| Arc assisted activating TIG welding, in short AA-TIG, is a highly efficient welding method that combines the advantages of activating TIG welding and twin-TIG (in short T-TIG) welding. Characterized by two parallel tungsten-electrodes within the welding torch and two independent power supplies during welding, the coupling arc is thus formed. And the indraft of certain volume of active gases such as O2could significantly enlarge the weld penetration. In this paper, S30408stainless steel is chosen as the base metal for the procedure test of AA-TIG welding. The main and auxiliary arcs are protected respectively by pure argon and a certain amount of oxygen and argon. The current value of the former is greater than that of the latter. Moreover, the single-pass weld penetration is up to11.06mm, and the depth-to-width ratio can reach more than1.3. Its production efficiency is at least5times higher than that of the ordinary TIG welding.This paper mainly studies the following four aspects, including:firstly, designing and manufacturing the welding torch that is applicable to the characteristics of such welding technique; secondly, observing the arc morphology features of AA-TIG welding; thirdly, researching on the welding technique that applies to the butt welding of AA-TIG welding to the8mm thick S30408stainless steel, as well as on the influencing rules of the tungsten electrodes pitch, the length of the arcs, the intake volume of active gases, the intensity of the current, etc. on the morphology of the welding joints to obtain better welding parameters; finally, studying the influence of the main welding parameters on the mechanical properties of the butt weld.As an important part to realize the welding process, the welding torch is firstly designed and manufactured. Its design features are mainly:that the two tungsten electrodes should be insulated from each other and their power should be supplied by different sources to meet arc couplings at various degrees; that it should contain two independent air chambers to meet the protection for the main and auxiliary arcs respectively from different protective gases; and that the pitch between the two tungsten electrodes should be inimitably adjustable between lmm and12mm. Then the structure of the welding torch is further optimized by analyzing the flow behavior and component of the protective gases within the torch through numerical simulation. Finally, the arc morphology is observed and the butt test is conducted with the self-designed and self-manufactured torch.From the analysis of the arc topography images obtained, it is not difficult to find that, different from the bell-shaped appearance generated by the ordinary TIG welding, the coupling arc of AA-TIG welding is an obviously contracted "abnormal" arc formed in the bottom area between the two tungsten electrodes. The coupling arc is closer to the tungsten electrode where the current is intensive along the current distribution.In addition, the procedure test of AA-TIG welding is carried out. By comparing the weld surface formation and the joint cross-sections of the ordinary TIG welding, T-TIG welding and AA-TIG welding, the conclusions can be drawn that AA-TIG welding can significantly increase the weld penetration as the AA-TIG welding combines the advantages of both activating TIG welding and twin-TIG welding, and that the weld joints show good surface formation and deep penetration due to the lower arc pressure of T-TIG; Furthermore, the influence of spot welding time, arc length and current ratio on the weld joint formation is studied through AA-TIG welding spot welding test.The joint performance of the butt welding of AA-TIG welding against S30408stainless steel is tested through its mechanical properties. Besides, the tensile test at room temperature and the low temperature impact toughness at-40℃are also performed. The test results show that the tensile strength and the impact toughness at low temperature of the welding joint are both slightly lower than that of the base metal. According to the corresponding criteria, it can be seen that the welding joint performance of S30408stainless steel welded by AA-TIG welding is qualified. The corrosion resistance property test of the butt joint indicates no intercrystalline corrosion or cracks, which is in accordance with the inspection requirements stipulated by GB/T4334-2008E method. Moreover, the inspection of the welding joint’s plasticity via the face and root bend test finds no cracks, either.This paper indicates that the self-designed AA-TIG welding torch can meet the requirements of the welding parameters via the procedure test and the inspection of the related properties of the joint. The studies in this paper also show that AA-TIG welding can dramatically improve the disadvantages of the ordinary TIG welding, such as the shallow weld penetration, the low efficiency, etc. The welding process of the activating TIG welding is also changed, so that the coating of active agent is no more required, thus more easily to realize the automatic activating welding. The equipment used by AA-TIG welding is the same with that of the ordinary TIG welding, the only change of which is the welding torch. The low production cost makes it a promising method of welding. |
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