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How much do you know about TIG welding? TIG welding is a welding technique that builds upon the principles of conventional arc welding. It utilizes argon gas to protect the metal filler material. A high electric current causes the filler material to melt into a liquid state, forming a molten pool on the base metal being welded; this enables metallurgical bonding between the two metals. Since argon gas is continuously supplied during this high-temperature melting process, the filler material remains isolated from oxygen in the air, thereby preventing its oxidation. TIG welding, as a common welding method, is widely used in various industries. However, to ensure the welding quality and safety, there are several details that we must pay attention to during the process. Types and polarity of power supplies: The power supplies used for manual TIG welding include DC power supplies and AC power supplies, with DC power supplies further divided into direct current positive polarity and direct current negative polarity types. Direct current positive polarity: The workpiece is connected to the positive pole, while the tungsten electrode is connected to the negative pole. In this configuration, electrons move at high speed toward the workpiece, resulting in a high welding temperature and a deep but narrow weld pool. Positive ions rush toward the tungsten electrode, resulting in low heat loss and minimal damage to the tungsten electrode. This method is suitable for welding metals such as heat-resistant steel, alloy steel, stainless steel, copper, and titanium. DC reverse polarity method: The workpiece is connected to the negative pole, while the tungsten electrode is connected to the positive pole. During welding, electrons move at high speed toward the tungsten electrode, causing it to become very hot and wear out quickly. Therefore, this method is generally not used. Aluminum, magnesium, and their alloys used for welding high-melting-point oxide films. Due to the alternating polarity of AC power, it not only has the effect of “cathodic sputtering”, but also results in less tungsten electrode consumption compared to the DC reverse polarity method. Therefore, it is suitable for welding aluminum, magnesium, and their alloys. Selection of nozzles: The size and shape of the nozzle directly affect the coverage area and effectiveness of the argon shielding gas. Commonly used nozzles include sizes 6, 7, 8, and 10. The diameter of the nozzle should not be too large; otherwise, it will hinder operations and waste argon gas ； However, it should not be too small either, as otherwise the molten pool will not be properly protected, defects are likely to occur, and the nozzle may be damaged. For example, for 50 mm small pipes, either No. 6 or No. 7 nozzles can be used for both root and cover passes. For 159 mm pipes, No. 6 nozzles can be used for the root pass, while No. 8 and No. 10 nozzles can be used for the cover pass. Depending on the welding material, we need to choose different types of electrodes. For example, for easily oxidizable metals such as aluminum alloys, we generally choose electrodes containing activators to break down the oxide film, thereby ensuring good welding results. At the same time, the selection of the electrode diameter directly affects the magnitude of the welding current, which in turn influences the shape of the weld and the overall welding results. Therefore, it is also necessary to make a reasonable choice based on actual conditions. Due to the high sensitivity of TIG welding to the environment, it is necessary to provide a dust-free and wind-free environment as much as possible. Furthermore, high humidity can also affect the welding quality, so it needs to be carried out in a dry environment. Flow rate and selection principles of argon gas: In manual TIG welding, the flow rate of argon gas is generally 5~10 L/min. The argon flow rate should vary depending on the environment. Indoors, it can be set to a lower value of 5–7 L/min. Outdoors, in windy conditions, the flow rate should be increased to 7–10 L/min. Wind protection measures must also be taken to prevent air from entering the molten pool, which could otherwise lead to porosity. In the argon gauge, each division on the flow meter scale represents 1 MP; one division corresponds to an argon flow rate of 1 L/min. The scale indicated by the float shows the rotation direction of the flow value switch: clockwise rotation turns it off, while counterclockwise rotation turns it on. It should be noted that to ensure the purity of argon, when the gas pressure in the argon cylinder is 0.5 MPa, the gas should be replaced rather than being used up. Another aspect that needs to be paid attention to is the purity of argon. As a shielding gas, the purity of argon directly affects the quality of the weld. If the argon is impure, it may lead to quality issues such as weld oxidation and porosity. Therefore, when selecting an argon supplier, it is essential to choose one with a good reputation and consistent product quality. Additionally, the purity of the argon should be tested prior to use. Pre-welding gas leakage test method: If there are leaks at the connections between the argon hose, argon regulator, and TIG torch; if the TIG torch hose is damaged, the tungsten electrode is misaligned or bulges in the middle; or if the flow rate of argon is either too high or too low, the purity of argon will fall below 99.99%. This increases the likelihood of porosity formation and reduces the pass rate of welds. Therefore, a gas leakage test must be conducted prior to welding. When testing the purity of gases, find a thick scrap steel plate and grind it until the metallic luster is exposed. The first step is to self-fuse the grinding area. In the second step, fill the self-fluxing portion with welding wire for welding. Step three: Self-fusing the weld surface. Step 4: Perform filler welding on the self-fluxing portion. In the fifth step, the surface of the previous layer of weld is welded again using filler wire. If the argon gas is impure or there are leaks in certain areas, pores will appear during testing. Self-fusion refers to melting the base material or the weld surface without the need for filler wire. Welding current, voltage, and welding speed are the key factors that determine the welding quality. If the current is too high, it may cause the weld to melt excessively or even burn through ； If the current is too low, it may result in incomplete penetration, affecting the mechanical properties of the weld. Therefore, before welding, the current and voltage should be set appropriately based on the properties and thickness of the welding material, as well as the type of electrode. At the same time, the welding speed also needs to be controlled properly; too fast or too slow can affect the shape and quality of the weld. Selection and maintenance of tungsten electrodes: The non-consumable electrodes used in TIG welding are typically made of pure tungsten or thoriated tungsten alloy. Choosing the correct tungsten electrode diameter plays an important role in ensuring arc stability and improving pool fluidity. At the same time, keeping the tip of the tungsten electrode clean to prevent burned metal from contaminating the weld is also crucial for ensuring welding quality. Another point to note is the post-weld treatment. After TIG welding is completed, the weld seam must be cleaned to remove any slag and oxide film on its surface. Subsequently, necessary inspections and tests, such as non-destructive testing and mechanical property tests, should be carried out to ensure that the quality of the weld meets the required standards.