| In recent years, hybrid welding technology has always been a research focus in the field of welding. Compared with ordinary single arc welding, hybrid welding technology can elevate welding efficiency and quality dramatically. In order to take full advantage of plasma arc welding and TIG welding method, Plasma-TIG hybrid welding(P-T) is realized in this paper through fixing small-sized plasma torch and TIG torch into one independent hybrid welding gun. As the characteristics of hybrid welding method, arc physical properties and welding processing performance are investigated systematically in this research.Arc shape images captured by CCD camera are enhanced by pseudo-color image processing technique. The “static small hole†method is carried out to measure the arc pressure. The research results show that the two arcs pull each other into one uniform arc-“coupling arc†under the action of Lorentz force. As the major factor of coupling arc pressure, plasma arc current determines the change of the plasma arc pressure peak value before and after the combination. The coupling arc pressure is distributed in a “gourd†shape. In aspect of static arc properties, the I-U curves of two arcs are in upward trend. Compared with the single arc voltage, in hybrid condition, the plasma arc voltage decreases, but the TIG arc voltage lessens first and then enlarges.The research of hybrid weld formation of low carbon steel is carried out, including analyzing weld formation characteristics, studying the effect of wire feeding mode and welding factors on the weld formation as well as explaining the improvement mechanism by the observation of weld pool morphology and force analysis. The results suggest that, Plasma arc can be assisted by TIG arc in the arc stress and heat input, which makes the surface forming and weld penetration of the hybrid weld obviously superior to the single arc weld. The flow pattern of the molten pool shows that the molten pool is in a dynamic oscillation state under the combined action of plasma arc stress, TIG arc stress as well as the gravity of liquid metal. The parameter range of side feeding is very narrow; front and back feeding can get a good weld, and the latter can acquire a larger weld penetration. Plasma arc stress at the left edge of molten pool will be larger than the sum of TIG arc stress and gravity of local liquid metal when plasma current or electrode spacing is too large, which can result in a great number of pores in the weld.The characteristics of PAW-TIG hybrid welding and P+T welding method in 5 mm low carbon steel butt welding test are analyzed comparatively and the properties of weld are evaluated. The results show that, with a beautiful front-back surface weld formation, hybrid welding seam shows an integrated weld metal zone in the interface morphology, while the metal zone of P+T weld is consist of two parts, which has the characteristic of double pass welding. The power consumption of P+T welding method is 1.5 times as high as that of P-T hybrid welding with the precondition of obtaining good front-back weld formation. Compared with P+T welding method, thanks to the dynamic oscillation state in the molten pool, epitaxial solidification in the hybrid weld fusion zone is inhibited obviously. Meanwhile, acicular ferrite in the lower part of weld metal zone increases apparently. The results of tensile strength of weld area show that the average tensile strength and mechanical property homogeneity of hybrid joint are better than that of P+T welding method. In addition, the upper part hardness value of the hybrid weld is less than that of P+T, and the lower part hardness value is obviously higher than that of P+T. |
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