Shop What is Tig Welding?
What is Tig Welding?
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atmospheric contamination by an inert shielding gas (argon or helium). A filler metal is normally used, though some welds, known as autogenous welds, or fusion welds do not require it. When helium is used, this is known as heliarc welding. A constant-current welding power supply produces electrical energy, which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma. GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminum, magnesium, and copper alloys. The process grants the operator greater control over the weld than competing processes such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds. However, GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques. A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.
Equipment Used for GTAW.
Machines for TIG welding are classified as constant current (variable voltage) machines. They have a drooping output slope. When welding output voltage goes down as arc length shortened. Arc length is a important variable in the Tig welding process, pool width is directly proportional to to the arc length, to a lesser extent arc length changes the weld bead penetration profile and shielding gas coverage. Arc length is usually an essential variable in welding procedures.
Polarity and current characteristics of the tig welding process. What is the correct polarity for Tig Welding? When setting up a tig welder you must be mindful of the polarity characteristics required for the welding process, The most common polarity for tig welding is DCEN with this polarity the electrons flow from the electrode to the work piece and the positive ions are transfered back to the electrode. When DCEN is used with tig welding approximately 70% of the heat is generated in the base material, leaving 30% of the heat at the Tungsten or cathode, DC Electrode Negative provides the deepest penetration profile, albeit DC Electrode Positive Provides a cathodic cleaning action and is the most important when welding alloyed materials like aluminum. DCEP bombards the tungsten with heat, unlike DCEN which helps to cool the Tungsten Electrode, therefore when using DCEP very large electrodes are required.
When welding aluminum usually Alternating Current is used, AC reverses the polarity of DCEN to DCEP, the current will drop to a zero point in the middle, the thermionic electrode will become negative it cannot supply the electrons until the voltage is raised significantly to initiate the cold cathode emission, without the voltage the arc fails to reignite, stabilizing the arc during the voltage reversal is accomplished with high voltage high frequency sparks. Square wave power sources can change the direction of the welding current in a very short period of time, thus the heat from the welding pool and the short period of time allow the arc to be reinitiated without the need for continuous high frequency generation.
Duty cycle is an Important rating, expresses as percentage, portion of time power supply must deliver rated output in 10-minute interval.
- NEMA CLASS I. These machines deliver rated outputs at a 60%, 80%, or 100% duty cycle.
- NEMA CLASS II. These machines deliver rated outputs at a 30%, 40%, 50% duty cycle.
- NEMA CLASS III. These machines deliver rated outputs at a 20% duty cycle.
Most welding machines are not required to operate 100% of the time. If they are used to weld one hundred percent of the time, a machine with a 100% duty cycle would be required. Work must be loaded and unloaded, and electrodes must be changed. Metal must be chipped, cleaned, or inspected. The duty cycle normally recommended for manual welding is 60%. Automatic and semiautomatic welding operations usually require 100% duty cycles. Light duty work, such as that done in the home hobby shop, could possibly be done using a machine with a duty cycle as low as 20%. When welding work is done lower then the duty cycle current output, the duty cycle rating is increased.
Advantages of Gas Tungsten Arc Welding.
Tig Welding offers and extensive range of application for high quality, precise welds, for use in the aerospace, nuclear, and petrochemical industries, be it autogenous welding without filler metal, or adding filler metal with a hot wire, or cold wire, and the most popular manual feed process. Welds can be made in any position with relatively cheap power sources producing superior quality and minimal defects.
Disadvantages of Gas Tungsten Arc Welding.
Deposition rates are generally lower then other welding processes. More skill is required to produce quality welds in all positions. Low tolerance of contaminated materials. More expensive then other processes. Low tolerance to windy conditions.
Applications of Gas Tungsten Arc Welding.
Tig welding is often used when critical weld quality is required. The precise nature of Tig welding has the best control of heat input for joining thin materials be it sheet metal or process piping. Tig welding can be used to weld most materials including aluminum and magnesium, copper, brass and other difficult materials.
Equipment used with Gas Tungsten Arc Welding.
Water cooled torches are normally classified as medium to large style torches, albeit water cooled torches lend themselves to micro torches and small torches quite well for extended periods of welding, Coolant is passed through the torch hose to cool the power cable, it is provided by a separate hose that attaches to the coolant chilling unit. Liquid cooled tig torches are normally 20 series and 18 series units.
Air cooled Torches use the flow of shielding gas to cool the tig torch while welding, they lend themselves to their portability with a minimal cost, most gas cooled torches are limited to the 150-300 amp range. They are usually 9 series, 17 series or 26 series Tig Torches.
Collet Bodies are designed to facilitate the tightening of the collet providing radial clamping force on the non consumable tungsten. Collet bodies are sized to fit specific sizes of tungsten, the radial center hole helps to facilitate the transfer of current from the power source to the tungsten electrode, ensuring proper collet body size is key to the longevity of your tungsten and collet.
Nozzles used with tig welding are made of various types of material, including ceramics, alumina, fused quartz and even Pyrex. The nozzle size and shape depend on essential variables, if to small of a nozzle is used, turbulence can occur, if to large of a nozzle is used the view of the weld maybe hidden from the operator. Larger nozzles require higher flow rates there bye reducing turbulence but possibly wasting valuable shielding gas. Gas lenses help to reduce turbulence by producing a laminar flow of shielding gas, they contain a diffuser that produces undisturbed flow of shielding gas, allowing large nozzles to work further away from the work piece improving view, shielding gas coverage and quality of the weld pool.
Tungsten is a metallic element that is valued for its use in manufacturing. The electrodes necessary in GTAW are comprised of tungsten. Because of its strength and high melting point, it is a critical component; the tungsten electrodes essentially carry the heat.
Choosing the Right Electrodes for GTAW
As with most processes, quality tools and components positively impact the job as well as the result. GTAW is no exception. The correct Tungsten electrodes depend upon the project being built as well as the tools being used. To make the selection easier, electrode tips are color-coded. Understanding the differences is important in choosing the right one for the job at hand.
These electrodes contain both tungsten and zirconium and, as such, are also referred to as zirconiated electrodes. Of particular value in AC welding, these electrodes maintain their balled tip and are resistant to contamination. It is important to understand that brown electrodes should NOT be used in DC welding.
These electrodes, which contain both tungsten and lanthanum, can be fashioned (balled or sharpened) to meet the needs of the welder. Appropriate for use in specific AC and DC welding, these electrodes are incredibly versatile. The addition of the lanthanum increases their capacity. Also, gold electrodes do not contain radioactive elements.
Previously known as orange electrodes, these are non-radioactive and can be used on both AC and DC projects. They are easy to ignite and incredibly durable, which makes them popular among welders.
Often used in AC welding, green electrodes are composed of pure tungsten. For example, green tungsten electrodes are often used in AC welding because of their arc stability. These electrodes can be a good value. They are more inexpensive than others but do need to be replaced more frequently.
Also known as thoriated tungsten, these electrodes are both long-lasting and easy to use. Thus, they are the most popular. They can be used for both AC welding of thinner materials and specific DC welding products. It is important to recognize that thorium is radioactive and specific cautions should be taken when using them.
Purchasing GTAW Electrodes
Clearly, the options for electrodes for GTAW are considerable. And, selecting the correct ones for the job at hand is important. When purchasing electrodes and other welding components, working with a retailer who specializes in welding can be incredibly helpful. The experts on staff can help you select the most appropriate products for both your tools and the jobs you plan to undertake.
Badd Ass Welding is an online web store proudly supplying a broad range of welding products across the country and around the world. Our on-staff experts are available to answer all of your welding questions.
Shielding Gases are normally inert, either argon or helium, used separately or in tandem. Straight argon is normally used for all tig welding applications, but mixed argon helium blends work quite well with under powered small tig welding machines on aluminum due to its voltage current relationship, although arc stability becomes a issue.
Pure argon is used with most materials, steels, stainless steels except reactive and refractory metals, it provides the smoothest arc action, low cost, lower flow rate requirements and easier arc starting characteristics. Argon is the preferred gas to use with Tig welding. When choosing gas flow rates, determine weld pool size and reactivity of the weld material, remember you are trying to overcome the effects of the arc and any drafts, a good starting point for argon can be anywhere from 15 to 35 cubic foot per hour.
Author. Jon Lawson AWS CWI 12040921.