Experimental Study On Plasma Properties Of 316L Stainless Steel Fiber Laser-TIG-magnetic Hybrid Welding

As one of the sources of energy for the welding process,composite plasma has an important influence on the welding quality because of its dynamic behavior and physical properties.At present,the study of composite plasma is mainly focused on the dual-energy field plasma-arc and arc-magnetic plasma,but there is no systematic study on the properties of laser-TIG-magnetic hybrid plasma.In this paper,the arc plasma characteristics of laser-TIG-magnetic field hybrid welding of 316 L stainless steel have been experimentally studied on a self-built laser TIG-magnetic field hybrid welding platform.Furthermore,the dynamic behavior of the plasma,the distribution of spectral lines,the distribution of temperature field and the distribution of electronic density are analyzed in detail.On the basis of this,there have carried out a research on the interaction mechanism among different energy fields.When the single TIG welding is applied,the arc plasma fluctuation is very small,the stiffness is good,and the overall performance is relatively stable.The results are as follows:(1)As the current becomes larger,the volume of the arc plasma becomes larger and the horizontal drag length Lab becomes larger,which can reach 15.2 mm at 200 A.(2)with the increase of welding speed,the volume of arc plasma also increases,and the horizontal drag length Lab increases,which reaches 14.7mm at 2.0m/min.The composite arc plasma has undergone significant contraction and oscillation under the action of the laser.The main performance is as follows:(1)The more obvious the disturbance of the arc caused by the laser-induced plasma is,the more intense the arc is.When the laser power is 2.0KW,the horizontal drag length Lab is at least 7.3mm,and the effect of laser on arc contraction is most obvious.The amplitude of arc oscillation is the most uniform and the arc is most stable.(2)The smaller the light tungsten spacing DLW is,the larger the amplitude of the arc oscillation is,and the more severe the contraction and oscillation of composite arc is.And when DLW is 4mm,the amplitude of oscillation is the smallest,which is only 1.3mm.And the arc is the most stable.The arc,which is originally directed along the extension of the tungsten electrode toward the surface of the workpiece,will contract and deflect under the action of a magnetic field.The findings are as follows:(1)when the smaller magnetic induction intensity is 10 mT,the tail of the arc has obvious contraction,which shows the sign of deflection towards the right rear of tungsten.However,it is not very obvious.(2)When the medium magnetic induction intensity is 20 mT,the shrinkage and deflection of the arc tail are evident.The arc tail is dragged from the left side of the tungsten electrode to the right side of the tungsten electrode.(3)When the magnetic induction intensity B is 40 mT,the arc is directed vertically downwards along the tip of the tungsten electrode,and the whole becomes bell-shaped,and the bottom expands greatly.Under the combined action of the laser and the magnetic field,on the one hand,the arc is disturbed by the laser-induced plasma.On the other hand,the arc rotates at a high speed under the action of the magnetic field.Under the combined effects of these two facets,the arc stiffness is improved,and the interference of the laser-induced plasma to the arc is reduced.The spectral signals of the hybrid welding plasma are collected by using the self-built experimental research platform.Besides,the research on the spectral line distribution of welding plasma in different energy fields is carried out.The distribution of temperature field and electronic density distribution are calculated on the basis of Boltzmann mapping method and Stark broadening method.The findings show that:(1)With the increase of the distance from the surface to the workpiece,the temperature of plasma as a whole shows a rising trend.The closer the plasma is to the tip of the cathode,the higher the temperature is.And the highest temperature is about 19,000 K.(2)With the addition of fiber laser,the low-temperature laser-induced plasma ejected from the laser aperture has a great influence on the temperature distribution in the area where the LaserZ is applied and in the vicinity of LaserZ,which has a significant cooling effect.(3)With the addition of the magnetic field,the bottom of the arc is expanded,the heat dissipation area of the arc is increased and the bottom temperature of the arc can be lowered(2 mm below the surface of the workpiece).(4)Under the combined action of temperature reduction of laser-induced plasma and cooling effect of the magnetic field,the LaserZ region of laser-TIG-magnetic field composite arc plasma and the bottom of the arc(2mm below the workpiece surface)have a great influence on the overall cooling amplitude.The temperature is lower and the lowest temperature is located at point A in the LaserZ area,which is only 8360 K.The distribution of plasma electron density is opposite to that of temperature.As the distance from the surface of the workpiece increases,the overall plasma electron density shows a decreasing trend.The closer the plasma is to the tip of the cathode,the lower the electron density is.And it is about 6.2×1023m-3.The average electron density of the laser-TIG hybrid welding is the lowest,which is only 7.02×1023m-3,while the average electron density of the laser-TIG-magnetic hybrid welding is the highest,with 7.96×1023m-3.