<p>The structural components of an automotive chassis, including critical elements like the frame and cross-members, must possess high strength to distribute and support the vehicle’s load during operation effectively. In chassis manufacturing, slot welding has proven to be an effective method for improving support and durability under cyclical loading conditions. However, the absence of standardized guidelines for slot-filling during chassis welding poses a significant challenge, particularly concerning the fatigue life of components in the automotive industry. In this study, three different slot geometries were employed and welded by adjusting robotic programming to achieve complete filling (CF) or partial filling (PF) of the slots to improve fatigue life. A hot rolled 590-MPa steel sheet used for automotive applications with a cold metal transfer (CMT) technique was adopted to weld the samples. Digital image correlation (DIC) was conducted to identify stress concentration and the crack propagation path during the tensile loading of the sample. The fatigue crack initiation showed a location similar to the highest stress concentration area, as revealed by DIC. Additionally, an infrared camera was utilized during welding to monitor temperature variations, providing insights into the thermal aspects of each welding condition. The study revealed that higher effective weld width (W_eff) in the PF sample enhanced the tensile fatigue life by reducing stress concentration. However, the cross-tensile fatigue properties of the CF sample exhibited a longer fatigue life due to a larger weld size and associated weld width.</p>