Study On Droplet Transfer Behavior And Forming Characteristics Of High Nitrogen Steel GMAW

This project aimed at the problems including nitrogen precipitation,welding fume,spatter and nitrogen pores in the GMAW welding process of high nitrogen steel,the experimental research on the single and double wire GMAW welding process of high nitrogen steel was carried out,and revealed the influence of different welding process parameters including arc voltage,wire feeding speed,double wire angle,etc.on the droplet transfer behavior and weld formation of high nitrogen steel GMAW.The porosity problem was optimized in high nitrogen steel GMAW,and the typical high nitrogen steel robot welding process and specification parameters were obtained.Firstly,a forming test on high-nitrogen steel monofilament GMAW was performed,and it was found that the welding process was stable after adjusting the arc length to the wire feeding speed less than or equal to 6m/min,and the weld formation was poor.when the wire feeding speed was greater than 6m/min,the spatter and fume were larger in the welding process,but the welding effect was better,and the forming quality was better.Then,the droplet transfer process of high-nitrogen steel monofilament GMAW was studied,and it was found that with the increase of wire feeding speed and arc voltage,the droplet transfer process showed the characteristics of short-circuit transition and streaming transition in turn,without obvious large droplet transition.And when the current was large,the droplets were easy to expand and explode due to the precipitation of nitrogen,causing a lot of welding spatter.When the wire feeding speed was from 3 to 6m/min,a stable short-circuit transition can be obtained by using a suitable arc voltage.In order to achieve the effect of stable droplet transfer and large heat input deposition,lowcurrent twin-wire GMAW was used for high nitrogen steel.The effect of different twin wire angles and front and rear wire feeding speeds on the droplet transition process of high nitrogen steel twin wire GMAW was studied.The analysis showed that as the twin wire angle decreased,the overlapping area of the front and rear molten pool became larger and the height of molten pool increased relatively,the arc length was smaller,the droplet short-circuit frequency increased,and the transition period was relatively reduced.As the wire feeding speed of the rear wire increased,and the wire feeding speed of the front wire was less than 5m/min,the front wire was less affected.When the wire feeding speed of the front wire was greater than or equal to 5m/min,the arc was greater affected by the magnetic bias blowing,and the transition period of the front wire droplet would be longer.When the wire feeding speed of the rear wire remained unchanged,with the continuous increase of the front wire feeding speed,the transition period of the droplet of the rear wire would be shortened.Finally,according to double wire angles and front and rear wire feeding speed matching process,the forming characteristics and pore optimization of high nitrogen steel GMAW were studied.The analysis found that the spatter area in the welding process of smaller double wire feeding speed with the same total wire feeding equal to the single wire feeding speed was smaller,and the I and II welds were generally distributed at 45° and 60° welds.As the preheating temperature increased,the pores in the welds tended to increase first and then decreased.Only with swinging,the pore had a tendency to increase,under the condition of suitable preheating temperature,addition of proper swinging parameters could effectively reduce pores.Finally,the optimized process includes two options.one was that when the double wire angle was 45°,the front and rear wire feeding speed was 5/4m/min,the preheating temperature was 200?,and the appropriate swing parameters were added,the other one was that when the double wire angle was 60°,the total wire feeding speed was 10m/min,the front wire feeding speed was greater than the rear wire feeding speed and the difference was smaller,and the appropriate preheating temperature and swing parameters were added.