The Complete Guide to Gas Metal Arc Welding

Also known as metal inert gas welding (MIG welding), gas metal arc welding (GMAW) is one of the easiest welding techniques to learn. Using this welding technique, an operator feeds a solid wire electrode wire with a welding gun.

An electric arc melts this wire so that it forms a weld pool that then solidifies to form a weld joint. The welding gun also feeds shielding gas to ensure the hot weld pool of the molten metal remains free from corrosion and contamination.

MIG welding holds great attraction in the welding industry because it is a fast process. Among all common arc welding techniques, MIG welding allows operators to complete the maximum number of workpieces in a given time frame. Hence, productivity remains high with MIG welding. This is an important consideration for workshops and factories that want to maximize their rate of production.

Due to its simplicity, MIG welding is the preferred choice for beginners, hobbyists, motorsports enthusiasts, farmers, ranchers and DIY welders. It allows welding operators to easily carry out maintenance and repair welding on sections that are 24-gauge to half-inch thick.

Some people claim that MIG welding is no harder than using a glue gun. Although the technique is more involved, there is no doubt that almost anyone can learn it very quickly.

MIG Welding Safety

Before starting any MIG welding project, you must ensure that you have observed all safety measures. Make sure that you have complete safety apparel and equipment to protect yourself. Remove any potential fire hazards from the welding area.

MIG welding safety apparel may include leather boots, safety glasses, welding helmet, leather gloves, flame-resistant jacket, full-length pants and a skull cap to protect your head against spatter and sparks.

Workpiece Preparation

Flux cored and stick welding electrodes contain additives to withstand oil, dirt, grease and other contaminants. However, MIG welding utilizes solid electrode wires that lack the flux material to combat these contaminants. You will, therefore, have to prepare the surface meticulously to ensure that the surface is completely free from contaminants. Otherwise, a dirty surface will lead to porosity and other welding defects.

Besides direct welding defects, surface contaminants can also adversely affect the welding current, thereby reducing wire feeding performance and the quality of the weld.

You can use a grinder or a metal brush to clean the metal surface. Remove everything from the surface, including paint. Once the surface is cleaned to a shiny surface, you can connect the workpiece to a metal clamp and strike an electric arc to begin MIG welding.

For strong weld joints on thick metal sections, you should bevel the joints. This will ensure that the weld bead fully penetrates the full length of the metal section to produce a reliable weld joint. This is particularly important for welding butt joints.

MIG Welding Equipment Preparation

Check cables. Before striking an arc, make sure to thoroughly inspect your welding equipment to ensure that all cable connections fit tightly and no fraying or damage occurs.

Configure electrode polarity. MIG welding process works with DC electrode positive or with a reverse polarity. The polarity connections can be found within the MIG welding machine.

Gas flow. Open the valve to allow gas flow and adjust it so that it is between 20 and 25 cubic feet per hour. If you suspect that the hose has leaks or pinholes, then run a soapy solution onto the hose and observe any signs of bubbles. If you find a leak, then you should discard the hose and put a new one in its place.

Adjust tension. Too little or too much tension on the wire spool hub or the drive rolls can result in erroneous wire feeding. Check the user manual to know the right tension.

Check consumables. Make sure that there are no spatters on contact tubes. Remove them if they are present. Also, replace worn liners and contact tips. If the wire is rusty, then you should discard it and use one that is in good condition.

Wire Selection

Two wire types are commonly used for steel. For all-purpose welding, you can use the AWS classification ER70S-3. If you are welding rusty or dirty steel surface, use the ER70S-6 wire. This wire type has deoxidizers to deal with rust and corrosion.

As far as wire thickness is concerned, the 0.03-inch diameter wire is good for all-round performance and can be easily used for a wide range of motorsport, hobby and home repair applications.

For thinner metal sections, you can use a 0.023 wire to reduce heat input. This will help minimize the possibility of burnthrough.

For welding thicker metal sections, you will require thicker wire not just for more filler material but also for higher heat input. These two criteria are necessary for satisfactory and reliable welding of heavy workpieces. You can use a 0.035 or a 0.045 wire if your welding machine is capable of handling wire electrodes of this thickness.

Shielding Gas

For carbon steel, a shielding gas mixture of 25% carbon dioxide and 75% argon is suitable for a wide range of applications. It minimizes the likelihood of burnthrough in thinner steel sections. This mixture also leads to the best welding joint appearance and the lowest levels of spatter.

100 percent CO2 gas is cheap and allows deeper penetration, but it also causes more spattering and gives the weld joint a rough appearance. This makes the CO2 gas less suitable for applications where the weld joint appearance matters.

Current and Voltage

Numerous variables will determine the voltage and current level for a given MIG welding project. This includes factors like wire diameter, travel speed, shielding gas, welding position, joint type, metal type and workpiece thickness.

Wire Extension

The welding appearance and performance is also determined by how far the wire electrode extends from the welding gun tip. This length does not include the arc length.

In general, the wire electrode should protrude 3/8 in beyond the nozzle. If the extension of the wire is correct, you will hear a slight sizzling sound. If the arc is unstable or it sounds irregular, then you should carefully check the wire extension. This is a common error.

Pull or Push Method?

There are two general techniques for MIG welding. The push technique employs the forehand position where you must push the nozzle ahead of the weld puddle. This technique results in lower penetration and the welding bead is flatter and wider.

On the other hand, you have to point the welding gun back at the weld pool and drag the nozzle away from the molten metal in the pull or backhand method. This method is also called the trailing or drag technique. With this technique, you can create a weld with deeper penetration, which will produce stronger and more reliable joints. The bead is also more focused and narrow.

It might appear to you that the pull or backhand method is the better of the two aforementioned techniques. In terms of weld joint quality, it truly is a better option.

But then why is the push technique still used? The simple answer is that the push method gives an unobstructed view of the weld zone. This position makes it easier for you to direct your wire electrode.

However, with some practice and experience, you will become more proficient with the pull technique.

MIG Welding Techniques

Here are some of the workpiece and welding gun positions and angles for optimal welding results.

Travel Angle

The nozzle of the welding gun should be maintained within a particular range of angles for optimum welding performance. The travel angle is measured with respect to the nozzle in a perpendicular position. This angle (with respect to the perpendicular) should be maintained between 5 and 15 degrees. If possible, avoid going beyond this range. Otherwise, you will see more spatter, lower penetration and arc instability.

Work Angle

Work angle is the orientation of the nozzle with respect to the welding joint angle. It varies according to the joint type.

Flat Position

The butt weld is employed for a 180-degree joint. Keep the gun at 90 degrees to the workpiece. Direct the electrode carefully so that the filler material goes straight into the weld pool. For best results, you must ensure that the travel angle of 5 to 15 degrees is also included.

When you are making multiple passes, give a slight amount of back and forth motion to the nozzle so that a large gap can be filled easily. You can also avoid an undercut maintaining a small pause at the weave bead side.

The T-joint, as the name implies is a 90-degree joint. The weld applied to this joint is also known as a fillet weld. Maintain the gun at a 45-degree orientation with respect to either surface. The work angles must be adjusted slightly while executing multiple weld passes. With this technique, you can avoid undercuts and inconsistent weld beads.

The lap joint is also referred to as a fillet weld. Keep the gun at an angle of 60 to 70 degrees. The angle should be greater for thick metal.

Horizontal Position

Due to the effects of gravity, you should reduce the nozzle work angle between 0 to 15 degrees. If you don’t change the work angle, then the filler metal may roll over or sag at the bottom of the weld joint. Whether you use the push or pull technique, the travel angle must be the same if the weld joint is in a flat position.

You may have to employ weave beads to fill the weld joint in certain scenarios. For instance, when you want to fill a large gap or execute multiple passes on thick sections. You should pause slightly at the top of the weld to prevent the formation of undercuts and to ensure that the weld adequately penetrates the base metal.

The current and voltage settings for the horizontal position are usually the same as the settings for welding in the flat position.

The horizontal weld can be more challenging than flat position welds due to gravity. To counter the effects of gravity, position the welding nozzle slightly upwards towards the top side of the workpiece.

Vertical Position

Vertical welding can be rather challenging, be it in an upward or downward direction. So for making reliable welds, it is necessary to set up and clamp the workpiece properly for best results. Since you must cancel out the effects of gravity, it is advisable to reduce the current and the voltage by about 10 to 15 percent of the corresponding current and voltage values for welding in the flat position.

The vertical downwards welding method is suitable for welding thin sections since there is lower arc penetration (due to higher travel speed). Since vertical down welding poses a smaller likelihood of burnthrough, welding operators position thin metal sections in a vertical direction even if it is possible to weld them while keeping them flat.

If you need to weld vertical down, start welding from the very top and make your way downwards. In thin metal sheets where the risk of burnthrough is high, move the wire electrode away from the weld pool. Move the electrode wire so that it remains at the leading tip of the weld pool. You can flatten the weld crown by using a slight weave.

In the vertical up technique, you will start at the bottom of the workpiece and move the wire electrode upwards. This is a better option for thick metal sections since it allows deeper penetration. The vertical up method is the best choice for metal sections that have a weld thickness of ¼ in or more. Keep the travel angle of the gun at around 5 to 15 degrees lower than the perpendicular position. You can control the cooling, shape and size of the weld pool by using a slight weaving action.

Overhead Position

Perpendicular, push or drag methods are all suitable for overhead welding. Owing to the effects of gravity, the travel speed should be quick enough to prevent the molten filler material from falling out of the joint. For the very same reasons, you should not allow the weave beads to become too wide. You can keep the size of the weld pool small by reducing the current and voltage. For this, you must select a smaller diameter wire electrode. The weld pool will also be easily controllable.

More Welding and Practice Tips

Keep in mind that the travel speed has a great impact on the quality and shape of the weld. The travel speed is the rate at which you move along the wire electrode while welding.

The most skilled MIG welders can determine the welding travel speed simply by considering the weld pool size and the joint thickness. The key here is to realize that the weld bead should not be thicker than the thinnest point of the metal that is being welded. Therefore, adjust the weld travel speed according to this criteria.

With practice, you will be able the judge the required travel speed for a specific weld bead thickness. Hence, you should practice often for a better sense of judgment, which will allow you to determine the travel speed needed to create the right weld thickness.

Be sure that the electric arc remains on the leading edge of the molten pool. Don’t let the molten weld pool get ahead of the electric arc.

By keeping these tips and aforementioned techniques in mind, you can become a skilled MIG welder in no time.

MIG Welding Parameters

Now that you have a better idea of the right welding techniques, you also need to read about the optimal weld settings and parameters that will allow you to create the best weld joints.

New MIG welders often find themselves asking basic questions like what is the correct voltage? What is the correct wire diameter for my application? How much should the current be set to?

You can figure out the basics of setting up your MIG welding machine and how to spot potential issues just by looking at the weld joint.

With good quality MIG welding equipment, you can resolve several possible problems before they even transpire. With low quality welding equipment, you will suffer from poor weld quality and a lot of frustration. So make sure that you do your research properly before investing in a MIG welding machine.

You should opt for MIG welding machines that offer advanced features, which includes but is not limited to, an automatic setting feature that configures the welding machine current, voltage and feedrate automatically on the basis of wire diameter and material thickness. With this feature, you can achieve spatter-free and smooth start and focus on the right technique. This is a problematic area for most new welding operators.

You should visit a welding machine distributor with an on-site workshop where you can test the welding machine before buying it.

How to Get the Most from Your MIG Welding Machine

Forney Easy Weld 261, 140 FC-i MIG Welder

Make sure that you have read the owner’s manual before using the machine. While it’s understandable that you may be tempted to get started with your new gear and you do not want to read a boring book, it is important to read the manual. Read the entire manual to understand safety guidelines and correct operational techniques. There are several important safety and operational matters that are not immediately apparent. Hence, your first step should be to read the user manual.

The guidelines mentioned here are for MIG welding of steel using solid wire electrode. There are separate guidelines for flux-cored and aluminum welding. Position, joint design and other factors have a major impact on the settings and weld quality.

So whenever you achieve good welding results during your practice session, carefully record the parameters that you employed.

Here are the guidelines for MIG welding steel using a solid wire electrode.

Current depends on the material thickness. A rule of thumb is that you will need an extra 1 ampere of current for each 0.001-inch increase in material thickness. Hence, for a thickness of 0.125, you should set the current to 125 amperes.

The wire size should be chosen according to the current. To use the correct wire thickness the first time around, make sure that you refer to these specifications.

For 30 – 130 ampere current range, use 0.023-inch wire

For 40 – 145 ampere current range, use 0.03-inch wire

For 50 – 180 ampere current range, use 0.035-inch wire

For 75 – 250 ampere current range, use 0.045-inch wire

Setting the correct voltage. The voltage level has a direct effect on the width and height of the weld bead. You can follow this rule if there is no specification, manual or chart available for the right voltage. While you are in a position to weld on the metal workpiece, ask an assistant to turn down the voltage until the arc disappears. Note down the value of this voltage.

Now ask your assistant to keep increasing the voltage until the arc becomes difficult to control and unstable. Note down the voltage when this occurs. A voltage that lies halfway between these two extreme values is often adequate for most welding purposes.

The arc voltage has a direct effect on the arc length. With a low voltage, you get a short arc with a rope-like, narrow bead. With more voltage, you get a longer arc that creates a wider and flatter bead. With too much arc length, there is the possibility of undercut and overly flat weld bead.

Configure the wire feed rate. The rate of wire feed has a crucial effect on the current and weld penetration. If the wire feed speed is too high, then thin metal sections and sheets, in particular, are at a higher risk of burnthrough. If you cannot find a weld specification sheet or a manual, use the following chart to determine the correct feed rate.

For wire size Multiply by Ex. using 1/8 inch (125 amps)
.023 inch 3.5 inches per amp 3.5 x 125 = 437.5 ipm
.030 inch 2 inches per amp 2 x 125 = 250 ipm
.035 inch 1.6 inches per amp 1.6 x 125 = 200 ipm
.045 inch 1 inch per amp 1 x 125 = 125 ipm

You can verify whether or not you are working with the optimal parameters by inspecting the resultant weld bead. After all, the purpose of all these parameters is to produce high quality welds.

With a good weld, you will notice that the weld pool has full penetration that goes deep into the base metal. The bead has a rather flat profile and a medium width. The edges of the previously separate workpieces are securely joined and well-fused with adequate filler material.

Here are the different types of weld issues that can arise with the wrong range of parameters.

Excessive voltage. With excessive voltage, you can experience problems like poor arc control, low penetration and turbulent molten material, which does not go all the way into the base metal.

Very low voltage. If your voltage is too low, you will have difficulty in establishing the arc. The arc formed will be erratic and difficult to control. There will be excessive spattering and a convex- shaped weld bead cross section. The edges of the welded workpieces will not be adequately joined.

Fast travel speed. With a travel speed that is too low, you will get a convex-shaped bead profile that is too narrow. The edges of the workpieces being welded together will not be fused adequately into a reliable joint. It will also lead to inconsistent and insufficient penetration.

Slow travel speed. With very slow travel speeds, too much heat will be injected into the weld pool. This will result in a weld that is too wide and has inconsistent penetration. The excessive heat from slow travel will lead to a burnthrough in thinner materials.

High current and wire feed speed. This can lead to poor penetration, excessive spatter, burnthrough and an excessively broad welding bead.

Low current and wire feed speed. The weld bead will be too narrow and may have a convex profile. The ends of the workpieces being welded will not join adequately.

Lack of shielding gas. This problem is easy to identify. Pinholes and porosity will mark the interior and face of the weld.

Conclusion

You have now learned some of the fundamental aspects of MIG welding. You should now put this knowledge into practice in order to become a proficient MIG welder.

About Pierre Young

Photo of author
Hey, I'm Pierre Young a qualified AWS Certified Welder. I got into welding in 2009 as a side hustle. Ever since then, I've been doing all kinds of welds - both for business and pleasure. While immersing myself in this wonderful hobby, I've learned from hands-on experience what welding gear works and what doesn't. Welding Headquarters is the site where I share everything I've learned.

Leave a Comment