Study On The Plasma-MIG Welding Method And Its Dual-Arc Hybrid Characteristics

Plasma-MIG welding is a hybrid arc welding method. The method can provide high energy density and high efficiency, especially suitable for the welding of aluminum and its alloys. In this work, the principle of the method and the arc hybrid mechanism was investigated. The apparatus and torch used for the method were designed and manufactured. It is said that the welding method was firstly applied in engineering in China.By the coupling simulation of flow field and temperature field inside the plasma-MIG torch, the heat transfer process at each local part of the torch was studied. Besides, by the simulation calculation of heat diffusion of the key parts of the torch, the structure and cooling condition inside and outside of the torch were optimized. The cooling status of the torch at different water entrance diameter, hole length, water channel width and nozzle compressing angle were analyzed, and the optimal ranges of these torch parameters were given. These data provided some quantitative rules for the torch design.Based on finite element analysis of the gas flowing and temperature distribution around the arc, Paschen law was used to determine the breakdown path of plasma arc under the condition that the MIG arc has provided an electric path. The arc igniting process under the arc hybrid condition was studied by the theory. By setting an arc leading point on the torch nozzle, the separation of the duplex arcs come trued, and effect of arc the separation was tested by welding practice. The influence of the weld bead height, arc dragging and hanging droplet on the arc igniting and stable were analyzed too. Finally, the processes forecasted by the simulation were observed in the actual welding.By the simulation calculation, the welding temperature field formed by hybrid arc was analyzed and the shape of welding pool was calculated. The maximum width and depth of the weld metal formed at different arc space were determined.In this work, a special power system used for plasma-MIG welding was designed and developed. The power system included two inverter power sources with different external characteristic, they can meet the requirement of plasma arc and MIG arc. The power sources have excellent dynamic characteristic and regulating characteristic, and can be connected to computer through an interface circuit.