Comparison of IR emittance distributions along steel and aluminum surfaces during CO2 laser welding

Abstract

The radiation coming from the interaction zone during quasi CW CO2 laser welding was detected in IR and UV spectral regions. The intensity distribution of IR radiation coming from the surfaces of mild steel and aluminum was measured. The IR and UV signals were detected with photodiodes operating in the spectral region from 0.83 μm to 1.8 μm and from .23 μm to .33 μm, respectively. The laser provided 20 ms pulses with 10 ms between each pulse. The intrapulse duty cycle was modulated 60% with a frequency of 5 KHz, giving an average power of 1.9 kW. The molten metal surface was the main source of IR radiation between laser pulses. The maximum IR signal and, consequently, surface temperature was found in the weld metal at a distance of 2 - 3 mm from the laser beam axis in the case of mild steel. For aluminum welding, however, the maximum IR signal was located within the diameter of the laser beam. Comparison of the experimental data with numerical calculations showed that the temperature distribution observed in the case of mild steel welding is dictated by convective heat transfer effects resulting from the hydrodynamical movement of the molten metal. This is in contrast with the conduction dominated aluminum case. The high speed photography of the laser welding showed significant differences in the melt behavior for the cases of mild steel and aluminum.The radiation coming from the interaction zone during quasi CW CO2 laser welding was detected in IR and UV spectral regions. The intensity distribution of IR radiation coming from the surfaces of mild steel and aluminum was measured. The IR and UV signals were detected with photodiodes operating in the spectral region from 0.83 μm to 1.8 μm and from .23 μm to .33 μm, respectively. The laser provided 20 ms pulses with 10 ms between each pulse. The intrapulse duty cycle was modulated 60% with a frequency of 5 KHz, giving an average power of 1.9 kW. The molten metal surface was the main source of IR radiation between laser pulses. The maximum IR signal and, consequently, surface temperature was found in the weld metal at a distance of 2 - 3 mm from the laser beam axis in the case of mild steel. For aluminum welding, however, the maximum IR signal was located within the diameter of the laser beam. Comparison of the experimental data with numerical calculations showed that the temperature distribution observed...