Research On Arc Behavior And Droplet Transfer Of High Frequency Alternating Current Heterogeneous Inter-wire Indirect Arc

With the development of the aerospace field,7000 series aluminum alloys have been widely used.However,the 7000 series aluminum alloy has high strength and poor plasticity,cannot be smoothly processed into a wire that meets the requirements.Research on arc additive manufacturing of high-strength aluminum alloys has been hampered.In order to solve the problem of difficult processing of special wire materials,the heterogeneous inter-wire indirect arc welding technology is applied to the arc additive manufacturing process.Use AC heterogeneous double wire(aluminum copper and aluminum magnesium wire)indirect arc+bypass zinc wire to synthesize 7000 series high-strength aluminum alloy.Because there is no related research on heterogeneous inter-wire indirect arc,this article will conduct research from three aspects:develop high-frequency AC/DC pulsed twin-wire indirect arc power,construction of heterogeneous inter-wire indirect arc non-uniform melting model,observation of heterogeneous twin-wire AC/DC arc and droplet transfer behavior.The high-frequency AC/DC pulsed twin-wire indirect arc power realizes the following functions through the main circuit topology,control circuit design and control algorithm adjustment:the current can be AC/DC conversion,the output pulse frequency can reach100k Hz,the output AC frequency can reach 500Hz,the amplitude and duration of the pulse current base value and peak value are respectively adjustable.From the perspective of arc heat and resistance thermal physics,the effects of polarity,welding current amplitude,arc voltage,dry elongation and diameter of the welding wire on the melting speed of the welding wire are analyzed.With the goal of achieving controllable droplet transition volume,a mathematical model for heterogeneous twin-wire non-uniform melting model was constructed.The model can input current I and time T to output the wire feeding speed V of ER5356 and ER2319 under the corresponding current waveform.Achieved the purpose of adjusting the alloy composition content of the molten pool through that adjusting current waveform and double wire feeding speed.A test platform was established to study the melting characteristics of ER2319 and ER5356 welding wires under different polarities and currents,and to fit the melting speed formula of twin-wire.Analyze the arc behavior and droplet force through DC heterogeneous twin-wire indirect arc test.The results show that the shape of the indirect arc is"V"shaped under the influence of electromagnetic force.When the current frequency is 100kHz,the arc produces a high-frequency effect.The arc stiffness increases,the volume shrinks,the welding wire melts faster,and the droplet transfer frequency is higher.The influence of the frequency and waveform of the pulse current on the indirect arc behavior and droplet transition of AC heterogeneous twin-wires has been studied.The results show that as the frequency increases,the relative distance between the ends of the twin wires decreases during the droplet transfer.When the AC frequency is lower than 2.5Hz,the arc is extinguished due to the relative distance between the ends of the twin-wires.When the AC frequency is higher than 10 Hz,the ends of the double wires are easy to short circuit and cause difficulty in starting the arc.When the current amplitude is small,the arc is unstable and easily extinguished.When the current amplitude is large,the electromagnetic force will cause the droplets to repel each other,resulting in unstable transition of the droplets.In order to make the arc and the droplets burn and transition stably,a double-peak-base current waveform(that is,the double-peak current is set before and after the base current)is designed for experimentation.The results show that the duration and amplitude of the peak current mainly affect the arc stability.As the duration and amplitude of the peak current increase,the distance between the ends of the twin wires increases,and the electromagnetic force on the arc increases,causing the arc to be elongated.The duration and amplitude of the base current mainly affect the stability of the droplet transition.As the base current duration increases,the droplet size increases,but as the base current amplitude increases,the droplet size decreases,the mutual repulsive force increases,the droplet transition is unstable.The cladding test of DC heterogeneous twin-wire+bypass Zn wire(target close to7050 aluminum alloy)was carried out.After adding the Zn wire,the Zn wire will absorb a part of the heat and cause the arc to darken.The experimental results show that the structure of the cladding sample is mainly composed of dendrites,and the average hardness is 106HV.The common phases of 7050 aluminum alloy were formed in the sample:S phase(Al₂Cu Mg)and?phase(MgZn₂).This confirms the alloying of the three-wire components and preliminarily verifies the possibility of synthesizing 7000 series aluminum alloy.