TWI Frequently asked question
by Steve Westgate
Flash welding is an electrical resistance based butt welding process used for joining components end-to-end across the full joint area. A range of section sizes and complex shapes can be joined (for example from bicycle wheel rimsto railway rails). The parts to be joined are clamped and brought together slowly while a flashing voltage is applied. The process can be manual, but most welding machines are automatic or semi-automatic.
Where small contacts are made between the components, there is a high current density and the material resistance heats, melts and blows out of the joint in a shower of melted particles, giving the characteristic flashing action.This flashing progressively introduces heating and a softened zone at the component ends, while eliminating oxides and contaminants from the interface. After a pre-set 'burn-off' length of the parent material, a forge force is appliedto the parts to consolidate the joint. This produces a forge butt weld with no melted metal remaining in the joint.
