Study On The Sringback Control In TWBs’ Bending Based On Drawbead Technology

The tailor welded blanks (TWBs) become more and more important in the automobile industry, for their advantages such as low manufacturing cost, vehicle weight reduction, environmental protection and safety improvement, etc. Despite of these advantages of TWBs, there are also some technical problems in welding and punching, and there are great differences of stress and strain in the each side of blank for the difference in the thickness between the two side of TWBs which makes the formability more complex compared with the base blank, such as cracking, wrinkling, weld line movement and springback. Researchers have done a great deal of works on cracking, wrinkling and weld-line movement, but little work has been done on springback, and only a few references are available. Along with the more and more strict demand on dimensional precision, especially the 2 mm engineering, the research on springback of TWBs is getting more and more important.In this thesis, the control of longitudinal-welded TWBs’ springback was researched. And the principal contents studies are presented as follows:1. Theoretical analysis. The principle of bending springback of blank and the cause of weld line movement were analyzed theoretically. And the formula of controlling weld line movement of TWBs was derived. It also analyzed the impact of the extent of plastic deformation and uniformity of deformation on the springback.2. The modeling of similar U-shaped of TWBs and springback characteristic analysis. The numerical model for TWBs considering welded-line and geometrical central coincidence was created; and the impact of different types of blank holder on the TWBs’ forming properties was studied. The influence of blank holding force (BHF), sidewall included angle, die profile radius and mold gap on springback of TWBs was researched. Results showed that BHF, sidewall included angle, die profile radius and mold gap had important influence on springback. It’s possible that the capability of plastic deformation was improved to attain the purposes of springback control by adjusting BHF, die profile radius and mold gap appropriately.3. Introduce drawbead technology into TWBs bending springback control. First, the difference of TWB’s forming properties and springback was analyzed before and after adding the drawbead. Then, the many shape parameters of drawbeads on the impact of bending springback of TWBs were studied. Through study it can be found that the drawbead height of the influencing factors to the bending springback is the largest, drawbead fillet and groove fillet have a certain effect. At the same time, the impact of drawbead on the springback was also studied when the BHF was different, and it can be found that the greater of the BHF, the evener of TWBs’ forming, the smaller of the springback. Finally, it also studied the distribution of drawbeads to control the springback of TWBs’ bending. It can be found that the springback are different when the drawbeads in different locations of TWBs, and springback can be effectively controlled through setting drawbead position reasonably.4. Application of mathematical formula of weld line movement control. First the validity of the formula was verified, and it can be found that there were some connections between springback and welded-line movement of TWBs. The springback could be controlled, with weld line movement controlled. Finally, BHF and drawbead resistance had been optimized by the integration this formula used and the orthogonal test, which made the springback fall the acceptable scope.