To perform TIG welding properly, you must keep these processing taboos in mind!

Thread Content

Taboos in TIG welding process: 1. In general welding, the DC reverse polarity welding method should be avoided. During DC TIG welding, the heat generated at the anode is much greater than that at the cathode. Therefore, when using DC straight polarity (with the workpiece connected to the positive pole), the tungsten electrode generates less heat and is less likely to overheat; as a result, a higher current can be used with a tungsten electrode of the same diameter. At this time, the workpiece generates a large amount of heat and has a deep penetration depth, resulting in high productivity. The tungsten electrode has a stronger ability to emit hot electrons than the workpiece, which helps to keep the arc stable and focused. Therefore, for most metals (except aluminum, magnesium, and their alloys), direct current electrode positive welding is preferred. During DC reverse welding, the situation is the opposite of what was described above, and it is generally not recommended. 2. The proportion of the on-time for the negative half-cycle in rectangular-wave AC TIG welding should not be too large. In rectangular-wave AC TIG welding, the DC component can be balanced and the intensity of the cathode cleaning effect can be adjusted by varying the ratio between the on-times of the positive and negative half-cycles. However, an appropriate minimum ratio should be selected based on the welding conditions, so as to meet the need to remove the oxide film while achieving maximum penetration and minimal tungsten electrode consumption. Although an excessively high proportion can result in a certain degree of cathode cleaning, it causes severe erosion of the tungsten electrode and makes the weld pool shallow and wide, which is detrimental to welding. 3 When the welding current is too high, it is not advisable to use a tungsten electrode with a sharp cone shape. Using a tungsten electrode with a thin diameter and a sharp cone shape at high welding currents results in an excessive current density, which causes the tip of the tungsten electrode to overheat and melt, as well as increasing wear and damage. Meanwhile, the arc also extends to the conical surface at the end of the tungsten electrode, causing the arc column to significantly expand and become unsteady, thus affecting weld formation. Therefore, for high-current welding, a tungsten electrode with a larger diameter should be used, and its tip should be ground into a blunt cone shape or a flat-topped cone shape. 4. The gas flow rate and nozzle diameter must not exceed their respective permissible ranges. Under certain conditions, there is an optimal range for the combination of gas flow rate and nozzle diameter. For manual TIG welding, when the flow rate is 5–25 L/min, the corresponding nozzle diameter is 5–20 mm. Within this range, if the airflow is too weak or the nozzle diameter is too large, the stiffness of the airflow will be poor, its ability to displace surrounding air will be weak, and the protective effect will be inadequate ； If the airflow is too strong or the nozzle diameter is too small, turbulence will occur due to the excessively high airflow velocity. This not only reduces the protection range, but also causes air to be drawn in, thereby diminishing the protective effect. 5. For gas shielded welding, an excessively high welding speed should be avoided. The appropriate welding speed is primarily determined by the thickness of the workpiece; it must also be coordinated with parameters such as welding current and preheating temperature to ensure that the desired penetration depth and weld width are achieved. However, during high-speed automatic welding, the effect of welding speed on the gas shielding effectiveness must also be considered; thus, excessively high welding speeds should be avoided. Due to an excessively high welding speed, the shielding gas flow lags significantly behind; this may cause the tip of the tungsten electrode, the arc column, and the molten pool to be exposed to the air, thereby compromising the shielding effect. 6. The distance between the nozzle and the workpiece should neither be too large nor too small. This distance reflects the relative length of the electrode’s protrusion and its curvature. When the length of the electrode extension remains constant, changing the distance between the nozzle and the workpiece alters both the length of the arc and the condition of gas protection. If the distance between the nozzle and the workpiece increases, the conical shape of the arc will become larger, which significantly affects the gas shielding effect. However, being too close not only affects visibility but also makes it easy for the tungsten filament to come into contact with the molten pool, resulting in tungsten inclusions. Generally, the distance between the tip of the nozzle and the workpiece is between 8–14 mm. 7 For tungsten inert gas welding, the contact ignition method should be avoided. Contact ignition involves directly short-circuiting the end of the tungsten electrode to the workpiece and then quickly pulling it away to ignite the arc. This arc-starting method has poor reliability; the tungsten electrode tends to burn out, and the tungsten metal that mixes into the weld can cause a \"tungsten inclusions\" defect. Therefore, contact ignition has many drawbacks and is not easy to adopt. 8. For TIG welding, a simplistic welding procedure should be avoided. An overly simple procedure tends to result in noticeable weld depression, porosity, and crack defects; this is especially true for materials with a high tendency toward hot cracking. The proper welding process should involve starting and ending the arc under argon protection, in order to prevent oxidation of the tungsten electrode and the weld metal, which could affect the quality of the weld. At the same time, the method of current attenuation is used to reduce the welding current, thereby preventing cracks from forming by gradually decreasing the heat input to the weld pool. 9 During flat welding, the welding torch should not move in a jumping manner. Flat welding is a welding position that is relatively easy to master, and it is suitable for both manual and automatic welding. During welding, the position of the tungsten electrode relative to the workpiece must be accurate, and the angle of the welding torch should be appropriate. Special attention must be paid to the stability of the arc and the uniformity of the torch’s movement speed, in order to ensure that the depth and width of the weld are consistent. For manual welding, the leftward welding method is recommended, with the welding torch moving in a steady straight line. To achieve a certain weld width, the welding torch is allowed to swing horizontally, but should not jump. The diameter of the filling thread generally does not exceed 3 mm. 10 In hot-wire TIG welding, aluminum and copper welding wires should not be used. The resistive heat generated by an additional power source at the front end of the welding wire can heat the wire to a predetermined temperature, thereby increasing the welding deposition rate. However, for aluminum and copper, due to their low resistivity, a very powerful heating power source is required, which leads to excessive arc magnetic deflection and uneven melting; therefore, aluminum and copper welding wires are not suitable for hot wire welding.