Keyhole behavior in high power laser welding

Abstract

Dynamic keyhole behavior has been observed to elucidate the formation and suppression mechanism of the porosity in 20 kW CO2 laser welding with the depth of 20 mm. The results indicate that the bubble is formed by capillary instability of the cylindrical keyhole. The tip of the keyhole is broken up by instability during rapid decrease in the depth, so called spiking phenomenon. Spontaneous fluctuation in the keyhole depth and spontaneous keyhole perturbation during welding promotes the bubble formation. Pulse modulation of the laser power is effective in stabilizing the keyhole and hereby suppressing the porosity if the frequency coincides with the eigenfrequency of the molten pool oscillation. The suppression effect is enhanced if the waveform is controlled appropriately.