Welding refers to a wide variety of processes in which metals are joined by fusion. The metal at the interface of two or more parts is melted or fused by application of intense, localised heat. A fitter metal, supplied by an electrode, is commonly used. When the joint solidifies and cools, a metallurgical bond results, and with proper selection of consumables, the weld should have strength at least equivalent to the base materials.
On the other hand, brazing does not involve fusion of the workpiece, and the resulting joint does not normally achieve the base metal mechanical properties.
Welding permits ready and economical joining of components and is able to be used in a wide variety of situations, from home or hobby welding to specialised production facilities performing fabrication involving a wide variety of ferrous and non-ferrous materials.
Processes commonly used in industry include the following:
• Arc Welding
• Shielded Metal Arc Welding
• Gas Metal Arc Welding (GMAW)
• Flux Cored Arc Welding (FCAW)
• Gas Tungsten Arc Welding (GTAW)
· Submerged Arc Welding (SAW)
• Other Processes for Specific Applications
This applies to the wide variety of welding processes that use an electric arc to generate sufficient heat for melting and fusion.
The arc is developed between an electrode and the workpiece. The majority of arc welding is performed with a consumable wire or rod electrode, but non consumable electrodes such as tungsten electrodes are also used, typically with a filter wire.
Shielded Metal Arc Welding (SMAW)
This utilises a cooled electrode, clamped in a holder and connected to a power source. The workpiece is connected to the power source terminal. The electrode coating provides slag cover for the molten weld pool, a gas cover and arc stability.
Gas Metal Arc Welding (GMAW)
This utilises a continuous solid wire electrode surrounded by a shielding gas, which protects the weld zone and arc from atmospheric contamination and imparts the appropriate arc characteristics. A feeder supplies the wire through a holder which has electrical and gas connections and also guides the wire.
Flux Cored Arc Welding (FCAW)
This is very similar to gas metal arc welding, but uses a tubular electrode, the core material providing a gas cover, either wholly (self-shielded) or partially (externally shielded).
Gas Tungsten Arc Welding (GTAW)
This technique uses a non-consumable tungsten electrode in conjunction with an inert gas cover. A fitter rod is often used, this being melted together with the weld zone by the arc between the electrode tip and the workpiece.
Submerged Arc Welding (SAW)
This uses a continuous solid wire, fed through a flux cover to the weld zone. The arc is generated below a layer of molten flux overlaid with unfused, solid grains of flux. The process tends itself to mechanisation and is characterised by high metal deposition rates and the ability to economically weld thick sections.
Other Processes for Specific Applications
Other processes used for specific applications include:
• Electroslag welding
• Flash butt welding
• Thermit welding
• Friction welding
• Electron beam welding
• Laser welding