9 Oct 2023

What is MIG welding?
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MIG Welding

Welding is a fabrication process that uses high heat and pressure to melt two or more materials together, mainly metals and thermoplastics. When the base metal or parent material melts, a filler material or consumable is added to form a pool of molten material called a weld pool. As the weld pool cools down, the materials join together to form a joint or ‘weldment’.

There are multiple welding techniques and types that are used according to the materials used, the difficulty level and the desired final effect. One of the most popular types of welding is MIG welding, which is used by both hobbyists and advanced professionals alike due to its convenience, versatility, speed and straightforward use. Learn all about what MIG welding is, the process of MIG welding and its advantages and disadvantages below.

What is MIG welding?

MIG welding stands for metal inert gas welding, but it’s also known as gas metal arc welding (GMAW). During the process of MIG welding, constant voltage power is supplied to the welding torch, creating an electrical arc or short circuit between an electrode wire (positive anode) and the parent metal (negative cathode). This electric arc melts the base/parent metal and the wire to create a weld pool. 

The electrode wire is a consumable filler wire that’s continuously fed through the weld torch. As the filler wire melts onto the parent metal, this creates a weld pool that cools and solidifies into a solid weld joint. Once this is complete, two or more pieces of metal have been successfully joined together. 

To protect the weld pool from atmospheric gases during fusion, an inert shielding gas (such as argon or helium) is fed through the welding torch. This gas prevents contamination without affecting the properties of the metal, ensuring that the weld is strong.

Due to its ease of use and the strength of its welds, MIG welding is commonly used in heavy-duty welding applications. Although techniques like TIG welding are generally preferred for more precise and detailed work, MIG welding is an excellent technique that can produce very strong weld joints quickly and cleanly.

Types of MIG welding

There are two main types of MIG welding: bare wire and flux core MIG welding. Both types are suited to different applications based on their properties.

Bare wire

Bare wire MIG welding is commonly used when thin pieces of metal need to be joined together. This solid, uniform wire can produce a strong and neat weld, but it needs an inert shielding gas to stop the weld pool from becoming contaminated.

Flux core

With flux core MIG welding, shielding gas is used to enhance the fusion process. The filler wire has a hollow structure with a flux in its core, which forms a layer of slag as the wire melts to protect the weld pool from contamination. Due to the use of internal flux to protect the weld pool, flux core MIG welding is perfect for outdoor applications because the wind won’t affect the gas supply (a common issue for bare wire MIG welding). However, this technique is messier due to the amount of slag produced, which needs to be cleaned off the weld joint after it has cooled down. 

Materials used in MIG welding

What do you need to get started with MIG welding? Here are the main materials used in the process of MIG welding:

1. Safety equipment

Before you can even begin welding, you need to have the right safety equipment. While welding, you’ll be exposed to very high temperatures, extremely bright light, and ultraviolet (UV) and infrared (IR) radiation.

To protect your skin from burns and radiation, you’ll need heat-resistant gloves, flame-retardant overalls, and a welding helmet. Most importantly, you’ll need eye protection to shield your eyes from the damaging light and radiation from the sparks. Looking directly at the light can cause short-term vision loss and long-term vision problems over time, with repeated exposure leading to serious consequences such as blindness. A welding helmet with suitable lenses will be essential for protecting your eyesight. 

Finally, to protect yourself from harmful welding fumes, particles and odours, you’ll need a respirator even when working outside. This will protect your lungs against long-term damage caused by inhaling harmful gases. When working inside, you should also ensure that the room is well ventilated and has a proper ductwork and extraction systems

2. Wire electrode

One of the most important elements is the wire electrode or filler wire, which is the consumable part that’s fed through the welding torch to melt onto the parent material, forming a weld pool that cools into a solid weld joint or weldment. Choosing the right wire material, such as stainless steel, mild steel or aluminium is essential to produce a correct weld finish.

3. MIG welding gas

In both cases you’ll need a shielding gas to stop your welding pool from getting contaminated and weakened. The type of gas you choose will depend on the material you’re welding, but the most commonly used ones are argon, helium, carbon dioxide and oxygen.

Again, in both cases, using a mix of inert argon with a smaller amount of carbon dioxide (an active gas) in a 75/25 ratio will allow for deeper penetration, but using too much active gas can lead to increased spatter and porosity which will affect the weld quality.

4. Welding torch

These elements are all brought together in the welding torch or welding gun, which is the equipment that you’ll handle to weld metal together. There are two main types of welding torch to choose from:

  • Gas-cooled welding torches – These welding torches are cheaper but prone to overheating, making them better suited for smaller projects rather than large-scale, intensive work.
  • Water-cooled welding torches – These torches provide more power, more control and less overheating, but they’re more expensive.

5. Power

Finally, you’ll need a power source to get your welding torch up and running. The vast majority of MIG welders will use DC power, as this provides a constant voltage supply for the electrical arc. AC power is hardly ever used in MIG welding, but it’s more common in TIG welding.

You’ll need to choose your electrode polarity too before getting started. The DC positive polarity setting is used when you want a stable arc, better penetration and less spatter. DC negative polarity is used when you want faster deposition rates, but the downside is that there’s less heat in the weld pool and less penetration overall. This makes DC negative polarity suitable for welding thin sheet metal but not thicker materials.

Process of MIG welding

So, how do all of these materials work together in the MIG welding process? Let’s take a look at this below:

1. Pre-weld clean up

Before you get started, it’s important to clean your workspace and materials first. This will help prevent contamination during welding, so you can produce stronger and cleaner weldments. You need to ensure that there are no contaminants like rust, oil, debris, dust and dirt on your electrode wire and your base materials.

2. Welding position and angle

One of the great things about MIG welding is that it can handle multiple welding positions and angles with ease, including horizontal, vertical, flat and overhead positions. However, it’s still important to plan out the right position in advance to prevent the filler from rolling over the side of the joint and making it look messier. 

3. Welding speed

Combine the right welding position with an appropriate speed to get a clean and strong weld joint. Moving too slowly can lead to excessive deposition, and if you’re welding thinner materials, the extra heat transfer can lead to you burning through them. Conversely, moving too quickly will mean that less heat is transferred to the metal, leading to inadequate melting and thin, weak weldments. Always evaluate the size of your weld pool in relation to the joint thickness to work out the right welding speed.

4. Metal transfer

In MIG welding, there are four basic metal transfer modes: short circuit transfer, globular transfer, spray transfer and pulse transfer. These different modes affect how the metal filler wire is transferred across the arc to the base metal. 

  • Short circuit transfer: This mode uses a low voltage and is the coldest form of MIG welding. It’s usually used with smaller diameter filler wire, allowing you to get a precise, controlled weld with thinner materials. However, it’s susceptible to increased spatter and incomplete fusion defects.
  • Globular transfer: In this transfer mode, the wire is heated for longer with higher voltage levels to create a large volume of weld metal that drips onto the joint. Penetration can be inconsistent and you need to weld from a flat position. 
  • Spray transfer: With this method, current and voltage are increased further so that small droplets of metal from the filler wire are sprayed onto the weld joint. Again, you’re limited to flat welding positions, but the deeper penetration of this method makes it ideal for thicker materials (although you risk burn-through with thinner materials).
  • Pulse transfer: This mode uses a special power source to pulse the voltage many times per second, with a droplet forming with each pulse. This reduces spatter, and the lower heat output makes this mode ideal for welding thinner materials.

Advantages of MIG welding

With so many types of welding to choose from, why would you opt for MIG welding for your business or personal projects? Here are the main advantages of MIG welding:

1. Versatile

MIG welding can be used to weld many different types of metals and different metal thicknesses, making this welding method extremely versatile. Although TIG welding is usually used for the most precise applications with thin sheet metal, MIG welding is a great all-rounder method used by advanced welding professionals and hobbyists alike. All you need to do is adjust your welding position, speed and metal transfer mode to adapt to a wide range of materials. 

2. Easy to learn

MIG welding is perhaps the most straightforward type of welding for beginners to learn. This makes it the number one welding choice for welders of all experience levels.

3. Fast

Another major benefit of this type of welding is that it’s typically very fast. The speed of MIG welding is mainly due to its continuously fed electrode wire, which enables uninterrupted welding and therefore shorter lead times. As a result, MIG welding can increase productivity (and profits) for your business.

4. Can handle multiple welding positions

The versatility, convenience, ease of use and speed of MIG welding are all made possible by the fact that this method can handle many welding positions and angles confidently. This allows you to work with many types of materials and create a wide variety of weld joints to suit your needs.

5. Minimal clean up

MIG welding creates much less spatter and slag compared to traditional stick welding, so you aren’t left with too much cleaning to do after you finish your weldments. Although TIG welding is even cleaner, MIG welding is still very fuss-free and doesn’t create a lot of waste. Plus, with the continuously fed wire, you end up using all of your electrode wire during MIG welding, so you aren’t left with electrode stub waste products like with stick welding. 

Disadvantages of MIG welding

Naturally, there are also some disadvantages to this welding process. So why might MIG welding not be right for you?

1. Higher initial investment

The materials and equipment for MIG welding can be more expensive. Therefore, you may have to make a higher initial investment compared to other types of welding.

2. Potentially less portable

MIG welding equipment also isn’t as portable because it requires an external gas source, which can be an issue if you need to use your welding kit in different locations. However, modern MIG welding equipment can be much more compact.

3. Can be less controlled and precise than TIG welding

For the most precise and detailed work on thin sheets of metal, TIG welding is still generally preferred. However, since MIG welding is very versatile, it can be used on a wide range of materials and metal thicknesses, so it’s a great all-round solution if you only want to invest in one type of welding.

4. Less convenient for outdoor welding

It can be more difficult to perform MIG welding outdoors due to the effect of wind on the inert shielding gas. This may mean that you need to keep your welding equipment indoors.

Workplace safety is paramount when working with any type of welding. In particular, ventilation is key to prevent the inhalation of harmful gases and debris. Here at Airmatic, we produce the highest-quality ductwork, fabrication and extraction solutions to promote safety and productivity in your business. Get in touch today to discover more about our ventilation solutions.

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