Research On Forming And Spring Back Contral Of Front Rail With High-strength Laser Tailor Welded Blanks

High strength laser tailor-welded blankets(TWB) with itsadvantages in weight lossand energy saving and emission reduction, used in automobile manufacturing, will get agreat economic and social environmental benefits, therefor, they’ve been graduallypopularized in domestic motor industry. In the stamping process, however, due to thedifference of forming property on two sheet metal both side ofweld joint，a series ofquality problems such as cracking，weld-line movement，uneven bigspringback areprone to occuring.The springback problemof high strengthtailor-welded sheet formingin auto longeron is especiallysignificant and complex, which has become a difficulty inthe domestic industry to promote the application of high-strength laser welded blanks.In this paper,the precisesimulation and control technology forthe springbackofTWBmultipleprocessare discussed in detail. Taking a automotive front floorlongitudinal beamas the research object,using the simulation and multi-objectiveoptimization algorithm to predictthe forming and springback and optimizeprocessparameters, thenCompensation for the die surface by combining simulation andscanning experiment, found a effective method tocontrolthe springbackin TWBformingprocess.First of all, through the preliminary analysis and optimizingthe blank shape size,addendum surface, blank holder form, drawbead layout, the problem of lacking plasticforming and weld-line movement was solved. Then,by using multi-position singleprocess simulation method, consideringthe effect of unloading analysis aftereachforming process, the complete stamping processspringbacksimulation finite elementmodelswere established,meanwhile,the springbackafter every step is fully considered.Inaddition, for the two simulation methods, witch consideringsheet metal springback afterevery step or not, have a comparison inthis paper. Studies have shown that there exsistsdifferences between the two springback prediction results, and the formerpredictedresult is more conforms to the actual measured result.The paper combined the process parameters optimization techniquesand diesurface compensation technology to control the springback problemof the longitudinalbeamwith TWB. In the process of parameters optimization,fracture and springbackobjective functions were established. Consideringblank-hold force, drawbead resistancecoefficient, the curvature radium of the matrix mouth ofthe supplement surface as optimized variables,then, through central composite design and simulation，regressionmodelreflecting the relationship between theoptimized target and variables wasestablished.Based on this condition,using multi-objective optimization technologyaccording to genetic algorithm, the optimizated target parameters of fracture andspringback were found.Then these parameters was used in finite element simulation, theresults show thatthe cracking problem has been effectively eliminated andthespringback problemhas been significantly reduced, but it’s still beyond the allowedrange. In the process of die surface compensation, the springback compensationiterativecalculationbased on dynaform in combination with the white light scanning experimentwere used, when the compensation factor is0.8, The springback deviationaftercompensationreached the allowable range. According to the negative angletest results ofmodecompensation surface, considering mainly compensating the top plane at drawingprocess,and two sides negative angle compensation were carried out in the final shapingprocess.The test results show thatthe springback has been improved, but both sides ofthe wall and flange still were beyondthe range,and white light scanning was performedto realize the measurement the springback in3-dimensions, according to the generatedspringback points cloud model anddeviation calculationcompared with designedproduct model,the shaping mould surface was carried out reversecompensation.Qualified part was got eventuallyafter trying stamping,meanwhile,thedifference between simulation and actual compensation was discussed, which providesreference and basis for the springback and control problem in the similar forming case.