Guide to TIG Welding (GTAW)
Table of Contents
TIG welding (GTAW or gas tungsten) is an arc welding process that operates at high temperature (over 6,000 degrees Fahrenheit) to melt and heat metals. While it is more expensive than stick welding, it is cleaner and more versatile (works on steel, aluminum, brass and many other metals).It results is high quality welds.
On the downside the equipment is more expensive and the process is slower than other welding processes. Unlike GMAW or MIG welding, a non-consumable (doesn't get melted) tungsten electrode is used. The electrode creates an electrical arc which produces the required heat. The Tig torch is cooled by air or water and the process uses a filler metal in rod form.
GTAW also requires a shielding gas such as argon or helium to protect the weld from the atmosphere.
The gas tungsten arc welding process is generally not commercially competitive with other processes for welding heavier gauges of metal if they can be readily welded by the shielded metal arc, submerged arc, or gas metal arc welding processes with adequate quality.
Tig Welding Example
Gas tungsten arc welding (GTAW) is a process in which the joining of metals is produced by heating therewith an arc between a tungsten (non-consumable) electrode and the work.
A shielding gas is used, normally argon.
normally done with a pure tungsten or tungsten alloy rod, but multiple electrodes are sometimes used.
The heated weld zone, molten metal, and tungsten electrode are shielded from the atmosphere by a covering of inert gas fed through the electrode holder.
Filler metal may or may not be added. A weld is made by applying the arc so that the touching workpiece and filler metal are melted and joined as the weld metal solidifies.
This process is similar to other arc welding processes in that the heat is generated by an arc between a nonconsumable electrode and the workpiece, but the equipment and electrode type distinguish itfrom other arc welding processes.
See figure 10-32.
Advantages and Disadvantages
- Works on almost all types of metals with higher melting points. Gas tungsten arc welding is the most popular method for welding aluminum stainless steels, and nickel-base alloys. It is generally not used
for the very low melting metals such as solders, or lead, tin, or zinc
It is especially useful for joining aluminum and magnesium which form refractory oxides, and also for the reactive metals like titanium and zirconium, which dissolve oxygen and nitrogen and become embrittled if exposed to air while melting.
- Pinpoint accuracy and control. The process provides more precise control of the weld than any other arc welding process, because the arc heat and filler metal are independently controlled.
- Good looking weld beads
- For metals of varying thickness including very thin metals (amperage range of 5 to 800, which is the amount of electricity created by the welding machine). The gas tungsten arc welding process is very good for joining thin base metals because of excellent control of heat input.
- creates strong joints. It produces top quality welds in almost all metals and alloys used by industry.
- clean process with minimal amount of of fumes, sparks, spatter and smoke
- High level of visibility when working due to low levels of smoke. Visibility is excellent because no smoke or fumes are produced during welding, and there is no slag or spatter that must be cleaned between passes or on a completed weld.
- Minimal finishing required. In very critical service applications or for very expensive metals or parts, the materials should be carefully cleaned of surface dirt, grease, and oxides before welding.
- Works in any position
- TIG welding also has reduced distortion in the weld joint because of the concentrated heat source.
- As in oxyacetylene welding, the heat source and the addition of filler metal can be separately controlled.
- Because the electrode is non-consumable, the process can be used to weld by fusion alone without the addition of filler metal.
- Brighter UV rays when compared to other welding processes
- Slower process than consumable electrode arc welding processes.
- Takes practice
- More expensive process overall. Expensive welding supplies (vs. other processes) because the arc travel speed and weld metal deposition rates are lower than with some other methods.
Inert gases for shielding and tungsten electrode costs add to the total cost of welding compared to other processes. Argon and helium used for shielding the arc are relatively expensive.
Equipment costs are greater than that for other processes, such as shielded metal arc welding, which require less precise controls.
- Not easily portable, best for a welding shop
- Transfer of molten tungsten from the electrode to the weld causes contamination. The resulting tungsten inclusion is hard and brittle.
- Exposure of the hot filler rod to air using improper welding techniques causes weld metal contamination.
TIG Welding Example 2
As mentioned, since tungsten welding operates at high temperatures, ideal metals are those that have a low melting point. This includes:
- Aluminum: use on AC output and high frequency setting. Keep the tungsten from touching the piece being welded to avoid contamination. Conducts heat. Clean aluminum with a wire brush (even if it looks clean) to remove aluminum oxide. Use high heat settings to increase welding speed.
Not all aluminum alloys can be welded. An alternative to TIG welding aluminum with a simpler process is to use HTS-2000 aluminum brazing.
- Magnesium: similar properties to aluminum
- Copper alloys (brass, bronze, copper nickel, copper aluminum, silicon): use DC current with electrode negative
- Stainless steel: requires the use of a filler rod with high chrome component. Use gas lenses for better gas coverage of weld. Keep gas flow at 15 to 20 cfh.
- Mild steel: use rods with deoxidizers. The ungsten electrode should be 2% thoriated. Clean the steel before welding.
If TIG weld cracking occurs preheat the metal to 400 degrees Fahrenheit. This helps with the contraction and expansion of the metals when welding.
- operate with safety in mind
- ensure that the argon or helium gas supply has low moisture
- use filler rods that are clean and keep the weldiing area dry
- tungsten electrode selection and parameters for welds are guidlines not absolute
- follow the welding safety precautions provided by all material providers. Since tungsten has soem radioactivity, if grinding wear a respirator
- bigger rods are easier to handle
- the tungsten electrode should be the smallest needed to do the job
- keep the rod and torch at different angles
- wind drafts will reduce effectiveness of shielding argon or helium gas resulting in pin holes in weld
- higher amps require larger orifice
- if the tungsten moves or wiggles during the welding process it indicates that the tungsten is near its capacity. Use the balance dig dial moved to the penetration side.
- 100% Argon (most common, coolest)
- 75% Argon/25% Helium
- 75% Helium/25% Argon (hottest gas, higher % of helium can result in arc starting issues)
- 100% Helium (hard to start arc, very hot.)
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Page Author: Jeff Grill