mig welding

MIG Welding (GMAW) Overview

MIG welding or Metal Inert Gas welding is an arc welding process that uses a continuous solid wire electrode and shielding gas for laying welds. GMAW (Gas Metal Arc Welding) is another name of MIG welding. At some places, peoples use ‘wire welding’ as a slang name for it. Being a common welding process, manufacturing industries like automotive repair, rebuilding equipment, overlay of wear-resistant coating, welding pipes, and repairing railroad tracks use MIG welding for various purposes.


Post Highlights:

  • What is MIG Welding?
  • Principle of MIG
  • MIG Welding Equipments
  • Setting of MIG Welding Parameters
  • Consumables for MIG Welding
  • Welding Environment while MIG Welding Process
  • How Does MIG Welding Work?
  • MIG Welding Employment Areas
  • Job Types for MIG Welding
  • MIG Welder Salary Trends

What is MIG Welding?

MIG welding (GMAW) is a gas shielding metal arc process that uses the heat of continuously fed an electric arc between consumable electrode wire and the base metal. GMAW uses argon, a mixture of argon-helium, and CO2 as well. DC Constant Voltage Machine performs MIG welding. Generally, the MIG welding process is quicker than traditional processes.

Principle of MIG Welding

The GMAW welding process works on the following principles:

1) The arc is struck between the workpiece and a metal wire electrode that is continually fed forward into the arc.

2) The wire is supplied on a reel and is fed to the welding gun by the drive rollers. It pushes the wire through a flexible conduit in the hose package to the gun.

3) The contact tube in the welding gun passes electrical energy for the arc to the electrode. It is normally connected to the positive pole of the power source, and the workpiece to the negative pole.

4) Striking the arc completes the circuit.

5) The gas nozzle surrounding the contact tube supplies shielding gas for the protection of both the arc and the weld pool.

Equipment for MIG Welding

MIG uses different equipment the same as other welding processes. The most common equipment are as follows:

1. Welding Gun

It is one of the essential parts of the MIG welding equipment. They are contact tubes, trigger switch, electrode, shielding gas nozzle, flexible conduit, hose package, shielding gas hose, and power cable. It brings the shielding gas, electrode, and welding current to the arc. It is difficult to design a robust welding gun for this tough environment. Rather than make it light and small enough to be acceptable for working in narrow spaces in different positions.

2. Wire Feed Unit

With adjustable friction, the wire reel is placed on a brake hub. Intentionally, by doing so, it stops rotation when the feeding has stopped in order to keep the wire in place. The electrode is passed to the drive rolls, which then push the wire through the hose package. The wire speed must not vary too much. Consequently, it could result in unwanted variations in the welding data. The motor equipped with a pulse-generator and feedback system can achieve the superior control of the wire feed speed. The drive rolls have a trace that fits the wire. The number of driven rolls influences the feeding force that can be achieved.

3. Feeding Properties

For avoiding disturbances and deforms, careful maintenance is necessary. The main cause of disturbances is a constant hot and heavy operation. For best result, follow or set the following properties:

i) Choose the proper size of a gun to avoid temperature overload

ii) Keep the gun, free from spatter

iii) Use a water-cooled gun when necessary

iv) Choose a proper wire extension, too short can cause the risk for burn back of the arc.

v) Choose the clearance between wire and the diameter of the conduit

vi) Blow it clean now and then to avoid feeding problems

4. Power Source

The power source is the most important equipment in welding. MIG welding uses DC power sources with relatively straight characteristics. Traditionally, the tap-changer rectifier units used. The thyristor-controlled rectifier units are larger and more advanced. The inverters are the most advanced types of power sources.

5. Cooling Units

The water-cooled welding torches often use a current ranging from 300-500 A. further, the cooling water is circulated from a cooling unit, which may be incorporated in the power source. Then, it cools the copper conductor in the hose and cable bundle, the gas nozzle, and the contact tip. The cooling units consist of a pump, a water container, and a fan-cooled radiator.

Setting of MIG Welding Parameters

The welding parameters of the MIG/GMAW welding type are as follows:

i) Choice of Shielding Gas and Gas Flow Rate

ii) Electrode Stick-out

iii) Electrode Diameter

iv) Inductance

v) Torch and Joint Position

vi) Voltage

vii) Welding Speed

viii) Wire Feed Speed and Current

All the above parameters should be in order as per the required welding process and metal type.

Consumables for MIG Welding

Metal Inert Gas welding is used for low alloyed, mild steel and copper, stainless steel, aluminum, copper alloys and nickel, and nickel alloys, etc.

It can weld the plate thicknesses down to 0.7 mm. Upward, there is no technical limitation, but the risk for cold laps at low heat input or oversized pool will increase. The filler material has a similar chemical composition to that of the base material.

1. Filler Wires

The MIG welding electrodes are available in the 0.6-2.4 mm range with many different types of materials. Wires are normally supplied on reels making sure that it does not snag when being withdrawn. The wires coated with a thin layer of copper have the best feeding performance. For good results from the arc, the current will be transferred to the electrode close to the opening of the contact tip.

2. Cored Wires

Both the cored wires and solid wires are different. The cored wires are mainly employed for thicker plates. The cost of cored wires is considerably higher than solid wires. Cored wires are superior to solid wire in some respects. The high deposition rate and good sidewall penetration are the main features of cored wires.

Applications of Cored Wires – The use of these wires being increased in parallel with the introduction of new types of wires. The usage examples are as follows:

i) Both butt and fillet welds

ii) Manual welding in all positions

iii) Robot welding in the horizontal position

iv) Sheet thicknesses from 4 mm and upwards

Advantages of Cored Filler Wires – These wires have multiple benefits.

i) They are basic electrodes and tolerant of contamination in the material, producing a tough, crack-resistant weld.

ii) Cored wires have better transverse penetration than with solid filler wires.

iii) They can ease of varying the alloying constituents.

iv) They can stabilize substances in the powder extend the range of usable welding data.

v) They have a high deposition rate as a result of the high current density.

Disadvantages of Cored Wires – Despite so many benefits, still the cored wires have some drawbacks.

i) Cored wires require finishing work when using slag-forming wires.

ii) They are self-shielded wires that produce relatively large quantities of fume.

iii) Cored wires have a higher price than solid wires (not a higher total cost).

iv) They have troublesome thermal radiation at higher welding currents.

3. Solid Wires

These wires have a metallic outer sheath with flux or metal powder inside. They can have either rutile or basic filling or self-shielded for use without shielding gas.

Welding Environment while MIG Welding

Almost every arc welding process emits gases and fumes or ultraviolet radiation. They are a great risk to health and eyes in this or that way. Comparatively, MIG welding is less risky to health. But it does not mean MIG is totally risk-free. Take a look at the fact data of MIG welding emission.

Fumes and Gases

Normally MIG welding emits less fume than others which use coated electrodes. As a fact, the fume consists of solid airborne particles from electrode or surface coating. Sometimes, there is an oil fume if the workpiece is oily or greasy.

Noise

Almost every welding process is noisy and rattling. The short arc welding produces noise levels up to 80dB. But by using a suitable welding process, shielding gas, and welding technique, the noise problem can be decreased to some extent.

Arc Radiation

Another health risk is radiation from the arc while welding activity. Welding is a source of radiation in the infrared, visible and ultraviolet ranges of the spectrum. Welders must use all protective gear such as special protective glasses for eyes and fully-covered clothing for the skin.

How Does MIG Welding Work?

The MIG welding working process is sequence is as follows.

1. Preparing Metal for MIG Welding – This is the first step before starting Metal inert gas welding. Metals should be clean, free from dirt, rust, etc. Welders can clean this by using either a special brush or grinder.

2. Selecting/Preparing Equipment for MIG Welding – Selection of equipment is very crucial in any welding process. Welders should check the following things before starting welding activity.

  • Check tension
  • Check the cables
  • Inspect consumables
  • Select electrode polarity
  • Set gas flow

3. Wire Selection for MIG weldingBasically the selection of wire type depends on weld and metal types. For steel, it can be used either ER70S-3 for all-purpose welding or ER70S-6 wire for welding on dirty or rusty steel with a .030-inch diameter.

4. Selection of Gas for MIG Welding – Welders should use a blend of 75 percent argon and 25 percent carbon dioxide (75/25 or C25). Generally, this mixture is good for all purposes.

5. Selecting of voltage and amperage, push or pull, wire stick-out, work angle, travel angle, etc.

6. MIG Welding in Various Positions

i) Horizontal Position – In this position, the angle of the gun is dropped from 0° to 15° due to the force of gravity. The base metal remains stable for the time being and the filler metal may sag.

ii) Flat Position – In a flat position, the position of a weld and the angle of the gun are important ones. Look at the following angles.

  • Lap joint or fillet weld (the angle of gun is between 60° to 70°)
  • T-joint (90° joint) and the gun at a 45° angle
  • Butt Weld (180° joint) and the gun at a 90° angle

iii) Vertical Position – In this position, both up and down welds are difficult. Normally, welders need to reduce the amperage and voltage 10% to 15% due to the effect of gravity.

iv) Overhead Position – The most difficult position of all, welders need to maintain good travel speed or the molten metal will fall. They should apply drag, push, or perpendicular gun techniques.

Where is Metal Inert Gas Welding Used?

Being a common welding process, MIG is employed at various places in the welding industries.

1. MIG welding in Automotive Industry – Welders can it in different sizes of vehicles light, heavy, small, or large. MIG welding is capable of laying good quality welds even down to 0.5mm.

2. MIG welding in Pipe Industry – The piping industry uses it due to its economic nature, productivity, flexibility, weld quality, and use of robots with the latest technologies.

3. MIG welding in Rebuilding Industry – The welding type is used in rebuilding equipment i.e. dismantling, repairing, and reassembling an old vehicle. GMAW welding can fix broken parts of cars by cutting, removing, preparing new parts or joints, and clean-ups of welds.

4. MIG welding in Railway Industry – The main use here is in railway tracks for worn-out surfaces. Generally, welding different types of metals are difficult, but selecting the right filler wire is the solution.

5. MIG welding to Overlay of Wear Resistant Coating – Mainly employed for coating on the following things:

  • Hard Bearing Surfaces
  • Low Friction and Non-stick Properties
  • Resistance to Erosion
  • Resistance to Fretting and Surface Fatigue
  • Resistance to Abrasion
  • Soft Bearing Surfaces

Metal inert gas welding is a big improvement over traditional techniques. As a result, it made possible the creating of bridges, automobiles, and the like many huge structures.

Employment Areas for GMAW Welding

Some of the companies hiring MIG welders are as follows.

  • Arcosa, Lancaster, SC
  • Caterpillar, Athens, GA
  • FactoryFix, Chicago, IL
  • K&N Engineering, Riverside, CA
  • Progress Rail Services Corp., Boaz, AL
  • RailWorks Corporation, Chicago, IL
  • Walt Disney World Resort, Lake Buena Vista, FL

Job Types for MIG Welding

  • Manufacturing Associate (Welder)
  • MIG Weld Trainees
  • Production Welder
  • Welder
  • Welder (Helper)
  • Welder and Pipefitter Helper
  • Welder/Grinder

Salary of Welder or MIG Welders

The salary trends in the welding industry change from time to time depending on the place you are working at and your profile. Generally, a welder earns more in developed countries than in developing countries. On average, a MIG Welder earns $31,594 per year or $16.20 per hour in the USA. The figures may vary in other countries.

Conclusion

Metal Inert Gas welding or GMAW is one of the common types of welding processes. The process is beneficial for aspiring students, welders, and other professionals in many ways in their respective fields.

Related: Other Welding Types

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