Classification Based on Type of Welding

 Fusion welding: These processes involve fusion of the base metal to complete the weld. Fusion welds generally  do  not  require  theapplication of pressure and they may be completed with or without the addition of filler material. All the arc welding processes are covered in this category.

Solid state welding:  These are processes in which the two sides of a joint are brought into intimate atomic contact either by mechanical deformation or by atomic diffusion or by a combination of both.

• Cold pressure welding uses mechanical deformation at room temperature.
• Hot pressure welding uses heat to render the metal ductile.
• Friction welding employs rubbing at the interface to generate heat.
• Pressure butt welding used to join bar and sections, end to end using heat generated by electric arc, electric induction or electric resistance across the joint.

• Diffusion welding employs modest deformation, but the temperature and its duration are sufficient to allow atomic diffusion across the interface. The various welding processes are classified depending on the nature of application of these processes.