MIG welding is a versatile method of welding used in a wide range of industries.
What is MIG Welding?
MIG welding stands for Metal Inert Gas. It is a technique that utilizes a consumable metal wire electrode to create an electric arc that melts and welds metals together. The wire is continuously fed through the handle of the welding gun and melted into the weld pool. This pool of melted wire and base material then becomes a solid joint.
While “MIG welding” is what it is most commonly referred to, the process is also called “Gas Metal Arc Welding”, or "GMAW" for short.
Inert gas is used in this process for two different reasons. Firstly, it acts as a shield to protect the melted metal from airborne elements such as oxygen, carbon dioxide, nitrogen, and water vapor. These can contaminate the weld pool and weaken the integrity of the joint. The second reason is inert gas does not easily react with other elements or affect the polarity of the electrode. The most common types of inert gases used are argon and helium. They are often mixed with low percentages of reactive gases like carbon dioxide and oxygen.
What is MIG Welding Used For?
The MIG welding technique is a versatile method that can be used in a variety of situations with a variety of metals. Essentially all types of commercial metals and alloys can be welded using this technique.
In addition to its usefulness, it is also an easier technique to learn than others. This makes it the popular method chosen by hobbyists, artists, DIY-ers, and other individuals who are not professionally trained welders.
MIG welding is also used in most sectors of industries. The most popular industry is the automotive industry where it is often used to make repairs. It is also used in sheet metal and pipe welding.
What are the Limitations of MIG Welding?
Like all techniques, MIG welding has its limitations. One of the most notable limitations is location. It is not the ideal method to use for outdoor projects. Instead, it is better suited for an enclosed area where the conditions of the environment are more easily controlled.
Another limitation of MIG welding is the appearance of the weld bead. It is a faster process and typically results in less aesthetically pleasing welds than other techniques such as TIG welding (Tungsten Inert Gas).
What is Required for MIG Welding?
Certain equipment is required when using this technique.
Firstly, you need to ensure you have a power source capable of handling the electric current required for welding with a MIG welder. There are both lower voltage and higher voltage welders. Lower voltage welders are designed to plug into a regular home outlet. A higher voltage welder will need a high-capacity plug, like the kind used for electric appliances.
The amount of current or voltage depends on the welding technique and wire diameter. Table from www.twi-global.com.
The gun serves as a multifaceted tool. Its first function is to direct the consumable wire to the joint. It also transfers the electric current from the power source to the wire to heat and melt it into the weld pool. Lastly, it supplies a constant flow of shielding gas to protect the melted metal.
A spool of metal wire, also known as the consumable wire, is needed to deposit a weld.
Two common types of wire used on mild steel are ER70S-6 and ER70S-3.
A tank of shielding gas is required to produce clean welds free of harmful airborne contaminants that can damage the joint. These are delivered from a tank to the welding gun using hoses. A variety of mixes including argon, helium, carbon dioxide, and oxygen are used in MIG welding. Deciding which one to use depends on the project at hand.
This SPARC flow meter is a useful tool to help monitor gas flow.
A flow meter is a helpful tool that allows you to control the flow rate of the gas. It also shows how much gas is left in your tank. Both are vital to a job that requires quality and precision.
Deciding on Gas and Wire
Before beginning a welding project, it is important to choose the correct gas and wire that will provide the best results.
Choosing the Correct Gas
Inert gases are used in MIG welding. They are known as “shielding gases” and act as a shield to the arc weld. Their job is to protect the molten metal from contaminants that can cause defects and weaken the weld.
For each method, there are a variety of gases to choose from.
When using the MIG welding method, the most common shielding gases are argon, carbon dioxide, oxygen, and helium. The project and the materials will determine which gas is best to use.
The type of gas used determines the depth of weld penetration and the components of the arc.
Selecting a Consumable Wire
The first thing to consider when choosing a wire is the types of metal you plan to weld together. They are often called base metals and will determine the type of consumable wire you will want to use.
For best results, you want to match the type of metal wire you use with the type of base metals you are working on. Keep in mind that welding wire typically contains other elements in addition to the main metal type. You will need to ensure the primary metal in the wire matches your base metals.
How the gun is positioned relative to the angle of the joint is called the work angle. The American Welding Society's technical definition is, "the relationship between the axis of the electrode to the welder's workpiece."
Welding may require several positions - all of which are not always comfortable. The position the job requires affects the work angle. There are four basic positions.
The flat position is one of the easiest work angles.
Flat welding is one of the easiest of the positions. In this position, the MIG gun pointed straight down towards the materials. The tip of the gun is held at an angle of about 45 degrees in reference to the plate surface. This position is also called downhand.
The horizontal position is a more difficult work angle in welding.
This position is more difficult than the flat position as it is far more affected by gravity. In this position, there is a constant risk of the filler metal sagging over the bottom of the weld joint.
The MIG gun should be held at a degree anywhere between 35 and 45-degree angles and pointed upward. Moving in circles will help equally distribute the heat to both sides of the joint.
The vertical welding position is more difficult because of gravity.
Similar to the horizontal position, gravity plays a role in this position. A common problem in the vertical position is the tendency for the melted metal to flow to the bottom and pile up.
To prevent an uneven weld, the MIG gun should be pointed upwards at a 45-degree angle. Moving from side to side or in an oscillating motion will help create a uniform bead.
The overhead position is a difficult position requiring speed and a small weld pool.
This position is when the underside of a joint is welded. With this position, sag and drop are an issue because of gravity pulling down the weld pool. Increasing travel speed and keeping the weld pool small and controllable will help in this position.
Common MIG Welding Defects
Although it is an easier method of welding, there are several common defects to watch out for when MIG welding.
Porosity is a common defect that occurs with unclean surfaces or poor gas use. Image from www.weldinganswers.com.
One of the most common defects is porosity. Porosity occurs when gases are trapped in the weld. This can happen when the weld site is not clean, the shielding gases are inadequate, or poor technique.
Spatter is a common defect that leaves a sloppy weld appearance. Image from www.weldguru.com.
An unsightly defect, spatter is caused by a variety of conditions. High current, unstable arc, or the use of the wrong shielding gas all contribute to increased spatter.
Travel angle can also produce spatter. A typical travel angle ranges from 5 to 15 degrees. When travel angles are beyond 20 degrees, the amount of spatter will increase.
This defect is easy to identify as it is made up of fine particles of metal surrounding the weld site.
Lack of Fusion
Lack of fusion leaves an inadequate bond between the weld and base metals. Image from www.millerwelds.com.
Also called “cold lap,” lack of fusion occurs when there is not enough heat at the start of the weld. Without adequate heat, there is little or no bond between the weld metal and base material.
Undercutting can leave visible cracks and weak weld joints. Image from www.archelmets.com.
Undercutting cuts away at the base metal along the weld edge. This defect can be the result of poor technique, excessive heat, low wire-feed speed, or using the wrong type of consumable wire electrode. Undercutting affects the overall integrity of the weld and can lead to significant cracking at the weld site.
A burn-through is a defect caused by excessive heat and improper technique. Image from www.australwright.com.au.
Just like it sounds, burn-through occurs when the weld metal burns through the base material. This defect is often caused by excessive heat. Even when burn-through does not occur but excessive heat is used, the strength of the material can still significantly be compromised.
Irregular Weld Shape
This defect occurs from poor technique or from using the wrong gas. Image from www.weldguru.com.
Irregular weld shape is another aesthetically unpleasing weld defect that leaves an uneven weld bead. It is usually due to poor techniques such as slow travel speed, improper arc voltage, or using the wrong shielding gas.
Recommended Best Practices
Improving the quality and integrity of welds can be accomplished by following a few best practices for MIG welding.
Although it is an easier technique to perform, there are several major hazards to be aware of when MIG welding. Electric shock, burns, inhalation of gases, and arc rays are all dangers to avoid.
The best way to ensure your safety is to work in a well-ventilated area and wear appropriate welding attire to cover any exposed skin. This includes welding helmets, thick gloves, close-toed shoes, and clothes made of flame-resistant natural materials.
Finally, a fire extinguisher and a first aid kit should always be kept on-site to put out fires and treat minor injuries.
Clean the Welding Surface
Cleaning the surface before welding will help remove contaminants. This will help prevent porosity which will weaken the weld joint.
Use Two Hands
The hold a welder has on the gun directly affects the appearance of the weld. It is best to use two hands for better support and control.
Check Your Equipment Before Beginning
Before you start melting metal, it is important to ensure your equipment is working properly. This means checking to make sure there are no gas leaks or damaged electrical cords.
The best way to become a better welder is to practice often. The experience will help determine which techniques work for your preferred welding style. Things like speed, pushing or pulling the weld puddle, and grip is all characteristics unique to your technique.
Advantages of MIG Welding
MIG welding is used in almost all industries to form and repair joints between metals.
The reason it is one of the most widely used techniques in nearly every industry is that there are several advantages to MIG welding.
Easy to Learn and Use
Often compared to using a glue gun, MIG welding is an easier method for novice welders to use. Although it requires much more skill than using a glue gun, it doesn’t require as much precision as other techniques. Its ease of use makes it the method of choice for DIY-ers, hobbyists, and artists alike.
Another advantage of MIG welding is that it is easy to execute as it is a semi-automatic process. Both the feed rate of the consumable wire and the length of the arc are controlled by the power source. This makes the method faster than others like TIG welding.
One of its biggest advantages is that MIG welding can be done on a wide variety of metals and alloys. Stainless steel, carbon steel, and aluminum are the most commonly used metals.
In addition to being used to weld an assortment of metals, it can be used for both thick and thin materials.
Its versatility makes it a commonly utilized process in numerous industries requiring manufacturing, fabrication, or repairs.
Faster to Execute
Two factors make this method one of the fastest. Number one, the skill level required is lower. Secondly, the consumable wire is constantly fed through the welding gun. Other techniques, such as TIG welding, require more precision and a manually fed consumable.
Manufacturing industries are now able to use this method using robotic machines, speeding up the process even more.
Capable of Quality Welds
Although it is an easy technique to learn and execute, MIG welding still can produce quality joints. Like anything, it takes practice to achieve perfection, but it is possible to produce X-ray quality welds.
Disadvantages of MIG Welding
Along with the advantages that come with utilizing this technique are a few disadvantages.
Compared to other more time-consuming methods, MIG welding is infamous for producing less than precise welds.
Welders using this technique have less mobility as they have to stay close to the MIG welding machine.
Confined to Indoor Locations
Wind can have a major impact on the MIG welding process. This technique is best suited for indoor jobs where conditions are unlikely to change.
Requires More Expensive Gas
Argon gas is not only one of the most frequently used shielding gas in MIG welding, but also one of the most expensive.
What is Gasless Welding?
Gasless welding refers to the process in which a tube of wire with a flux core is used instead of a solid metal wire. While it is often called “gasless welding,” the flux inside the wire tube produces its own shielding gas when melted. The more accurate name is “self-shielding.”
Benefits of Welding with Self-Shielding Wire
It’s convenient. Unlike using cylinders of gas, self-shielding wire allows for a more mobile welder.
Another advantage is it can be used outside in the wind whereas MIG welding is better for indoor sites.
Drawbacks of Welding Without Gas Tanks
A major drawback is the flux core creates a significant amount of smoke. This makes it hard to see what’s going on with the weld pool. It is recommended to do this outside.
Another drawback is the flux causes spatter and slag that needs to be removed with a wire brush to leave a neat-looking weld. This adds an extra time-consuming step to the process.
MIG welding is a method used in nearly every industry. The process requires a welding gun, a consumable wire, an electric current, and inert gas.
It is a multipurpose technique that is easier to learn than others. This makes it an ideal method of choice for both industry professionals and novice welders who want to make at-home repairs.