Relative Effect of Material and Geometric Parameters on the Forming Behaviour of Tailor Welded Blanks
Tailor Welded Blanks (TWB) are blanks in which two or more sheets of similar or dissimilar materials, thicknesses, coatings etc. are welded together to form a single sheet before forming. It is known that the forming behavior of TWBs is affected synergistically by thickness ratio, strength ratio, weld conditions such as weld properties, weld orientation, weld location etc. In this work, the relative effect of different parameters on the forming behavior of TWB is dealt with using FE simulation. Some of the influencing factors considered are thickness ratio, yield strength ratio, strain hardening exponent ratio of the blanks welded, weld yield strength and weld strain hardening exponent. The percentage effect of these individual parameters and some interaction factors on the forming behavior of TWB will be obtained separately for longitudinal weld orientation and transverse weld orientation. The response variable is quantified by forming limit strains of TWB. The limit strains are predicted by a novel thickness gradient based necking criterion in the simulation. Taguchi's design of experiments and Analysis of Variance (ANOVA) methodology are followed to obtain the percentage contribution of factors considered. Tensile test and Limit Dome Height (LDH) test are simulated by a commercial FE code, PAM STAMP and forming limit strains are predicted. It is observed from the analyses that, yield strength ratio has more percentage contribution on the forming limit strains in the case of TWB with transverse weld orientation and thickness ratio dominates in TWB with longitudinal weld orientation. Both tensile test and LDH test simulations show similar kind of behavior in terms of relative percentage contribution of parameters. Among the weld parameters, in TWB with transverse weld orientation strain hardening exponent of weld shows more effect than yield strength of weld. In the case of TWB with longitudinal weld orientation, both yield strength of weld and strain hardening exponent of weld show less effect. The statistical models developed in this work predict the forming limit major strains accurately both in transverse and longitudinal weld orientation TWBs, within the range of factors considered in this work.
R. Ganesh NARAYANAN, K. NARASIMHAN
Tailor Welded Blanks, Limit Strains, Taguchi Technique, Statistical Models.