In the joining processes described thus far, the energy required for welding (typically
chemical, electrical, or ultrasonic energy) is supplied from external sources. In
friction welding (FRW), the heat required for welding is generated through (as the
name implies) friction at the interface of the two components being joined. You can
demonstrate the significant rise in temperature caused by friction by rubbing your
hands together or by sliding down a rope rapidly.
In friction welding, developed in the 1940s, one of the workpiece components
remains stationary while the other is placed in a chuck or collet and rotated at a
high constant speed. The two members to be joined are then brought into contact
under an axial force (Fig. 31.3). The surface speed of the rotating parts may be as
high as 900 m/min. After sufficient contact is established, the rotating member is
brought to a quick stop (so that the weld is not destroyed by shearing) while the
axial force is increased. Oxides and other contaminants at the interface are removed
by the radially outward movement of the hot metal at the interface.
The rotating member must be clamped securely to the chuck or collet to resist
both torque and axial forces without slipping. The pressure at the interface and the
resulting friction produce sufficient heat for a strong joint to form.
The weld zone usually is confined to a narrow region; its size depends on the
following parameters:
° Amount of heat generated.
° Thermal conductivity of the materials.
° Mechanical properties of the materials being joined at elevated temperatures.