What is Arc Welding? – Arc Welding Definition and Process Types

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Categories: Welding Technology

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.

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Shielded Metal Arc Welding Basics
Shielded Metal Arc Welding Basics

How Does Arc Welding Work?

At a very basic level, all arc welders have five components:

  1. An Electrode and electrode cable
  2. A Ground Cable and Clamp (sometimes called a working cable)
  3. A Power Supply
  4. Metal workpieces
  5. An Arc

The power supply provides AC or DC to create and sustain the arc, and the electrode is either mechanically or manually moved along the joint to create the weld.

So, how hot is a welding arc that melts and fuses metal? About 6,500°F. This does the job of melting and fusing the metal pieces, but it also creates another problem.

At these high temperatures, molten metal can react with gases in the air. This causes problems like porous and weak welds, excessive spatter, and reduced productivity.

To eliminate these welding defects, it is common to provide some form of protection to the molten pool when arc welding. This usually comes in two forms.

One option is a special shielding gas flooded over the hot weld. The type of gas and flow rate must be correct for the shielding gas to keep the atmospheric air away from the molten metal.

The second choice is flux, which creates its own shielding gas and slag when exposed to the high arc welding temperature. The flux’s inert gas and slag “encapsulate” the weld and keep the gases in the air away.

AC vs. DC Currents

DC provides current that flows in one direction, and AC alternates the direction of current flow multiple times a second. For example, a 60 Hz AC supply would alternate the flow direction 120 times a second.

The current differences are important. For example, with DC, magnetic fields can form, induced by the consistent flow of electric current in one direction.

Magnetic fields can move the arc so that it does not travel the shortest gap between the electrode and metal. This can cause spatter, porosity, and incomplete fusion and often happens at inside corners or at the end of welds. This is called arc blow.

So, it’s an issue with DC. But AC oscillates the current, and the magnetic fields are constantly being disrupted and never organize enough for arc blow to be an issue.

Also, DC welders are a bit more expensive to purchase. So, arc blow and initial costs are the two main cons for DC. You may even say just use AC arc welders. But for certain processes, like MIG welding, DC’s advantages far outweigh these disadvantages.

DC arc welders offer a smooth, easy-to-control arc, and they work better on thin materials. You also get less spatter, and in general, DC beads are “prettier.” For these reasons, you see DC is often used in arc welders, and many users prefer it over AC.

AC arc welders are often inexpensive and do not allow magnetic fields to be set up. So, it can be used in situations prone to arc blow. AC welders also penetrate well and are used in places like shipyards that regularly deal with thick pieces.

Another benefit of AC, it handles metals with problematic oxide layers on the surface, like aluminum. As the current oscillates, it efficiently removes the oxide layer that can interfere with and inhibit the fusion of the metal pieces.

What are the Different Types of Arc Welding?

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.

Flux Cored Arc Welding (FCAW)

Created as an alternative to SMAW, 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)

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)

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.

Arc Stud Welding (SW)

Similar to flash 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. 

Plasma Arc Welding (PAW)

Similar to TIG, 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.

New Arrivals Multi-Process Welding Machines
New Arrivals Multi-Process Welding Machines