The effect of shielding gases and laser variables on weld fusion zone configuration have been investigated in the pulsed spot welding of AISI 1018 steel using a CO2 laser with 610 watt output power. Laser parameters chosen were tube discharge current levels of 50, 100, 150 mA; laser pulse lengths of 0.5, 1, 2, 4, 8, and 16 ms and focal positions of 2.5 mm above, at, and 2.5 mm below target surface. He, CO2, N2, Ar as individual gases and their binary gas mixtures at 50 cfh and air (no flow) were the shielding gases studies. Average laser power densities in the range of 0.3 to 0.8 × 106 watts/cm2 were employed. The fusion zone configuration studied included weld penetration, weld pool diameter and fusion zone volume. Spectrographic analysis of the laser plasma plume was undertaken to identify the predominant species in the plasma plume with He and Ar gas shielding.
Results show that the depth of penetration is determined by discharge current level and focal Laser pulse length is found to influence the fusion zone volume. With regard to their beneficial effect on improved weld penetration and fusion volume, the shielding gases listed in order of maximum to minimum benefit are He, CO2, Air, N2, and Ar. This behavior of shielding gases is primarily determined by their thermal conductivity and secondarily by their dissociation properties. The plasma plume is found to contain excited neutral iron atoms and singly ionized iron. No evidence of excitation or ionization of He or Ar is found.