MIG Welding and Arc Welding: A Comparison

Welding is the process of joining together materials through the use of heat.  Welding is a fabrication process that is used prominently in manufacturing and construction industries, as well as for automotive, aerospace, and railroad building. There are four types of welding, but the two main types are arc and MIG welding.

Type	Shielding gas source	Process	Benefits	Ideal for
MIG Welding	External	Metal transfer/Shielding	Versatility	Cross-industry use
Arc Welding	Flux core	Circuit/shielding	Strength	Heavy machinery

Arc and MIG welding are similar types, but they are characterized by some different features and are each suited for various uses. Read on to find out more about these two main types of welding and how they compare to each other.

What Types of Welding Are There?

When it comes to welding, you will typically encounter four main types that offer different features and different uses. 

MIG Welding

MIG or Metal Inert Gas welding is a type of arc welding that uses an external gas source and feeds electrodes through a wire at a continuous pace and a set speed with a gun made for this purpose. The interaction created by this gun between the electrodes and the metal forms an arc that melts the wire and gives way to a strong weld.

Arc Welding

Arc welding also uses a flux-cored wire to feed electrodes continuously. The flux core is the main difference between how arc welding and MIG operate. With arc welding, the flux core in the wire creates a gas shield around the weld. 

TIG Welding

Tig welding is another type of welding that uses the electric arc but, in this case, long rods are used to fuse metals. This type of welding is popular because it reduces the need to replace electrodes as no feeding is necessary.

Stick Welding

Stick welding is one of the types of welding that can be traced back the furthest. It is known for the strength of the welds it creates. Stick welding uses a consumable rod wrapped in flux. The electrode heats up before eventually melting and welding the materials. 

The Bare Bones of Welding Terminology

These are some of the terms you’ll encounter when discussing welding, and knowing what they are referring to can shed more light on this fabrication process.

• Parent metal: This is the base metal that is brought into the process to be welded.
• Filler metal: This the metal added to the parent metal and joined to it through welding.
• Weld metal: All the metal that has been melted during the welding process.
• Fusion line: Also known as a junction, this line creates a border between the weld metal that has been melted and the heat-affected zone.
• Weld zone: An area created from the weld metal and the heat-affected zone.
• Heat-affected zone: This is the part that remains from the parent metal that stays unmelted though it is affected by the welding process.
• Workpiece: Another name for the metal that is being worked on through the process.

What is MIG Welding?

MIG welding, also known as Gas Metal Arc Welding, is a welding process known for how it feeds electrodes through a specialized gun explicitly made for this action. Feeding the electrodes through this wire at a constant and predetermined speed causes the melting of the wire and the fusion of the base metal, which allows for a strong weld.

MIG welding uses an external gas source and creates a shielding gas around the welding area that keeps it safe from external contaminants.  It was first patented in 1949, when it was used primarily to weld aluminum, particularly in the USA. The shielding gases initially used for welding aluminum were argon and helium. 

This type of welding can be used on both thick and thin materials. Learning the process is straightforward, and the success of it depends mainly on choosing the correct shielding gas that suits the materials being welded. The process also involves understanding the welding gun’s specific parameters and how it uses the constant speed for maximum effect.

How Does It Work?

There are a few steps involved in the process of MIG welding. First, the trigger of the welding gun is deployed, and an arc will appear between the wire electrode continuously fed to the gun and the metal that is being welded (also known as the workpiece). This arc melts the wire and the workpiece, which creates a weld pool. 

Shielding gas is delivered to the workpiece through a nozzle surrounding the wire. The shielding gas protects the workpiece from external contaminants like oxygen and nitrogen. These contaminants can cause damage to the workpiece, the arc, or the electrode, and should be avoided. 

There are various types of gas that can be used for shielding, and selecting these will depend on what materials you are welding and the use of the welding. Combinations of argon, helium, oxygen, and CO2 are usually the most popular choices.

The electrode wire and the arc length will depend on the power source, but the gun’s speed and the position of the wire will be controlled manually. The wire is positively charged and has standard polarity. 

Modes of Metal Transfer

Once the welding machine is triggered, there are four modes of metal transfer:

Pulsed

The pulsed mode of metal transfer is one of the most used with MIG welding. It has numerous advantages, like: 

• Reduced spatter
• Low heat distortion
• High electrode efficiency
• Increased resistance
• Minimal fusion defects
• Great-looking weld beads

It is also easier to use for the operator. It’s easily implemented in robotic or automated processes too.

Globular

This mode of metal transfer combines the short-circuiting method with large irregular drops. The two methods alternate, with the large drops following once the short-circuiting ends. This method is known for its speed and its affordability, as it makes use of CO2 for shielding and also of electrodes made from cheaper materials.

Spray

This is a high-energy mode of metal transfer that uses consistently shaped small drops of molten metal. This method comes with various benefits such as great weld beads, adaptable to the range of metals and electrodes. It’s also one of the easiest-to-use methods and has no spatter. 

Short-Circuiting

This method uses repeated electric short-circuits sessions to deposit electrodes, which then transfer the metal once physical contact has occurred. Short-circuiting can be used from any position, and it has a low-heat input, which helps minimize the risk of heat distortion. Short-circuiting is easy for the user to handle, and has excellent electrode efficiency.

Characteristics of MIG Welding

Two main components characterize MIG welding: the welding gun and the wire electrode, which is part of the gun. 

The Welding Gun

The welding gun used for MIG welding has many features, some of which are customizable. These include a control switch, gas nozzle, contact tip, power cable, gas hose, electric conduit, and a flow that delivers the shielding gas to the nozzle. The contact tip tends to be made from copper and chemically treated to reduce spatter. 

The contact tip is powered by the power source, which sends electrical energy to the electrode. The tip size is essential in achieving the desired result because it directly impacts the area it covers as it connects the electrode to the base metal.

The Wire Electrode

The wire electrode is one of the defining characteristics of MIG welding. The wire is thin and fed to the welding gun through a wire reel. Depending on the need, the wire can be either cored or solid. The wire is doubly essential to the process of MIG welding, as it provides both a heat source and a filler metal.

The wire goes through the welding gun’s contact tip, which conducts current back into the wire. There is a nozzle around the electrode wire through which the shielding gas acts as protection during the process. The electrode uses direct conduct that goes from the negative to the positive terminals. 

MIG welding is powered by a constant voltage power supply that can be adjusted and controlled according to the user’s specifications and the weld.

Benefits of MIG Welding

There a plenty of benefits that explain the popularity of MIG welding:

• Versatility: MIG welding can join different types of materials and different types of thickness.
• Affordability: The materials used in this type of welding are both readily available and on the cheap side.
• High electrode efficiency: The electrode efficiency of MIG welding rests between 92 and 98%, which consistently stands out compared to others.
• Straightforward: MIG welding is suitable for all levels of experience because it isn’t a highly complex process. Beginners can tackle this with only some lessons.

Practical Uses of MIG Welding

MIG welding is one of the most popular types of welding used across industries. You’ll encounter it in construction, manufacturing, aerospace, railroad, as well as automotive fabrication. It is also frequently used in the construction of automobiles, railroad reinforcing, and even welding pipes! For the latter use, special equipment has to be applied.

MIG welding is behind over 50% of the metal deposited worldwide. It’s a very flexible and versatile method that is suitable to adapt to automation processes.

What is Arc Welding?

Arc welding is a process that features intense heat. This is a similar method to MIG welding, but the main difference lies in what gives arc welding its other name: flux-core welding. The flux core produces the shielding gas used during arc welding, as opposed to the external gas source that MIG welding uses.

Arc welding typically uses a consumable electrode fed with wires and creates an electric welding arc. There are two main categories of arc welding: consumable electrode methods that include MIG welding, and non-consumable electrode methods that include Tungsten Inert Gas Welding and Plasma Arc Welding.

How Does It Work?

The electric arc that occurs between the electrode and the workpiece creates intense heat that melts the metal. The arc can either conduct or carry the current and then melts into the weld pool and the filler metal. The appropriate shielding gas will protect the workpiece from external contaminants while the arc can be guided either mechanically or manually.

In some instances, you can also use dual shielding during the process of arc welding. This will incorporate an external gas source that will provide even more protection to the workpiece alongside the flux core. 

Characteristics of Arc Welding

Some of the most prominent arc welding features involve the way its welding circuit works, the arc shielding mechanism, and the flux core.

Welding Circuit

The power source that feeds the power cable can be either DC or AC, leading to the electrode and the workpiece. The electrode will then interact with the workpiece and create an electric arc that generates intense heat that reaches around 6500F and melts the metal and the electrode wire or rod. The melted material is called a weld pool, or a crater.

The weld pool then solidifies as the electrode moves along the fusion line, creating the fusion bond.

Arc Shielding

The welding process can be easily compromised by external contaminants like oxygen and nitrogen found in the air. These contaminants can affect the weld’s strength; arc welding uses a shielding gas to protect it. This shield protects the arc and the workpiece from intrusion. Vapor and slag can also be used to fulfill this purpose.

The arc shielding prevents the exposure of the welding process to the air. It can also improve not just the safety of the process but also its quality. Certain types of arc shielding, like granular flux, can add elements like deoxidizers to the weld. 

The choice of shielding will depend on the nature of the weld and the types of materials involved. The most frequent choices are combinations of several gases like argon and helium.

Flux Core

The flux core is one of the highest-prized arc welding elements, as it includes the shielding element within it instead of relying on an external source. This significantly reduces the time spent on the weld, which leads to high-efficiency rates. The flux core is part of the consumable wire delivered through a metal-covered rod. 

During the intense heat generated in the arc welding process, the flux core melts with the consumable wire, and while doing so, it creates the shield. This is formed from slag cover and can even deoxidize the weld, significantly reducing the risk of contamination while preserving the quality.

Benefits of Arc Welding

Arc welding is known for its high efficiency level that only requires minimal clean-up once it is finished. It’s also a popular type of welding because it provides shielding during the process. Arc welding is one of the quickest types, and it reduces the amount of smoke and sparks that may occur during the weld. 

Arc welding produces a smooth joining known for its minimal distortion if used on the correct materials. The high speed and the temperature make quick work of the welding while reducing the impact on the material. The versatility of the process allows you to carry it out in any condition and at affordable prices.

When You Should Use Arc Welding

Arc welding generates intense heat and should only be used on materials that can withstand that without fully distorting. This type of welding is ideal for work involving heavy machinery from thick steel or other materials used in heavy construction. The thicker and heavier the material, the better it can take the heat.

Arc welding is also well-suited for extensive repairs on heavy materials, particularly those used on building sites. Although it requires more expertise than other welding types, this process can create highly smooth-finished products at high speeds in the right hands.

Is Arc Welding Stronger Than MIG?

The strength of the finished product in MIG or arc welding depends on numerous factors that go beyond the differences in processes, but arc welding is known for the resistance of its impact strength. This makes it one of the most preferred choices across industries, as the more significant impact strength allows the weld to withstand higher loads.

MIG welding is a type of arc welding and shares many of the same features, making them both popular choices. Different materials and projects require different criteria, but the intense heat involved in arc welding makes it more suited to use on thick and heavy materials, which in turn creates thicker and heavier welds.

Conclusion

MIG welding is a type of welding that is part of the arc welding processes. These two types share many characteristics and are only fully set apart by the welding shielding. These welding types are some of the most popular across the manufacturing and construction industries and are frequently used in building automobiles and heavy-duty repairs.

Which type of welding you choose is entirely up to you, but clearly both MIG and arc are designed with particular projects in mind.