Tungsten Inert Gas Welding (TIG), also known as Tungsten Arc Welding (GTAW), is an arc welding process that uses a non-consumable tungsten electrode to weld.
Tungsten Inert Gas (TIG) welding became an instant hit in the 1940’s for joining magnesium and aluminum. By using an inert gas shield instead of slag to protect the weld pool, the process has proven to be a very attractive alternative to gas welding and manual metal arc welding. TIG has been instrumental in the acceptance of aluminum for high quality welding and construction applications.
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Process Features
In the TIG welding process, the arc is created between a pointed tungsten electrode and the workpiece in an inert atmosphere of argon or helium. The small, intense arc generated by the sharp electrode is ideal for high-quality and precise welds. Since the electrode does not wear out during welding, the TIG welder does not have to compensate for the heat input of the arc when the metal is deposited from the consumable electrode. If filler metal is required, it must be added separately to the weld pool.
Power Source
TIG welding must be performed with a DC or AC dip power source.A constant current source is required to avoid excessive current being drawn in the event of a short circuit between the electrode and the surface of the workpiece. This can be done intentionally when striking the arc or accidentally while welding. If a flat-curve power source is used, such as in MIG welding, contact with the workpiece surface could damage the electrode tip or fuse the electrode to the workpiece surface. Since with direct current the heat of the arc is distributed approximately one-third to the cathode (negative) and two-thirds to the anode (positive), the electrode is always negatively poled to avoid overheating and melting. However, the alternative connection of the power source with the positive polarity of the DC electrode has the advantage that the surface is cleaned of oxidic impurities when the cathode is in place.For this reason, materials with a permanent surface oxide layer, such as aluminum, are welded with alternating current.
Arc ignition
Welding arc ignition can occur by scratching the surface and causing a short circuit. The main welding current only flows when the short circuit is broken. However, there is a risk that the electrode will stick to the surface and cause tungsten inclusions in the weld. This risk can be minimized by using the “lifting arc” technique, where the short circuit is created at very low current levels. The most common way to start a TIG arc is to use HF (high frequency).HF consists of high voltage sparks of several thousand volts lasting a few microseconds. The high-frequency sparks create or ionize the gap between the electrode and the workpiece. Once the electron/ion cloud has formed, current can flow from the power source.
Note: Because HF produces extremely high electromagnetic (EM) emissions, welders should be aware that its use can cause interference, particularly with electronic equipment. Because EM emissions can be transmitted in the air, as radio waves, or along electrical wires, care must be taken to avoid interfering with control systems and tools in the vicinity of the welding area.
HF is also important for AC arc stabilization; With alternating current, the polarity of the electrode is reversed about 50 times per second, so the arc is extinguished with each polarity change. To ensure that the arc is re-ignited with each polarity change, HF sparks are generated across the gap between the electrode and the workpiece at the start of each half cycle.
Electrodes
DC welding electrodes are typically made of pure tungsten with 1-4% thorium content to improve arc initiation. Alternative additives are lanthanum oxide and cerium oxide, which offer better performance (arc ignition and reduced electrode wear). It is important to select the correct electrode diameter and tip angle for the level of welding current.In general, the lower the current, the smaller the electrode diameter and tip angle. AC welding uses tungsten with zirconium to reduce electrode erosion as the electrode operates at a much higher temperature. It should be noted that due to the large amount of heat generated at the electrode, it is difficult to maintain a sharp tip and the tip of the electrode becomes a sphere or “sphere”. Profile.
