Effect of Die Design and Sheet Placement on Self-Piercing Rivet of Automotive Steels and Comparison with Resistance Spot and Friction Stir Spot Welding

The present work addresses the impact of die design (flat die or pip die) and sheet placement on the self-piercing riveting (SPR) of automotive grade CR210 and CR340 galvanized steel sheets. Actual rivet head height, interlock distance, bottom sheet thickness, maximum riveting force, lap-shear fracture load, and fracture modes are monitored. Later, the lap-shear tensile performance of SPR joints is compared with joints made using resistance spot welding (RSW) and friction stir spot welding (FSSW). Both die design and sheet placement impact the SPR outputs significantly. Flat die results in improved rivet penetration irrespective of sheet placement. Maximum riveting force in the case of pip die is higher irrespective of sheet placement. Pip die results in better interlocking than the flat die, irrespective of sheet placement. The effect of die design on lap-shear fracture load and fracture mode is marginal for the sheet combination. However, optimization of sheet placement is critical for SPR. Locating the CR210 (weaker, thinner) sheet at the top would be beneficial if riveting force and interlock distance are referred to. However, if the bottom sheet thickness and tensile-shear fracture load are considered, placing the CR340 (stronger, thicker) sheet on top would be acceptable. Sheet placement has a marginal influence on RSW joint formation and tensile-shear performance. Sheet placement is also critical for FSSW in terms of joint formation. The lap-shear fracture load of RSW joints was higher than that of SPR and FSSW joints. However, SPR joints exhibited significantly higher displacement at fracture than RSW and FSSW.