What is main advantage of welding?

Resistance welding is the generation heat by passing current through resistance due to contact between metal surfaces. At the weld zone, small pools are formed of molten steel when high current (1000 to 100,000 A) passes through the metal. Resistance welding methods are generally efficient and produce little pollution. However, their use is limited and can cost a lot. Spot welding can be used to join metal sheets with overlapping thicknesses up to 3 mm. Two electrodes are used simultaneously in spot welding to hold the metal sheets together. The method is highly efficient in energy use, low workpiece deformations, high production rates and easy automation. There are no filler materials required. It is less strong than other welding methods making it suitable for limited applications. It is widely used in automotive manufacturing. Ordinary cars may have hundreds of spot welds that were made by industrial robots. Spot welding stainless can be achieved using shot welding.

World War I led to a surge in welding. Military powers attempted to determine which of several new welding methods would be most effective. British used arc welding extensively, even constructing the ship "Fullagar" using a fully welded hull. As a result, some German aircraft fuselages were built using arc welding. Notable is also the Maurzyce Bridge from Poland (1928), which was the first welded road bridge. The 1920s saw significant advancements in welding technology. Automatic welding was introduced in 1920. It used continuous feed electrode wire. Shielding gas gained much attention as scientists tried to protect welds in the environment from the effects of oxygen or nitrogen. These were the main problems. The solutions included hydrogen, argon, or helium as welding environments. In the tenth century, more advances enabled the welding of reactive materials like magnesium and aluminum. This, along with advances in automatic welding and alternating current, led to a huge expansion of arc welding during the 1930s and into World War II. M/S Carolinian, the first all-welded merchant ship, was launched in 1930.

The history of joining metallics dates back many centuries. Examples of this are found in Europe's Bronze and Iron Ages, as well as the Middle East. Herodotus the ancient Greek historian writes in The Histories of Fifth Century BC that Glaucus of Chios "was one of the first to invent iron welding." Welding was used for the construction of the Iron column of Delhi. It was built in Delhi, India around 310 AD. Its weight was 5.4 tons. Welding can be done with many different energy sources, such as a gas torch (chemical), an electricarc (electrical), a beam, friction, or ultrasound. Welding can be done in open and closed spaces, as well under water and in space. Warnings should be taken when welding.

The equipment is inexpensive and easy to use. It uses the combustion in oxygen of acetylene to produce a flame temperature of 3100°C (5600°F). It is slower than an electric arc because it has a lower concentration of flame. This can cause more residual stresses and distortion. But it allows for easier welding of high alloy steels. An alternative process is called oxyfuel-cutting. This allows for the cutting of metals. These processes employ a welding power source to create and maintain an electrical arc between the electrode and the base material in order to melt the metals at their welding point. They can be used with either direct current (DC), or alternating currents (AC), as well as consumable or non-consumable electrodes. The weld area can be protected with a semi-inert or inert gas known as a shielding, and sometimes a filler material.