Study On Characteristics Of Laser Inducing Plasma For Triggering TIG Arc Discharge

The high-frequency triggering technique was applied in automatic tungsten inert gas (TIG) arc welding system widely because of its good triggering performance; convenience and facility to realize automatic welding. However, the high-frequency method may possibly disrupt operation of peripheral computer systems and is harm to human body. According to these problems, some scholars suggest using the laser induced plasma to ignite the TIG arc.Laser plasma triggering arc discharge is a physical process that ignites the TIG arc by conducting the gap of tungsten rod and the workpiece with the plasma induced by the interaction between the laser and material. In this paper, the laser plasma was researched. The variation of triggering arc performance with the processing parameter was analyzed through the experimental method. The necessary condition physical phenomenon of the laser plasma triggering TIG arc discharge was analyzed in theoretically.By analysis of the related character of laser plasma, a paraxial visual sensing system was established to detect the process of laser induced plasma triggering arc discharge. Using the morphological character of laser plasma, the variation of triggering arc performance with the processing parameter was analyzed. The physical phenomenon of the laser plasma triggering TIG arc discharge was analyzed in theoretically.In this paper, a pulsed CO2 laser whose pulsed width is 1ms was used to ignite the TIG arc. A paraxial visual sensing system was established to detect the process of laser induced plasma triggering arc discharge. The influence of main factors, such as shielding gas, workpiece materials, defocusing amount, pulsed laser width etc., on the shape and volume of laser plasma and the triggering arc performance of laser plasma were obtain. The experimental results indicate, only when the plasma contacted the tungsten rod, the TIG arc can be ignited. When use the mixture of Ar and He as shield gas, titanium alloy as the workpiece, the triggering arc performance of laser plasma is better. It was also found, gas flow changes will affect the size of the plasma, the triggering arc performance of laser plasma is best when the gas flow rate is 15L/min. Meanwhile, when the proper defocused laser and proper width of pulsed laser was used, the metal vapor content and the triggering arc performance of laser plasma were improved.Furthermore, in order to study the influence of electric-field intensity in TIG arc on the triggering arc performance of laser plasma, the main factor, such as tungsten rod position, voltage polarity, the shape and electrode standoff distance etc. were studied in this article. The experimental results indicate, when using the workpiece as cathode, the cathode electron emission became easier, and the difficulty of igniting TIG arc will decrease. When the shape of the tungsten rod is topiary, the electric-field intensity nearby the tungsten rod is stronger, which was advantage to the cathode electron emission. When the electrode standoff distance was increased, the difficulty of igniting TIG arc will increase. It is also found, the minimum laser power required for triggering arc discharge increases linearly with an increasing electrode standoff distance when the electrode standoff distance is near, and increases exponentially with an increasing electrode standoff distance when the electrode standoff distance is far.