The welding is a technique used to join the metallic parts with the application of heat. In olden time iron used to manipulate into useful shapes like welded blade-shaped by Arab armors at Damascus Syria as a sword. The welding was developed at the end of the 19th century but a real attempt to use welding on large scale happens during world war 1. The oxyacetylene process was developed by the year 1916 and still used with elan.
The major improvement since the beginning is in the equipment and safety. The modern electrode initially was introduced in 1907 with bare wire coated with minerals and metals and Arc welding was not used universally until world war 11 when a sudden need was required.
The long before Arc welding the resistance welding was invented in 1877 by Elihu Thomson for joining by spot, seam and projection welding. In the year 1920 Butt welding was developed to join rods and bars to make a chain. In 1940 Tungsten electrode was introduced for fusion welds.
In the year 1948, another gas shielded process of wire electrode introduced. Recently many new ways of joining like friction welding, diffusion welding, ultrasonic welding, and laser welding have developed.
Basics of Welding Principles
A coalescence of metals by heating to a requires temperature with /without pressure application, and with /without filler material. The molten pool is generated with the help of heat source which may be supplied by electricity/ by a gas flame. The high current 10-2000 amperes and low voltage 10-50 volts are produced from the electric arc. The DC (Direct Current) is commonly used but alternate current (AC) may be used for Arc. The total energy production as input is more than the energy requires to produce a joint as there is energy loss in the transfer of the arc. On heating the metal the oxide layer is produced over the metal due to reaction of the atmospheric contamination leading on to make the eld joint brittle and weak.
The arc weld has three basic zones (1) weld/fusion zone (2) Heat zone (3) unaffected zone as per temperature at the welding zone and the surrounding zone. The welding leads to contraction and expansion of the weld metal and this stress can be removed by heat treatment of the whole welded fabrication.
The Damascus sword is the ancient example of a fusion technique where a small iron piece joined and shaped. The metal heated, forged, hammered and pressed together until the tougher sword was produced. The middle-aged canons were the result of forged welding. Nowadays blacksmith uses this forging for chain making.
The largest volume of total welding today is attributed to the Arc welding process. The tiny molten metal transferred from the electrode to the workpiece by alternating or direct current though the electrode holder. The arc is shielded by an inert gas such as argon/ helium with ac/dc current with the inert tungsten electrode. The other type is carbon dioxide as shielded gas with a consumable electrode. Both arc processes produce rapid, tough and protected weld. The hot plasma is another type of arc welding with better energy concentration with a better and stable arc.
Thermochemical or Gas Welding
It was as popular as arc welding but now confined to sheet fabrication. This is a process of fusion where acetylene and oxygen used to produce a controlled and an intense flame and filler wire is added to the joint as cold filler material.
The joint is produced when electrical resistance produces heat which is generated at the interface as in the process of spot, seam and projection welding. The short time weld made with low voltage, high current and a force application to the joint through the two electrodes in resistance welding. The joint strength depends upon the number of spots and size of the welds. The seam is a continuous process where the electric current is pulsed successively to form a series of an overlapping and continuous seam. The flash is another form of resistance welding.
Electron Beam welding
The heat is produced from a high-density electron beam which is being bombarded at the workpiece in the vacuum. The intense heat creates a hole through the joint.
The joining the surfaces without heat with only pressing the two surfaces produce deformation at the joint and joining as in cold butt welding.
The workpiece is joined when one is brought under the load with one of them revolving rapidly and produce heat at the interface until material changed to plastic.
The light energy from the laser once focused on the workpiece fuses the material although in limited places.
It is achieved by clamping the two pieces to be welded between an anvil and a vibrating electrode.
Two plates impacted together under the explosive force lead on to welding.