Experimental Research Of The Plasma Signal In The Process Of CO₂ Laser Welding

Plasma is closely linked to the quality of the joint in laser welding. Effective control the plasma signal is one of the main research directions in deep penetration laser welding. In this work, deep penetration laser welding was carried out by using a 2kW CO₂ laser and the laser welding plasma was studied with orthogonal experiment, optical spectrometer, UV and infrared light as well as plasma voice.Firstly, a monitor system based on Labview was designed according to the characteristics of the plasma signal. Secondly, orthogonal experiments were carried out to research the three influential factors of laser welding plasma. The results show that the effects of different welding parameters on plasma are different during CO₂ laser welding A3 steels. For example, the sequence is laser power, welding speed, rate of the side-blown gas, respectively. In addition, Ti alloy (BT20 plate), 304 stainless steel and A3 steel were welded by a 2kW CO₂ laser and the results of spectrum analysis show that the welding material plays an important role in the spectrum distribution during deep penetration laser welding. The A3 steel spectrum mainly falls within the range of 300nm-450nm.Thirdly, different ultraviolet and infrared light signals in different welding process parameter were obtained according to the result of orthogonal experiment and spectral analysis experiment. The results indicate that the ultraviolet and infrared light signal increase when the laser power is increased whereas the signals decreases as the laser speed is increased. Moreover, there is a critical value in the rate of side-blown gas.Finally, based on the regression to the ultraviolet and infrared light signal, the relative error is small and is about 5%. The Lyapunov index was calculated and the chaos analysis to the sound signal was carried out. The results show that the Lyapunov index of plasma sound signal is in the range of [0,1]. At the same time, the data has a characteristic of the strong quasi, which makes the limited step predictability is possible. The bigger the Lyapunov index, the bigger of complexity laser welding plasma voice signal's curve and the more bad of the welding quality. On the contrary, the smaller the Lyapunov index, the smaller of complexity of laser welding plasma voice signal's curve and the better of the welding quality.