Study On The Arc Behaviour And Metal Transfer In Laser- MIG Double Wires Hybrid Welding

Based on the requirement for the high productivity and good quality in the welding, a novel welding method named laser-MIG double wires hybrid welding is developed with combining laser welding and double wires welding. In this study, the welding process and the arc behaviour and metal transfer are studied in order to lay the foundation for the development of welding technology, the theoretical study and the practical application.(1) The welding system of laser- MIG double wires hybrid welding is developed. The electrical signal and high-speed photography collection system are built. There are three modes for the output power source which include double direct current(DC), pulse- direct current(P-DC), double pulses(P). Therefore, the laser- MIG double wires hybrid welding can be divided to three methods including laser-DC MIG double wires hybrid welding, laser- P-DC MIG double wires hybrid welding and laser-P MIG double wires hybrid welding. The pulse controller is designed for out-of-phase current pulse. The effect of laser power, wire feeding velocity, laser-arc distance and laser defocusing distance on welding stability, arc behavior and metal transfer are investigated. Meanwhile, some parameters are selected to evaluate the welding stability, arc behavior and metal transfer including the coefficient of variance of welding voltage, the arc intensity, and the arc offset angle, the mode and frequency for metal transfer.(2) In laser-DC MIG double wires hybrid welding, it is found that when the laser power is 1000 W, the welding process is the most stable. With the laser power increasing, the arc offset angle decreases firstly and then increases. For the leading wire, the metal transfer is globular transfer and the metal transfer frequency increases firstly and then decreases. When the wire feeding velocity is 4m/min, the stability for the leading and trailing arc is the best. As the wire feeding velocity increases, the arc offset angle decreases firstly, then increases and finally keeps unchanged. When the laser defocusing distance is-1mm, the metal transfer frequency reaches the maximum value. For leading and trailing wire, the maximum frequency is 8.6Hz and 6.3Hz respectively.(3) In laser- P-DC MIG double wires hybrid welding, the metal transfer is spray transfer for the leading wire and globular transfer and short circuit transfer for the trailing wire. The wire feeding velocity has little influence on the stability of the leading wire. And when the wire feeding velocity is 4m/min, the stability of the trailing wire is the best. When the laser-arc distance increases, the welding stability becomes worse and then has little influence. When the laser defocusing distance is 0mm, the metal transfer frequency reaches the minimum value. For leading and trailing wire, the minimum frequency is 75 Hz and 3Hz respectively.(4) In laser-P MIG double wires hybrid welding, with the laser power increasing, the welding stability decreases firstly and then increases, the arc offset angle and the metal transfer frequency both increase. As the wire feeding velocity, the welding stability improves. At 4m/min, the arc offset angle keeps unchanged. When the wire feeding velocity is 2m/min, the laser-arc distance is smaller than 8mm, there is short circuit metal transfer. When the laser-arc distance increases, the welding stability becomes the worst at 6mm and then has little influence. The minimum arc offset angle occurs at laser-arc distance 4mm. When the laser defocusing distance is 0mm, the metal transfer frequency reaches the minimum value. For leading and trailing wire, the minimum frequency is 27 Hz and 12 Hz respectively.