Mitigating Weld Defects in AISI 4145 Medium-Carbon Steel During Shielded Metal Arc Welding

Welding defects pose significant challenges to product quality and productivity in manufacturing industries. Shielded metal arc welding (SMAW) is the most widely used welding method in developing countries such as Ethiopia. This thesis identifies and addresses the root causes of welding defects in SMAW of medium carbon steel (AISI 4145) at Akaki Basic Metal Industry (ABMI), and optimizes welding parameters to enhance weld quality and reduce defect rates. Pareto analysis identified porosity and undercut as the most critical defects, together accounting for a 6% rejection rate in production over two years. Ishikawa (cause-and-effect) diagrams were used to analyze the root causes of these defects in detail, including incorrect welding parameters, inadequate preheat/post-heat treatment, improper technique, and inconsistent quality checks. A Taguchi L9 orthogonal array was then applied to optimize welding current, voltage, and speed. Welding current had the greatest effect on tensile strength (72.18% contribution), followed by voltage (19.73%) and speed (3.88%). Applying the optimized parameters (140 A, 40 V, 80 mm/s) reduced the defect rate from 6% to 2.7%. The study concludes that systematic optimization of welding parameters can effectively mitigate defects, improve weld quality, and enhance productivity in SMAW processes.