Gas tungsten arc welding is known for producing superior and high-quality welds.
Therefore, it is a leading option for applications where the appearance and strength of the weld joint are both important. Despite its long list of benefits, it also has some drawbacks, the top one being that it is slower and less productive than other welding methods.
Read the complete guide to gas tungsten arc welding to understand how this welding process works.
What Is Gas Tungsten Arc Welding?
Gas tungsten arc welding or GTAW is also called tungsten inert gas welding – TIG welding. This versatile welding technique works by means of an electric arc created between the base metal (that is to be welded) and a tungsten electrode (non-consumable).
A welder operates a torch, which steadily feeds shielding gas to protect the hot base metal and molten weld pool from environmental corrosion and contamination. Argon gas is usually deployed for TIG welding since it is an inert gas and is therefore ideal for safeguarding the weld joint.
The shielding gas is odorless and lucid, so the operator can easily see the weld and arc. Hydrogen gas is included in some scenarios for greater travel speed.
In gas tungsten arc welding, temperatures can reach as high as 35,000 degrees Fahrenheit. The TIG welding torch directs intense heat to the base metal. If a filler material is required for the welding process, it has to be fed manually—just like in oxyacetylene gas welding. Cold wire feeders are also available, and filler materials can be added when appropriate.
Thus, the electric arc creates a weld pool, which melts filler metal and base metal. The weld pool solidifies to form a powerful bond between the previously separate surfaces.
GTAW is a truly versatile welding technique not just because it is suitable for a wide range of alloys and metals, but also because it permits all kinds of intricate welding movements.
GTAW is an excellent welding option for stainless steel, all types of nickel alloys, such as inconel and monel, aluminum, titanium, copper, magnesium, bronze, brass and gold. GTAW can fuse dissimilar metals with each other, such as stainless steel with mild steel and brass with copper.
GTAW Advantages
- An intense arc allows highly controlled heat input to the base metal, creating a relatively narrow heat-affected region.
- GTAW welding does not produce any slag. Flux is not needed for this welding procedure. Hence, there is no slag to chip off once the weld is complete, nor does slag reduce or obscure the weld joint.
- No spattering. Unlike stick welding that produces a lot of sparks and spattering, there is no spreading of molten metal around the arc. There are no sparks if the base metal is free of contaminants.
- Less fumes and smoke. GTAW generates lower levels of fumes compared to stick and flux-cored welding. The reason for this is that shielding gas is used in place of flux material to safeguard the weld. Consequently, GTAW is far less hazardous than welding methods that produce toxic fumes out of flux.
- However, the base alloy itself can produce toxic fumes from metals like nickel, copper, zinc, lead and other elements. The workpiece may also have a coating, which can disintegrate to toxic fumes due to the high heat.
- While welding, you should keep your head away from the rising fumes. For confined spaces, in particular, you must have proper ventilation, such as a fume hood to extract the hazardous gases.
- Highly flexible and versatile. GTAW can handle more metals than other welding techniques.
- GTAW is well suited for welding thin sheets and sections, which are difficult to weld with other techniques due to the likelihood of burn-through.
- GTAW is a very good option for welding together dissimilar metals.
GTAW Disadvantages
- GTAW is slower compared to other welding methods, such as MIG welding. Hence, it has lower productivity.
- Comparatively lower deposition rate of filler material. This means that that you can weld fewer sections with GTAW in a given time period compared to other welding methods.
- GTAW requires high level of manual dexterity.
- Produces more intense UV rays compared to other processes.
- GTAW equipment is more sophisticated and, therefore, expensive.
- Running costs are higher since shielding gases such as helium and argon are required for GTAW welding, which are quite costly.
- Shielding gases can displace air from the environment. Hence, in confined areas, ventilation must be installed to remove excessive buildup of shielding gases and noxious fumes. The welding operator can also wear an air-supplied respirator.
GTAW Power Source
Your selection of a GTAW power source depends on the type of base metal that is being welded as well as the thickness of the workpiece. You must consider the following while choosing the power source.
- Type of metal that is being welded (such as stainless steel, low carbon steel, aluminum, etc.)
- Thickness of the metal section
- Package solution that is appropriate for the welding application
- Relevant accessories that can speed up and ease the processes
- Size of machines, such as rectifiers, transformers and inverters.
Tungsten Electrode
The tungsten electrode employed in GTAW is non-consumable. However, prior to use, you must ensure that the tungsten electrode tip is well formed; otherwise, the arc produced will not be stable.
Small amounts of other elements may be added to the tungsten metal to improve its welding properties. The most common elements that are added are zirconium, lanthanum and cerium.
Electrodes have different colored bands to indicate the included elements. You should always consult manufacturer specifications to select the best electrode for the application. Keep in mind that manufacturers use different color codes.
Grinding Tungsten Electrode
Tungsten electrodes have three types of tips: truncated, pointed, and balled. The right tip matters as it influences arc characteristics.
Balled tips are suited for AC welding, while pointed tips work well for DC welding.
The balled tip is employed for zirconated and pure tungsten electrodes. It is also recommended for square wave and sine wave GTAW machines running on AC. To ball the tip correctly, you must apply the current recommended by the manufacturer for the given electrode diameter.
The balled end diameter should not be more than 1.5 times the electrode diameter. A large sphere at the electrode tip that exceeds this limit is detrimental for arc stability. It can also get damaged during welding.
Truncated and pointed tips can be used for thoriated, lanthanated, ceriated, and pure tungsten for welding processes powered by inverters AC and DC. To correctly grind the electrode tip, utilize a grinding wheel that is specifically designed for tungsten electrode grinding. This will help to prevent contamination.
The grinding wheel should be made from diamond or borazon to resist the hardness of tungsten metal. Do not use the grinding wheel for any purpose; otherwise, the tungsten electrode may become contaminated. While grinding tungsten electrodes, you must ensure that there is adequate ventilation. Refer to the manufacturer’s instructions and specifications.
Tungsten electrode grinding can produce lots of sparks and dust. You should deploy forced ventilation or use a respirator to avoid the toxic dust. Thoriated electrodes contain low levels of radioactive metal.
Always avoid radial grinding. The electrode is oriented parallel to the grinding wheel axis in radial grinding. This is an incorrect preparation method since it will produce a wandering arc that is difficult to control.
The electrode should be placed along the tangent to the grinding wheel circular cross section and its length should be perpendicular to the grinding wheel axis. In other words, you must grind the electrode lengthwise, NOT radially. The length of the tapered tip should be 1.5 to 4 times the diameter of the electrode. The angle of the tapered tip should range between 15 to 30 degrees. The wheel should spin against the length of the electrode. This will create the ideal tip for a stable arc.
How GTAW Welding Is Done
Given below are the basic tips and procedures for TIG welding.
Arc Initiation
You must know the proper technique to initiate the arc so that you can get to work right away without wasting time. The procedure is known as the lift-arc start method.
Start by touching the tungsten electrode with the workpiece at the starting point of weld travel. Turn on the shielding gas. Maintain contact between the workpiece and electrode for 1-2 seconds and then gently lift the electrode. An arc will develop as the electrode separates from the workpiece.
If the high-frequency feature is present on your GTAW welding machine, you can start the arc even more conveniently. This feature is automatic. The high frequency falls down to normal operating frequency as soon as the arc is developed. It initiates automatically whenever the arc is interrupted. Hence, starting and sustaining the arc is simple with the high-frequency feature.
Steps of GTAW Welding
The first step is to choose the correct electrode for the welding application and to make sure that its tip has been finished properly according to the method outlined above.
You can then start TIG welding the workpiece.
To begin, you must locate the gas valve. It may be positioned on the machine interface or on the welding torch. Turn on the gas flow.
This shielding gas will protect the weld against contamination and corrosion. Shielding gas must be fed at a rate that lies between 10 and 25 cubic feet per hour.
The gas cup inner diameter must be 3 times the tungsten electrode diameter for an adequate shielding gas supply.
The tungsten extension should not exceed the inner diameter of the gas cup. Tungsten extension is the length of the electrode that protrudes from the torch. Arc length is the distance of the electrode tip from the workpiece.
You should hold the welding torch so that it hovers above the area that is to be welded without making any contact. If you are right-handed, then you should move the torch from right to left. The direction of weld travel should be reversed if you are left-handed.
Initiate the arc using the high-frequency feature or the lift arc start method described above.
The torch tip should be tilted at a 15 to 20 degree angle from the vertical away from the direction of weld travel. This will improve visibility. While moving the torch, make sure that it remains centered. If you are using filler material, then make sure that the wire is oriented at a small angle to the horizontal.
The arc will keep melting the base metal and filler wire to create a molten weld pool. Allow it to cool so that the two previously separate metal interfaces are now fused together very strongly.
GTAW Welding Equipment
A GTAW welder is more expensive compared to MIG and stick welding machines. Investing in the right TIG welder will allow high quality welds as well as safety. You should do your research to find out about the most suitable TIG welding machine for your projects.
Protective Gear
Ensure you have the full list of protective gear before you start GTAW welding. You should buy goggles, mask and helmet to protect your face and eyes. The eye protection tint should be dark enough to filter out the intense UV rays produced by TIG welding.
You will also need an apron, gloves, long-sleeved garment, shoes, and jacket to cover and safeguard your whole body from burns.
Plenty of welding machines come with free stuff, such as a handheld face mask. Do not rely on these unless you are certain that they are adequate for your needs.
Controlling TIG Pulse
TIG pulse can be controlled via a foot pedal or just by configuring the machine to a fixed current setting. This is important from several different points of view. The pulse allows you to:
- Control the heat input, especially when lower heat is required for TIG welding thin metal sections
- Create a strong and defect-free weld easily by giving you control over the weld pool
- Carry out intricate welding steps and minimize heat and filler material for tight spaces
TIG welders operate between 20 and 150 pulses per second. With higher pulse, you can weld neatly in a shorter time period. Low pulse will let you weld more slowly where thinner sections or complicated joints are involved that requires more care. TIG pulsing gives you control and accuracy in your TIG welding jobs.
Shielding Gases
Your TIG welder works with 3 kinds of shielding gases. These gases are essential for TIG welding since they protect the weld pool from water vapor, oxygen and other contaminants that can ruin the weld.
Argon
Argon gas is very commonly used on its own since it is highly inert and therefore suitable for a wide variety of metals. This gas permits you to make narrow and precise welds that do not affect adjoining areas with high heat. Argon is a noble gas that can be used for almost any type of metal.
It creates a very effective protective shield. It generates focused and narrow arcs for precision in welding.
Argon and Helium Mixture
In order to utilize higher welding current, you will need a gaseous mixture of argon and helium. Helium is included to increase the fluidity and penetration power of the weld pool. This gas is lighter than air and has high thermal conductivity.
Since it has a higher ionization potential, it will create hotter electric arcs at bigger voltages that can create welding beads that go wider and penetrate deeper. Helium and argon are suitable for nonferrous alloys including aluminum. This mixture also works well for thick metal sections.
However, helium is more expensive than argon. It also requires a higher flow rate since it is lighter than air. This adds to its high costs.
Argon and Hydrogen
To carry out TIG welding in stainless steel, you should use a shielding gas mixture that contains argon and less than 5 percent of helium. Hydrogen is also a good choice for TIG welding of nickel-based alloys thicker workpieces. It can enhance the fluidity of the weld pool and cleans out the surface.
Addition of hydrogen to the shielding gas mixture narrows down the electric arc while raising its temperature. As a result, the arc is more focused and has greater penetration capability. At higher concentrations, hydrogen also works well for copper. However, this gas is not suitable for magnesium, aluminum and steel since it can cause hydrogen embrittlement and porosity in these materials.
Tungsten Electrodes
A tungsten electrode is fitted inside the welding torch in order to carry out TIG welding. There are different types of tungsten electrodes for various GTAW applications.
Pure tungsten electrodes are cost-effective and can create a stable arc for magnesium and aluminum with a balled tip.
Thoriated electrodes are a very common electrode variety because the addition of thorium to tungsten gives the metal a stronger and more resilient electrode tip. The tip will maintain its sharpness for a longer time period compared to electrodes made from pure tungsten.
Therefore, thoriated electrodes have a longer service life. One major problem, however, is that thoriated electrodes are slightly radioactive. You must have adequate ventilation whenever you are working with thoriated electrodes.
Ceriated electrodes are well suited for DC applications that utilize lower currents for TIG welding of intricate and small parts.
Lanthanated electrodes are highly versatile since they can be used on both DC and AC machines. They work well even at low current settings. The arc produced by lanthanated electrodes is very stable and therefore easy to work with.
Zirconiated electrodes are found to be extensively used in AC projects that require a resilient electrode with high resistance to contamination.
Rare earth electrodes are also quite versatile since they can produce a stable electric arc on both DC and AC machines. They can also last longer.
Factors Behind TIG Welding Problems and Their Solutions
There may be situations when you get poor weld quality and porosity. Here are the possible factors and their solutions.
Condensation on base metal can deteriorate the weld joint. Hence, you must clean away all condensation prior to welding. If the metal was stored in a cold environment, then there will be condensation when it is shifted to higher temperatures. So you should be careful in this regard.
Loose fittings on hoses and torches can also cause GTAW welding issues. It is good practice to ensure that all torch and hose fittings are tight prior to welding.
Excessive or inadequate gas flow can also deteriorate weld joints. You should adjust the gas flow rate to somewhere between 10 and 25 cubic feet per hour.
Loose connections and defective gas hose can also create problems. So check hoses and connections at regular intervals for pin holes, cuts and leaks.
The wrong choice of filler material or contaminated filler material can also cause porosity. Make sure that you have selected the right filler wire and also inspect the wire for oil, dust and grease prior to using it.
One common cause for poor weld quality is contaminated workpiece surface. Always ensure before welding that the surface of the workpiece is free from mill scale, dirt, rust, corrosion, oil, grease, paint and other such materials.
Novice TIG welding operators also experience problems with welding stainless steel. Most problems with stainless steel welding transpire due to excessive heat input. Compared to other alloys, stainless steel is relatively slower when it comes to heat transfer. This slow rate of heat transfer is responsible for warping defects.
The solution to this problem is to decrease the current and increase travel speed. You can also try reducing the filler rod diameter.
Difficulty Level
There is no doubt that GTAW requires the highest level of manual dexterity among the most common welding techniques. It is, therefore, more suitable for intermediate and advanced welding operators who have a good deal of experience with MIG and stick welding.
It is always a wise idea to master stick and MIG welding before moving on to TIG welding.
There are a number of different factors that make TIG welding more tricky and intricate compared to other welding techniques.
The biggest issue that you will have to use both your hands for TIG welding. You must use one hand to hold and control the welding torch while the other hand must hold and feed the filler rod. You must be adroit with both hands and have a good sense of coordination to be successful in TIG welding. In addition, you must also control the foot pedal to regulate the current.
You just need to be patient and work your way up towards TIG welding by first perfecting MIG and stick welding. You will acquire plenty of dexterity with these welding methods, which will help you a lot with TIG welding.
You will be pleased to discover that your GTAW learning endeavor has paid off after you start creating strong and precise welds with superb appearance.
TIG Welding Tips and Tricks
If you are new to TIG welding, then you should start with a steel sheet having a thickness of 3 mm. It is better to start learning TIG welding on thicker metal sheets since you can control the weld pool more easily. You can take the welding current to 50 amperes and use filler rod and tungsten electrode with 1.6 mm diameter.
Getting into a comfortable and steady position is important since you must try and maintain a constant distance between the electrode and the workpiece. The arc length is important because it can control the level of heat input into the weld pool. If you increase the arc length, then the voltage barrier will rise and this will lead to greater heat input into the molten pool.
Beginners often make the mistake of keeping too much distance between the electrode and the workpiece for fear of contaminating the tungsten electrode. This distance should be no more than 1.5 times the electrode diameter. So, if you are using 1.6 mm diameter tungsten electrode, then the maximum allowable distance will be 2.4 mm.
If you increase the arc length beyond this limit, then you will experience difficulty in controlling the arc. The tungsten electrode will also become very hot and may become contaminated if it dips into the weld pool.
Conclusion
The basics of GTAW have been explained in this complete guide to gas tungsten arc welding, including how it works, best practices, steps involved and much more.
If you are serious about a career in welding, then you must learn TIG welding after mastering stick and MIG welding. The demand for TIG welding will only increase in the future due to its myriad benefits.