Reasearch On The Structural Improvement Of Torch And Process Experiment In Plasma-Mig Welding

Plasmas-MIG welding combined of plasmas arc and metal electricity arc is a kind of reunite arc welding method, applying primarily to welding aluminum, magnesium.In order to solve the problems of arc igniting and stabilizing which appear in the process of plasma-MIG welding, improve the torch structure. The use of the improved torch carries out plasma-MIG welding tests to improve the inspection of the torch effect; Welding joint formation and metal transfer compared to MIG welding is analyzed.First, in order to solve plasma arc unstable problem in the process of arc igniting according to the first MIG arc and the latter plasma arc, the structure of torch is improved. But increasing a water cooling outer nozzle's first structural improvement causes plasma arc igniting difficultly. Changing the arc igniting way, MIG arc igniting is after plasma arc igniting. There are some problems in the process of plasma arc igniting including non-transfer and transfer arc according to the new way. The problems are solved by improving distance of upper and lower torch, improving inner and outer nozzle structure, changing material of seal circle, increasing insulation circle.Then, first improved and second improved plasma-MIG welding torches are used individually to carry on the welding experiments. It indicates that the cathode atomization zone narrows from 15.5-16mm to 13-13.5mm, the depth of fusion increases 2.99%-5.26%, the melt width decreases 1.53%-2.65% and the surplus is nearly invariable. All these improve that the improved torch solves problems of arc igniting and is advantageous for appearance of weld. In plasma-MIG welding, appearance of weld is controlled by total current and MIG arc occupies the main status. Compared to MIG welding, the depth of fusion increases 205%-220% and the melt width decreases 101.56%-105.45%. It turns out that plasma-MIG welding is more advantageous in weld thickness and width and is effective welding method.Finally, oscilloscope was used for study of arc voltage waveform and metal transfer at the different forms of features in plasma-MIG welding aluminum. It shows that metal transfer primarily is drop and jet flow transfer; MIG arc play a decisive role; Compared to MIG welding, existence of plasma arc reduces the critical MIG current of drop transfer to jet flow transfer; Critical current of drop transfer to jet flow transfer is measured by total current approximately 280-300A.