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How Does a MIG Welder Work? Inside the Machine

Last updated on May 25th, 2023

MIG welding is a popular welding method that is pretty straightforward to learn. Yes, it might take a bit of practice to master but is a versatile method that has tons of applications.

But have you ever wondered what goes inside the hood? What mechanics or magic make MIG welding possible?

MIG welders are very different from other types of welding machines and have specific components that make the overall welding process easier and more efficient than other welding methods.

In this article, I will be moving beyond the basics and discussing the mechanics of the MIG welder machine.

Let’s dive into the details of a MIG welding setup and explore every part of the machine.



MIG Welder Core Components

Let’s start with the core components of the welding machine that make it possible for the machine to weld.

The Power Source

The power source is the heart of the MIG welding setup. The machine typically uses a direct current (DC) power source which only flows in one direction.

MIG welding ensures a stable arc and smooth welding technique. The power source is single handedly responsible for generating heat and melting both the base metal and the filler metal.

MIG welders use DC Electrode Positive (DCEP) polarity for most projects which is also known as reverse polarity. In this, the electrons flow from the welding gun to base metal which provides better penetration and high weld quality.

The DC Electrode Negative (DCEP) Polarity is not commonly used in MIG welding because it is not effective against thicker material. However, when welding thin sheets of metal, you can use it too.

Alternating Current (AC) polarity is hardly used in MIG welding because there is a risk that you will lose arc control and cause more spatter. However, it is still used for welding non-ferrous metals in some special cases.

Wire Feed System

The wire feed system is a unique component of a MIG welder that you won’t find in other welding setups.

This component is responsible for steadily feeding the electrode wire from the spool through the welding gun.

It plays a critical role in the overall welding process. The speed by which the welding wire is fed into the weld pool often determines the size and depth of the weld.

The Welding Gun

The welding gun is your primary weapon and the conduit of your creation. It is responsible for forming the electric arc, on which the whole welding process is reliant.

The welding wire is heated in the electric gun and the arc is also generated inside it. This component is also responsible for directing the shielding gas into the weld pool.

One thing which really makes the welding gun of a MIG welder unique is its ability to directly feed the wire into the weld while taking it from a large spool inside the welding machine.

Shielding Gas

Unlike TIG welding, the shielding gas in MIG welding is not only responsible for protecting the weld pool from contamination but plays a dual role by enhancing the welding process itself.

The gas is responsible for stabilizing the arc and is also a significant component of a MIG welder.

These components combined are responsible for making a MIG welder work efficiently.

Related: What Gas Does a MIG Welder Use? Role of Gas in MIG Welding

The Two Types of Wire Electrodes in MIG Welding

You have multiple options to choose from when it comes to selecting a wire electrode in MIG welding, The choice will depend on the type of metal being welded and the specific requirements of the project.

Generally, there are two types of wire electrodes.

Most commonly, MIG welding uses a hard wire electrode. This wire electrode is affordable and easy to control. The wire comes in the form of large reels or spools and can be used at different angles.

Flux-coated wire is a special kind of wire that has a coating of flux on the wire which removes the need for shielding gas. So, obviously, it is much more expensive than hard wire.

You must keep in mind that welding with a flux-coated wire is known as flux-cored arc welding (FCAW) but since the wire is being used in a MIG welding setup, it can be considered MIG welding too.

Cooling Systems

MIG torches come with built-in cooling systems that are responsible for keeping the welding gun cool while you are working.

There are two types of cooling systems that are integrated with your welding gun.

The gas-cooled welding torches are commonly used with portable MIG welders that are used for smaller projects. With such projects, overheating is not much of an issue, and you only need a bit of cooling down.

However, when you are working on big projects where high amperes are adopted, you will need a water-based cooling system.

Welding guns that come with a water-based cooling system are more costly than the previous ones, but they are a mandatory component of the MIG welding setup.

Related: How to Use a MIG Welder?—Ultimate Guide & Expert Tips

The Electrical and Metallurgical Processes in MIG Welding

Now that we are clear on the core components, let’s take a look at how the welding process starts and what electrical and metallurgical processes start the fusion.

Creating an Electrical Arc

The generation or creation of an electric arc is the central process of MIG welding. When the gun is triggered, it will complete the electric circuit which will create the electric arc.

The electricity that jumps from the electrode to the workpiece is responsible for arc generation and is an intense heat source. There are various methods to generate an arc in MIG welding.

Understanding the Weld Pool

Once the electric arc is generated, it will create an extreme amount of heat which will melt both the wire electrode and the base metal.

The molten area formed by the melting of both of these components is known as the weld pool.

As you move the welding gun along the joint, the weld pool will also move. The area you leave behind will cool down and solidify which will create the bead of fused metal.

Maintaining a Stable Arc

You will have to maintain a stable arc in order to ensure a smooth weld. You can do so by adjusting the welding parameters like voltage and wire feed speed.

High voltage can lead to more spatter while low voltage can cause the arc stutter to go out.

Similarly, welding too fast or too slow can also disrupt the stability of the arc. You will have to maintain the optimum settings and speed which you will only learn through practice.

The Metallurgical Reactions

MIG welding is not only an electrical process but also a metallurgical one. How?

When the base metal and filler material melt, they will mingle and fuse and will form a strong joint when they cool and solidify.

So, the metallurgical processes are involved in welding mechanics. The shielding gas also plays a role there which will protect the weld pool from contamination and also enhance the weld.

Understanding the Impact of Welding Parameters: Voltage, Wire Speed, and Gas Flow

The welding parameters have a significant impact on the MIG welding process. It is crucial to understand this impact to know how a MIG welder actually works.

Voltage and Its Effect

Voltage is the steering wheel of MIG welding. It will direct the arc, shape it and also guide it.

The higher voltage you set, the bigger arc you are going to get and the wider and flatter the weld bead will be.

Alternatively, if you set the voltage at a low level, you will get a shorter arc which will result in a narrower and deeper weld bead.

Hence, understanding how to set your voltage is the key to getting the required weld shape, appearance, and penetration.

Wire Speed and Its Influence

In MIG welding, the wire speed also has a significant impact on the process itself. It is linked to the accelerator pedal of the welder.

The pedal will determine how fast the welding wire will be fed into the weld pool, which will also impact the size and quality of the weld.

Faster speed will result in larger weld beads while slower speed will result in smaller weld beads.

However, if you set the speed at too fast or too slow, then you can run into various welding problems that will ruin the quality of the weld.

With speed faster than necessary, you will get incomplete fusion and with slower speed, you will burn through.

Gas Flow Rate and Its Impact

Shielding gas plays a very important role in MIG welding. It is the bodyguard of your weld pool that protects the molten weld pool from atmospheric contamination.

In the absence of shielding gas, there is a high risk of contamination that will cause porosity or weaken the quality of the weld.

The gas flow rate is responsible for determining how fast the gas is dispensed. If you keep the gas flow rate too low, you will risk contamination.

However, setting the speed too high will blow the molten metal around causing a lot of spatter.

Why Inert Gas Matters? —The Role of Shielding Gas in MIG Welding

There is a very minor difference between Metal Inert Gas welding and Metal Active Gas welding because of which you might have never heard of the latter method.

Both are considered generally MIG welding processes.

Argon is the inert gas of the MIG welding process and is used widely because of its low ionization potential that helps you maintain a stable arc.

It forms a heavy and protective blanket on the weld pool that will protect it from all sorts of contaminants.

Carbon Dioxide is much cheaper than argon, which can be mixed in argon or used independently. It will provide deeper penetration but also causes more spatter.

The mixture of argon and carbon dioxide is considered ideal and is used for multiple welding applications. Finding the right balance of the gasses helps you achieve gold weld at a reasonable cost.

There is also a wide range of other mixtures you can use to get specific welding tasks done with maximum efficiency.

Heat Input and Its Impact on MIG Welding

Heat input also plays a critical role in MIG welding. It can greatly impact the weld’s strength, ductility, and resistance to cracking.

Understanding heat input is a must when you are working with MIG welding. If you are using too much heat, it can lead to warping or excessive penetration.

On the other hand, if you are using too little heat, it can result in a weaker weld.

So, managing heat input is crucial to get the welds of desired quality. You can balance the heat by balancing the welding speed and current.

If you are moving the welding gun too slowly, it can result in excessive heat build-up in the area or Heat Affected Zone (HAZ) which can cause a burn-through.

If you are moving it too fast, the joint will not receive enough heat which will result in a weaker weld.

Similarly, if you are using too much current, it will generate more heat which can cause the metal to expand and then contract leading to distortion and warping.

Several techniques can be used to manage heat. Professional welders often use techniques like stitch welding or backstep welding to deal with this issue.

Related: What is a MIG Welder Used For? Applications of MIG Welding

Frequently Asked Questions

How does a MIG welder work without gas?

It is a special type of welding that is also considered gasless MIG welding. It has the flux inside the welding wire which melts and releases its own gas. So, in a technical sense, it is not a gasless welding process but rather one that doesn’t use gas from a cylinder.

How does a MIG welder produce heat?

MIG welding produces heat by the use of electric current. The current travels through the wire electrode and when the electric circuit is completed, it generates an arc which is responsible for producing the heat.

How does a MIG welder work with gas?

The gas nozzle is in the welding gun. You connect the welder with the required gas cylinder or cylinders if you are using a mixture. The flow rate of the gas can be adjusted through the regulator on the gas cylinder.

Why does a MIG welder need gas?

MIG welding is a process that fuses metal pieces together by using heat. The joint is created by melting the pieces and adding a filler material to create a weld pool. To protect this weld pool until the joint is cooled down and solidified, shielding gas is required.

What are the main components of MIG?

The four main components of a MIG welder are the power source, the welding gun, the shielding gas, and the welding wire. The welding wire acts as both the electrode and the filler materials to create the weld.

What is inside a MIG welder?

Inside a MIG welding machine, you have a wire spool that directly connects to the welding gun and releases the wire as per the set speed. Other than that, you have circuits and boards that are used to adjust the welding parameters.

Wrapping Up!

To sum it all up, a lot of things go inside a MIG welding machine and understanding them not only helps you satisfy your curiosity but also enables you to harness the full power of the welding machine during its use.

By understanding how different components work and interact with one another, you will be able to become a more efficient welder.

You will be able to troubleshoot problems, adapt to welding situations, and produce better and more consistent welds.

Just like with any craft, knowing the insides of your tools will elevate your skills and enable you to become better by becoming more creative and experimental.

Got something on your mind? Drop it in the comment section below and I will get back to you as soon as I can.

Sheila James

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