MIG
Metal Inert Gas (MIG) Welding or Gas Metal Arc Welding (GMAW)?
MIG stands for Metal Inert Gas Welding. The name MIG became a household name for welding and fabrication industry.
MIG describes an arc welding process where shielded gas is applied. In this case it is an inert gas (which does not react with other particles).
However, one-day carbon dioxide proved to be a good shielding gas. Since then the MIG name has been changed to a general GMAW (Gas Metal Arc Welding).
Why? Well, carbon dioxide is not an inert gas. Thus, Gas Metal Arc Welding is a term which describes both MIG welding (uses inert gases - helium, argon) and MAG welding (Metal Active Gas - uses carbon dioxide).
Funny enough, welding industry still uses MIG name to describe any GMAW process.
MIG (Metal Inert Gas)/GMAW (Gas Metal Arc Welding) Process
MIG/GMAW welders use consumable/filler wire electrode shielded by a gas (inert, active or both). This is contrary to TIG (GTAW), where electrode is not part of the weld puddle.
The electrode is fed through a welding gun. A DC (direct or constant) voltage and DC current is commonly used to heat the wire to form an arc.
The welding arc is formed between filler wire and the metal. The filler wire becomes the weld deposit. The gas shield around deposit prevents contamination of the weld.
In case of MIG (Metal Inert Gas) the shielding gas (helium, argon) is inert and does not react with other particles. In case of MAG (Metal Active Gas) the gas (eg. Carbon dioxide) can be reactive.
Both MIG welding and MAG welding are classified as a general GMAW (Gas Metal Arc Welding).
The welders for MIG / GMAW welding consist of:
- Power Supply to deliver voltage and current during the welding process
- Wire Feed Unit to supply filler/consumable wire for weld deposit
- Shielding Gas supply to shield weld pool (puddle) from contamination
- Contact tip, which forms short circuit with the welded metal during MIG welding
- Nozzle, which contains electrode engulfed in the shielding gas
The MIG / GMAW operator controls the power and amount of filler wire which is fed for the weld deposit. It requires a certain amount of welding skill to avoid undercuts and valleys in the weld.
MIG / GMAW welders use four metal transfer modes:
- Dip or short arc
- Spray
- Globular
- Pulsed-Spray
Note: MIG gives off more infrared radiation than other welding processes. Safety (like proper filter lenses are paramount!)
Metal Inert Gas / Gas Metal Arc Welding Welder's Components
The typical MIG / GMAW welder station has five distinct components:
- Power Supply
- Wire Feed Unit
- Welding Torch/Gun
- Shielding Gas Supply
- Work, workpiece or welded material
MIG / GMAW Welder's Components: Power Supply
MIG / GMAW welders power supply generally uses a constant voltage and current. The alternating current is rarely used.
This means that heat is directly proportional to changes of voltage. From electrical theory Power/Heat = Current * Voltage. On GMAW or MIG welders both voltage and current can be altered.
It is important to note that GMAW or MIG welder has amperage control incorporated in the wire feed. Thus, the voltage knob mainly controls the heat from the power supply unit.
MIG / GMAW Welder's Components: Wire Feed Unit
The Wire Feed Unit controls amount of filler wire being supplied as the weld deposit. The speed of the wire also controls the amperage.
If the consumable electrode is fed too quickly then the weld pool is surrounded by spatter.
Alternatively, slower feed results in incomplete fusion and the weld being weak. The wire feed is initiated with the control switch (trigger). Trigger also starts electric power and the shielding gas flow.
Metal Inert Gas / Gas Metal Arc Welding: Welding Torch/Gun
MIG / GMAW welding torch or gun consists of number of components. This include handle, shielded gas nozzle, contact tip and nozzle output face.
MIG / GMAW operator or welder uses only handle to keep the gun. All other areas of the welding torch should not be touched when welding.
The shielded gas nozzle must always be free of spatter and blockage. The nozzle supplies the shielded gas, which prevents contamination of the weld pool.
The contact tip is normally copper (improved, chemically treated variation are available). The contact tip transfers electrical energy into the consumable filler wire.
MIG / GMAW Welder's Components: Shielding Gas Supply
Metal Inert Gas / Gas Metal Arc Welding uses shielding gas to prevent contamination of the welding pool. Oxygen and Nitrogen can easily cause porosity or fusion during welding process.
Inert gases such as argon or helium are mainly used for nonferrous welding. Pure carbon dioxide has application in deep penetrating welds.
Shortcomings and benefits of shielding gas results in mixtures being deployed. 75% argon and 25% carbon dioxide or 90% argon and 10% carbon dioxide are commonly used in MIG / GMAW welding.
MIG / GMAW Welder's Components: Work or Welded Material
The workpiece is a material on which weld is being deposited. It is also connected to power supply to complete the short circuit during welding.
MIG / GMAW Welder Component Summary
- MIG / GMAW Power Supply
- MIG / GMAW Wire Feed Unit
- MIG / GMAW Shielding Gas Supply
- MIG / GMAW Welding Torch/Gun
- MIG / GMAW Work, workpiece or welded material
- MIG / GMAW shielding gas released during welding
MIG / GMAW Welding Machine
- MIG / GMAW Wire Feed Unit
- MIG / GMAW Power Supply
- MIG / GMAW Welding Trolley where consumable filler wire is stored
- MIG / GMAW hose attached to the torch or gun
- MIG / GMAW Shielding Gas Supply