아연 제거 효과를 고려한 아연도금강판 레이저 용접에서의 기공제어

Abstract

Porosity Control in Laser Welding of Galvanized Steel Sheets Considering Zinc Removal Effect Kim Hyo Sung Advisor : Prof. Bang, Hee-Seon, Ph.D. Department of Welding and Joining Science Engineering, Graduate School of Chosun University This study focuses on addressing the quality issues related to welding defects in overlapping zinc-coated steel sheets for automobiles. To achieve this, the application of the 3-step laser stitch welding process is emphasized. This method effectively resolves welding defects occurring in resistance spot welding and offers economic benefits and industrial feasibility. The research investigates the welding characteristics by varying process parameters such as laser output, focal distance, welding speed, and pitch interval in both single laser stitch welding and 3-step laser stitch welding. The 3-step laser stitch process consists of three stages, each with different parameters. The first stage involves an output of 1.6 kW, focal distance of 20 mm, and welding speed of 20 mm/s. The second stage has an output of 0.8 kW, focal distance of 20 mm, and welding speed of 60 mm/s. The final stage includes outputs of 2.0 kW, 2.4 kW, and 2.8 kW, focal distances of 20 mm, 25 mm, and 30 mm, and welding speed of 35 mm/s. The pitch intervals are set at 20 mm, 40 mm, and 60 mm. Through visual and non-destructive inspections, the experiments demonstrate a significant reduction in defects, particularly when using the 3-step laser stitch welding process. The SEM-EDS analysis indicates that the zinc (Zn) content at the joint interface is 1.78% for single stitch welding but 0% for 3-pass stitch welding, indicating effective zinc removal when using the 3-step process. These findings contribute valuable information for securing high-quality welding joints and effectively addressing zinc-coated steel sheet welding quality issues in the automotive and industrial sectors.