| On the premise of ensuring reliable welding quality,improving welding efficiency has increasingly become the primary goal of modern manufacturing.For traditional monofilament GMAW,the means to improve welding efficiency is often to increase welding current.However,when the welding current reaches a certain value,the droplet transfer form of monofilament GMAW changes into rotating jet transfer,which leads to unstable welding process,poor weld formation or even no weld formation.For Tandem and other traditional twin-wire GMAW,the welding efficiency is indeed improved,but the interference between twin-wire arcs often leads to the instability of the welding process.At present,the commonly used solution is to adjust the phase difference and alternate arc burning,but this method fails to give full play to the high efficiency advantage of twin-wire high current.In addition,Tandem twin wires are mostly used for automatic welding,and their flexibility is poor,which makes it difficult to play their role in some narrow spaces.Based on this,a new high-efficiency welding method,single-source double-wire GMAW,is proposed.Its welding system consists of a special welding power source,a double-wire wire feeder and a special double-wire welding gun the size of a conventional single-wire welding gun.While ensuring flexibility,the electromagnetic force between the two wires is restrained mutually,which solves the problem of rotating jet transition under high current of monofilament GMAW,and successfully expands the welding current to700 A.And the unique advantage of double wire single arc avoids the interference between arcs.In this thesis,the arc physical behavior,droplet transfer behavior and weld formation law of single-source twin-wire GMAW are studied by means of numerical simulation and experimental detection,so as to provide theoretical guidance and basis for the process and popularization of single-source twin-wire GMAW.In this thesis,the arc numerical analysis model of single power supply and double wire GMAW is established.Using the model,the temperature,velocity and pressure distributions of single-wire GMAW with and without spacing under different welding currents are simulated,analyzed and discussed by Fluent software.The research shows that the formation mechanism of double wire single arc can be considered as the coupling mode of "lower overlap + upper attraction".At 300 A current,the maximum arc temperature fields of single-wire GMAW with spacing,single-wire GMAW without spacing and single-wire GMAW with common single-wire are 18222.4K,18923.4K and 28619.5K,respectively.The maximum current densities are 5.77×107A/m2,5.89×107A/m2 and 1.50×108A/m2,respectively.The maximum velocity in z direction is 106.4 m/s,174.2 m/s and 450.5 m/s respectively.The maximum arc pressures are 231.9 Pa,310.9 Pa and 964.8 Pa,respectively.Generally speaking,the temperature distribution,arc pressure,current density and z-direction velocity of arc plasma of single-source double-wire GMAW are lower than those of ordinary single-wire GMAW,and the spacing is lower than that of no spacing.In addition,the maximum values of the distributions of the single-source twin-wire GMAW with spacing often appear near the ends of the twin-wire,while the single-source twin-wire GMAW with no spacing is closer to the common single-wire GMAW,and the maximum values of their distributions often appear on the central axis.In this thesis,a single-source double-wire GMAW welding test platform integrated with high-speed camera system is built,and the welding process tests of single-source double-wire GMAW with and without spacing under different welding currents are carried out,and the high-speed camera results are processed and analyzed.The results show that,under the same welding current,the arc width of single-source double-wire GMAW with spacing is not much different from that of single-source double-wire GMAW with no spacing,but the arc length of single-source double-wire GMAW with no spacing is lower than that of single-source double-wire GMAW with no spacing.Secondly,for twin-wire GMAW with spaced single power supply,the droplet transition is basically large-drop transition with multiple pulses and one drop at the current of 300 A to 400 A,and between large-drop transition with one pulse and one drop at the current of 450 A to 500 A,and the large-drop transition occurs frequently.When the current reaches 550 A,the droplet transition changes into one-drop transition with one pulse and one drop,and when the current reaches 600 A,the droplet transition is between droplet transition and submersible arc jet transition.When the current is 550 A,the transition frequency is fast,the welding process is stable,and the weld shape is better.At last,for double-wire GMAW with single power supply without spacing,the droplet transfer is a large-drop transfer with multiple pulses at the current of 300 A,and a large-drop transfer with one pulse at the current of 350 A to 400 A.When the welding current reaches 450 A,the droplet transfer is between large-drop transfer and jet-drop transfer,but the frequency of large-drop transfer is relatively high.When the current exceeds 450 A,the droplet transfer basically changes into jet transfer.Among them,when the welding current is over 400 A,the whole welding process is more stable,the droplet transfer frequency is faster,and the weld shape is better. |
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