Arc Source

Arc welding (AW) is a fusion welding process in which the joining of metals is achieved by the heat of an electric arc established between an electrode and the workpiece. The same fundamental process is also used in arc cutting operations. An electric arc is the discharge of electric current flowing through a gap in a circuit. This discharge is sustained by the presence of a thermally ionized gas column, known as plasma.

In arc welding, the arc is initiated by bringing the electrode into contact with the workpiece and then quickly pulling it back a short distance. This generates electrical energy capable of producing temperatures of 5500°C or higher, which is sufficiently hot to melt any type of metal. In most arc welding processes, filler metal is added and melted either between or onto the parts to be joined.

Electrodes

Electrodes used in arc welding are classified as either consumable or non-consumable. Consumable electrodes provide the filler metal for the weld. These electrodes are available in two main forms: rods or wire. Welding rods typically have a length between 225 and 450 mm and a diameter between 2.5 and 5 mm. Non-consumable electrodes are made from materials resistant to melting by the arc, such as tungsten (and rarely carbon).

Arc Welding General Information

Arc Shielding

At the high temperatures of arc welding, the metals being joined can chemically react with oxygen, nitrogen, and hydrogen in the surrounding air. These reactions can severely degrade the mechanical properties of the weld. Therefore, nearly all arc welding processes employ a method to shield the arc from the surrounding atmosphere. These methods are listed below.

• Protection is provided by coating the electrode tip, arc, and molten weld pool with a flux layer that prevents exposure of the weld metal to air.
• Protection is provided by using common shielding gases such as inert argon and helium. In some arc welding processes for ferrous metals, oxygen and carbon dioxide are used, often in combination with argon and/or helium, to create an oxidizing atmosphere or to control weld shape.

Flux Application

Flux is a substance used to prevent the formation of oxides and other undesirable contaminants or to dissolve and remove them. During welding, the flux melts and forms a liquid slag that covers the weld zone and protects the molten weld metal. After cooling, the slag solidifies and must be removed by chipping or brushing.

Flux is typically formulated to perform several additional functions:

1. Provide a protective atmosphere for the weld,
2. Stabilize the arc,
3. Reduce spatter.

Common Arc Welding Methods in Industry

1. Shielded Metal Arc Welding (SMAW – MMA)
2. Gas Metal Arc Welding (GMAW – MIG)
3. Gas Metal Arc Welding (GMAW – MAG)
4. Flux-Cored Arc Welding (FCAW)
5. Submerged Arc Welding (SAW)
6. Wire Welding / Gas Metal Arc Welding (GMAW-MIG/MAG)

Advantages of General Arc Welding

• Wide material compatibility: carbon steel, alloy steel, stainless steel, nickel alloys, titanium, etc.
• Deep penetration with high heat input
• Many processes are portable
• Highly suitable for automation
• High deposition rate and efficiency
• Welding in various positions

Disadvantages of Arc Welding

• High heat input can cause distortion and residual stress.
• Dependence on welder skill
• Sensitivity to wind in gas-shielded processes (GMAW, GTAW).
• Smoke and UV radiation pose safety hazards.
• Lower speed and efficiency in some methods (TIG).