Analysis of Defects in Thermostat Spot Welding Process for Coffee Maker Components

Abstract

PT XYZ is a manufacturer of electrical household appliances, where the assembly of coffee maker thermostats relies on the resistance spot welding process. The quality of the welding joint is critical, as it serves as both a mechanical connection and an electrical conduction path for the heating system. However, the production line frequently experiences welding defects, specifically burn-through, overheat, and broken weld, which compromise the thermostat's performance and reliability. This research aims to analyze the impact of key process parameters charge voltage, weld time, and electrode pressure on the formation of these defects. An experimental approach using a full factorial design was conducted with three levels for each parameter: charge voltage (213 V, 224 V, 235 V), weld time (20 ms, 28 ms, 35 ms), and electrode pressure (0.1 MPa, 0.2 MPa, 0.3 MPa). The resulting welds were evaluated through visual inspection, joint strength testing, and electrical continuity assessment. Data analysis reveals that excessive heat input, governed by the interaction of charge voltage and weld time, is the primary cause of overheating and burn-through, while unstable electrode pressure and insufficient heat input are linked to broken welds. The experimental results identify the optimal parameter combination as 224 V, 20 ms, and 0.2 MPa. Implementation of these parameters demonstrated a significant reduction in the defect rate from 42.22% to 10%, ensuring superior joint strength and electrical stability.