What Is MIG Welding and How to MIG Weld?

What is MIG Welding?

Metal Inert Gas (MIG) welding, more formally referred to as gas metal arc welding (GMAW), is an arc welding method where a continuous solid wire electrode is heated and directed into the weld pool via a welding gun.

During the process, both base materials are melted, resulting in a strong joint. Alongside the wire electrode, the welding gun also supplies a shielding gas, which plays a crucial role in protecting the weld pool from contamination by airborne particles.

At its core, MIG welding joins two separate metals by generating heat from an electric arc. This arc forms between the workpiece and a constantly supplied filler electrode, allowing the metals to fuse effectively. The presence of shielding gas is essential; it safeguards the molten weld pool from any undesirable reactions with gases present in the surrounding environment.

Tracing back to its origins, MIG welding was first patented in the United States in 1949, originally intended for welding aluminum. At the time, helium gas—readily available—was used to shield the weld pool created by a bare wire electrode.

A few years later, around 1952, the process gained popularity in the United Kingdom, particularly for welding aluminum with argon as the shielding gas, and for carbon steels using carbon dioxide (CO₂). Mixtures of CO₂ and argon, known as metal-active gas (MAG) processes, also became common practice.

Compared to manual metal arc (MMA) welding, MIG welding is often preferred because it delivers higher deposition rates and boosts productivity. For many, the combination of efficiency and versatility makes MIG welding a valuable technique in a range of industrial settings.

What You Need for Mig Welding and Its Preparation

As with all jobs that involve risk, you should make safety the number one priority.

• Suitable facemask.
• Protective gloves.
• Welding respirator (if you are working in confined spaces or with limited ventilation).
• Fume extractor (if desired).
• Weld jacket or leather jacket.
• Weld sleeves.
• Enclosed, are hard-wearing work boots.

Now that you’ve taken care of the safety aspect, let’s look at the equipment you will need.

• MIG welder and torch.
• Argon gas canister.
• Carbon dioxide canister.
• Power supply.
• Gas regulator.
• Ground clamp.
• Wire feed.

Safety first

Before beginning any welding task, it is essential to wear appropriate protective clothing and clear the workspace of any potential fire hazards.

Standard safety gear for welding typically consists of leather shoes or boots, trousers with cuffs, a long-sleeved jacket made from flame-resistant material, leather gloves, and both a welding helmet and goggles. Additionally, it is advisable to use a headscarf or skull cap to shield the top of the head from sparks and spatter.

Metal Preparation

Compared to stick and flux-cored electrodes, which are formulated with a greater quantity of specialized additives, solid MIG wire offers much less resistance to common surface contaminants like rust, oil, or dirt.

For that reason, it’s important to take the time to clean the metal thoroughly using a wire brush or grinder before you start welding. Pay attention to your work clamp, too; it needs to be attached to a clean section of metal, as any resistance in the electrical connection can interfere with the wire feed and compromise your results.

When working with thicker metals, another key step is to bevel the joint. This helps the weld penetrate fully into the base material, which is particularly critical when you’re welding butt joints and want to ensure the strength and integrity of your weld.

Equipment preparation

• Inspect Your Cables: Before beginning the welding process, take a moment to examine all cable connections. Make sure each one fits securely and shows no signs of fraying or other wear. Addressing any damage at this stage can prevent issues later on.
• Set Electrode Polarity: For MIG welding, you’ll need to use DC electrode positive—also referred to as reverse polarity. Typically, you’ll find the polarity settings inside the welding machine, so double-check there before you start.
• Adjust Gas Flow: Activate the shielding gas and set its flow rate between 20 and 25 cubic feet per hour. If you’re unsure about the integrity of your gas hose, try brushing on a bit of soapy water and watch for bubbles that would indicate a leak. If you do find any leaks, it’s best to replace the hose right away.
• Verify Tension: Both the drive rolls and the wire spool hub require the right amount of tension; too much or too little can disrupt wire feeding. Refer to your owner’s manual for guidance on making these adjustments.
• Check Consumables: It’s worth clearing any spatter from the contact tubes, swapping out contact tips or liners if they’re worn, and tossing out any wire that looks rusty. A little attention here can make a big difference in your welding performance.

Wire selection

When it comes to welding steel, there are generally two types of wire that are most commonly used. For most general welding tasks, the AWS ER70S-3 wire is a reliable choice. If you’re dealing with steel that isn’t perfectly clean maybe it’s a bit dirty or has some rust—you’re better off using ER70S-6, as it contains extra deoxidizers to help with those conditions.

Selecting the right wire diameter also makes a noticeable difference. A 0.030-inch wire is versatile enough for a range of metal thicknesses, which makes it popular for both home projects and motorsport work.

If you’re working with thinner metals, dropping down to a 0.023-inch wire helps keep the heat input lower and avoids burning through. On the other hand, for thicker materials where you need more heat, a 0.035-inch wire or even 0.045-inch, as long as your welder can handle it will do the job more efficiently.

Gas selection

• A shielding gas mixture consisting of 75% argon and 25% carbon dioxide often referred to as 75/25 or C25 is widely regarded as the optimal choice for general welding applications involving carbon steel. This particular blend tends to minimize spatter, delivers a smoother bead appearance, and reduces the risk of burn-through on thinner materials.
• On the other hand, using pure carbon dioxide (100% CO2) as a shielding gas does offer the advantage of deeper weld penetration. However, it comes with notable trade-offs: welders typically observe increased spatter and a bead profile that is noticeably rougher compared to what is achieved with the 75/25 mixture.

Voltage and amperage

The voltage and current needed for welding are influenced by several factors, such as the thickness and type of metal, the configuration of the joint, the position in which the weld is made, the choice of shielding gas, and the speed as well as the diameter of the wire, among other considerations.

Wire stick-out

The term “stick out” refers specifically to the portion of the unmelted electrode that projects from the tip of the contact tube, excluding the arc length itself. As a rule of thumb, maintaining a stick out of approximately 3/8 inch is advisable.

One practical way to monitor this is by listening for a steady sizzling sound, reminiscent of bacon cooking. If the arc produces irregular or unstable sounds, it often points to excessive stick out an error that many individuals make when welding.

Push or pull Gun?

In welding, the push or forehand technique refers to moving the welding gun forward, away from the weld puddle. This approach tends to create a bead that is wider and flatter, with less penetration, since the arc force is aimed ahead of the molten pool rather than into it.

On the other hand, the drag or backhand technique—sometimes known as the pull or trailing method involves angling the gun back toward the weld puddle and moving it away from the already deposited metal. This technique is generally associated with deeper penetration and produces a bead that is narrower and has more buildup.

For MIG welding mild steel, both the push and pull techniques are viable. However, many find that pushing the gun provides a clearer line of sight and makes it easier to guide the wire accurately into the joint.

Travel angle

The travel angle refers to the angle at which the welding gun is held in relation to a perpendicular, or straight-up, position. Typically, effective welding across different positions requires maintaining a travel angle between 5 and 15 degrees. If the angle exceeds roughly 20 to 25 degrees, it tends to create additional spatter, reduces weld penetration, and often results in an unstable arc.

Work angle

The work angle refers to how the welding gun is positioned in relation to the angle of the joint being welded. This angle isn’t fixed it shifts depending on the specific welding position and the type of joint you’re working with.

What gas for MIG welding?

MIG (Metal Inert Gas) welding relies on an electric arc formed between a consumable wire electrode and the workpiece, with shielding gases protecting the weld zone. When working with non-ferrous metals like aluminum, welders typically reach for argon or helium to ensure the best results.

Selecting the Appropriate Shielding Gas:

There isn’t a one-size-fits-all answer when it comes to shielding gases in MIG welding. Before making a decision, it’s worth taking a closer look at what you’re aiming to achieve with your weld, as well as the specifics of your application. As you weigh your options, keep these factors in mind:

• The cost of the gas
• The properties you expect from the finished weld
• The level of preparation and clean-up required
• The nature of the base material
• The type of weld transfer process involved
• Your overall productivity targets

Among the many options, four shielding gases tend to stand out for MIG welding: argon, helium, carbon dioxide, and oxygen. Each brings its own set of advantages and limitations, depending on the context. Finding the right fit often comes down to balancing these trade-offs with your specific welding needs.

1. Carbon Dioxide (CO2)

Carbon dioxide (CO₂) stands out as the most commonly used reactive gas in MIG welding. Notably, it is unique among shielding gases in that it can be employed in its pure form, without the need to blend it with an inert gas.

From a practical standpoint, CO₂ is also the most economical option among the typical shielding gases, which explains why it often becomes the preferred choice in situations where controlling material costs is essential.

Using pure CO₂ as a shielding gas results in significant weld penetration a clear advantage when working with thicker materials. That said, there are some trade-offs to consider.

Welders often find that pure CO₂ leads to a less stable arc and increases the amount of spatter produced, especially when compared to mixtures that include inert gases. Furthermore, the application of pure CO₂ is generally restricted to the short circuit transfer process.

2. Argon

For organizations that prioritize both weld quality and appearance, while also aiming to minimize post-weld cleaning, a shielding gas blend consisting of 75 to 95 percent argon with 5 to 25 percent CO₂ is often the preferred choice.

This mixture tends to strike a practical balance, offering better arc stability, improved control over the weld puddle, and noticeably less spatter compared to using pure CO₂.

Additionally, this gas blend makes it possible to utilize the spray transfer process a technique that not only boosts productivity but also results in welds with a cleaner and more polished appearance.

The presence of argon contributes to a narrower and deeper penetration profile, which can be especially advantageous for fillet welds.

On the other hand, when working with non-ferrous metals such as aluminum, magnesium, or titanium, it is necessary to rely exclusively on pure argon as the shielding gas.

3. Oxygen

Oxygen, known for its reactive properties, is commonly added in small amounts typically no more than nine percent to enhance weld pool fluidity, penetration, and arc stability when working with soft carbon, low alloy, and stainless steels.

That said, its use does have a downside: it promotes oxidation in the weld deposit. Because of this tendency, oxygen is generally avoided when welding materials like aluminum, magnesium, copper, or other less conventional metals.

4. Helium

Much like argon, helium is commonly selected for welding non-ferrous metals and finds use with stainless steel as well. What sets helium apart is its ability to produce a broad, deep penetration profile, which proves advantageous when working with thicker materials.

In most cases, helium is blended with argon, with typical mixtures ranging from 25–75% helium and 75–25% argon. Adjusting this balance directly influences key aspects of the weld: the penetration depth, the appearance of the bead, and the travel speed during welding.

One notable property of helium is that it generates a “hotter” arc, supporting faster travel speeds and often leading to higher productivity. That said, helium does come with higher costs, both because the gas itself is more expensive and because it requires a greater flow rate compared to argon.

As a result, it’s important to weigh the gains in productivity against the added expense. When it comes to stainless steel, helium is generally used as part of a three-gas blend that includes argon and CO₂.

How to MIG Weld?

This guide is intended to provide a foundational overview rather than serve as an exhaustive manual. Throughout the following sections, I will walk you through the key stages involved in MIG welding steel, aiming to offer a clear understanding of what the process entails.

Before delving into the actual welding method, it is essential to address several preparatory steps. Proper setup forms the backbone of successful results, so giving due attention to these preliminary practices cannot be overstated.

1. Setting up the Machine

Begin by taking a moment to become acquainted with the welding machine itself. Start by inspecting the wire coil typically copper-colored inside the welder.

Ensure the coil is held firmly in place by the tension nut, yet still able to spin smoothly when the feed rollers draw the wire toward the welding gun. If your task involves welding aluminum, you should see a silver-colored wire instead of copper.

2. The gas Tanks

The gas tank, situated at the rear of the MIG welder, typically contains either pure argon or a blend of argon and carbon dioxide. To check whether the tanks are adequately filled, open the main valves and observe the gauges they should display a pressure reading somewhere between 0 and 2,500 PSI.

When it comes to adjusting the gas flow, set the regulator to a range of 15 to 25 PSI, making sure to tailor the setting to suit the specific welding task at hand.

3. The Welding Gun

Ensure that the lead wire is properly positioned within the welding gun, extending slightly beyond the metal tip. It is important to note that these tips are consumable and should be selected based on both the type and thickness of the metal being welded.

Before beginning your work, gently squeeze the trigger to confirm that the wire advances smoothly and that there are no operational issues.

4. The Ground clamp

The ground clamp functions as the cathode within the circuit, serving to complete the electrical path between the welding gun, the welder itself, and the workpiece.

It is important to ensure the clamp is firmly attached to the project, and that the point of contact is free from rust or debris, as any contaminants can interfere with proper operation. After verifying that these connections are secure and clean, you are ready to proceed with the welding process.

5. Prepare the weld

The preparation of a weld plays a crucial role in ensuring its overall strength and reliability. Taking the time to remove surface blemishes and grind away any rust is not just a preliminary step; it directly impacts the integrity of the final weld. Neglecting this stage can compromise the quality, so careful attention here truly pays off.

6. Prepare the area

Molten metal has the potential to travel considerable distances during welding operations. For this reason, it is crucial to ensure that no flammable materials are left within the possible trajectory of molten spatter. Items such as plastic, paper, or cloth, which can easily catch fire or smolder, should be removed from the work area beforehand.

It is wise to have a carbon dioxide fire extinguisher nearby in case of emergencies. If a fire does break out, avoid the instinct to reach for water especially when operating high-voltage equipment. Mixing water and electricity is widely recognized as extremely hazardous, and it is a risk no one should take in the workshop.

7. Put on your safety equipment

Begin by positioning the face mask securely on your head; however, at this stage, there is no need to lower the mask until you have finished preparing your welding area.

Next, put on welding gloves and ensure that your arms are fully covered with protective welding sleeves. If you are working in a confined space or an area with inadequate ventilation, it is important to wear a respirator to minimize the risk of inhaling hazardous fumes.

It is essential to avoid welding galvanized steel. When galvanized steel is subjected to heat, the zinc coating releases toxic fumes. Inhaling these fumes can lead to flu-like symptoms, sometimes described as a “metal shower,” which may persist for several days.

While these symptoms are usually temporary, repeated exposure or higher doses can have severe and lasting effects on lung health.

8. Attach the ground clamp

You can attach this to any metal surface to establish the electrical circuit. In most cases, the metal workpiece itself or the welding table will serve this purpose effectively.

9. Open the gas Cylinder

Begin by loosening the adjusting nut on the gas regulator, followed by turning the wheel located on top of the canister. It is important to keep your hand around the edge of the wheel rather than directly over it; this precaution helps prevent injury in case any pressure causes the wheel to spin unexpectedly.

When opening the valve, avoid leaning over the canister. Instead, position yourself across from the canister and maintain an arm’s length distance. You’ll see the PSI reading on the meter begin to climb. Once the pressure surpasses 1,000 PSI, you’re ready to proceed with welding. At this stage, tighten the adjustment screw on the regulator so that the PSI reading falls within the range of 15 to 25.

10. Find the welding setting

In many MIG welding machines, you’ll often find the recommended settings right under the lid. This chart isn’t just for show it serves as a straightforward reference for adjusting both voltage and wire feed speed.

For the purposes of this explanation, let’s assume you’re working with 0.035-inch wire and a shielding gas mixture of 75% argon to 25% carbon dioxide. At this point, the main factor left to consider is the thickness of the material you’re welding; that’s what will ultimately guide your final adjustments.

11. Power up the welder

Connect the welder to the appropriate power supply and turn it on. Before beginning, take a moment to ensure your workspace is clear of any objects or debris that might obstruct your work or create a safety hazard.

12. Set the wire speed and voltage

Referring back to the table from Step 4, adjust the wire speed and tension according to your requirements. For instance, when working with 18-gauge metal, you’ll typically set the wire speed at 16 and the voltage at 120.

Be mindful of your settings as you work. If they’re too high, you may notice holes forming in the workpiece this happens when the weld becomes too hot and melts right through.

On the other hand, settings that are too low tend to produce a weld that builds up in uneven bursts, as excessive wire is fed without enough heat to bond it properly, resulting in a weaker joint.

You’ll find you’ve landed on the right settings when the weld flows smoothly and steadily, without resistance. Pay attention to the sound as well; a lively, crackling noise almost reminiscent of an enthusiastic bee is a good sign that your voltage and wire speed are in sync.

As a side note, when welding aluminum, don’t expect the usual sparks or popping. Instead, you should hear a steady, low hum.

13. Check the wire in the welding torch

Ideally, the welding wire should extend approximately one inch beyond the tip of the welding torch. If you notice the wire is sticking out farther than that, simply trim it back to the recommended length.

14. Weld away

Before beginning the weld, lower your face shield for safety. You have the option to use either the push or pull method, each offering distinct results: the push technique produces welds that are flatter and wider, while pulling typically leads to a tighter bead with deeper penetration.

As you work, consider laying down your welds in either a zigzag motion or in small, overlapping circles, which can create a visually appealing, swirling pattern. The angle at which you position the torch should correspond to the type of joint you’re working on; adjusting this angle can help ensure proper weld quality.

Guide the torch steadily downward from the top of the joint, aiming to keep each bead to about an inch or two in length. Spending too much time on one section can cause the metal to overheat, increasing the risk of warping or weakening the joint.

To prevent this, it’s wise to weld one area, then move to another, gradually working your way across the entire piece. Once all sections are complete, you can connect them to form a continuous weld.

When you reach the end of your workpiece, don’t forget to set the wire feeder to its lowest setting to finish the job safely.

15. Close the cylinder valve

Using your hand, turn the gas canister valve until you feel it is firmly closed.

16. Bleed the Regulator

To vent the regulator, press the trigger on the welding gun and observe the Cubic Feet Per Hour (CFH) as it decreases to its minimum value. The wire will continue to feed at this stage, since the wire feed setting is above zero.

Alternatively, you can simply loosen the adjustment screw on the regulator until it no longer offers resistance.

17. Turn off the welder

Begin by switching off the welder, ensuring you turn it off both at the machine itself and at the power supply. Once the equipment is powered down, take off your welding helmet and other protective gear, but keep your gloves on for the time being.

Avoid making contact with the metal immediately, as it can retain heat; allowing it to cool on its own will help maintain the integrity of your weld.

When the area is safe to approach, disconnect the ground clamp and carefully coil any wires for storage. Only after completing these steps should you remove your gloves.

Advantages of MIG welding

• Increased Productivity: One noticeable benefit for many welders is the boost in productivity. With MIG welding, the time-consuming steps of frequently changing rods, chipping away slag, or endlessly brushing the weld are largely eliminated. This means welders can complete their work not only more quickly, but with greater cleanliness as well.
• Ease of Learning: Perhaps one of the most appealing aspects of MIG welding is how straightforward it is to pick up. Many welders can become comfortable with the process in just a few hours, and some instructors even claim that basic skills can be taught in as little as twenty minutes—most of which is simply spent cleaning the weld. In contrast, TIG welding requires significantly more time to master, which can deter hobbyists or those tackling home projects. More than one instructor has likened MIG welding to a “point and shoot” activity.
• Consistently Good Welds: The process also offers excellent visibility of the weld pool. Combined with the simplicity of the method and the steady control offered by the auto-feed wire, it becomes relatively easy to achieve clean, visually appealing welds.
• Clean and Efficient Operation: Because MIG welding relies on shielding gas to protect the arc, loss of alloying elements during metal transfer is kept to a minimum. Unlike stick welding, there’s no need to worry about removing slag, and only a small amount of spatter is produced. As a result, the post-weld cleanup is minimal, allowing welders to resume work with very little downtime.
• Versatility: The versatility of MIG welding is another significant advantage. It is suitable for a broad range of metals and alloys and can be used in both semi-automatic and fully automatic modes. While MIG welding is an excellent option for home projects, it is also widely adopted across numerous industries. Its applications cover metals such as aluminum, copper, stainless steel, mild steel, magnesium, nickel, and many of their alloys, along with iron and most of its variants.
• Improved Welding Speed: With a continuously fed wire, welders have both hands free to guide the process, which not only speeds up the work but also enhances weld quality and overall control.

Disadvantages of MIG welding

• Cost Considerations: One of the first things welders tend to notice about MIG welding is the complexity and expense of the equipment. Not only are the machines themselves on the pricier side, but there are also recurring costs to keep in mind. Shielding gas, electrodes, and the occasional replacement of tips and nozzles can all add up over time. Portability is another trade-off here; these setups aren’t exactly easy to move around.
• Limitations in Welding Positions: MIG welding has its boundaries, especially when it comes to working out of position. The weld puddle is quite fluid, and the high heat output makes vertical or overhead welding impractical. Some welders might never need to weld in these positions, but it’s definitely something to weigh before investing in a MIG welder, particularly if you’re planning a variety of projects.
• Not Suited for Outdoor Use: There’s also the matter of working outdoors. MIG welders depend on shielding gas to protect the weld from contamination, but even a modest breeze can disrupt that gas and compromise weld quality. For anyone hoping to make repairs out in a field, this can be a real drawback. On the other hand, for jobs in the garage—like automotive work—MIG welding works beautifully.
• Rapid Cooling Rates: Unlike some other welding processes, MIG welds are left uncovered when finished, which means the metal tends to cool more quickly. This can affect the final properties of the weld, depending on the application.
• Challenges with Thick Materials: Another limitation is that MIG welding is generally best for thinner metals. When working with thicker steel, it struggles to achieve the deep penetration needed for a strong, reliable weld.
• Handling Shielding Gas: Swapping out the bottle of shielding gas isn’t just a minor inconvenience—it can interrupt your workflow. The cylinder itself can also feel cumbersome, sometimes getting in the way as you work.
• Preparation of Materials: Lastly, MIG welding calls for extra attention to surface preparation. To ensure a solid and safe weld, the material needs to be free of rust and dirt before you even strike an arc.

What is MIG welding used for?

MIG/MAG welding stands out as a highly adaptable method, capable of handling everything from delicate sheet metal to hefty, thick sections. The process works by striking an arc between the tip of a wire electrode and the workpiece itself.

As both the wire and the base material melt, a weld pool forms, allowing the wire to function as both the heat source thanks to the arc and the filler metal that builds the joint.

In most cases, metal inert gas welding comes into play when working with larger, thicker materials. The technique uses a consumable wire that does double duty, acting both as the electrode and as the filler that’s deposited into the joint.

If you compare MIG/MAG welding to TIG welding, you’ll quickly notice the difference in speed—MIG/MAG gets the job done much faster. This not only shortens production time but can also help keep costs in check.

On top of that, the learning curve is relatively gentle, and the resulting welds typically need minimal cleaning or finishing. The trade-off, however, is that MIG/MAG welds may not match the precision or pristine quality you get from TIG welding.

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