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MIG welding is an arc welding technique of using a continuous solid wire electrode which is served via a welding gun into the weld pool to melt and join pieces of metal together.
In this article you will learn more about the MIG welding process and get some tips and tricks.
Table of Contents
What is MIG welding?
MIG stands for Metal Inert Gas.
MIG welding is a welding process in which an electric arc forms between a wire electrode and the workpiece metal.
A constant voltage power supply is used to generate the arc. This electric arc heats the metals and thus the parts melt together. Together with the electrode which is being consumed during welding the inert gas exits the nozzle and avoids oxygen to enter the weld area.
MIG was developed during World War II. It was used to weld aluminum to help produce equipment and weapons. It was then used in the growing postwar economy, mostly in factories and shops.
MIG welding can be used on different types of metals; steel, aluminum, stainless steel, copper, silicon bronze, magnesium, copper, nickel, and other alloys.
Compared to other methods of welding, MIG welding is hands down, fast, inexpensive, and welders can be easily trained to produce quality work.
Moreover, MIG welding is a subtype of GMAW welding.
back to menu ↑What is gas metal arc welding (GMAW)
Gas Metal Arc Welding (GMAW) is an arc welding process in which an endless wire electrode melts in combination with a shielding gas. The gas protects the weld area from oxidation and external influence. Because of the help of the additional shielding gas, gas metal arc welding allows many materials that are suitable for welding to be joined together.
The procedure is also known as Gas Metal Arc Welding (GMAW) and Metal Active Gas welding (MAG) as well as wire feed welding.
back to menu ↑Equipment for MIG welding
To perform MIG welding, the necessary essential equipment is a power supply, a wire feed unit, a conduit, a welding gun and a shielding gas supply.
We conducted also a full review on the Best MIG welder for welding.
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MIG output power is usually operated with a DC power supply. This constant power source also controls the welding voltage/current association, since in MIG, the wire feed speed determines welding current, and the power source voltage level controls arc length.
MIG welding guns – 2 types of welding guns
There are two types of welding guns: Water cooled and air cooled welding guns.
Wire feed system
welder with Argon
The second crucial equipment in MIG is the wire feed system. The performance of the wire feed system is vital to the stability of MIG welding. Great care should be observed to the feed liners and rolls so as the system must be able to proficiently feed the wire. Miller Millermatic 211 and the Hobart Handler 140 are two solid MIG welder systems to check out.
You can use either the pinch-roll, push-pull or the spool-on gun feeding system. Thirdly you require the conduit, it should measure up to 5 meters in length and keep straight to facilitate wire feeding.
In addition to guiding the wire into the joint, you require the welding gun to transfer the welding current to the wire and provide the gas for shielding the weld pool and arc.
The nozzle
To get the shielding or reaction gas to the weld pool you need the right nozzle for your application. A well designed nozzle focuses the gas to the weld pool and avoids turbulent gas flows.
back to menu ↑Wear skin and eye protection during operation
Moreover, MIG welding produces a lot of dissipated heat and lots of harmful UV light. You need to wear a safety gear to protect your skin and eyes from UV light.
Additionally, safety clothes will protect your skin from molten metal splattering off from your workpiece. Ultimately you reduce the risk of an electric shock when wearing welding gloves. Ideally your welding gear includes the following items:
- Welding mask / welding helmet
- Welding gloves
- Leather overall
- Closed shoes
You may want to check out an overview of auto-darkening welding helmets here.
Also, weld in a well-ventilated area as welding produces harmful fumes.
back to menu ↑MIG welding gas – types
For MIG welding, Argon, Helium, CO2 and Oxygen are the most common used shielding gases. Depending on the weld application each shielding gas has its advantages and disadvantages. Check out the Praxair shield gas manual for in depth details.
Argon (Ar)
Argon is an inert gas and does not react under normal circumstances with any other material. Many shielding gases include argon as a component. All metals can be welded with Argon. The arc voltage of argon is pretty low.
Helium (He)
Helium is (like Argon) an inert gas. Because of its difficult production, helium is more expensive than the other gases. It can be used with all common metals. Compared to argon, Helium provides a wider and deeper weld penetration. Usually it is mixed with Argon in the ratio 25% up to 75%.
Carbondioxide (CO2)
CO2 is the most common used reactive gas. It provides a wide deep weld seam. Although it is the cheapest among the gases, it causes quite a lot of weld spatters.
Oxygen (O2)
Oxygen reacts with the metal in the weld pool so it is not recommended to use for aluminium, copper & similar. Moreover, oxygen increases arc temperature and stabilizes the arc when using with mild or stainless steels.
MIG welding shielding gas
Shielding gases are necessary for MIG welding in order to protect the welding area from contamination and oxidation. Contamination can cause porosity, fusion defects, and weld metal embrittlement if they come in contact with the arc, electrode, or the welding metal.
back to menu ↑How to MIG weld – techniques
There are mainly two types of MIG welding techniques used in the industry today.
The forehand welding technique and the backhand welding technique.
Forehand welding technique
The forehand is a procedure where the MIG welder thrusts the puddle and keep the arc a little ahead of the puddle. MIG Gun is pointed facing the traversing path. The angle of the gun can be between 5 and 35 degrees in the direction of the travel.
Backhand welding technique
The backhand, on the other hand, is a technique where the MIG gun is pointed to the weld while moving away from it.
weld seam
Generally, forehand welding is more commonly used than the backhand as it produces a shallow yet wide penetrating weld that has a flat look which is required by most weld joints.
back to menu ↑MIG welding stainless steel
Stainless steel’s main advantage is its good corrosion resistance. You can MIG weld stainless steel. Most common stainless steel type is austenitic, but there is also ferritic, martensitic, duplex type of stainless steel. You can read more here about how to weld stainless steel.
Shielding gases to weld stainless steel:
- 98% Ar + 2%O2
- 97% Ar + 3% CO2
- 90% He + 7.5 % Ar + 2.5 % CO2
Differences between MIG and TIG welding.
TIG welding uses an electrode made of tungsten that is not burnt during the welding process. While MIG welding uses a metallic electrode and is heated during welding.
In TIG welding the primary shielding gas is argon, with helium occasionally used. Argon is also the primary shielding gas in MIG welding but mixes with carbon dioxide for different applications.
TIG welding necessitates a different filler material in rod because the electrode is not consumed while MIG welding provides the filler material via the electrode.
TIG welding is thought to be more challenging than MIG welding because strict tolerances have to be observed among the filler rod, the electrode, and the workpiece.
If you like, you can enroll in a welding institute to learn how to MIG weld or take an online course and practice a lot alongside other experienced MIG welders. Besides that check out the MIG welding tutorial video below:
back to menu ↑Why to MIG weld?
Actually you can earn quite a bit money with MIG welding, check out my huge collection of welding projects and welding ideas.
back to menu ↑How to check weld seams
weld seam cross section
On the right hand side, you can see a cross section image of an actually laser-welded seam. Two parts were joined together and the melted area shows a different texture. As you can see in the cross section, the seam shows only little porosities. Of course, this is a destructive testing method.
Furthermore, non-destructive testing helps to verify that a weld seam has no defects. At high risk applications (reactor, pipelines…) every weld seam is 100% checked. Methods like CT scan, ultrasonic scans, radiographic analysis and eddy current testing are commonly applied.
Here you can see the top bead of a weld seam. If you do not have testing equipment, you can visually inspect your weld seam. On the top bead you often can already see the quality of the weld seam. It should be free of cracks and porosities.
weld seam top bead
