The Flash butt welding machine can be divided into continous flash butt welding machine & preheating flash butt welding machine.

Continuous flash butt welding consists of two main phases: flashing & upsetting.
Preheating flash butt welding flash just increases additional warm-up phase before flashing.

The main role of the flash is to heat workpiece. At this stage, firstly power on, let two surfaces of workpiece contact slightly to form many contact points. When the current goes through,  the contact points melted and become the liquid metal lintel to connect surfaces. Since the liquid lintel has high density current, so make the liquid metal evaporated & lintel exploded. With the slow advance of the movable jaw, lintels continue to produce and explode. Under the action of vapor pressure and electromagnetic force, the liquid metal particles continuously ejected from joints, forming spark rapids - flash.