Basic principles and classification of welding

Update:06 Nov 2020

Welding is a process and connection method in which two […]

Welding is a process and connection method in which two identical or different workpieces are joined together by heating, pressing or combining. Welding is not only widely used in metals, but also in non-metals. According to the state and process characteristics of the metal during the welding process, welding methods can be divided into fusion welding, pressure welding and fusion welding. This is a welding method that uses local heating to heat the metal in the molten state. Three categories in welding. Under heating conditions, the kinetic energy of metal atoms is enhanced and the diffusion between atoms is promoted.
When the welded metal is heated to a molten state to form a liquid molten pool, the atoms can completely diffuse and make close contact to cool and solidify. A strong welded joint can be formed. Common gas welding, arc welding, electroslag welding, gas shielded welding, plasma arc welding, etc. belong to the category of fusion welding.
Pressure welding, as the name suggests, is a method of using welding to apply a certain pressure to complete welding. There are two forms of this welding. One is to heat the contact part of the weld metal to a plastic state or a partial melting state, and then apply a certain pressure to make the metal atoms combine with each other to form a solid welded joint. Such as forging welding, contact welding, friction welding, air pressure welding, etc. are all pressure welding methods of this type. Secondly, without heating, apply sufficient pressure on the contact surface of the weld metal, and use the plastic deformation caused by the pressure to bring the atoms close to each other to obtain a solid extrusion joint. This pressure welding method includes cold pressure welding and explosion Welding etc.
Brazing is a method in which solder is melted and has a lower melting point than solder metal to a liquid state, and then fills the gap between the solder metal joints. During the welding process, the weld metal is in a solid state, and the workpiece is only properly heated without pressure, and only depends on the diffusion of atoms between the liquid metal and the solid metal to form a solid welded joint. Brazing is an ancient permanent metal welding process, but the welding mechanism of brazing metal is different from fusion welding and pressure welding. It has some special properties and still occupies a certain position in modern welding technology. Commonly used brazing methods include brazing iron, flame brazing and induction brazing.