Friction Welding (FRW)

Friction Welding (FRW)
Produces a weld by simultaneously applying
compressive force and relative motion (usually rotation)
between the faying surfaces. Heat is produced as the
faying surfaces rub together. However, the process is
considered “solid-state” because melting generally does
not occur. The compressive force causes plastic flow
(displacement), expelling material from the joint. The
expelled material is called “flash”. Filler metal, flux and
shielding gas are not required.
Figures 23.1, 23.4, 23.5, 23.6 and 23.7 illustrate variations of
the process.

Energy Input Methods
Direct Drive Welding (conventional) - One workpiece is
restrained while the other is attached directly to a motor
drive unit.
Inertia Drive Welding (flywheel) - One workpiece is
restrained and the other is attached to a flywheel.
Note: Flywheels are devices used to store kinetic energy.
For instance, a small motor can be used to rotate a
relatively large and heavy wheel. Once the wheel is at full
speed, the energy stored within it can be used to perform
work that the small motor is not capable of doing by itself.

Types of Relative Motion
Most friction welding is performed by holding one of the
two workpieces stationary while the other is rotated
about an axis of symmetry with the faying surfaces
perpendicular to that axis. (See figures 23.1 and 23.4.)
Other types of motion include:
Radial - figure 23.5
Orbital - figure 23.6
Friction - figure 23.7A
Angular Reciprocating - figure 23.7B
Linear Reciprocating - figure 23.7C

Process Characterization
2 Main Mechanisms (fig. 23.2 & 23.3):
Friction Stage
Forging Stage
Primary Process Variables:
Speed
Pressure
Time

Friction Welding Advantages
No filler metal needed.
Flux and shielding gas not required.
Environmentally clean (no arc, sparks, smoke or fumes).
Surface cleanliness not as critical as some processes.
Narrow heat-affected zone (HAZ)
Suitable for most materials and many dissimilar
combinations.
Less operator skill required.
Good for mass production. (drill bits)
Rapid process.

Friction Welding Limitations
One workpiece must have an axis of symmetry that it
can be rotated about.
Preparation and alignment are critical.
High equipment and tooling costs.
Some materials cannot be friction welded.
Special machines required for parts longer than 3-foot.
Process turns the grain direction 90º creating potential
for preferential corrosion.
• Source (all slides) - AWS Handbook, Volume 2, eighth edition.