A combined approach to improve and assess the formability of tailor welded blanks

Tailor Welded Blanks (TWBs) are sheet metal blanks where different sheets of material are welded together prior to the forming process. Creating the blank in this fashion allows the automobile designer to “tailor” the location in the blank where specific material properties are desired. This type of blank, in particular those produced from Aluminum, provide an excellent opportunity for automakers to progress towards meeting CAFE requirements as they decrease vehicle weight as well as improve crashworthiness and reduce manufacturing costs, thus negating concerns created by Aluminum for steel substitutions. However, when conventional forming methods are used to fabricate TWBs, formability concerns, such as tearing and wrinkling, occur. One cause of tearing failure in TWBs is changes in the material properties in the weld and Heat Affected Zone. In particular, the potential strain in the material near the weld line is significantly reduced in a TWB. Another tearing formability concern is created if one material in the TWB is weaker than the other, for instance a thinner and thicker TWB material combination. In this case, the thinner material will take a majority of the deformation in the process leading to weld line movement and premature tearing failure in the part.; In this dissertation, research is presented that both improves and assesses the formability of TWBs. First, an advanced sheet metal forming process, which utilizes segmented dies with local adaptive controllers, is outlined (Cao and Kinsey 1999). This innovation was shown through both numerical simulations and physical experiments to significantly improve the formability of a test panel by reducing the strain in the weaker material. Then, an analytical model is presented to assess the formability of TWBs, including the expected weld line movement and forming height for a given strain state. The validity of the model was verified through numerical simulations. This analytical tool would be instrumental in assisting design engineers analyze TWB applications prior to costly and time consuming numerical simulations and physical implementation. The research work presented here will allow automobile companies to utilize TWBs to their fullest potential thus creating numerous environmental and economical benefits.