Welding – is the process of obtaining of permanent joint by establishing inter-atomic connections between the welded parts under their local or general heating, plastic deformation or their joint action. Depending on the type of welding energy, they are divided into three classes: thermal, thermomechanical and mechanical.

The thermal class includes the types of welding by means of melting in which thermal energy is used for melting of a metal:

• arc welding – heating by electric arc;
• plasma-arc welding – heating by constricted arc;
• gas welding – heating by gas flame;
• electroslag welding – heating by heat emitted during the passage of electric current through molten electrically conductive slag;
• electric-ray welding – heating by electric ray as a result of directed electron flux attack of the welding zone;
• laser welding – heating by the light ray energy obtained from optical oscillator;
• thermit welding – heating by combustion of thermit flux which contain aluminium and ferric oxide.

The thermomechanical class includes types of welding, in which heat energy and pressure are used:

• contact welding – by use of pressure and heating during the passage of electric current through contact surfaces;
• diffusion welding passes through the mutual diffusion of contact surfaces atoms with prolonged exposure to elevated temperature and slight plastic deformation;
• press welding – heating is carried out by a flame of gases (gas press welding), arc (compression welding), an electroslag process (slag-press welding), induction heating (induction and press welding), termite (thermo-press welding).

The mechanical class includes welding, which is carried out using mechanical energy and pressure:

• ultrasonic welding – pressure is created by ultrasonic oscillations;
• cold welding uses pressure with significant plastic deformation without heating;