Preliminary experimental investigation on hemming of curved edge parts by means of incremental sheet forming

Abstract

In the context of versatile and environmentally friendly joining techniques, joining by forming has proven to be a very useful tool. From this category, hemming is widely used for sheet metal parts like car body panels. Still, hemming of concave and convex geometries represents a challenge for conventional hemming as well as for the more flexible roller hemming. Especially for smaller radii and greater flange lengths, these methods can reach their limits. In the present work, incremental sheet forming (ISF), a flexible forming process without dedicated tools and high formability, is utilized to implement the hemming process. Due to its local and incremental deformation characteristics, a favorable material flow in the flange area is expected, which might prevent cracking and wrinkling. Therefore, the material flow in ISF-hemming will be investigated. Closed circular specimens with radii of 50 mm and 200 mm and varying flange lengths are analyzed. Conclusions about the material flow are drawn by measuring the change in sheet thickness and elongation of the flange. The results show that, for stretch hemming, considerable thinning and elongation of the flange takes place and no cracking is detected. For shrink hemming, significant thickening of the flange and elongation in radial direction is observed, which suppresses wrinkling.