Subscribe to our newsletter to receive the latest news and events from TWI:

Subscribe >
Skip to content

What is Arc Welding?

   

Arc welding is a type of welding process using an electric arc to create heat to melt and join metals. A power supply creates an electric arc between a consumable or non-consumable electrode and the base material using either direct (DC) or alternating (AC) currents.

This article is one of a series of TWI frequently asked questions (FAQs).

How Does it Work?

Arc welding is a fusion welding process used to join metals. An electric arc from an AC or DC power supply creates an intense heat of around 6500°F which melts the metal at the join between two work pieces.

The arc can be either manually or mechanically guided along the line of the join, while the electrode either simply carries the current or conducts the current and melts into the weld pool at the same time to supply filler metal to the join.

Because the metals react chemically to oxygen and nitrogen in the air when heated to high temperatures by the arc, a protective shielding gas or slag is used to minimise the contact of the molten metal with the air.

Once cooled, the molten metals solidify to form a metallurgical bond.

Types

This process can be categorised into two different types; consumable and non-consumable electrode methods.

Consumable Electrode Methods

Metal Inert Gas Welding (MIG) and Metal Active Gas Welding (MAG), also known as Gas Metal Arc Welding (GMAW), uses a shielding gas to protect the base metals from contamination.

Shielded Metal Arc Welding (SMAW), also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding or stick welding is a process where the arc is struck between the metal rod (electrode flux coated) and the work piece, both the rod and work piece surface melt to form a weld pool. Simultaneous melting of the flux coating on the rod will form gas, and slag, which protects the weld pool from the surrounding atmosphere. This is a versatile process ideal for joining ferrous and non-ferrous materials with a range of material thicknesses in all positions.

Created as an alternative to SMAW, Flux Cored Arc Welding (FCAW) uses a continuously fed consumable flux cored electrode and a constant voltage power supply, which provides a constant arc length. This process either uses a shielding gas or just the gas created by the flux to provide protection from contamination.

Submerged Arc Welding (SAW) is a frequently-used process with a continuously-fed consumable electrode and a blanket of fusible flux which becomes conductive when molten, providing a current path between the part and the electrode. The flux also helps prevent spatter and sparks while suppressing fumes and ultraviolet radiation.

Electro-Slag Welding (ESW) is a vertical process used to weld thick plates (above 25mm) in a single pass. ESW relies on an electric arc to start before a flux addition extinguishes the arc. The flux melts as the wire consumable is fed into the molten pool, which creates a molten slag on top of the pool. Heat for melting the wire and plate edges is generated through the molten slag's resistance to the passage of the electric current. Two water-cooled copper shoes follow the process progression and prevent any molten slag from running off.

Similar to flash welding, Arc Stud Welding (SW) joins a nut or fastener, usually with a flange with nubs that melt to create the join, to another metal piece.

Non-consumable Electrode Methods

Tungsten Inert Gas Welding (TIG), also known as Gas Tungsten Arc Welding (GTAW), uses a non-consumable tungsten electrode to create the arc and an inert shielding gas to protect the weld and molten pool against atmospheric contamination. 

Similar to TIG, Plasma Arc Welding (PAW) uses an electric arc between a non-consumable electrode and an anode, which are placed within the body of the torch. The electric arc is used to ionise the gas in the torch and create the plasma, which is then pushed through a fine bore hole in the anode to reach the base plate. In this way, the plasma is separated from the shielding gas.

Hot wire TIG cladding process at TWI

Services

TWI has been at the forefront of developing arc welding processes and, as such, offers a number of associated services. Achievements include the invention of the twin wire MIG welding process (used to increase weld speed and metal deposition rate or to shape the weld bead) and transistor control technology, which paved the way for TWI to develop pulsed TIG, short-circuiting MIG and pulsed MIG processes.

Our team of over 20 welding professionals, including highly qualified International Welding Engineers, are able to provide expert guidance on any issue related to the joining of materials.

 

Where it is Used

This common joining process is used across all industry sectors, including automotive, aerospace, oil and gas, power, and construction.

Rod Types

The arc process uses a variety of rods which have different strengths, weaknesses and uses which can impact weld quality. The rod is connected to the welding machine and a current is passed through to join work pieces together.

In some cases, such as with SMAW, the rods melt to become part of the weld - these are consumable electrodes. In other instances, such as with TIG, the rods to do not melt - these are non-consumable electrodes. 

Rods are generally coated, although the exact type of coating varies. While uncoated rods are available, these are far less common, create more spatter, and can make it difficult to control the arc.

Coated rods are better to reduce or eliminate contaminating oxides or sulphurs. The three types of coating include cellulose, minerals. or a combination of the two.

Whether coated or uncoated, the correct rod needs to be selected to create clean, strong welds with the right bead quality.

The Advantages

There are many advantages compared to other welding processes. As the cost of equipment is relatively low, this is an affordable technique which also requires less equipment due to the lack of gas

It is a portable method of joining, which can also be used on uncleaned metals. While many arc processes use shielding gas, this is not always necessary, which means work can be undertaken regardless of weather conditions, while spatter is not an issue.

The Disadvantages

Although there are a great many advantages, there are some drawbacks with this process. This type of welding produces more waste than other methods, meaning that project costs can be higher for some jobs. This process also requires a high level of skill and training for arc welders, while it can also be difficult to join thin materials using arc processes.

Related Frequently Asked Questions (FAQs)

For more information, please email:


contactus@twi.co.uk