When it comes production work, construction and high grade components, TIG welding is the standard method for welding together components. What is TIG welding, how does it work, and what makes it good at these tasks?
What is TIG Welding?
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.
Electrodes
Electrodes come in three main formulas: Pure tungsten, zirconium tungsten and thoriated tungsten.
Pure tungsten goes under the American Welding Society (AWS) classification EWP. Zirconium tungsten (AWS EWLa-1) electrodes are available in blends containing 0.25 to 0.5% zirconium oxide. The zirconium helps them maintain a ball tip, and reduces contamination and splitting. Pure tungsten and zirconium tungsten electrodes are used for AC welding on magnesium and aluminum.
Thoriated tungsten typically uses electrode negative electricity. Adding thorium oxide helps the electrode flow more current at low temperatures for easier arc starting. This electrode is compatible with most metals, aside from aluminum and magnesium. This includes carbon steel, stainless steel, chromium alloy and nickel. AWS EWTh-1 electrodes contain 1% thorium oxide, while EWTh-2 electrodes contains 2% thorium oxide.
Electrodes come in widths from 0.04 inches up to ¼ inch. Larger electrodes can handle more amperage, making them suitable for welding thick metal.
Shaping Electrodes
Electrodes come with a square cut end. Grinding or melting the tip into different shapes changes how they weld.
Pointed tips are used to weld ferrous metals with DC negative current. This concentrates the heat on the metal next to the electrode. Electrodes can be ground to a point with a grinding wheel or a tungsten sharpener. Tungsten sharpeners work like pencil sharpeners, shaving off the end with a series of angled blades.
Rounded and tapered ball electrodes are used on non-ferrous metals, including aluminum and magnesium. The rounded tip spreads out the heat for better control of metal temperatures. Rounded tips are used with alternating current. The tip is formed by setting the generator to DC electrode positive and shutting off the shielding gas. Welding on a piece of copper or other clean metal concentrates heat on the electrode, melting it. This rounds off the corners. From there, the generator can be switched to AC mode and the shielding gas turned on to weld metal.
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.
Filler Wire
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.
Carbon Steel:
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.
Stainless Steel:
ER309L is the most common stainless steel wire. It works on both stainless steel and carbon steel.
Aluminum:
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.
Preparing Pieces for TIG Welding
TIG welding can produce high quality welds, but only on pieces that are clean. Surfaces need to be ground down or wiped down with cleaners to remove anything on top of the metal, including oils, paint, oxidation and rust.
To get the best results when TIG welding, all surfaces need to be shielded from oxygen. Otherwise, the weld will produce fine slag called “sugar” on the side opposite of the weld. Flat pieces can be placed in a bath of argon. Since argon is heavier than air, it stays in the confines of the work container, shielding all sides of the metal being welded. Pipes are purged by pumping them full of an inert gas.
Purging Pipes
Purging pumps helium, argon, nitrogen or carbon dioxide into the pipe at a rate that is fast enough to displace oxygen and prevents air from leaking inside.
This process starts by taping over any holes or gaps in the pipe, including the area to be welded. Two holes are made in the tape. One hole is for the shielding gas hose, while the other hose lets the gas pass out of the pipe. When using heavier than air gasses, the hose goes at the bottom of the piece and the vent hole at the top to trap the gas. With lighter than air gasses, the hose is the top and the vent hole at the bottom.
The amount of gas needed varies depending on the flow rate of the gas, the pipe size and the thickness of the metal. There are charts with pre-calculated estimates, as well as formulas that can be used to calculate the gas needed. You can also use an oxygen monitoring tool, which uses a probe to measure how much oxygen is inside the pipe.
Once the pipe is filled with shielding gas, it can be welded. The tape over the welding area is slowly peeled back during the weld to minimize gas loss.
Setting up a TIG Welder
TIG welders have two main settings: amperage and gas flow rate. Like other types of welding, increasing amperage adds more heat, helping the electrode penetrate thick metal. Larger electrodes need more power. Typically, a 1/6 inch tungsten electrode uses 50-100 amps, while a 1/8 inch electrode needs 100 to 250 amps.
Gas flow rate varies depending on the cup size and amount of draft in the area. More gas is needed to keep the weld covered in windy conditions. This can be anywhere from a few Cubic Feet per Hour (CFH) to 50-60 CFH. Most jobs fall in the 10-25 CFH range.
Welding Technique
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.
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