# Research and Development of a Novel TIG Welding Torch for Joining Thin Sheets
## 1 Introduction  
Generally, welding in the plat position is the easiest way to keep the arc stable, preventing a drop of molten metal before solidification. However, in automatically production lines, welding in this position is not always applied. Sometimes, joints are required in the vertical position. On the other hand, for in welding in the vertical position, due to the critical influence of gravity force and the difficult set-up experimental process, no reports were found in the case of thin sheets. Only a few papers were published recently for joining thin plates by a micro-tungsten inner gas (TIG) welding process [1], micro-Plasma welding [2; 3], and laser welding [4] in the plat position. For the laser welding process,because of the complexity in set-up, high cost and restricted safety conditions, it is difficult to apply in factories rather than laboratories and universities. For the micro-TIG welding process, since the tungsten electrode can be freely moved inside the nozzle, its position in comparison to the target weld position is difficult to adjust. Furthermore, arc plasma is too freely oscillated without orientation. This leads to the instability especially in the case of welding thin sheets (high welding speed and low current). In addition, micro-TIG and micro-Plasma welding equipment is normally small and flexible with the torch in semi-automatic status. In order to integrate automatically production lines, a hand-arm for keeping and controlling the welding torch needs to be specially developed. This can cause an increase in cost. As a result, these conventional welding methods have low efficiency in automatically production lines of thin sheets, especially in vertical welding position. In vertical welding, the melting material of the weld pool is tended in the downward direction according to gravity force direction. Therefore, the heat input is increased, resulting in a large and long weld pool. In this case, the molten metal of the weld pool is easy to drop. So, adjustment of welding parameters is strictly requested to prevent this phenomenon [5]. On the other hand, the stainless steel is easily distorted by the thermal process, especially in welding thin plates [6; 7]. As a result, welding thin plates of stainless steel in the vertical welding position is easy to cause overheating, resulting in welding defects such as burn-through. In order to prevent burn-through, it is necessary to control the penetration through welding parameters such as: reducing the welding current, increasing the welding speed, etc. [8]. However, decreasing the welding current or increasing the welding speed, it may result in other defects such as a blowhole, lack of fusion, under cut, or incomplete penetration due to insufficient heat input. In order to solve these problems, in recent years, an automatic TIG welding device using a novel TIG torch has been developed for joining thin plates [9; 10]. This novel torch has two nozzles. One of them has a small diameter covering the surrounding zone of the tungsten electrode. This nozzle is called the constricted nozzle. A real image and schematic of this nozzle is shown in Figure 1. As shown in this image, the constricted nozzle was with six small slits and six guides. The distance between the two guides was about 1.63-1.65 mm. This nozzle was long and extend outside conventional nozzle. Furthermore, the tungsten electrode diameter was 1.6 mm. As a result, it is impossible for the tungsten electrode to move freely inside the torch. A small amount of shielding gas from the torch flows between the tungsten electrode and this nozzle with a very high speed. This nozzle is called the \"constricted nozzle\" and this shielding gas is called the inner gas. Another kind of nozzle has a similar diameter to the nozzle of a conventional TIG welding torch (conventional nozzle). This nozzle has a large diameter to orient the shielding gas flow away from the electrode. This nozzle is called the outer nozzle and the shielding gas was controlled by this nozzle as the outer gas.