Study On The Effect Of Current Phase On Metal Transfer Of Al Alloy Double-wire Pulsed MIG Welding With A Median Current

Aluminum alloys are widely used in automobiles,high-speed rails,construction and aviation due to their excellent physical and chemical properties.Due to its low melting point,excellent thermal conductivity,and high melting point of the dense oxide film formed on the surface,Al alloys are difficult to weld using metal inert gas welding(MIG).Defects such as spatter and pores form easily,so tungsten inert gas welding and friction stir welding are mainly used to realize joining.Double-wire pulsed MIG welding(DW-GMAW)has high efficiency and yields good weld quality,so it is widely used in the welding of medium and thick plates.However,its application in Al alloy welding is limited due to its high heat input.At present,there are no studies on the effect of current phase on the metal transfer of Al alloy DW-GMAW with a median current.At the same time,current waveform control can help improve the heat input of the welding process.Therefore,in this paper we start from the current waveform and study the influence of the current phase on the metal transfer process,heat input characteristics and weld formation of Al alloy DW-GMAW with a median current.We first analyze the waveform and heat input characteristics of single pulse,double pulse,front median,middle median and back median current in different phases,and select of suitable integrated power supply control chips.We then design the software program to realize stable output for 14 kinds of pulse currents with different waveforms and phases.A welding test platform was built to conduct resistance load testing and welding process tests,and a highspeed camera was used to film the metal transfer process and analyze the influence of current mode and phase on metal transfer and weld formation.Subsequently,the difference between the resistive load and the U-I characteristic curves of the weld under different current modes and phases are analyzed and used to study the stability of the welding process.Combined with the electrical signals and theoretical analysis,it is pointed out that the arc load impedance is capacitive.Under the experimental parameters and conditions investigated in this study,the metal transfer of single pulse,front median and double pulse alternate phase is one drop double pulse;in the back median and middle median modes,metal transfer occurs at one drop per pulse;in the strong pulse stage of the double pulse synchronization pulse phase,the metal transfer is poor and there no specific governing rule.In the weak pulse stage,it is one drop double pulse.The current phase affects the transfer phase of the droplet.When the current phase angle of the master and slave is 0°,the droplet exhibits a synchronous transfer characteristic.With the phase angle changes,the transfer phase changes accordingly.The metal transfer control effect of middle median current mode is better than that of other current modes.The metal transfer and total heat input affect the quality of weld formation.When the phase angle of the master and slave current is 0°,the total heat input is the highest,and the master and slave droplets are transferred synchronously and are prone to collision,so the weld formed is poor.When the phase angle of the master and slave current exists,the arc interference is reduced,the master and slave droplets transfer alternately,and the total heat input variation gradually decreases and tends to be stable,so the weld quality is improved.The middle median current under phase 4 mode shows the lowest heat input variation,and the droplets transfer alternately,resulting in the best weld quality.