Influence of Die Geometry on the Joint Interlock of Aluminum Sheets Thickness by Using Self-Piercing Rivet

This study investigates how die geometry affects joint interlock in aluminum sheets of variable thickness joined by self-piercing riveting (SPR). Lap shear and T-peel tests were conducted to evaluate the effects of die configurations and sheet thickness on joint quality. Joint interlock, rivet head height, and minimum remaining material thickness were measured experimentally under a constant riveting load of 17 kN. Three sets of similar sheet combinations (0.9+0.9 mm, 0.7+0.7 mm, and 0.5+0.5 mm) and different thickness distributions (e.g., 0.5+0.7 mm, 0.5+0.9 mm, and 0.9+0.7 mm) were tested using twelve different die configurations. A finite element model was established to forecast the flow of material in rivets, and a neural network approach was implemented to analyze the combined experimental and simulated results. The findings show that joint interlock increased with sheet thickness, from 0.691 mm for (0.5+0.5 mm) to 1.2385 mm for (0.5+0.9 mm). Rivet head height decreased from 0.2239 mm to 0.1301 mm with thicker sheets, while the minimum remaining material thickness increased, reaching 0.2614 mm in the (0.9+0.7 mm) configuration compared to only 0.021 mm in (0.5+0.5 mm). Higher interlock and thicker lower sheets improved load-bearing capacity in lap shear and T-peel tests, with the (0.9+0.9 mm) sheets showing the best performance. Joint success was strongly linked to the minimum remaining material thickness. Neural network analysis further demonstrated the potential to generate optimal die designs, reducing both cost and time.