Droplet Transfer Behavior And Weld Formation In MIG Welding Of Aluminum Alloy

Droplet transition is directly related to the stability,weld formation and spatter size of MIG(Metal-Inert Gas Welding(MIG)welding process,and ultimately affects the welding quality and production efficiency.Therefore,it is of great significance to study the droplet transition process for welding process selection and optimization.In this paper,the droplet transition behavior of aluminum alloy in different MIG welding process was studied by using high-speed camera system and electrical parameter acquisition system,and the influence of welding process parameters on weld formation was analyzed.In this paper,the waveform characteristics of cold arc welding technology of aluminum alloy are studied first and compared with the traditional short circuit transition welding.It is found that the cold arc welding technology has stable droplet transition,small welding splash,and better technology than the traditional short circuit transition welding.The wire feeding speed is increased from 6m/min to 8m/min,and the droplet transition frequency is increased from 21 Hz to 40 Hz.When welding at the maximum wire feeding speed of 8m/min,instantaneous short circuit occurs.As soon as the molten drop contacts the molten pool,it is pushed away from the molten pool by the electromagnetic contraction force generated by a large current(175A),sometimes causing splashing.When the wire feeding speed is kept constant at 6m/min and arc voltage is 15.6V and 17.5V for welding,the droplet transition is stable and no splash,and the transition frequency is 21 Hz and 14 Hz respectively.When the voltage is 13.2V,the droplet transition frequency reaches 91 Hz,but the wire feeding speed is too fast,and the welding wire will have solid short circuit and explosion fracture.Secondly,waveform characteristics and droplet transition behavior of "cold arc + pulse" welding of aluminum alloy were studied."Cold arc + pulse" welding technology combines the characteristics of cold arc and pulse welding.A waveform cycle has two stages: cold arc and pulse,which are composed of several cold arc and pulse waveforms respectively.The average current in the cold arc stage is relatively low to avoid the temperature of the molten pool rising too fast.The average current of pulse stage is high,which can melt the welding wire quickly and complete the droplet transition.The wire feeding speed increases from6m/min to 8m/min,the cold arc waveform in one wave cycle increases from 5 to 7,the average current increases from 49.8 to 68.4A,and the heat input increases by 47J/mm.While the pulse waveform increases from 28 to 63,the average current increases from 109 A to 195 A,and the heat input increases by 306J/mm.It can be seen that when the wire feeding speed increases,the system makes the welding wire melting speed match the wire feeding speed mainly by adjusting the pulse stage energy.The effect of bypass gas on droplet transition in aluminum alloy welding was also studied.The addition of bypass gas increases the frequency of droplet transition and makes the droplet transition from short circuit transition to subjet transition,and the welding process is stable.When the wire feeding speed is set unchanged at 8m/min and the bypass gas flow rate is changed,the number of short circuits increases first and then decreases with the bypass gas flow rate,and reaches the maximum at 20L/min,reaching 28 times.It increases with the increase of bypass gas frequency,reaching a maximum of 28 times at 40 Hz.The weld forming under different bypass gas parameters was observed.When the gas flow rate was20L/min and the frequency was 20 Hz,the weld forming was the best,the surface was flat and the weld width was uniform.