The effect of pulsed carbon dioxide laser spot welding variables on plasma plume formation in argon and helium, and resulting spot weld characteristics in AISI 1015 steel have been investigated.
Two penetration modes were found to occur. At high peak power densities, and with the focal point held at the target surface, a vapor cavity penetration mode was observed. This was associated with a blue plasma plume which absorbed laser energy. At low peak power densities, or with the focal point above the target surface, a heat conduction penetration mode was observed. This mode was associated with a red vapor plume which did not significantly absorb laser energy. Both plume types were larger in argon than in helium. In addition, in argon at higher power densities, the blue plasma plume associated with the vapor cavity penetration mode can decouple from the target surface preventing further heat input.