What details should be noted in TIG welding?

Thread Content

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 base metal and the filler material. 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. Tungsten inert gas 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 for the tungsten electrode. This method is suitable for welding metals such as heat-resistant steel, alloy steel, stainless steel, copper, and titanium. Direct current 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; due to the high heat generated, the tungsten electrode wears out quickly, which is why 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 alternating current, it has both a \"cathode atomization\" effect and the advantage of less tungsten electrode wear compared to the DC reverse polarity method; it is suitable for welding aluminum, magnesium, and their alloys. Nozzle selection: The size and shape of the nozzle directly affect the range and effectiveness of the argon shielding zone. Commonly used nozzles include sizes 6, 7, 8, and 10. The nozzle diameter should not be chosen to be too large, as this will hinder operation and result in waste of 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 tubes, nozzle No. 6 can be used; both nozzle No. 7 for the base coat and nozzle No. 7 for the top coat will work. For 159, nozzle No. 6 can be used for the base coat, while nozzle Nos. 8 and 10 can be used for the top coat. Depending on the welding material, we need to choose different types of electrodes. For example, for easily oxidized metals such as aluminum alloys, we generally use electrodes containing activators to break down the oxide film and ensure good welding results. At the same time, the choice of electrode diameter also directly affects the magnitude of the welding current, which in turn influences the shape of the weld and the quality of the welding process; therefore, a reasonable selection must be made based on the actual conditions. Due to the high sensitivity of TIG welding to the environment, it is necessary to provide an environment that is free from dust and wind as much as possible. Additionally, excessively high humidity can also affect the welding results; therefore, it must 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 lower, at 5–7 L/min. Outside, when there is wind, the argon flow rate should be higher, at 7–10 L/min, and windproof measures should be taken to prevent air from entering the molten pool and causing pores. On the gauge for argon, each mark on the flow meter represents 1 MP; one mark corresponds to an argon flow rate of 1 L/min. The position indicated by the float determines the rotation direction of the flow rate control switch: clockwise rotation means off, while counterclockwise rotation means 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 factor that needs attention is the purity of argon. As a shielding gas, the purity of argon directly affects the quality of the weld. If the argon gas is not pure, it may cause 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, and to test the purity of the argon before use. Pre-welding gas leakage test method: If there are leaks at the connections between the argon hose, argon regulator, and TIG torch, or if the TIG torch hose is damaged, the tungsten electrode is misaligned or bulges in the middle, or if the argon flow rate is either too high or too low, the purity of the 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 piece of scrap steel 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 four: Perform filler wire welding on the self-fusing portion. In the fifth step, the surface of the previous layer of weld is welded again using filler wire. If the argon gas is not pure 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 must also be properly controlled; either too fast or too slow can affect the formation 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 thorium-tungsten alloys. 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 contaminated metal from burning off and affecting 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 should be cleaned to remove any slag and oxide films from 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 seam meets the desired standards.