamping rate of 500mm/s.The minimum thinning rate was18.674% and the minimum thickening rate was 15.367% under the process parameters of stamping rate of 500 mm/s.Subsequently,the response surface analysis was used to find the parameters that had the greatest influence on the molding effect were the molding temperature and the crimping force.The optimal combination of process parameters was found to be 734.1°C for forming temperature,10 KN for crimping force,0.1677 for friction coefficient,and1085.95mm/s for stamping speed by NSGA-II genetic algorithm.9.864%.The error with the optimized results is within a reasonable range,which verifies the goodness of the model fit.On this basis,the press forming performance of square box parts under variable crimp force was further investigated,and firstly,the effect of forming high-strength steel square box parts with linear loading method of variable crimp force was evaluated,and it was found that the maximum thinning rate and the maximum thickening rate obtained by the loading method of first increasing and then decreasing were 15.76% and 9.51%,respectively.It is the best effect among several loading methods.The BP neural network was then used to establish the prediction model,and after verifying the reliability of the prediction model,a set of suitable crimp force values was selected and Fourier fitting was performed to obtain a definite curve-type variable crimp force curve.The results were obtained by inputting the crimp force curves into Dynaform for simulation,which showed that the maximum thinning rate of the square box part was only 14.41%,while the maximum thickening rate reached 9.68%. |
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