Developed after World War II, MIG welding is an ever-popular welding process. The process was developed from gas-shielded metal welding. It's the best welding process for steel applications, most especially for stainless and mild steel.
You should understand that this topic is not really for seasoned professionals who handle the MIG welding machine on a daily basis. But if you are experienced, and want to add welding wire to your arc for DIY projects at home, inert gas welding, better known with the acronyms MIG or GMAW, will be of interest to you for sure. In this in-depth guide, we will tell you all about this welding technique and everything you need to get started.
Jump To A Section:
- What is MIG Welding?
- The Science Behind MIG Welding
- What Supplies Do You Need to MIG Weld?
- Getting Started With a MIG Welder
- MIG Welding Applications
- MIG Welding Pros and Cons
- MIG Welding FAQ
- Next Steps: What to Do After Learning MIG Welding
What is MIG Welding?
The MIG welding process is a continuous arc welding process in which the welding pool is protected by an inert shielding gas that flows from the torch onto the piece to be welded.
The fact that it is a continuous wire welding process makes the technique ideal for high productivity projects. At the same time, the presence of gas allows it to operate without slag.
What Does MIG Mean?
MIG is an acronym for metal inert gas. It is also known as wire welding or gas metal arc welding (GMAW). This is one of the most popular welding processes after shielded metal arc (stick) welding. MIG welding is part of the four types of welding processes. The other three are tungsten inert gas welding (TIG), stick welding or shielded metal arc welding (SMAW), and flux-cored arc welding (FCAW).
MIG is usually compared to TIG, which stands for tungsten inert gas. Here’s how the two procedures differ.
The Science Behind MIG Welding
Metal inert gas welding uses electricity to melt and then assemble pieces of metal to derive a strong, durable, and relatively aesthetic weld. The science behind it involves the use of shielding gas to prevent the contamination or oxidation of the weld pool while reducing the combustibility of the materials.
How Does It Work?
MIG welding uses electrical current to create an arc between an electrode wire and the piece of metal to be welded. The arc melts the wire which is then deposited to create the actual weld.
When the source of heat (a torch) is removed, the weld pool cools, solidifies, and forms a new piece of molten metal (the weld). All of this happens at the nozzle of the MIG torch, a handheld device similar to a fuel dispensing gun. The torch simultaneously feeds the electrode wire and inert shielding gas into the weld.
What Supplies Do You Need to MIG Weld?
Below is the list of supplies you will need to have when you are ready to start MIG welding.
The MIG welder is the most important supply for welding. You can get a budget welder for less than $500. The MIG welding machine is a versatile machine. It is often suitable as a MAG welding machine as well. Your skill level, welding process, welding project or application, and budget should be considered while choosing a MIG welder according to the Tulsa Welding School. An adjustable amperage between 30 and 200 A is recommended.
Gas Tank and Shielding Gas
You need a gas tank for the inert gas. They are usually available in different sizes from 40 to 80 to 125 cubic feet capacity tanks. Remember, gas cylinders have special safety precautions. The cylinder must have at least 10 years of hydro test date. It must also meet the standards of regulatory organizations such as DOT, CE, and ISO. For general use, you can choose argon as your inert gas when you are intending to weld carbon steel materials with high quality, stainless steel, and nonferrous materials like aluminum and copper alloys.
MIG welders use continuous wires. With these wires, you can have a higher current density than those that can be tolerated by coated electrodes used in other processes. In coated electrodes, an excessive current density causes cracking of the coating due to the different expansion coefficients between the metal core and the coating itself. However, with continuous wires, it is possible to obtain greater penetrations.
Most wires in MIG welding have a diameter of 0.8 to 1.2 mm, although there are thick wires with a diameter of 1.6 mm and 2 mm. Also, particularly thin wires with a diameter of 0.6 mm are not uncommon.
Wires with a diameter of 0.6 mm are particularly suitable for smaller welding machines and thin sheets. The thicker the materials, the thicker the wires.
Usually, the welding machine is the limiting factor in the choice of wire. Choose a wire that can be processed with your equipment.
Welding sparks and free-flowing UV light can damage your retina and conjunctiva, which can result in temporary blindness. If the exposure continues, the eyes can be permanently blinded. This is why welders put on a helmet, and not just any helmet; a special auto-darkening helmet.
This welding helmet is an optoelectronic hood that was developed to protect the eyes and faces from sparks and splashes when welding.
A metal brush is needed for cleaning the welded surface before welding. This can be used to remove slags, rusts, and dirt. Make sure the brush has stainless steel bristles.
To get precise welds, the piece of material to be welded must be stable so you can concentrate on the actual welding. A C-clamp or G-clamp can be used to hold the metal workpiece.
You need an angle grinder for pre-welding and post-welding operations. Before starting, the grinder is used for removing rust, paintworks, or dirt from your workpiece. It's also used for removing weld spatters when you're done welding.
Safety should be your priority when welding with shielding gas. It’s not only for preparing against fire hazards, your safety considerations should involve the use of personal protective equipment (PPE):
Long sleeve shirts and pants
Getting Started With a MIG Welder
In this section, you'll learn about everything you need to get started setting up the welder from preparing the tools and workspace to adjusting the screws and more.
Prepare Your Tools and Workspace
Note that this welding process is unsuitable for outdoor applications because of the use of gas. So, the first thing to put in place is your workshop.
Don't forget to install a fire extinguisher in your workshop and keep a bucket of water nearby to cool the welds if necessary. Get your PPE on and bring all your supplies into the workspace.
Check the Adjusting Screw and Set the Gas Flow
First, this adjusting screw can be found on your gas tank below the knobs. The screw should be loose enough so you can twist with one hand.
Ensure the screw reaches 10 to 15 CFH pressure. You'll find a handwheel on the tank. This is used for opening and closing the tank. Turn the knob and you'll be able to increase the gas flow.
Make Your Adjustments
To start welding, you need to adjust the machine and set your wire size. As soon as you have decided on wire size, it is time to install it on the welding machine. Choose your MIG welding wire size depending on your workpiece material thickness.
Charts are usually provided to guide you on the right setting for each material. Next, you need to adjust the welder to work with the metal thickness. If you have a C-clamp, use it to hold your workpiece before you start welding.
Set Up the Welder
The welding machine needs to be set correctly to achieve optimal results. With the wrong materials, you will have no joy. The MIG welder must be set between 30 to 130 amps: 40 to 145 amps should be set for .023-inch materials, 50 to 180 amps for .035-inch materials, and 75 to 250 amps for 0.45-inch materials.
The welding wire must be fed into the welding machine so that the wire supply to the welding gun can spool continuously. Since the electrode is constantly melting, you save yourself having to change it frequently.
You proceed as follows:
- Open the welder.
- Attach the wire spool to the suspension provided for it. The MIG wire must be on the underside of the spool in the direction of the roller. This is the only way to ensure an even wire feed.
- Now thread the wire into the wire feed unit. When inserting the wire through the infeed of the feed rollers, make sure that the wire is not bent or twisted.
- If necessary, a push button must be pressed to regulate the tension on the wire.
- Now attach the bobbin with the bobbin cap.
- Remove the MIG nozzle and contact tip with pliers.
- Now press the trigger to feed the wire through the gun.
- Replace the nozzle and contact tip.
Types of Gas Needed for MIG Welding
You can use different gases for MIG welding. The most popular are pure argon, pure helium, or a mixture of argon and helium.
- Pure argon: Pure argon should be used to weld steel when high-quality welds are required. It is suitable for MIG welding aluminum and other nonferrous metal for thin sections which do not exceed 10 mm due to low heat input of arc as compared to that of MIG with using helium as a shielding gas.
- Pure helium: The usage of helium is a must when high heat inputs are required such as in the case of welding thick sections of nonferrous materials like aluminum and copper alloys.
- Mixture of argon and helium: This mixture is used when high heat input arcs are required with lower cost as compared to pure helium -- as helium is more expensive than argon.
Using a Gas Cylinder
You need to be careful when handling the gas cylinder. All safety instructions must be observed, otherwise, unexpected dangers may arise. If a filled gas bottle tips over and knocks off the gas regulator, it flies through the room in an uncontrolled manner. Pay attention to the necessary safety precautions when transporting the gas and nothing will go wrong.
Adjusting the Screw and Handwheel
When you've got your shielding gas and tank set up and have connected the cylinder to the machine via a hose, twist the cylinder's adjusting screw to your left. You'll find a handwheel for opening and closing the tank on the top of the cylinder. The handwheel is used for controlling the gas flow. Turn the knob and you'll be able to increase the flow.
MIG Welding Applications
MIG welding does not have the steep learning curve that you find in TIG welding or traditional oxyacetylene welding. It is a technique used by beginners as well as professionals. Some of its uses are described below.
Used for Most Types of Sheet Metal Welding
MIG welding is especially suitable for most types of sheet metals and low alloys. The process is a clean welding technique that lets you evolve at your own pace. It does the job very well on different metals and alloys: mild steel (carbon), magnesium (including stainless steel), and aluminum.
Fabrication of Pressure Vessels and Steel Structures
MIG / MAG welding is used in almost the entire welding industry. The largest users are the heavy and metalworking industries. These include the shipbuilding industry, manufacturers of steel structures, pipelines, and pressure vessels.
Automotive Industry and Home Improvement Industry
Although MIG welding is a technique popular with beginners and occasional DIY enthusiasts, it also remains popular with metalwork professionals in the home improvement and automotive industry. This is because it allows great productivity.
MIG Welding Pros and Cons
The main advantage of MIG welding is that no slag is produced while welding. MIG welding has a lot to offer -- especially for hobby welders. However, no welding technique can claim to be perfect for all applications, and MIG is no exception. Below is an overview of the most common pros and cons of welding with metal inert gas.
The welding techniques produce high-quality welds
Minor weld spatters
Good weld speed
Can be used to join dissimilar metals
The welding technique can be full or semi-automatic
The gas makes it unsuitable for welding outdoors
Not ideal for thick metals
Requires metal preparation
MIG Welding FAQ
Why Is MIG Welding Popular?
MIG welding began in the 1940s but it has become so popular because of the availability of inert gases such as helium and argon. Other reasons MIG welding has become common are it doesn't create a lot of weld spatters, has high welding speed, and allows the possibility of joining dissimilar metals.
What Is the Difference Between MIG and TIG Welding?
The difference between both welding processes is in the arc used.
- MIG welding makes use of continuous feed wire that melts to form a weld. TIG welding makes use of long rods for fusing the metals directly.
- MIG welding uses filler wire feed (as the consumable electrode) to have an arc with the work material, but in the case of TIG, a nonconsumable electrode of tungsten is used to generate the arc -- with work material and consumable filler wire fed to the arc during welding -- so this process is slower than MIG.
What Type of Gas Is Used for MIG Welding?
The most commonly used MIG welding gases are argon and helium gases. While argon is heavier than air, and stagnant on the weld pool guaranteeing greater protection, helium is lighter than air. Therefore, it provides less protection. However, having a thermal conductivity about 10 times that of argon allows a greater penetration. For this reason, the use of helium is limited to joints of high thickness or materials with high thermal conductivity.
Why Is Inert Gas Used in MIG Welding?
The inert gases used in MIG welding help keep the oxygen contained in the air away from the weld so the weld does not oxidize. The weld seam should not oxidize. Oxidized metal will be weak and can become porous. You probably know oxidized metal better by the term "rust." If the weld seam does not oxidize, it has long-lasting stability and binding force. This is why you need shielding gas. If you don't use a shielding gas, the seam will react with the oxygen and nitrogen in the air.
Can I Teach Myself to MIG Weld?
It's possible to learn MIG welding yourself, but it can take time. Besides, MIG welding can be hazardous in the hands of a rookie with no basic knowledge as you'd be dealing with highly flammable inert gases, weld spatters, and damaging ultraviolet light. But with this guide, you know the dos and don'ts of MIG welding for safety and efficiency.
Next Steps: What to Do After Learning MIG Welding
The next steps depend on what you want to do. Here are some suggestions.
- YouTube Courses: YouTube has it all from welding courses for beginners to courses for experts in steel construction industries. Here are our recommendations for the top 5 best welding YouTube channels
- Trade Career Certification: There are online classes where you can learn the basics and keep evolving. Some of these include Certified Welder (CW), Certified Welding Inspector certification (CWI), and Certified Welding Educator certification (CWE).
- Workshops: There are person-to-person opportunities where you can learn the basics. These workshops can either be virtual or in a physical setting.