CNC Incremental Stretch-Expanding of Welded Blanks : 1st Report, Conical Stretch-Expanding of Welded Blanks with The Same Sheet Thickness and Grade

Abstract

The process of CNC incremental forming in which a blank is formed to fit on a tool-envelope surface made by relative motion of a tool around the blank, has the advantage of not only adaptability to small-lot production of thin shell parts but also improvement of forming limit due to the effect of preventing the plastic localization. Although many cases of the effect of preventing the plastic localization on the process have been reported for one-piece blanks, the effect has not been illuminated previously for welded blanks, such as Tailored blanks. Here we report the possibility of CNC incremental stretch expanding of welded blanks so as to clarify the effect. Welded steel sheets with the same sheet thickness and grade were stretch expanded to conical shells with various half-apex angles, α, and the deformation behavior was examined experimentally. It was found that, when α is larger than abouth 35°, conical shells can be formed from the welded blanks by means of the process with a single tool-path: the forming limit of the welded blank is similar to those of the one-piece blank. Furthermore, experimental results showed that the deformation modes of the welded blank is similar to those of the one piece blank, because the strain distributions in the weld regions as well as in the unweld regions were approximately equal to those obtained from the Sine law. These results suggested that the effect of preventing the plastic localization holds for the welded blanks.