Plastic bending of adhesive-bonded sheet metals

Adhesive bonding is becoming one of the popular joining techniques in sheet metal industries, since it has some advantages over other techniques such as welding and diffusion bonding, e.g., any dissimilar metals are easily adhesive-bonded together, and the adhesive layer existing between the two sheet metals can play the role of vibration damping. Usually, press-formed sheet metal elements are jointed together at the final stage of assembly. However, if it could be possible to press-form adhesive-bonded flat sheet metals into the final products, this would be an excellent technique from the viewpoint of high productivity. In the present work, the plastic bending of adhesive-bonded sheet metals was investigated by performing V-bending experiments. A serious problem encountered in the V-bending was bending-induced large transverse shear deformation of the adhesive layer, which leads to geometrical imperfection of the bent sheets (so-called ‘ gull-wing’ bend), and in some extreme cases, it causes the delamination of the sheet. It was found both from experimental observations and from elasto-plastic stress analysis that the large shear deformation progresses rapidly only at the final stage of V-bending. Consequently, the air-bending operation for adhesive-bonded sheet metals is recommended for suppressing the shear deformation of the adhesive layer to within an acceptable limit.