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Posted on September 17, 2020

Arc Welding Definition and Process Types

Arc welding is one of many fusion welding processes used to join metals. It uses an electric arc to create intense heat to melt and join metals. A power source generates an electric arc between a consumable or non-consumable electrode and base metal.  Arc welders can use either direct current (DC) or alternating current (AC).

How Does it Work?

Arc welding works by using an electric arc from an AC or DC power source to generate a staggering heat around 6,500 degrees Fahrenheit at the tip, to melt the base metals, and to create a pool of molten metal and join the two pieces.

The arc is formed between the work piece and the electrode, which is moved along the line of the joint either mechanically or manually. The electrode can either be a rod that carried the current between the tip and the work piece, or it can be a rod or wire that conducts current as well as melts and supplies filler metal to the joint.

Metal tends to react chemically to elements in the air such as oxygen and nitrogen when heated to extreme temperatures by the arc. This creates oxides and nitrides, which ruin the strength of the weld. Therefore, a protective shielding gas, slag, or vapor needs to be used to lessen the contact of the molten metal with the air. After the piece has cooled, the molten metal is able to solidify to create a metallurgical bond.

What are the Different Types of Arc Welding?

Arc welding can be broken down into two different forms:

Consumable Electrode Methods

Metal Insert Gas Welding (MIG) and Metal Active Gas Welding (MAG)

This form of arc welding is also known as Gas Metal Arc Welding (GMAW). MIG uses a shielding gas such as argon, carbon dioxide, or helium to protect the base metals from being destroyed from contamination.

Shielded Metal Arc Welding (SMAW)

This form of welding is also known as stick welding or manual metal arc welding. In this process, the arc is placed between the metal rod that is electrode flux coated and the work segment to melt it and form a weld pool. The electrode flux coating on the metal rod is melted to form a gas, which shields the weld pool from the air. This process does not use pressure and the filler metal is formed by the electrode. This process works best for ferrous metals because they can be welded in all positions. Ferrous metals are alloys that are made up mostly of iron and contain carbon.

Flux-Cored Arc Welding (FCAW)

This form of welding can be used as a substitute for SMAW. FCAW uses the gas formed by the flux to shield the work piece from contamination. This enables the operator to weld outdoors even if it is windy. It works by using a constantly fed consumable flux cored electrode and a continual voltage power supply in order to generate a constant arc length. This form of welding is great for general repairs and shipbuilding because it works well with thicker joints.

Submerged Arc Welding (SAW)

SAW involves the formation of an arc between a constantly fed consumable electrode or wire, and the work piece. This process creates a cover of fusible flux, which generates a protective gas to shield the work area. The process becomes conductive when molted and generates a current path amongst the electrode and work piece. The flux is great because it prevents spatter and sparks while simultaneously quelling fumes and ultraviolet radiation.

Electro-Slag Welding (ESW)

ESW is a welding process that uses heat which is generated by an electric current moving between the consumable electrode and the workpiece. This creates a molten slag, which covers the weld surface. The molten slag’s resistance to the passage of the electric current creates heat for melting the wire and plate edges. The metal solidifies as it is hit with water. This is a vertical process that is used to weld thick plates that are above 25 mm in a single pass.

Arc Stud Welding (SW)

SW joins a metal stud such as a nut or fastener, to a metal work piece by heating both parts with an arc of electricity.

Non-consumable Electrode Methods

Tungsten Inert Gas Welding (TIG)

This process is also referred to as Gas Tungsten Arc Welding (GTAW). TIG uses a non-consumable tungsten electrode to generate an electric arc. The arc also works as a shield of gas to protect the weld from the air, which can cause oxidation. This is a favored method for welding aluminum.

Plasma Arc Welding (PAW)

This method uses an electric arc between a non-consumable electrode and a base metal. The electrode is placed in a torch and the plasma forming gas is separated from the shielding gas, which produces narrow and deep welds.

Where is it Used?

Arc welding is commonly used to join materials and is used across a lot of different industries.

The aerospace industry uses arc welding to manufacture and repair aircraft, join sheeting, and for precision work. The automotive industry uses arc welding to bond exhaust systems and hydraulic lines. Arc welding can deliver extremely strong bonds even between thin metals.

The construction industry uses arc welding to guarantee strong, sustainable connections within buildings, bridges, and other infrastructures. Other industries that use arc welding are the oil and gas industry and the power industry.

Rod Types

Arc welding uses a wide range of rods that have various strengths, weaknesses, and uses. These factors all affect the quality of a weld. The rod is attached to the welding machine and the current moves through it to connect work pieces. The rod can either melt to become a part of the weld, known as consumable electrodes or it does not melt, known as non-consumable electrodes.

The rods that are generally used are coated. Less commonly, uncoated rods can be used, but they create more spatter and make it hard to control the arc. Coated rods are better for reducing contaminating oxides and sulfur because of the chemicals they give off. Rod coating can be cellulose, mineral, or a mixture of both. It does not matter if the rod is coated or uncoated, a user needs to pick the correct rod for their work piece to create durable, uncontaminated welds.

Arc Weld Advantages

Arc welding provides a plethora of advantages compared to other types of welding. These advantages include:

  • Low cost. This is an affordable technique because the cost of equipment is low. It also requires less equipment due to the lack of gas.
  • Portability. The materials in this technique are easy to transport.
  • Used on unclean metals. Arc welding can be performed on dirty metals.
  • Work in any environment. A lot of arc processes use shielding gas so work can only be done in one place. With arc welding, there is no need for shielding gas so work can happen regardless of weather conditions.

Arc Weld Disadvantages

While there are many great benefits to arc welding, there are also some shortcomings. These disadvantages include:

  • Cost. While cost is considered an advantage, it is also a disadvantage because it produces more metal waste than other methods, resulting in higher project costs.
  • Requires a high level of skill and training.  Not all operators have a high level of training and skills.
  • Thin metal. Arc welding does not work well on certain thin metals.