Welding Overview
Welding is a general term for a variety of processes used to join metal parts by creating a coalescence, or weld, at the joint. This is typically achieved by applying heat and energy while bringing the metal pieces together.
Common Welding Processes
The most widely used welding methods are gas welding and arc welding. Welding has numerous applications, including the fabrication of ships, aircraft, automobiles, electrical and electronic components, and construction projects. While over 50 welding processes exist today, gas and arc welding remain the most common.
Hazards of Welding
Welding is inherently hazardous because it involves melting a metal workpiece and, often, a filler metal to form a strong joint. All welding, cutting, and brazing operations generate high temperatures capable of causing serious injuries.
Coalescence
Coalescence is the process by which two metals merge into a single body at the base metal surfaces upon contact. There are two essential requirements for coalescence: heat and intimacy of contact.
- Heat: Welding processes differ based on the heat source, method of application, and intensity of heat. Common sources of heat include:
- Acetylene or hydrogen in air or oxygen
- An electric arc
- Electric, gas, or oil furnaces
- Resistance of metal to electric current
- Chemical reactions, such as between metal oxide and finely divided aluminum
- Intimacy of Contact: The second requirement for coalescence is achieved through either pressure processes or non-pressure processes:
- Pressure processes: Surfaces are in direct contact with no gaps, and welders apply pressure while heating the metal to allow plastic flow.
- Non-pressure processes: A small gap exists between the surfaces, which is filled with molten metal to form the weld.