Analysis of plasma oscillations by electrical detection in Nd:YAG laser welding

Plasma oscillations were investigated by electrical detection under different operating parameters during bead-on-plate welding of 304 stainless steel with a Nd:YAG laser. The varied parameters were the laser output power, welding speed, assistant gas type and assistant gas flow rate. The plasma electrical signals were detected by a passive electrical probe and analyzed in the frequency domain by power spectral density analysis. Combined with observation of the corresponding weld cross sections, the fluctuating characteristics of the plasma in different welding modes were obtained. A high-speed camera was employed to observe the plasma during experiments using different types and flow rates of side assistant gas. The features of plasma, including the plasma area and inclination angle, were extracted by the mathematical morphology method. By comparing the electrical signal of plasma with the extracted plasma features, the effects of the side assistant gas on the oscillations of plasma were discussed.