Flash butt welding

Flash butt welding is a type of resistance welding without using any filler metal. It is used for joining two metal parts together using heat and force. Each of the two parts to be joined are clamped against an electrode, usually a copper alloy. The electrodes themselves being connected to the secondary side of a transformer. The ends are brought slowly together until they just touch. At this point a high current flows through the touching points, rapidly heating and melting the metal at the points of contact. The molten metal is then expelled by its own rapid expansion. This part of the welding cycle is called the flashing and generally creates a spectacular shower of sparks. Voltage used is generally low (typically between 4 and 20 volts) but the current usually very high, often in the tens of thousands of amps. The heat generated raises the temperature of either side of the joint. Once the temperature is above the forging temperature (typically around 1,250°C for steel) the ends are rapidly pushed together with great force. The high speed expels any remaining molten metal and the high force generates enough pressure at the joint (around 90 megapascals for steel) to 'forge weld' the ends together.