Butt welding (hereinafter referred to as butt welding) uses the thermal resistance of two workpieces to weld together along the whole end face of a class of resistance welding methods at the same time. High productivity and easy automation make it widely available.


Butt welding is divided into resistance butt welding and flash butt welding.
Resistance butt always press two workpiece surfaces, use resistance heating to heat the plastic state, and then quickly apply the forging force to the top (with or without upsetting force, only maintain the welding pressure) to complete the welding. Like spot welding, the contact resistance of resistors depends on the surface condition at the contact surface, temperature and pressure. When the contact resistance is significantly oxidized or other stolen goods, the contact resistance is high. By reducing the contact resistance, increasing the temperature or pressure will increase the effective contact area. At the beginning of welding, the current density at the contact point is very high; the temperature at the back end rises sharply and the contact resistance decreases sharply. When heated to temperature (600 degrees steel, 350 degrees aluminium alloy), the contact resistance completely disappears. The same is true for the heat resistance of the welding heat generated in the resistance welding area. When resistance welding, contact resistance exists for a very short time and produces less than 10-15% of the total heat. But because part of the heat is generated in a narrow area near the contact surface. Therefore, the temperature in this area will rise rapidly and the internal resistance will increase rapidly. Even if the contact resistance disappears completely, the intensity of the heating area is still higher than that of other places.


Flash butt welding can be divided into continuous flash butt welding and flash butt welding preheating. Continuous flash butt welding includes two main stages: phase flash stage and upsetting stage. The flash stage of preheating flash butt welding before the increase of preheating stage. The main function of flash heating workpiece. At this stage, the first power supply makes the two workpieces contact slightly, forming many contact points. The current contacts through the melting point to form the liquid metal connection end face of the beam. Because the current density of liquid beam is too high, the liquid metal beam evaporates excessively and the beam is blasted. With the slow progress of the dynamic fixture, the lintel also continued to produce and blasting. Under the action of electromagnetic force and vapor pressure, liquid metal particles eject from a continuous interface. Form spark jet - flash. At the end of the flash stage, sufficient pressure is applied immediately on the top of the workpiece, and the gap between the lintel fittings decreases rapidly. The blasting stops and enters the forging stage. After blasting the crater, the extrusion of liquid metal and oxide inclusions makes the plastic metal contact tightly, and produces a certain deformation of the plastic joint surface, promotes recrystallization, and forms a strong combination of grains. In flash butt welding process, although the molten metal is heated, it is basically in the plastic state of welding.