TIG welder

How it works

Miller Electric describes the process: a non-consumable tungsten electrode in a hand-held torch heats the metal while a shielding gas, commonly argon, protects the weld from contamination, and filler metal is added with a separate rod as the weld progresses. Because the process uses both hands, operators generally control the current to start, adjust and stop it with a foot pedal or a torch-mounted control.

Russell Meredith’s 1941 patent, the earliest in this entry for the combination, describes striking an electric arc between a tungsten rod and the work in an atmosphere of helium supplied to the arc region at low pressure, with current from a direct-current generator. The patent states that tungsten does not deposit in the weld.

For aluminum, which carries a tough surface oxide, Miller explains that alternating current is used. The electrode-positive half of the cycle cleans the oxide and the electrode-negative half melts the base metal and fuses the joint.

Anatomy

Power source: Miller says a direct-current-only machine is sufficient for steel and stainless steel, and an AC/DC machine is chosen for aluminum.
Torch: Holds the tungsten electrode in a collet and directs shielding gas through a nozzle. Meredith’s 1941 torch has a tungsten rod passing axially through a hollow delivery nozzle that ends in a flare.
Tungsten electrode: A non-consumable rod. Lincoln Electric’s data sheet identifies the type by the color at the end: gray for 2 percent ceriated (EWCe-2), blue for 2 percent lanthanated (EWLa-2) and purple for a multi-oxide (WX).
Collet body or gas lens, and nozzle (cup): Miller says a collet body has several holes that introduce gas perpendicular to the nozzle, while a gas lens uses multiple screens to make the flow more uniform.
Gas cylinder, regulator and flowmeter: Miller recommends a flowmeter regulator placed as close to the power source as possible.
Foot pedal or torch-mounted amperage control: Starts, adjusts and stops the current, according to Miller.
Filler rod: Added by the free hand at the leading edge of the puddle.

Variants

DC-only machine: For steel and stainless steel, per Miller.
AC/DC machine: For aluminum, or where the metals to be welded are not known in advance. Miller says AC balance control, which sets the share of the cycle spent in electrode-negative and electrode-positive, became adjustable only in recent years; older machines split the cycle 50/50.
Inverter machine: Miller states that inverter technology has removed the size and weight barriers of earlier equipment so that a person can carry a machine or move it on a cart.
Pulsed TIG: Miller says pulsed TIG gives better control of heat input, warping and arc stability on stainless steel.
Water-cooled torch: Miller’s history says the water-cooled torch was developed at Linde Air Products after Linde licensed the process.
By shielding gas: Miller names 100 percent argon, 100 percent helium, and argon–helium mixtures of 25 to 75 percent helium.

Specifications

Tungsten diameter and direct-current (electrode negative) range · in; A: Lincoln Electric lists 0.040 inch for 10 to 75 A, 1/16 inch for 60 to 150 A, 3/32 inch for 150 to 250 A, 1/8 inch for 225 to 330 A and 5/32 inch for 330 to 480 A.
Shielding gas flow · cfh: Miller: usually between 10 and 35 cubic feet per hour, depending on consumables and surrounding atmosphere; use the lowest effective flow.
Electrode-to-work arc length · in: Miller: about 1/8 to 3/16 inch.
AC balance, electrode-negative share, starting point for aluminum · percent: 75Miller: a typical starting point is 75 percent electrode negative; dirtier or older aluminum may need as low as 65 percent, and a value below 60 percent usually means the part needs more mechanical cleaning.
Filter lens shade · shade number: OSHA 1910.252: shade 12 for gas-shielded arc welding of ferrous metals and shade 11 for nonferrous, with electrodes from 1/16 to 5/32 inch.

Made to

AWS A5.12
ISO 6848
AWS A5.18
AWS A5.10
ISO 14175
EN 60974-1
EN 60974-7
AWS Z49.1
OSHA 29-CFR-1910-254

Safety and care

Safety

Wear a helmet or hand shield with a filter lens during arc welding; the helmet must protect the face, neck and ears from direct radiant energy from the arc (OSHA 1910.252).
Ground the frame of the machine, and make sure there are no leaks of cooling water or shielding gas (OSHA 1910.254).
Provide local exhaust or general ventilation that keeps fumes and gases below the allowable concentration (OSHA 1910.252).
Keep combustible material 35 feet from the work or shield it, and use a fire watch where required (OSHA 1910.252).
Thoriated tungsten contains thorium; Lincoln Electric offers a non-radioactive multi-oxide composition as a replacement. Handling instructions for thoriated electrodes are not sourced here (see gaps).

Care

Clean aluminum of dust, debris and oil before welding, with acetone and a wire brush, or with a heavy file or carbide burr where the oxide is thick (Miller).
Regrind the tungsten when it balls or deforms, using a lengthwise grinding pattern (Lincoln Electric).
Replace cables with damaged insulation (OSHA 1910.254).

Tips

Read the color band on the tungsten
Lincoln Electric’s data sheet says the type is indicated by the color at the end of the electrode: gray is 2 percent ceriated (EWCe-2), best at low to medium amperage and mainly on direct current; blue is 2 percent lanthanated (EWLa-2), for medium to high amperage on both direct and alternating current; purple is a multi-oxide (WX) for all amperages and both currents.1
Grind the tungsten lengthwise
Lincoln Electric advises a lengthwise grinding pattern to reduce arc wander and inclusions, and warns against a short tip angle, which can cause arc wander. It recommends a sharp point with a small blunt for most direct-current work on 1/16-inch tungsten and larger, and a sharp point for low-amperage starts on 0.020- to 1/16-inch tungsten and very thin material.1
Size the tungsten to the current
On direct current, electrode negative, Lincoln Electric’s table puts 1/16-inch tungsten at 60 to 150 amperes and 3/32-inch at 150 to 250 amperes. On AC with a 50/50 balance the same diameters take 40 to 110 and 65 to 150 amperes.1
Set AC balance by looking for pepper
Miller explains that aluminum oxide melts at about 3,600 degrees Fahrenheit while aluminum melts at about 1,200. A starting point is 75 percent electrode negative. Specks like pepper in the puddle mean more cleaning is needed, so lower the electrode-negative share to no less than 60 percent. If the tungsten balls or erodes, raise it to just before pepper appears.1
Use argon, the lowest effective flow, and a gas lens for critical work
Miller calls 100 percent argon the best all-around TIG gas. Higher flow increases turbulence and the risk of contamination, so Miller advises the lowest effective flow. A gas lens gives more uniform laminar flow than a collet body and lets the tungsten extend past the nozzle inside diameter, while with a collet body the extension should stay within it.1
Keep the arc short and the torch tilted
Miller advises holding the electrode tip about 1/8 to 3/16 inch from the metal and starting with a torch angle near 15 to 20 degrees. A closer electrode gives a smaller puddle and a farther one a larger puddle. At 45 degrees or more, shielding coverage is lost and the puddle becomes long and narrow.1
Rehearse the pass before striking the arc
Miller notes that many professional welders move their hands along the path before every pass, with support blocks in place, and that resting wrists on the work or on blocks gives better control of the torch.1
Pick a DC-only or AC/DC machine by the metal
Miller advises that steel and stainless steel can be welded with a DC-only TIG welder, while a user planning to weld aluminum, or not sure what will be encountered, should choose an AC/DC machine.1

History

Earliest documented

4 January 1941 (application date of the first patent read for the tungsten-and-helium torch)

Los Angeles, California (Northrop Aircraft, Hawthorne)

US Patent 2,274,631, “Welding Torch,” was applied for on 4 January 1941 by Russell Meredith of Los Angeles, assignor to Northrop Aircraft, Inc., of Hawthorne, California, and issued on 24 February 1942. It describes striking an arc between a tungsten rod and magnesium in a helium atmosphere supplied at low pressure. Welding in argon had been patented by General Electric’s Philip K. Devers in a patent issued in 1930 (see timeline).1 2

The tungsten-electrode torch arose from a problem in aircraft construction. Meredith’s 1941 patent opens with the trend toward light, strong alloys and the increasing use of magnesium, which had generally been joined by riveting. It states that magnesium will burn in oxygen, carbon dioxide and nitrogen but that blanketing it with a monatomic inert gas such as helium prevents ignition. The patent adds that magnesium alloys lose stiffness at low temperatures and that scarfed edges sag, so the weld is formed against a molded backing.

The idea of a protective gas was older. Miller’s history says Alexander and Langmuir used hydrogen in the 1920s and that Hobart and Devers refined the concept using helium and argon. Devers’s 1930 General Electric patent describes an arc in argon that strikes at about 20 volts, runs near 15 volts, and deposits metal slowly, which the patent calls well suited to thin metals. Miller also credits C. L. Coffin with a 1890 idea of welding in a nonoxidizing gas. The Coffin patent read for this archive, US 428,459, describes the arc heating of rod ends that are then pressed together and does not mention a gas, so that attribution remains unverified (see gaps).

The patent describes the tool recognizable today: a handheld torch in which a tungsten rod passes through the axis of a gas nozzle, a gas cylinder and reducing valve, a generator, and a separate filler rod. Meredith notes that, in the arc, the tungsten does not deposit in the weld. That feature explains the two-handed nature of the process, since the electrode is not consumed and the filler must be added separately. Miller’s guide says that is why operators use a foot pedal or torch control to modulate the current.

The process was commercialized and renamed. Miller’s history says the process was named Heliarc and that it was later licensed to Linde Air Products, where the water-cooled torch was developed. Argon displaced helium for most work: Miller calls argon the most common choice because it is affordable and widely available and gives excellent arc stability and starting, while helium gives higher heat input for thick material and mixtures of 25 to 75 percent helium trade stability for heat.

Later changes were to current control and electrode material. Miller explains that early AC machines split the cycle 50/50 because that is what the wall supply gave, and that adjustable balance followed in recent years. Lincoln Electric’s data sheet shows ceriated, lanthanated and multi-oxide tungstens, with the multi-oxide described as a non-radioactive replacement for thoriated. Miller claims TIG can weld more metals and alloys than any other process and produces no sparks, spatter or slag, and it describes aerospace and custom automotive work, the same field as the process’s origin, as places where appearance matters.

Timeline

1920s
Researchers test shielding the arc with external gases. Alexander and Langmuir work with hydrogen, using carbon and then tungsten electrodes, according to Miller.1
1930
US Patent 1,746,191 is issued to Philip K. Devers, assigned to General Electric, for arc welding in the presence of argon. Miller says Hobart and Devers refined the concept in the late 1920s, using helium and argon for shielding respectively.1 2
1941
Russell Meredith applies on 4 January for a patent on a welding torch that strikes an arc between a tungsten rod and magnesium in helium, assigned to Northrop Aircraft; Miller says the process was perfected in 1941, patented by Meredith and named Heliarc welding.1 2
1942
The patent is issued on 24 February as US 2,274,631. The specification gives a helium pressure of about one-third of a pound per square inch and direct current from a generator.1
after 1941
Heliarc is licensed to Linde Air Products, where the water-cooled torch is developed, according to Miller.1
recent years
Machines with adjustable AC balance appear; before this, alternating-current TIG machines split the cycle 50/50, according to Miller.1
2020
Lincoln Electric publishes a data sheet offering a non-radioactive multi-oxide tungsten as a replacement for thoriated tungsten.1

Where the sources disagree

When was the process patented or perfected?

The process was perfected in 1941, patented by Meredith and named Heliarc welding.1
Miller Electric
Meredith applied for the patent on 4 January 1941 and it was issued on 24 February 1942 as US 2,274,631.1
The patent itself
Welding in a non-oxidizing gas atmosphere was an idea of C. L. Coffin, patented in 1890; Hobart and Devers refined it in the late 1920s.1
Miller Electric
The only Coffin patent read here, US 428,459 of 20 May 1890, describes welding by heating currents and an arc between the parts and a conductor, with the parts then pressed together; it does not describe a protective gas.1
The patent text itself

Gaps in the record (8)

Other accounts name additional developers at Northrop alongside Meredith; none was read for this entry, so they are not stated here.
The Heliarc trademark and the Linde license have not been checked against a primary source; they are known through Miller’s history.
No Coffin patent describing a protective gas has been located.
Whether Hobart patented helium shielding has not been checked; no Hobart patent was read.
The filing year of Devers’s patent is ambiguous in the scanned text (the drawing sheet reads 1926, the header text reads 1928).
The date of the first adjustable AC balance machine is given only as “recent years” by Miller.
Handling and grinding precautions for thoriated tungsten have not been sourced.
Tungsten standards (AWS A5.12, ISO 6848) have not been read; the color list here comes from Lincoln Electric’s data sheet.