| A new type of laser-assisted alternating current(AC)inter-wire indirect arc welding technique is developed to meet welding processes in high efficiency and quality.AC indirect arc between two wires is established to melt wires.Laser beam hybridize with indirect arc at the intersection of the double wire axis which is also the focus of laser beam.In view of different melting rates of cathode and anode,desired mass droplets can be formed alternately at the focus of laser beam by matching double synchronous wire feed speed.Droplets detach from wires under recoil pressure subject to pulsed laser irradiating and transfer to base metal.This process is summarized including droplets alternately active targeting laser and laser-assisted droplet transfer along desired diretion.This technique takes advantages of laser beam and indirect arc characterized by low heat input and high deposition rate,leading to arc welding with high quality and efficiency.The non-equilibrium melting model of wires in AC inter-wire indirect arc is proposed.The behavior control of droplets alternately active targeting is studied.The mechanism of droplets detachment under arc forces and evaporation recoil pressure is established.(1)Establishment of non-equilibrium melting model of wires of AC inter-wire indirect arcArc behavior,metal transfer and melting characteristics of wire are first analyzed at different polarities and different current waveforms in AC tungsten-consumable indirect arc.The climbing law of cathode spot along wire is studied,and the effect of cathode climbing on arc stability is revealed.The model of predicting melting rates of wire as cathode and anode is obtained at different current magnitude.Based on dynamic melting of the wires and alternate reciprocating motion of double droplets in AC inter-wire indirect arc,the non-equilibrium melting model of wires is established.Input data of the model are AC current waveforms,whereas output results are double synchronous wire feed speed,droplet volume and centroid position.(2)Controllability and stability of double droplets alternately active targetingStable inter-wire indirect arc is the fundamental for ensuring the droplet actively targeting.The maximum arc length is considered as the characteristic index for stability of arc.Influence of current magnitude,current frequency and angle between twin wires on the maximum arc length is theoretically analyzed and experimentally studied which provide guidance for the process range of droplet actively targeting.The behavior of double droplets alternately active targeting in AC square wave current is analyzed from which the range of current frequency is determined.With parameter optimization,controllable melting mechanism at desired position and mass and droplet alternately active targeting in double base AC pulsed square wave current are achieved which provide prerequisites for laser-assisted metal transfer.(3)Behavior and mechanism of droplet detachment under action of laser-indirect arc.Laser-assisted droplet transfer is simulated by COMSOL Multiphysics software.The effects of parameters such as incident position and laser power on the shape,spatter and detached direction of droplets are predicted and experimented.When laser irradiation is at solid-liquid interface and power is above 1200 W and 10 ms pulse width,droplets are detached from wire tips.As power is 1400 W,droplets exhibit regular shape and little spatter.Direction of detached droplets follows the laser incident direction,in accord with desired direction of laser-assisted droplet transfer.(4)Laser-assisted AC inter-wire indirect arc welding technological testThe test system including welding systems,laser systems,process control systems,image and data collection and storage systems is structured.Relative position between twin wire tips and laser focus can be accurately adjusted by hardware of the system.Software are developed for synchronous control of welding current and pulsed laser output,wire feeding speed in real time,synchronous collections of arc formation,welding current and welding voltage,etc.Based on the system,laser-assisted inter-wire indirect arc welding is carried out,the effects of laser on indirect arc and frequency of metal transfer are analyzed,and the advantage of melting rate in AC interwire indirect arc is illustrated.The influence of laser-indirect arc parameters on formation of deposited metal is revealed.The deposition rate of laser-assisted inter-wire indirect arc welding is compared with CMT welding which has also the characteristic of low heat input,and the advantage is illustrated. |
