Experimental Optimization of Robotic CMT Welding for 0.5 mm AISI 304 Stainless Steel under Assembly Misalignment Conditions

• Validates robotic CMT welding for 0.5 mm AISI 304 steel to meet Euro 7 and EPA27 cold-start emission standards. • Identifies asymmetric thermal fields as the primary driver of humping defects in vertically misaligned thin-gauge joints. • Demonstrates a robust process for bridging 1.0 mm horizontal gaps, representing 200% of the base material thickness. • Interrupted CMT welding combined with rigid copper backing achieves 100% repeatability where suspended fixtures fail. • Validated welds exhibit tensile strength equal to the parent material, ensuring durability for automotive exhaust applications. As global regulations move toward more stringent vehicle exhaust emission limits, particularly with standards such as Euro 7 and EPA27, the development of Low Thermal Mass (LTM) exhaust components has become necessary to improve cold-start aftertreatment efficiency. A challenge in manufacturing such components is the welding of extremely thin stainless-steel parts. This study aimed to optimize the robotic Gas Metal Arc Welding (GMAW) Cold Metal Transfer (CMT) technology to manufacture LTM exhaust components by stamping and welding 0.5 mm thick AISI 304 austenitic stainless steel. A key goal was to determine the acceptable limits of assembly deviations on Vertical Edge Misalignment (GapZ) and Horizontal Welding Gap (GapX) while maintaining stable and defect-free GMAW joints. The experiments were performed on a Yaskawa GA50 Robot equipped with a Fronius TPSi 500 CMT power supply. The collected data show fundamental process intolerances to the presence of preset vertical edge misalignment, resulting in failures in which a humping defect forms. It was hypothesized that the mechanism behind this mode of failure was the creation of an asymmetrical thermal field leading to a self-perpetuating cycle of material deformation. Using a rigid copper backing fixture to control weld thermal distribution enables reliable production of defect-free welds with a horizontal gap of up to 1.0 mm. Implementation of interrupted welding cyclogram, establishing more precise control over both heat input and arc pressure, allowed welding that consistently passed visual, radiographic, macro-structural, and tensile strength testing verification with equal mechanical properties to those of the base material. .