Joining different metallic sheets without protrusion by flat hole clinching process

The existing joining by forming technologies all have limitations in the connection of metallic sheets with large differences in thickness and mechanical properties. This paper developed a new clinching method called flat hole-clinching (FHC) that is suitable for assembling two layers of sheets with dissimilar (as well as similar) materials and thicknesses without protrusion at the joints. The method utilizes a simple punch to force the material of one plate (the upper plate) to flow into the cavity of a specially prepared hole on another plate (the lower plate), forming an interlocked structure. Al 6063 and AZ31 plates with thicknesses of 0.8 and 1.0 mm, respectively, were employed in the experiment and numerical simulation to examine the impact of tool and hole geometries, material properties, and relative thicknesses on joints. Inverted conical holes were used as the precut hole. The results confirmed that various combinations of sheets can be connected reliably by FHC, with even higher joining strengths in comparison to conventional clinching. Besides the diameter d (H) of the precut hole, hole conicity beta and punch diameter d (p) were found to have a significant influence on the strength according to the results of the response surface analysis (RSA). The suitable beta-value is about 25 degrees in this case.