TIG welding is becoming increasingly popular in the motorsport industry. 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. The tungsten and weld puddle is protected and cooled with an inert gas, typically argon. TIG welding is similar to oxy-acetylene welding in that you use a filler material for build-up or reinforcement.
With the growing popularity, it is important to know how TIG welding works. In race car fabrication, TIG welding uses aluminium and 4130 chrome-moly steel. If you are going to weld either of these materials, you need a quality TIG welder. However, 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’s 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 areas that are considered out of position. The remote adjusts the heat while you are 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 for this. It is very important that you 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. The tungsten can be sharpened 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. The ceramic cup can be unscrewed and replaced 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 and allow the tungsten to be removed for sharpening or replacement.
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 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 prevent temperature shocking the metal. Many alloy sheets of steel 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 the balance, which maintains the cleaning versus penetration levels on aluminium. 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 aluminium, 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.
The key difference between the two is that MIG welding uses a continuously-fed wire that also acts as a filler material, while TIG welding uses a non-consumable tungsten electrode. This makes it so that TIG welding has to make the objects being welded hot enough to form a bond, while MIG welding can join objects by using the melting electrode as a filler material.
Because it uses filler material, MIG welding often performs better for welding thicker objects, since it doesn’t have to heat the material all the way through to form a bond. Also, the use of filler material makes it relatively easier to control than TIG welding. While the filler material could allow for the use of MIG welding to join dissimilar metals, it’s generally recommended that you avoid joining dissimilar metals whenever possible.
TIG welding, on the other hand, can join objects without filler to create neater welds. However, TIG welding requires a great degree of precision to avoid over-heating the metal being welded (which could cause stress cracks and other welding issues). Thankfully, computer numerical control (CNC) systems create a degree of precision that makes achieving consistent results very easy with TIG welding.
So, when should you use one of these two welding techniques over the other?
A basic rule of thumb when choosing between MIG and TIG welding is to consider the following:
- How thick are the two pieces of metal being joined? Thicker pieces of sheet metal are very difficult to weld by simply heating them up until they fuse—the thicker they are, the more energy it takes to heat them to the melting point and the less efficient TIG welding becomes. If metals are especially thick, then MIG welding may be more effective.
- What is the electrical conductivity of the metal being joined? Another variable to consider is how ductile the metal being joined is. The heat used to fuse metal in an electric arc welding process is generated by the metal’s inherent electrical resistance as the electric arc tries to pass through the weld site. If metal is highly ductile, it will take more time to heat up, which consumes more energy. Electrically-resistant metal will heat up faster, making it easier to weld without filler material.
- Am I welding dissimilar metals? While it isn’t usually a good idea to weld dissimilar metals since it could cause numerous issues (weak bonds, weld corrosion, etc.), there are times where it may be unavoidable. If two dissimilar metals are being welded, it’s usually better to use a welding technique that supplies a filler material to create a bond. However, this filler material needs to be carefully chosen.
- Is surface condition/smoothness important? Filler materials increase the risk of weld spatter being left on the surface of a workpiece, requiring extra work to smooth out if the elimination of surface flaws is important. Direct metal-to-metal welds sidestep this issue to create welds that are typically much cleaner than filler-dependent ones.
For more information regarding TIG welding, or for a quotation, contact Silverton Radiators today.