The characteristics of the plasma in laser keyhole welding

The plasma is an important characteristic during laser keyhole welding processing; the weld quality is related to the shape and stability of plasma directly. By using a CCD sensor system, the optical emission of the plasma was investigated. It was found that the gas in the laser path would be cascade ionized due to the effects of the thermal lens and reflection of molten pool metal, which cause the plasma abnormally expanded and ejected. As a result, welding process was disturbed and penetration depth was in unstable state. The experimental results also indicated that, during the stable welding process, the dimensions of the plasma were corresponding to the weld depth on some degree, this can be used to monitoring the stability of laser welding process.