MIG welder

How it works

Miller Electric describes MIG, or gas metal arc welding, as a process that shields the weld from the atmosphere by directing gas over the weld area, with gas flow controlled by the trigger on the gun. The wire is the electrode and the filler. The farther the gun is held from the work, the farther the wire must extend to meet the metal, and Miller says that length of wire, the stickout, has a major impact on weld quality.

The 1950 Air Reduction patent describes the semiautomatic form: a bare filler wire constituting a consuming electrode is fed automatically to a hand gun, the operator moves the gun along the seam, and the arc is shielded by an inert gas. The 1950 patent says that at high current density and high wire feed speed the arc length regulates itself rapidly, so that unsteadiness of the operator’s hand is compensated at the arc.

The wire may be solid, used with an external shielding gas, or tubular with a flux core, used with or without gas. Miller states that self-shielded flux-cored wire protects the pool with gas generated by the burning flux and needs no gas cylinder.

Anatomy

Power source: Miller refers to gas metal arc welding as a constant voltage process, in which a change in the gun-to-work distance changes the amperage. The 1950 patent used a standard direct-current welding generator with a drooping voltage-current characteristic.
Wire feeder and spool: A motor drive that pays the wire out at a set speed. Miller says the wire feed speed controls amperage and penetration.
Gun and cable: The 1951 Air Reduction patent describes a molded casing with a barrel and a pistol grip, a trigger switch in the grip, a flexible conduit carrying the wire and the shielding gas, and a current-carrying block in the barrel. Miller lists air-cooled, water-cooled, push-pull, spool and fume-extraction guns.
Contact tip and nozzle: The contact tip passes current to the wire; the nozzle directs shielding gas. Miller defines electrode extension as the length from the end of the contact tip to where the wire melts off and stickout as the length from the end of the nozzle.
Gas cylinder and regulator or flowmeter: Sets the flow of shielding gas. Miller recommends purging the cylinder valve briefly before attaching the regulator.
Work clamp and lead: Returns the current to the power source.

Variants

Solid-wire MIG with shielding gas: Miller names carbon dioxide and argon–carbon dioxide mixtures as the most common gases for steel and 100 percent argon for aluminum.
Gas-shielded flux-cored: Needs an external gas; Miller says the slag is easy to remove and the wire suits thicker metal and out-of-position work.
Self-shielded flux-cored: Needs no gas cylinder, which Miller says makes it more portable and better suited to wind and outdoor work.
Spray and pulsed-spray transfer: Miller names 90 percent argon–10 percent carbon dioxide as suited to spray transfer on thicker plate, and 100 percent argon for spray or pulsed spray on aluminum.
Multiprocess machine: Miller offers multiprocess machines for users who want multiple welding capabilities in one unit.

Specifications

Wire diameter and usable current · in; A: Miller lists 0.023 inch for 30 to 130 A, 0.030 inch for 40 to 145 A, 0.035 inch for 50 to 180 A and 0.045 inch for 75 to 250 A.
Typical stickout · in: 0.375Miller’s beginner guide gives about 3/8 inch as typical.
Shielding gas flow, short-circuit transfer · cfh: Miller recommends 25 to 35 cubic feet per hour for short-circuit MIG and slightly more for other transfer modes.
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 A5.18
AWS A5.20
AWS A5.10
ISO 14341
ISO 14175
EN 60974-1
EN 60974-7
AWS A3.0
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, and provide helpers with eye protection (OSHA 1910.252).
Make sure there are no leaks of cooling water, shielding gas or engine fuel, and ground the frame of the machine (OSHA 1910.254).
Provide local exhaust or general ventilation that keeps fumes, gases and dusts 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).
Do not weld on used drums, barrels or tanks until they are cleaned of flammable material (OSHA 1910.252).

Care

Replace cables with damaged insulation or exposed conductors (OSHA 1910.254).
Check regularly for gas leaks (OSHA 1910.254).
Clean grease and oil from the work, and remove rust, paint and scale, before welding; Miller says MIG tolerates minor contamination better than TIG, but that cleaner metal means fewer problems.
Contact tip replacement intervals and liner care are not sourced here (see gaps).

Tips

Hold the stickout steady because it sets the amperage
Miller explains that in a constant voltage process, changing the distance from the contact tip to the work changes the resistance in the circuit and so the amperage. In its example of spray transfer, a distance of 3/4 inch gave 235 amperes, and a change from 5/8 inch to 1 inch moved the current across a window of 282 to 213 amperes. A short extension raises current and can damage the contact tip or burn through. A long one lowers current and reduces penetration.1
Set wire speed from the metal thickness
Miller’s rule for solid wire on steel is 1 ampere of output for each 0.001 inch of thickness, so 1/8 inch (125 amperes) needs about 125 amperes. Wire feed speed in inches per minute is then amperage times a multiplier by wire size: 3.5 for 0.023 inch, 2 for 0.030 inch, 1.6 for 0.035 inch and 1 for 0.045 inch. A 0.030-inch wire at 125 amperes therefore feeds at about 250 inches per minute.1
Trim the voltage by the behavior of the arc
After wire speed is set, Miller adjusts voltage to give a crisp stable arc. If the arc stubs into the work, increase the voltage. If it is erratic and burns at the tip, reduce it.1
Choose the gas by the metal
Miller names 75 percent argon with 25 percent carbon dioxide as very common for mild steel, with minimal spatter. Straight carbon dioxide costs less and may give a little more spatter. For aluminum Miller recommends 100 percent argon and advises avoiding carbon dioxide, which introduces contamination.1
Purge the cylinder valve before the regulator goes on, then set flow
Miller says to open the cylinder valve briefly and close it to clear dust from the connection before attaching the regulator. For short-circuit MIG it recommends 25 to 35 cubic feet per hour.1
Start with a 15-degree travel angle
Miller’s beginner guide says to angle the gun slightly in the direction of travel, with 15 degrees as a place to start. For fillet welds it gives a 45-degree work angle, and for inverted T joints it advises angling the gun slightly away from the vertical member to prevent burn-through.1
Use self-shielded wire outdoors
Miller explains that wind can blow away shielding gas and that the loss usually shows as porosity in the bead. Self-shielded flux-cored wire makes its own gas from the burning flux, so no windshield is needed.1
Select the lens shade for the metal
OSHA’s table gives shade 12 for gas-shielded arc welding of ferrous metal and shade 11 for nonferrous, for electrodes up to 5/32 inch.1

History

Earliest documented

1948

United States (Battelle Memorial Institute and the Air Reduction Company)

Miller’s history states that the Battelle Memorial Institute, under the sponsorship of the Air Reduction Company, successfully developed the gas metal arc welding process in 1948, replacing the tungsten electrode of the gas tungsten arc with a continuously fed electrode wire. The Air Reduction patent for a welding gun, filed in 1950, refers to a copending application filed on 29 June 1948 and since abandoned, and the first granted patent on the semiautomatic process was filed on 21 January 1949. Earlier work on arc welding in shielding gas, by General Electric, is recorded in a patent issued in 1930.1 2 3 4

The MIG welder follows from an older problem. An arc in air picks up oxygen and nitrogen, and Miller records that welding researchers of the 1920s tried external gas shielding. The 1930 General Electric patent of Devers describes welding in argon, an arc that strikes at 20 volts, runs at about 15 volts and deposits metal slowly, which the patent calls particularly good for thin metals. Miller says Hobart and Devers refined the idea in the late 1920s using helium and argon. The 1951 Air Reduction patent states that welding with non-consumable electrodes in a shielding gas such as argon or helium was well known, and that no satisfactory apparatus had been available for using a continuously fed consumable electrode with an inert-gas-shielded arc.

Miller’s account places the invention in 1948 at the Battelle Memorial Institute with Air Reduction as sponsor. The patents show the Air Reduction side of the work. An abandoned application filed on 29 June 1948 is cited in the 1951 gun patent. The 1950 patent names three Air Reduction employees and describes a new combination of current density, gas shielding, filler wire feed speed and direct-current reverse polarity. It does not mention Battelle. The two accounts do not conflict, but they credit different parties (see disputed).

The form of the machine follows from that patent. The wire is fed automatically to a hand gun, the operator guides the gun, and the arc regulates its own length. The patent says the wire should be consumed at an average rate of at least 100 inches per minute, and gives a smooth projected spray with aluminum wire at about 160 amperes or higher, a current density of at least 52,000 amperes per square inch. The 1951 gun patent has a motor with a centrifugal governor driving the feed rollers, and a trigger that controls both the wire feed and the gas valve. The 1950 patent used a standard drooping-characteristic welding generator. Miller says the process was made more usable by small-diameter wires and a constant-voltage power source, and says H. E. Kennedy had patented that principle earlier; Miller’s current guides treat wire feed speed and voltage as two separate settings on such machines.

The first application was to nonferrous metals. Miller states that the high deposition rate led users to try the process on steel, and that the cost of inert gas was high enough that savings did not appear at once. Miller’s present guidance names mixtures of argon with carbon dioxide, and straight carbon dioxide, for steel, and offers self-shielded wire for work in which no cylinder can be used. ESAB records that its own semiautomatic equipment for gas metal arc welding appeared in the 1960s.

Compared with the stick welder, the MIG welder replaced a rod of fixed length and a slag-forming covering with a continuous solid wire. Miller notes that on thinner work solid wire leaves no slag to remove and a bead that is ready to paint, while its explanation of stick electrodes describes a flux that forms a slag over the cooling weld. Miller adds that many automotive enthusiasts who work on bodywork and other thin applications prefer solid wire.

Timeline

1920s
Researchers test shielding the arc with externally applied gases; Alexander and Langmuir use a hydrogen atmosphere, according to Miller.1
1930
US Patent 1,746,191 is issued to Philip K. Devers of Lynn, Massachusetts, assigned to General Electric, for arc welding in the presence of argon. The specification states that the arc voltage in argon is about 15 volts and that argon is particularly good for thin metals.1
1948
Gas metal arc welding is developed at the Battelle Memorial Institute under the sponsorship of the Air Reduction Company, according to Miller; an Air Reduction application filed 29 June 1948 is later abandoned.1 2
1949
Muller, Gibson and Anderson, assignors to Air Reduction, file on 21 January an application for gas-shielded metal arc welding with a consumable bare wire, direct-current reverse polarity and high current density.1
1950
US Patent 2,504,868 is issued on 18 April. The specification gives a smooth projected spray transfer for aluminum wire at about 160 amperes or higher, a current density of at least 52,000 amperes per square inch.1
1951
US Patent 2,544,801, a welding gun with a pistol grip and a streamlined, laminar gas flow, is issued on 13 March to Air Reduction (application filed 14 July 1950).1
after 1948
Small-diameter electrode wires and the constant-voltage power source make the process more usable; Miller adds that H. E. Kennedy had patented the constant-voltage principle earlier.1
1960s
ESAB adds semiautomatic equipment for gas metal arc welding to its range.1

Where the sources disagree

Who developed gas metal arc welding?

The Battelle Memorial Institute, under the sponsorship of the Air Reduction Company, successfully developed the process in 1948.1
Miller Electric
Albert Muller, Glenn J. Gibson and Nelson E. Anderson, assignors to Air Reduction Company, filed the first granted patent on gas-shielded metal arc welding with a consumable wire on 21 January 1949; an earlier application filed 29 June 1948 was abandoned. Battelle is not named in the patents read.1 2
US Patents 2,504,868 and 2,544,801

Gaps in the record (8)

No document naming Battelle’s role has been read; it is known here only through Miller’s history.
The abandoned 1948 application (Serial No. 35,936) has not been located.
The filing year of Devers’s patent is ambiguous in the scanned text (the drawing sheet reads 1926, the header text reads 1928); it was granted 4 February 1930.
H. E. Kennedy’s patent on the constant-voltage principle has not been identified or read.
The date at which carbon dioxide and argon–carbon dioxide mixtures and flux-cored wire entered use has not been sourced.
Contact tip and liner replacement guidance has not been sourced, so care is thin.
The origin of the term MAG for active-gas welding has not been sourced.
A typical power rating or duty cycle for specs has not been sourced.