How a TIG Welder Works and When to TIG Weld
Learn the basics of TIG welding in motorsports applications and the proficiency of a TIG welder on aluminum and chrome-moly.
How does a TIG welder work?
TIG stands for tungsten inert gas and is technically called gas tungsten arc welding (GTAW). The process uses a non-consumable tungsten electrode that delivers the current to the welding arc. An inert gas, typically argon, protects and cools the tungsten and weld puddle. TIG welding is similar to oxy-acetylene welding in that you use a filler material for build-up or reinforcement.
In race car fabrication, we use TIG welding for aluminum and 4130 chrome-moly steel. If you are going to weld either of these materials, you need a quality TIG welder. Miller offers products to accommodate anyone — from a home hobbyist to an advanced user.
If you have ever welded with an oxy-acetylene torch, you can easily weld with a TIG machine. The TIG process uses an electric torch, and the welder hand feeds filler rod into the molten puddle.
The ability to soft start and soft stop the heat makes the TIG process different from other types of electric welding. Some people like the accelerator pedal to control the heat if they are working on a bench and others like fingertip remotes on the torch if they are working in out-of-position areas. The remote adjusts the heat while you are welding.
Getting started with TIG welding
Before you use a TIG unit, you should be familiar with the parts of the welder and the function of each part. The work lead, often referred to as a ground cable with a clamp, must be attached to the workpiece or to the metal surface that the workpiece is on. The welding lead will have an electric TIG torch on the end. Along with the cable is a small line that carries the argon gas. The inert gas performs like the flux coating on a stick electrode in that it protects the weld from airborne contaminants. You will need a gas bottle and a regulator. DO NOT use the same gas that you would use with a MIG welder.
The torch disassembles into several parts. The small tungsten rod (several sizes are available) is the electrode. This electrode does not burn up like a filler rod. You can sharpen the tungsten to a point or ball shape depending on what you are welding. A copper collet holds the tungsten and is used to adjust the length that the tungsten protrudes from the cup. You can also unscrew and replace the ceramic cup (usually pink) as needed. Several cup outlet diameters are available. In the collet body, there are several cross-holes that allow the gas to pass into the cup and surround the tungsten. This excludes oxygen that would contaminate a weld. Loosening the back cap will reduce the collet's grip on the tungsten so you can remove the tungsten for sharpening or replacement.
TIG machine controls
|This is the electric torch. It is air-cooled, making it light and easy to handle. Hold the torch in one hand and feed the rod with the other. The tungsten (T) is shielded by the inert (I) gas (G), normally argon. This gas shield is the flux that keeps oxygen from contaminating the weld by oxidizing the metal.
TIG machines use a foot-operated variable amperage control. After the maximum amperage desired is pre-set on the machine, this allows you to vary the amperage up to the maximum pre-set amperage. This is useful when TIG welding alloy steels, such as 4130 chrome-moly. The foot control allows you to slowly initiate the heat, and after the weld is complete you can slowly reduce the heat. This soft start and soft stop prevents temperature shocking the metal. Many alloy steels used in race cars are sensitive to thermal shock. Welding by other means may lead to brittle welds.
A TIG machine has numerous controls. One of the most vital controls for welding aluminum is balance, which maintains the cleaning versus penetration levels on aluminum. The higher the balance, the more penetration you'll get. Typical settings range from 70 to 80 percent, or 7-8.
You can also select normal or pulsed mode. When using pulsed mode on aluminum, the amperage is automatically varied. This can reduce the heat into the workpiece and help you achieve a better weld, as well as reduce the heat-affected zone. Pulsing automatically produces a stacked dimes look or a rippled wave pattern in the weld.
TIG Welding Basics
|These are the internal parts of the electric torch. The collet holder holds the collet on one end and a ceramic cup on the other. The collet holds and clamps the tungsten in position. The holes in the collet holder allow the gas to flow around the tungsten to prevent contamination of the weld.
Now, let's get ready to weld. The TIG process is not unlike welding with an oxy-acetylene torch. You hold the torch in one hand and feed a filler rod with the other. An auto-darkening welding hood makes starting the weld more accurate. For years I welded with a simple dark fixed-shade helmet. It must have taken me seven or eight seconds to adapt to the auto-darkening hood.
A common available filler rod for welding aluminum is the 4043 alloy. If you are trying to color match welds on parts to be anodized, use 5356, which will match better than most others. Use a filler material guide to better match the base material to the filler material. When TIG welding steel, use a filler material with a thin copper coating to inhibit rusting, similar to the filler rod used in oxy-acetylene welding. Welding professionals tell me that the copper coating is not detrimental to the welds even on chrome-moly. However, a non-coated filler rod is available and must be kept rust free.
To start, gather up some clean metal scraps. You should have a metal top table or at least a metal plate clamped firmly to the table. Pull up a stool. Once seated, place the foot pedal within easy reach. It is important to wear the proper protective welding gear, such as a long-sleeved shirt or coveralls, a welding helmet, and leather gloves and shoes — even when TIG welding.
Set the welder to the correct polarity for the base material type — AC for aluminum or DC for steels. Select the appropriate welding rod. Turn the gas bottle on. I set the regulator at about 20 cubic feet per hour (cfh). Check that the tungsten has the correct point for the metal you are welding. It should stick out of the cup by about 1/8 inch. Hold the torch up, away from your body, and depress and release the foot pedal. You should hear the gas flow. If not, then find out why. Did you turn on both the welder and the bottle?
|A ceramic cup shrouds the tungsten electrode directing the gas flow. These cups come in several sizes for different welding applications.
TIG tips and tricks
You are ready to weld. Let me explain a few TIG pitfalls to make your learning process easier. The tungsten should never touch the workpiece. When it does, you will notice a different sound and color, which means the tungsten is contaminated. Loosen the back cap and slip the tungsten (it is hot) out. Go to the grinder, preferably one with a wheel dedicated to tungsten, and clean the end of the tungsten. Reshape the end as necessary. You will dip the tungsten many times as you learn, but with more practice you'll be steadier and it will happen less.
|This is the tungsten electrode. It has been ground to a ball shape on one end and a point on the other. Each shape has its application. The tungsten is considered a consumable item and will be used up over time.
Back at the welding table, get some practice. Use different heats and different feeds of the rod on your scraps.
This article won't make you a proficient TIG welder, but it should give you a good understanding of how a TIG welder works and why you might need one. A good machine has the capacity to weld up to 1/4-inch aluminum and 3/8-inch steel or stainless steel.
|This is a very nice tool if you do a lot of TIG welding. Its a hand-held unit that automatically grinds tungsten to a point.
Just the thing for race-car welders! This is a foot control for the amperage control of the Miller TIG machine.
|Part of a weld joint has been completed. Too much heat directed to the thin edge has burned a hole in the metal of this .035-in. steel tube. With the foot amperage control, the heat can be controlled enough to repair this flaw. With a bit of practice, this won't happen again.
|Preparing to start a weld: the torch with the tungsten in place. The welding rod is ready to be added. With an auto-darkening helmet, everything can be positioned without having to shake your head to flip the hood down.
|The TIG welder in action. The rod is being fed with one hand while the other guides the torch. A comfortable position here means a lot to weld quality.
|This is the type of weld joint you should avoid. All these tubes converged at one point and were tack welded into place. It is virtually impossible to reach the inside edges of the tubes. The part should have been welded in sections that were stacked so that the last welds were properly positioned for welding.
|Here the welder is using the soft stop technique. He finished the weld and slowly reduced the amperage. The gas flow remains on for a few seconds to prevent weld contamination. This technique is reversed when beginning a weld by slowly bringing the heat up. All of this prevents thermal shock, which you must prevent on chrome-moly steels.
|A finished weld? No. This joint has been welded as much on the bottom as on the top. It is advantageous to weld a joint from side to side to control warpage. Turn the workpiece as necessary.
Originally written in 2007 by Sleepy Gomez, publisher and technical director, Oval Trak Digest.com. Parts of this article have been updated in 2023.