Butt welding

With butt welding, cross-sections of up to 2000 mm² can be welded. For example, vehicle rims. The contact surfaces must be plane-parallel, well prepared and have smooth ends. The material to be welded is fixed by means of two clamping electrodes. One side is fixed, the other is movable. Now the parts are pressed together and the power is switched on. After a period in which the material is heated, upset pressure (an increase in force) is initiated if necessary and the current is switched off. The material loses length and a compression bulge forms. These factors must be taken into account in the design.

There are two variants of flash butt welding: with preheating and without preheating.

Large surface cross-sections – for example sheet metal parts – are welded without preheating. Compact cross-sections such as rails, shafts and chain links are welded with preheating. The cross-sections here can reach up to 100,000 mm2 and no smooth butt joints are required. Unlike butt welding, the parts are not pressed together with force, but are moved lightly against each other under current. Due to the high contact resistances that occur when the material is touched, the material is heated and pre-flashing of the material occurs. The two ends of the material are heated up as the material is continuously fed and burns off as a result. If the material is heated sufficiently, the force increases and the compression process takes place. Only then is the power switched off. A reheating process can then take place.