| Tungsten inert gas shielded welding,because of its tungsten electrode carries a limited current,and it can only use the heat of anode region,the heat of cathode region is lost through the tungsten electrode,so the welding penetration of TIG welding is lower,and thermal efficiency of its arc is also lower than that of the gas metal arc welding,resulting in low welding efficiency and high cost.In this paper,combined with welding process image acquisition system,the effect of wire feeding through nozzle on droplet transfer,welding pool behavior,welding appearance and arc energy efficiency has been studied.It provides theoretical basis and empirical data for broadening the practical application of TIG welding.Firstly,the single wire feeding TIG through nozzle has been studied.There is two feeding direction-from the front and back of tungsten electrode.The reaching results show that with the increase of the wire feeding speed,droplets transfer mode was successively the free drop transfer,the contact drop transfer and the continuous contact transfer.The droplet transfer frequency was firstly increased and then decreased,as the increase of the wire feeding speed;Increasing welding current boosts droplet transfer;The droplet transfer frequency of wire feeding from back of tungsten electrode is lower than from front of it;As he increase of the wire feed speed,the size of the welding pool gradually decreases up to disappearing,the welding penetration gradually decreases,the reinforcement gradually increases,the welding width has first no change and then decreases;And the welding width wire feeding from back of tungsten electrode is greater than that of wire feeding from front of tungsten electrode,but the reinforcement is lower;Under certain welding speed,the optimal range of the wire feeding speed increases with increasing of welding current;Under a certain welding current,the optimal range of the wire feeding speed decreases with increasing of welding current;And the optimal range of the wire feeding speed of wire feeding from back of tungsten electrode is greater than that of wire feeding from front of tungsten electrode.When the wire feeding speed is too slow and too fast,the welding line discontinuous and hump defects occur respectively under wire feeding from front of tungsten electrode,generating the welding line discontinuous and incomplete bond of weld toe respectively.The optimal range of the wire feeding speed of wire feeding through nozzle is larger than that of the conventional TIG.This is because the welding wire that feeds from nozzle can absorb the heat from the nozzle and the arc column,making the arc energy efficiency larger than that of conventional TIG.This paper further designed a nozzle that can make double wire feeding simultaneously from front and back of the nozzle.And the difference between it and the single wire feeding TIG has been studied.The results showed that the droplet transfer mode of the double wire feeding TIG has four kinds:double wire free drop transfer,double wire contact drop transfer,contact drop transfer of front wire and continuous contact drop transfer of back wire,double wire continuous contact transfer;Under the same amount of feeding-wire,when welding pool of the single wire feeding disappeared and the weld appearance deteriorates,the welding pool of double wire feeding still exists,and the weld appearance is also good;This is because the heat absorbed by the welding wire of double wire feeding is twice as large as single wire feeding under the same amount of feeding-wire.Finally,this paper applied double wire feeding TIG to 2mm thick 304 stainless steel butt joint welding and 5mm thick Q235 steel overlaying.This paper achieved optimal process parameters at the welding speed of 0.5m/min and 1.0m/min,as well as the process parameters that make the dilution rate lower and the surfacing layer well. |
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