Comparison of melting efficiency between blue, green, and IR lasers in pure copper welding

Pure copper parts are commonly used in many industrial products because of their low thermal resistance and high electrical conductivity. However, connecting high-quality and high-efficiency copper materials remains a challenge. This is because pure copper has low absorption of near-infrared light, making it difficult to weld stably with a near-infrared laser. Visible light lasers should realize high-efficiency laser welding of pure copper. However, there are few reports comparing the laser wavelength dependence of welding efficiency for pure copper. In this study, bead-on-plate welding was performed on pure copper plates of 2 mm thickness using a 1.5 kW blue diode laser (445 nm), a 16 kW IR disk laser (1030 nm), and a 3 kW green disk laser (515 nm). Bead-on-plate welding of pure copper was performed in the thermal conduction mode or the keyhole mode by varying the laser spot diameter and power, and the amount of melting was measured from cross-sectional observations. As a result, compared to the IR disk laser, blue and green lasers showed higher melting efficiency in both the thermal conduction and keyhole modes, and the melting behavior was more stable. In thermal conduction mode welding, the melting efficiency was 0.2% with the IR disk laser and 0.7% with the blue diode laser. In keyhole mode welding, the melting efficiency with the blue diode laser or green disk laser was about 7%, which is equivalent to that with the IR disk laser with 2.5 times the output power.