Welding is widely used by metal workers in the fabrication, maintenance, and repair of parts and structures. While there are many methods for joining metals, welding is one of the most convenient and rapid methods available. In order to join two or more pieces of metal together by one of the welding process, the most essential requirement is heat. Pressure may also be employed, but this is not essential in many processes. Welding is the process of joining metals by heating them to their melting temperature and causing the molten metal to flow together. These range from simple steel brackets to nuclear reactors. Welding, like any skilled trade, is broad in scope and one cannot become a welder simply by reading a book, it needs practice and experience as well as patience.
Welding is not a new concept. The earliest known form of welding, called forge welding, dates back to the year 2000 B.C. Forge welding is a primitive process of joining metals by heating and hammering until the metals are fused (mixed) together. Although forge welding still exists, it is mainly limited to the blacksmith trade.
Many different welding processes are available and newer techniques are being developed at a rapid rate. Most of these commonly require heat to be supplied to the weld area. Heat is generated either by means of a combustible gas or by an electrical means. In some methods, pressure is employed to force the two parts together whilst the weld is made, and in other cases, the weld is made by fusing the metals together without the use of force. There are three possible metallurgical conditions over the joint area of the metals being welded together. These are:
(a) Both joint faces are in a liquid state. This is a fully fusion weld such as in oxy-acetylene welding.
(b) A condition of solid and liquid states. This is the brazing process where the two metals to be joined remain in the solid condition and the joint metal is liquid.
(c) Both joint faces are solid, but often in a plastic state, as when making a blacksmith type of welds.
Classification of Welding
The two main methods of welding i.e. oxy-acetylene and electric arc welding are now the established practical methods for welding and cutting. The welding of materials is now a very wide and highly specialized area of production technology vastly different from the days of the blacksmith’s welds. The smith has completely disappeared from the scene of production welding and the oxy-acetylene process is largely confined to metal cutting operations.
One of the most popular welding method which uses a gas flame as a source of heat. In the oxy fuel gas welding process, heat is produced by burning a combustible gas, such as acetylene, mixed with oxygen. Gas welding is widely used in maintenance and repair work because of the ease in transporting oxygen and fuel cylinders. Once you learn the basics of gas welding, you will find the oxy fuel process adaptable to brazing, cutting, and heat treating all types of metals.
Arc welding is a process that uses an electric arc to join the metals being welded. A distinct advantage of arc welding over gas welding is the concentration of heat. In gas welding the flame spreads over a large area, sometimes causing heat distortion. The concentration of heat is an advantage in arc welding. It is because; the concentration of heat reduces buckling and deformation. This heat concentration also increases the depth of penetration and speeds up the welding operation. Therefore, it is found that arc welding is often more practical and economical than gas welding. All arc-welding processes have three things in common: a heat source, filler metal, and shielding. The source of heat in arc welding is produced by the arcing of an electrical current between two contacts.