Process and apparatus for friction welding

A friction welding apparatus comprising a first holder to hold a first work piece, a second holder to hold a second work piece, an energy adjustment arrangement for imparting motion and thereby kinetic energy to the first work piece relative to the second work piece, a force applying arrangement for applying a force to move one or both of the first and second work pieces towards each other to create an upset length in the work pieces, characterised by a measuring arrangement for measuring the rate of motion of the first work piece relative to the second work piece, a processing arrangement for determining a predicted final upset length from the aforesaid measured rate of relative motion and the force, and for comparing the predicted final upset length with a desired final upset length, wherein the processing arrangement is configured to control the energy adjustment arrangement to adjust the aforesaid relative kinetic energy to achieve substantially desired upset length.