Process optimization of Gas Metal Arc Brazing technology
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Gas-metal-arc brazing (GMAB) technology is a transformative non-fusion joining process used in the joining of thin-gauge Zn-coated advanced high strength steels (AHSSs) employed in the automotive industry. Due to its lower heat input capability, the technology offers several benefits over the conventional gas-metal-arc welding (GMAW) process such as minimal Zn-coating burn-off, lower distortion, minimal welding defects, and a reduced heat-affected-zone (HAZ), which make GMAB more suitable for joining thin-gauge galvanized AHSSs. Being a relatively new technology compared to other conventional welding processes, the process technology of GMAB is yet to be fully optimized based on the existing literature. In this thesis, three factors of the process variables that were found to be critically influential on the mechanical properties of GMA brazed lap joint were investigated to further optimize GMAB process technology; the three factors are the torch angle and position, the gap clearance, and the Zn-coating type. The results showed that the torch parameters have a large influence on the behavior of arc and droplet transfer which have a direct impact on the bead geometry, heat distribution, and joint strength. The mechanical properties of the joint improved with the increase of torch angles and centering of the torch position at the root region. The effect of gap clearance has not been considered a factor of influence during the GMAB process as the capillary action does not play a role in the GMAB process. However, results showed that the presence of a gap and proper wetting of filler material through the gap greatly reduced the stress concentration developing at the root region due to the bending of base metal sheets driven by the eccentricity of load during the lap-shear tensile test. It was shown that the use of a gap size between 0.3–0.6 mm resulted in the optimal joint strength. The chemistry of zinc coating type (GI and GA) was shown to have a critical influence on the mechanical properties of the joint due to the formation of Cu-Zn alloy at the tail-end area of the root region. GI-coating had a detrimental effect on the joint strength due to the formation of extremely brittle zinc-rich-area in the root region which is highly susceptible to crack formation. On the other hand, GA-coated samples had superior joint strength in general due to the formation of a much more ductile zinc-rich area in the root region.
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Yong Hwan Cho (2022). Process optimization of Gas Metal Arc Brazing technology. UWSpace. http://hdl.handle.net/10012/18484