Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing fusion, which is distinct from lower temperature metal-joining techniques such as brazing and soldering, which do not melt the base metal.
In addition to melting the base metal, a filler material is typically added to the joint to form a pool of molten material (the weld pool) that cools to form a joint that usually stronger than the base material. Pressure may also be used in conjunction with the heat, or by itself, to produce a weld.
Types of Welding
- Oxy-fuel welding: also known as oxyacetylene welding or oxy welding, it uses fuel gases and oxygen to weld and cut metals.
- Shielded metal arc welding: also known as “stick welding or electric welding”, it uses an electrode that has flux around it to protect the weld puddle. The electrode holder holds the electrode as it slowly melts away. Slag protects the weld puddle from atmospheric contamination.
- Gas tungsten arc welding: also known as TIG (tungsten, inert gas), uses a non-consumable tungsten electrode to produce the weld. The weld area is protected from atmospheric contamination by an inert shielding gas such as argon or helium.
- Gas metal arc welding: commonly termed MIG (metal, inert gas), uses a wire feeding gun that feeds wire at an adjustable speed and flows an argon-based shielding gas or a mix of argon and carbon dioxide over the weld puddle to protect it from atmospheric contamination.
- Flux-cored arc welding: almost identical to MIG welding except it uses a special tubular wire filled with flux; it can be used with or without shielding gas, depending on the filler.
- Submerged arc welding: uses an automatically fed consumable electrode and a blanket of granular fusible flux. The molten weld and the arc zone are protected from atmospheric contamination by being “submerged” under the flux blanket.
- Electronic welding: a highly productive, single pass welding process for thicker materials between 1 inch (25 mm) and 12 inches (300 mm) in a vertical or close to vertical position.
- Electric resistance welding: a welding process that produces coalescence of laying surfaces where heat to form the weld is generated by the electrical resistance of the material. In general, an efficient method, but limited to relatively thin material.
Welding may be performed in many different environments, including in open air, under water and in outer space.
Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction and ultrasound.
What is an Arc?
These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use either direct (DC) or alternating (AC) current and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas known as a shielding gas and filler material is sometimes used as well.
Power Supplies
The most common welding power supplies are constant current power supplies and constant voltage power supplies.
- Constant current power supplies: In arc welding, the length of the arc is directly related to the voltage and the amount of heat input I related to the current. Constant current power supplies are most often used for manual welding processes such as a gas tungsten arc welding and shielding metal arc wielding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady and as a result, the arc length and thus the voltage tend to fluctuate.
- Constant voltage power supplies: Constant voltage power supplies hold the voltage constant and vary the current and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current.
