###### Abstract  
Owing to its enhanced production efficiency, roller hemming has become the mainstream process for forming and joining metal sheets in the automotive industry. This study investigates the roller hemming process of a specific car door panel through a combination of experimental analysis and finite element analysis (FEA) on both straight-edge and curved-edge flat surfaces. Consequently, the mechanical properties of the door panel, including tensile strength, yield strength, modulus of elasticity, and Poisson's ratio, were estimated through tensile testing and then underwent finite element modeling. The simulation results demonstrated the varying distribution of stress during the rolling hemming process, with the highest stress concentration observed in the bending area. Additionally, creepage and growing results were acquired from both simulation and experimental data to validate the precision of the numerical model. A comparison was made between the experimental and simulation results of the external forces exerted by the roller on the panel. In both straight- and curved-edge sections, the external force during final hemming exceeded that during pre-hemming, as revealed by experimental measurements of both normal and tangential external forces, surpassing their corresponding simulated values. roller hemming; simulation; experiment; external force; creepage/growing +
Footnote †: journal: Applied sciences  
0000-0002-4100-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-0000-0000  
behind surface warp and recoil and are not independent of hemming quality. The authors also evaluated the recoil and warp after the final-hemming stage and found that the pre-hemming angle had a significant effect on the final surface warp. Additionally, [PERSON] and [PERSON] [5] investigated the hemming quality indices, including creepage, recoil, and radial spring back, which are influenced by the hemming process parameters and geometry design. Regression analysis was performed to determine the relationship between input parameters and output quality indices, providing valuable insights into the significance of the selected parameters. [PERSON] and [PERSON] [6; 7] investigated the dynamic strain hardening phenomenon and its microstructural changes in steel sheets during the hemming process. Their study demonstrated the macroscopic bending mechanism of steel sheets and the associated changes in microhardness and morphology, providing insights into the dynamic strain hardening phenomenon. [PERSON] and [PERSON] [8] developed a simulation model for the sheet metal hemming process. Based on the ASTM-E140 standard [9], they proposed a hardness-to-strain conversion formula. By comparing the simulated strain results at the hemmed sheet cross-section with the results from hardness-to-strain experiments, they investigated the material hardening behavior during the hemming process. When it comes to studies on roller hemming processes, [PERSON] et al. [10] introduced a new and improved hemming process, namely roller hemming, which utilizes a roller guided by a robot along the hemming line, effectively bending the flanged height along the panel. [PERSON] and [PERSON] [11] investigated the effects of geometry and pre-strain on roll-in, load, and damage occurrence by comparing classical and roll-hemming processes. Their findings also provided valuable insights for the optimization of the roller hemming process. Additionally, [PERSON] [12] investigated the effect of using roller hemming replacements in conventional techniques in the automotive industry. Their numerical analysis could predict process outcomes and involved a comparison of five-element formulations, ultimately identifying the fully integrated formulation as the most effective method because the bending angle could influence wrinkling, hemming forces, and plastic strain. [PERSON] and [PERSON] [13] predicted the limits of roller hemming using a ductile fracture criterion.