What is MIG Welding?
Metal Inert Gas (MIG) welding is an arc welding process that uses a continuous solid wire electrode heated and fed into the weld pool from a welding gun. The two base materials are melted together forming a join. The gun feeds a shielding gas alongside the electrode helping protect the weld pool from airborne contaminants.
Metal Inert Gas (MIG) is also known as gas metal arc welding (GMAW). This type of welding is basically an arc welding process that joins two metals. This is done by heating the metals with the help of an arc. This arc is formed between the surface to be welded and a continuously fed filler electrode.
This type of welding uses a shielding gas to protect the molten pool of weld metal from reacting with elements present in the atmosphere.
Metal Inert Gas (MIG) welding was first patented in the USA in 1949 for welding aluminum. The arc and weld pool formed using a bare wire electrode was protected by helium gas, readily available at that time.
From about 1952, the process became popular in the UK for welding aluminum using argon as the shielding gas, and for carbon steels using CO2. CO2 and argon-CO2 mixtures are known as metal active gas (MAG) processes. MIG is an attractive alternative to MMA, offering high deposition rates and high productivity.
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, 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.
Before tackling a welding project, it is important to ensure that you have the correct protective clothing and that potential fire hazards are removed from the welding area.
Basic welding safety equipment includes leather shoes or boots, cuffed trousers, a long-sleeved flame retardant jacket, leather gloves, a welding helmet, goggles, and a headscarf or skull cap to protect the top of your head from sparks and spatter.
Unlike stick and flux-cored electrodes, which contain higher amounts of special additives, the solid MIG wire does not fight rust, dirt, oil, or other contaminants very well. Use a metal brush or grinder and clean the metal before hitting an arc. Make sure your work clamp is also connected to clean metal. Any electrical impedance will affect wire feed performance.
To ensure strong welds on thicker metal, bevel the joint to ensure that the weld penetrates completely into the base metal. This is particularly important for butt joints.
- Check your cables. Before striking an arc, check your welding equipment to make sure all of the cable connections are tight fitting and free of fraying or other damage.
- Select electrode polarity. MIG welding requires DC electrode positive, or reverse polarity. The polarity connections are usually found on the inside of the machine.
- Set gas flow. Turn on the shielding gas and set the flow rate to 20 to 25 cubic feet per hour. If you suspect leaks in your gas hose, apply a soapy water solution and look for bubbles. If you spot a leak, discard the hose and install a new one.
- Check tension. Too much or too little tension on either the drive rolls or the wire spool hub can lead to poor wire feeding performance. Adjust according to your owner’s manual.
- Inspect consumables. Remove excess spatter from contact tubes, replace worn contact tips and liners and discard the wire if it appears rusty.
There are two common types of wire for steel. For general purpose welding, use an AWS classification ER70S-3. Use ER70S-6 wire when more deoxidizer is needed to weld dirty or rusty steel. As for wire diameter, the 0.030-inch diameter is a good choice for welding a variety of metal thicknesses in-home and motorsport applications.
When welding thinner material, use 0.023-inch wire to reduce heat input. To weld thicker material with higher total heat ratings, use 0.035 “(or 0.045” wire if this is within your welder’s capabilities).
- A mixture of 75 percent argon and 25 percent carbon dioxide (also known as 75/25 or C25) is the best general-purpose shielding gas for carbon steel. It creates the least amount of spatter, the best appearance of the pearls, and does not encourage the thinner metals to burn through.
- 100 percent CO2 provides deeper penetration but also increases spatter and the bead will be rougher than with 75/25.
Voltage and amperage
The amount of voltage and current required to weld a weld depends on many variables, including metal thickness, metal type, joint configuration, weld position, shielding gas, and wire diameter speed (among others).
The stick out is the length of the unmelted electrode that extends from the tip of the contact tube and does not include the arc length. In general, keep a 3/8 inch stick out and watch for a sizzling sound of bacon. If the arc sounds erratic, it could be a culprit that your overhang is too long, which is an extremely common mistake.
Push or pull Gun?
- The push or forehand technique involves pushing the gun away from (ahead of) the weld puddle. Pushing usually produces lower penetration and a wider, flatter bead because the arc force is directed away from the weld puddle.
- With the drag or backhand technique (also called the pull or trailing technique), the welding gun is pointed back at the weld puddle and dragged away from the deposited metal. Dragging typically produces deeper penetration and a narrower bead with more buildup.
When MIG welding mild steel, you can use either the push or pull technique, but note that pushing usually offers a better view and enables you to better direct wire into the joint.
Travel angle is defined as the angle relative to the gun in a perpendicular position. Normal welding conditions in all positions call for a travel angle of 5 to 15 degrees. Travel angles beyond 20 to 25 degrees can lead to more spatter, less penetration, and general arc instability.
Work angle is the gun position relative to the angle of the welding joint, and it varies with each welding position and joint configuration.
What gas for MIG welding?
MIG (Metal Inert Gas) welding is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece. This process uses inert gases or gas mixtures as shielding gas. Argon and helium are typically used for the MIG welding of non-ferrous metals such as aluminum.
Choosing The Right Shielding Gas:
Many MIG welding applications lend themselves to a variety of shielding gas choices. You need to evaluate your welding goals and your welding applications in order to choose the correct one for your specific application. Consider the following as you make your selection:
- The cost of the gas
- The finished weld properties
- Preparation and post-weld clean up
- The base material
- The weld transfer process
- Your productivity goals.
The four most common shielding gases used in MIG welding are Argon, Helium, Carbon Dioxide, and Oxygen. Each provides unique benefits and drawbacks in any given application.
1. Carbon Dioxide (CO2)
The most common reactive gas used in MIG welding is carbon dioxide (CO2). It is the only one that can be used in its pure form without the addition of inert gas. CO2 is also the most cost-effective of the common shield gases, making it an attractive choice when the material cost is the top priority.
Pure CO2 provides very deep weld penetration which is useful for welding thick material. However, it also creates a less stable arc and more spatters than when mixed with other gases. It’s also just limited to the short circuit process.
For companies that value weld quality, appearance, and reduced cleaning after welding, a mixture of 75 to 95 percent argon and 5 to 25 percent CO2 may be the best option. It offers a more desirable combination of arc stability, puddle control, and reduced splash than pure CO2.
This blend also enables the use of a spray transfer process that can produce higher productivity rates and more visually appealing welds. Argon also creates a tighter penetration profile that is useful for fillet welds. When welding a non-ferrous metal – aluminum, magnesium, or titanium – you must use 100 percent argon.
Oxygen, also a reactive gas, is typically used in proportions of nine percent or less to improve the fluidity, penetration, and arc stability of the weld pool in soft carbon, low alloy, and stainless steels. However, it does cause the weld deposit to oxidize, which is why it is not recommended for use with aluminum, magnesium, copper, or any other exotic metal.
Like pure argon, helium is generally used for non-ferrous metals, but also for stainless steel. Because helium creates a wide, deep penetration profile, it works well with thick materials and is typically used in proportions between 25 and 75 percent helium to 75 to 25 percent argon. By adjusting these ratios, the penetration, the bead profile, and the travel speed are changed.
Helium creates a “hotter” arc that enables faster travel speeds and higher productivity rates. However, it is more expensive and requires a higher flow rate than argon. You need to calculate the value of the productivity increase versus the increased cost of the gas. In stainless steel, helium is typically used in a three-part formula of argon and CO2.
How to MIG Weld?
This is a basic guide, not a definitive instructional. We will talk you through the various stages of MIG welding steel to give you a rudimentary understanding of what the process involves.
Before we get to the method itself, there are some housekeeping practices we need to run through. The setup is crucial if you want the best outcomes.
1. Setting up the Machine
Take the time to familiarize yourself with the welding machine. The first thing to do is to check the copper-colored wire coil in the welder. Make sure it is secured with the tension nut but can rotate freely as the feed rollers pull the wire through the welding gun. If you are welding aluminum, the wire should be a silver color.
2. The gas Tanks
The gas tank is located behind the MIG. It’s either 100 percent argon or a mixture of argon and carbon dioxide. Open the main valves on each tank to see if they are full. The gauges should read between 0 and 2,500 PSI. Set the regulator to 15-25 PSI depending on what you are welding.
3. The Welding Gun
Make sure the lead wire is in the welding gun and protruding a little through the metal tip. The tips are sacrificial and vary depending on the thickness and type of metal being welded. Squeeze the trigger to make sure there are no issues and the wire goes through.
4. The Ground clamp
The ground clamp is the cathode in the circuit and completes the circuit between the welding gun, the welder, and the workpiece. Make sure it is attached to the project, and the connection is clean, with no rust or debris to hinder the operation. Once you are happy that everything checks out, it’s time to begin.
5. Prepare the weld
You cannot underestimate the importance of preparing the weld. Removing blemishes and grinding away rust spots will all help to increase the integrity of your weld.
6. Prepare the area
Molten metal can spit a long way. It is therefore important that there are no flammable materials within the welder’s spitting path. Remove any plastic, paper, or cloth that could smolder and ignite.
Have a carbon dioxide fire extinguisher ready in the event of a breakdown. Never use water to extinguish the flames while standing near a powerful machine that is pulsing with deadly electricity. We all know that water and electricity are a recipe for disaster.
7. Put on your Safty Equipment
Put the face mask on your head, but at this point, there is no need to fold the mask down while you prepare the welding area. Put on welding gloves and make sure that your arms are protected with the welding sleeves. When working in a narrow or poorly ventilated area, put on a respirator to avoid the risk of suffocation.
Never weld galvanized steel, as the zinc heats up during the galvanizing process and emits toxic gas. When inhaled, it causes flu-like symptoms that can last for a few days. This is sometimes referred to as a “metal shower”. While symptoms are temporary, longer-lasting effects on your lungs can be catastrophic.
Check out the article on What is Galvanizing?
8. Attach the ground clamp
This can be attached to any metal surface to complete the electrical circuit. The metal project or the welding table will suffice.
9. Open the gas Cylinder
Loosen the adjusting nut on the gas regulator and turn the wheel on top of the canister to loosen it. Make sure your hand is around the edge of the wheel and not over it in case pressure builds and the wheel takes off.
Also, do not bend over the canister when opening the valve. Stand across from him and at arm’s length. You will notice that the PSI on the meter begins to increase. You can start welding when you reach more than 1,000 PSI. Now it’s time to tighten the adjustment screw on the regulator until the PSI reads between 15-25.
10. Find the welding setting
A lot of MIG welders have welding settings located on the underside of the lid. This chart is a handy guide for determining voltage and speed. For this exercise, we will use a wire thickness of 0.035 inches, and the gas composition is 75 percent argon and 25 percent carbon dioxide. The only other variable to determine the settings is the thickness of the material.
For many MIG welders, the welding settings are located on the underside of the lid. This table is a practical guide to determining voltage and speed. For this exercise, we’ll use 0.035-inch wire and the gas composition is 75 percent argon and 25 percent carbon dioxide. The only other variable that determines the settings is the thickness of the material.
11. Power up the welder
Plug the welder into the power supply and switch it on. Make sure there are no objects or debris that will hinder your progress or place you in danger.
12. Set the wire speed and voltage
Using the same table from step 4, set the wire speed and tension to the desired settings. This example assumes you are welding 18 gauge metal. So the wire speed should be 16 and the voltage 120.
If the settings are too high, holes will appear in your workpiece as it melts through the weld. If the settings are too low, the weld will build up in bursts as too much wire will be fed and sprayed to create a weak weld.
You’ll know when the settings are just right when you start welding smoothly and evenly and welding freely. Also, listen to the sparkling sound, a bit like an over-excited bee. This should tell you that the voltage and speed settings are correct.
Tip: If you are welding aluminum, you should hear a low hum instead of sparks and popping.
13. Check the wire in the welding torch
There should be about an inch or so of the welding wire protruding through the welding torch’s tip. If it is too much, snip it to size.
14. Weld away
Lower the face mask and start welding the metal. You can use either the push or the pull technique. Pushing creates flatter but wider welds, while pulling creates tighter and deeper weld penetration.
Try laying the beads either in a zigzag pattern or in concentric circles that create a wavy, swirling pattern. The angle you work at also depends on the type of joint you are welding.
Move the torch down from the top of the weld. Make sure the beads are about an inch or two long. If you stay longer, there is a risk that the metal will heat up, which can warp and weaken. Weld one spot, then move on to another, and so on. You can then finish by joining each section at the end.
When you reach the end of the workpiece, turn the wire feeder to the lowest setting.
15. Close the cylinder valve
Turn the gas canister valve by hand, until it is tightly shut.
16. Bleed the Regulator
Depress the trigger on the welding gun as this will vent the regulator. Watch the Cubic Feet Per Hour (CFH) drop to the lowest possible level. The wire is still fed because the wire feed is higher than zero.
You can also loosen the adjustment screw on the regulator until it is loose.
17. Turn off the welder
Switch off the welder both at the machine and the power supply. Remove your welding helmet and safety equipment but keep your gloves on. Please don’t touch the metal as it may still be hot, and the trick is to allow it to cool naturally for the best weld.
You can now remove the ground clamp and neatly coil away any wires. Now remove your gloves.
Tips for MIG welding
Putting to practice any of these tips is likely to improve the quality and durability of your weld.
1. Clean, clean, clean
The main failure of a MIG weld is its porosity. The most common cause of porosity is welding a dirty, oily, painted surface. All of these contaminants become trapped in the weld, resulting in holes that resemble a sponge.
“Too often, farmers don’t prepare the metal adequately before welding,” says Miller Electric’s John Leisner. “This includes sanding or removing paint, rust, dirt and other surface contaminants as well as completely sanding down cracks that are often beyond what is immediately visible.”
2. Get a great ground
Collier considers this to be the most common mistake in MIG welding. “Your welder doesn’t care if you have a bad floor. It keeps pumping out welding wire anyway, regardless of whether your gun stutters or stutters,” he explains.
Karl Hoes of Lincoln Electric says that a welding arc requires current to flow smoothly through a complete circuit. The welding current seeks the path of least resistance. So if care is not taken to place the weld bed near the arc, the current can find another path. Firmly attach the clamp to the bare metal, as close to the arc as possible.
3. Keep your stick out short
As a general rule, keep the distance the wire sticks out from the end of the gun’s contact tip to between 1/4 and 3∕8 inches. “This simple tip can have the biggest effect on your MIG welding,” says Jody Collier.
4. Use both hands
“Use both hands whenever possible,” Collier urges. “Rest the crook of the gun neck in one hand and hold the part with the trigger in the other hand. Don’t hesitate when it comes to having your prop hand close to the weld. Get a heat-resistant, heavy welding glove if you need it.”
5. Listen to your welder
Music to your ears should be a steady buzz while welding. A steady hiss can indicate your voltage setting is too high, notes Leisner. “A loud, raspy sound could indicate the voltage is too low. A crackling sound like a machine gun going off indicates too high an amperage setting,” he adds.
6. Keep the arc upfront
“For better penetration, keep the arc at the leading edge of the weld puddle,” says Collier.
The exception to this rule would be when welding thin sheet metal. In this case, keep the arc back farther in the puddle to prevent burn-through.
7. Match drive rolls, gun cable liner, contact tip to the wire size
Surprisingly, this basic matching up is often ignored. If you are trying to run .030 diameter wire through .035 rolls, you will find yourself constantly changing feed speed and never getting that setting right, as the grooves on the rolls are too large. The same advice applies to the gun cable liner and contact tip size.
8. Push or pull
The most common method is to push the gun toward the direction of the weld (the forehand method). Forehand welding produces shallow penetration with a flat, wide, smooth surface.
The second approach comes when you drag the gun (the backhand method). This produces a deep penetration weld that is narrow and high in the center.
So what method should you use? That depends on the thickness of the metal you are welding and how deeply you need to penetrate the weld.
9. Watch when welding out of position
If you are welding vertically, horizontally, or overhead, “keep the weld pool small for best weld bead control, and use the smallest wire diameter size you can,” says Leisner.
10. Replace contact tips liberally
“Contact tips are cheap,” says Collier. “Keep a pack in your toolbox and replace them often.” Worn contact tips are typically oval and lead to an erratic arc. Also, if a tip enters the molten weld pool, it should be immediately replaced. For most casual welders, a good rule of thumb to assure high-quality welding is to change the tip after consuming 100 pounds of wire.
11. Read your bead
You can learn a lot by looking at your finished welding bead, says Leisner.
A convex-shape or ropy bead often indicates that your setting is too cold for the thickness of the repair and there isn’t enough heat being produced to penetrate the base metal. A concave-shaped bead indicates a problem with heat input.
Advantages of MIG welding
- Higher Productivity: Many welders will enjoy higher productivity due to time saved by not having to constantly change rods or chip away slag, as well as not having to brush the weld repeatedly. They’re able to work faster and cleaner.
- Simple to Learn: One of the top advantages of MIG welding is its simplicity. Welders can learn how to MIG weld in a few hours, and some instructors claim they can provide basic training in twenty minutes—with the majority of the time being spent on cleaning the weld. TIG welding takes a long time to learn, and most welders working on home projects won’t want to invest the time into it. One instructor described MIG welding as a “point and shoot” process.
- Simple and Great Welds: MIG provides better weld pool visibility. Add this to the simplicity of the process and better control offered by the auto-feed wire, and MIG makes it simple to produce a great looking weld.
- Clean and Efficient: Since MIG uses a shielding gas to protect the arc, there is very little loss of alloying elements as the metal transfers across the arc. There is no slag to remove, which is typical for stick welding, and only minor weld spatter is produced. After a brief clean up, MIG welders will be back on the job in a fraction of the time thanks to the minimal cleanup it requires.
- Versatile: MIG welding is extremely versatile and can weld a wide variety of metals and alloys, while operating at a variety of ways, such as semi and fully automatic. While MIG welding is useful for many home welding projects, it is also used by a large number of industries. MIG is used for the following metals: aluminum, copper, stainless steel, mild steel, magnesium, nickel, and many of their alloys, as well as iron and most of its alloys.
- Faster Welding Speed: The continuously fed wire keeps both hands free for MIG welding, which improves the welding speed, quality of the weld, and overall control.
Disadvantages of MIG welding
- Cost: Welders will notice right away that MIG welding equipment is more complex and costly, while also sacrificing portability. In addition, shielding gas, electrodes, and replacement tips and nozzles for MIG welding can add up.
- Limited Positions: The fluidity of the welding puddle and the high heat input of a MIG welder rules it out for vertical or overhead welding. While some welders would never even think of welding in one of these positions, take this factor into consideration when deciding whether or not to purchase a MIG welder to make sure it can accomplish all of the jobs planned for it.
- Unsuitable for Outdoor Welding: Besides not being portable, MIG welders are also unsuitable for working outside since they use a shielding gas to protect the purity of the weld. Wind will play havoc with the shielding gas and impact the quality of the weld. A MIG welder also can’t be hauled out into a field to repair a tractor, but works great in the garage for automotive work.
- Fast Cooling Rates: The welded metal will cool at rates that are higher since they aren’t covered by slag when the weld is completed.
- Unsuitable for Thick Metals: While MIG welding is suitable for thin metals, it does not deliver proper penetration for thicker steel that requires a solid weld.
- Shielding Gas: The bottle of shielding gas can take time to replace and can get in the way while welding.
- Metal Preparation Time: Before welding with a MIG welder, the material has to be free of rust or dirt in order to get a good weld and for safety’s sake.
What is MIG welding used for?
MIG/MAG welding is a versatile technique suitable for both thin sheet and thick section components. An arc is struck between the end of a wire electrode and the workpiece, melting both of them to form a weld pool. The wire serves as both a heat source (via the arc at the wire tip) and filler metal for the welding joint.
Metal inert gas welding is generally used for large and thick materials. A consumable wire is used which serves as both an electrode and a filler material.
Compared to TIG welding, it is much faster, resulting in shorter lead times and lower production costs. In addition, it’s easier to learn and creates welds that require little to no cleaning and finishing. However, the welds are not as precise, tight, or clean as the TIG welding processes.