# Research and Development of a Novel TIG Welding Torch for Joining Thin Sheets
## 1 Introduction
Among the shielding gases, the outer gas has a task similar to the shielding gas flow in the case of the conventional TIG welding process. In this case, the inner gas flow plays a main role in pressing the arc plasma, resulting in a more rigidified arc plasma in comparison to the conventional TIG welding process. Its gas flow rate was increased strongly because it is throughout a small gap between the tungsten electrode and the constricted nozzle. Using this nozzle, the plasma arc characteristics can be improved and the heat input can be precisely controlled to maintain the welding stability. In this case, the arc column is constricted through the thermal pinch effect to increase the temperature at the center area of the arc plasma [11]. Therefore, it leads a concentrated plasma flow with a high-speed plasma jet and high arc pressure impinging on the base metal surface. In addition, it accelerated the plasma jet through a high-speed inner gas flow, as mentioned above. Therefore, (1) the magnetic field acting on the arc; (2) the energy density of the arc plasma; and (3) the discharge capacity of electrons are increased strongly in comparison to the TIG welding process using a conventional TIG torch [12]. Another advantage of this gas flow is that it increases the cooling rate and decreases the temperature of the tungsten electrode, therefore the life cycle of the tungsten electrode can be extended and the stabilization of arc plasma can be kept during a long time. As a result, double shielding gas flows, thereby preventing the reduction of the shielding effect, which has been a problem in the conventional TIG welding process. In addition, due to the high-speed inner gas flow, the metal evaporation from the weld pool is pushed outside to prevent the attachment of evaporated metal on the tip of the tungsten electrode. Consequently, the tungsten electrode become cleaner, reducing contamination, and the arc length can be set up in extremely short distances. This is a useful characteristic in order to prevent the expansion of the arc plasma, which is an advantaged point that the conventional TIG welding process does not have. From all of the above, welding with high speed and low current can be obtained. Consequently, in comparison to the TIG welding process using a conventional TIG torch better welding quality can be obtained at a high speed and a low current for joining thin sheets. As a result, many factories worldwide have efficiently utilized our equipment. In order to clarify the advantages of this torch, our group has been starting to study the mechanism and examine the availability of this welding technology. In a paper by [PERSON] et al., the influence of the constricted nozzle was discussed using numerical simulation in the case of 3 mm arc length [13] with an anode of water-cooled copper. The results showed that, in comparison to the conventional TIG welding process, the heat flux on the anode surface was increased. Especially at the center of the arc, the heat flux was highly increased. However, the simulation is limited by boundary conditions and assumptions. Therefore, it is difficult to obtain comprehensive and full understanding about the mechanism of this process with only a numerical method. Therefore, the experiments are also indispensable. In a recent paper, [PERSON] et al. discussed the influence of oxygen contamination and heat input on the anode surface in order to ensure a high-quality welding [14] in the case of an anode of a water-cooled copper. The experimental results evidenced that in the case of TIG welding with a constricted nozzle, the oxygen content on the weld pool surface is lower in comparison to the conventional TIG welding process. In another paper, [PERSON] et al. performed experiments in practical welding conditions at industrial factories. This paper indicated that thin sheets of 0.1 mm can be welded with sound quality at an extremely short distance of arc length (0.1 mm), high welding speed and low welding current with no surface defects such as undercut and burn-through [15].