Tungsten Inert Gas (TIG) welding, also called gas tungsten arc welding (GTAW) or Heliarc welding, was originally invented to weld together magnesium parts used in aircraft.
In TIG welding, an arc of electricity between a tungsten electrode and the metal generates heat, while filler wire is fed into this hot area by hand to form a welding pool. The welding gun sprays the area with an inert gas, protecting the weld pool and electrode from oxygen contamination. The resulting weld is slag free and has the same corrosion resistance as the surrounding metal.
What is a TIG Welder?
A TIG welder is similar to a stick welder. Both welding machines use the same type of power supply, and some stick welding machines can be set up for TIG welding. The welder only controls the amperage, while voltage varies depending on the length of the welding arc.
Using a regular welding amperage, the electrode must come in direct contact with the metal to start the arc. However, most TIG welders made today have a high frequency start mode. This creates a high amperage pulse when the electrode comes close to metal, starting the arc without requiring direct contact. This makes it easier to start the arc, and reduces wear on the electrode.
Like MIG welders, TIG welders spray the area around the electrode with an inert gas to prevent oxygen contamination. To reduce contamination further, TIG welders have pre-flow and post-flow modes. These flow the shielding gas before the arc strikes and after it stops to shield the weld pool as it forms and as it cools.
TIG welding can use an AC, DC negative or DC positive connection. DC negative welding concentrates the heat on the metal, resulting in a deep weld. DC positive welding concentrates the heat on the electrode, creating a shallow weld that works well on thin metals and is better at self cleaning. AC current welds in short bursts, reducing the heat around the weld. The change in polarity also helps with self cleaning of the weld pool. The welding happens during negative current flow, while positive flow cleans the weld. The machine can vary the pulses, letting the user choose between faster welding or more cleaning. Most AC welding is done at 65-70% negative current. AC current is used to make clean welds on aluminum and magnesium.
Shielding Gas and TIG Cups
TIG welding is sometimes called Heliarc welding because the process originally used helium as the shielding gas. Today, most welding jobs use argon as the main shielding gas. Adding other gases improves different characteristics of the weld:
The TIG cup surrounds the electrode, directing shielding gas around the weld. Cups are numbered based on 1/16 inch measurements. For example, a #5 cup has a 5/16 inch opening. Cup size should match the electrode size. A 1/6 inch tungsten tip needs a #4-6 cup, while most larger tips need a #6-8 cup. Bigger cups are needed for applications that require large amounts of shielding gas, including drafty work areas.
TIG welding uses the same type of wire as MIG welding. This wire is usually sold in 36 inch segments. These wires use a standard code to indicate their characteristics, starting with “ER” for “electrode wire.” Different codes are used for different types of wires.
For example, let’s say you have some ER70S6 wire. This is electrode wire with tensile strength of 70,000 lbs, a solid core, and a large amount of deoxidizing and cleaning agents.
ER309L is the most common stainless steel wire. It works on both stainless steel and carbon steel.
ER4043 is made for 4000 series aluminum.
While you can use MIG wire off of a spool, it’s safer to use TIG wire for welding jobs. The wire may be identical, but TIG wire has the code stamped into each wire segment, so you can’t mix it up. Weld with the wrong wire, and you can ruin the piece you’re working on. TIG filler wire is available in thicknesses from 1/16 to 3/16 inches.
All TIG welding uses the same basic technique, with most of the changes revolving around the wire, current flow and gas used. The torch determines penetration, while the movement of the rod controls the flow. That means the angle and movement of the electrode doesn’t matter as much as other types of welding. That said, there are some unique challenges with different types of metal:
TIG welding can bond dissimilar metals. Generally, this uses the methods that work for the metal that is the most difficult to weld. For example, if you’re welding stainless steel to carbon steel, you would need to use a stainless steel-compatible electrode and gas.
What to Look for When Buying a TIG Welder
The cheapest welders are DC only, so they only weld carbon steel or stainless steel. They have a set preflow and post flow, which should fit most ferrous metal welding. You also won’t find high frequency starting on these models. These models can often be set up for both TIG and stick welding.
Professional models can generate both AC and DC power. All aspects can be altered to fit the job, including pre-flow, post-flow, gas flow rate, amperage and polarity.
There are TIG welders designed to run on either 120 or 240 volts, and some can run on both voltages. Machines using 120 volts can’t weld anything more than 1/8 inch thick. Keep in mind that peak amperage on a 120 volt welder can only be reached with a 20 amp socket. These sockets always have one T-shaped hole. Standard household outlets, which have two slot-shaped holes, top out at 15 amps. If you want to use a TIG welder at full power in your shop or garage, you need to add a full 20 amp circuit, including a circuit breaker, wiring and outlet.
Foot pedals offer the most precise amperage control, while using the trigger on the torch will send a set amount of current through the metal and electrode. Rocker foot pedals offer the most precise control. Professional models use the trigger to activate different modes, including high frequency starts and steady current.
Digital models offer functions that make it easier to do difficult weld jobs. Pulse mode varies amperage automatically, which helps with self cleaning and helps prevent warping on thin metal. These welders also save your preferred settings, making it easy to switch between metals.
Professional welders usually come with a torch that has a bendable tip. This makes it easier to get the electrode into tight spaces.
Welders have a duty cycle, which is how long you can weld before it overheats. For example, a machine with a 50% duty cycle can weld for 5 minutes out of every 10. The other five minutes are needed for cooling. Real world performance may be lower or higher. For most hobbyist uses, duty cycle isn’t a problem, because projects are small, and frequent repositioning is required. For production, a high duty cycle is useful because adjustments are minimal once you have your piece set up in a jig.
TIG torches can be air or water cooled. Air cooled torches are cheaper, but the handle can heat up after a few minutes of welding. Water cooled torches transfer heat out of the torch using coolant, so they can be held for hours during long welding jobs.