Definitions

Metal
Metal are kinds of chemical elements that are composed of atoms. Atom is a particle that is considered to be an irreducible part of a specified system. Metal can be divided into two groups, pure metal and alloy. Pure metals, such as gold, sliver, are not often been used in engineering fields. Metal Alloy is most common used in engineering fields, such as steel alloy, aluminum or bronze and so on. Metals are widely used in many fields because of their specific characteristics can fit different requirements. For example, steel structures are widely used in architectures and buildings because of their strength and economic.

Welding
The technology of using heat, pressure, and fuse to form a permanent joint of different parts of materials is called welding process. Welding is used to create a solid and light joint between same or different materials, such as steel structure of automobile, or the structure of pressure vessels such as a ship or a petroleum tank. The strengths of welding process are its efficiency and it’s economic. For example, a 50 meters steel seam can be complete in 50 minutes by using welding process. The weaknesses of welding process are hazardous substances and radioactivity, such as, carbon monoxide and arc, which are created during the welding process. Welding is like forging because both of them need to heat material to or close to the temperature of melting point. Welding is a kind of heating process.