Friction welding is a solid state welding process which produces
coalescence of materials by the heat obtained from mechanically-induced
sliding motion between rubbing surfaces. The work parts are held
together under pressure. This process usually involves the rotating of
one part against another to generate frictional heat at the junction.
When a suitable high temperature has keen reached, rotational notion
ceases. Additional pressure is applied and coalescence occurs.
There are two process variations:
In the original process, one
part is held stationary and the other part is rotated by a motor which
maintains an essentially constant rotational speed. The two parts are
brought in contact under pressure for a specified period of time with a
specific pressure. Rotating power is disengaged from the rotating piece
and the pressure is increased. When the rotating piece stops, the weld
is completed. This process can be accurately controlled when speed,
pressure, and time are closely regulated.
The other variation is inertia welding. A flywheel is revolved by
a motor until a preset speed is reached. It, in turn, rotates one of
the pieces to be welded. The motor is disengaged from the flywheel and
the other part to be welded is brought in contact under pressure with
the rotating piece. During the predetermined time during which the
rotational speed of the part is reduced, the flywheel is brought to an
immediate stop. Additional pressure is provided to complete the weld.
Friction Welding Video
Both methods utilize frictional heat and produce welds of similar
quality. Slightly better control is claimed with the original process.
The two methods are similar, offer the same welding advantages, and are
shown by figure 10-79 below.
There are three important factors involved:
The rotational speed which is related to the material to be welded and the diameter of the weld at the interface.
The pressure between the two parts to be welded. Pressure changes
during the weld sequence. At the start, pressure is very low, but is
increased to create the frictional heat. When the rotation is stopped,
pressure is rapidly increased so forging takes place immediately before
or after rotation is stopped.
The welding time is related to the shape and the type of metal
and the surface area. It is normally a matter of a few seconds. The
actual operation of the machine is automatic. It is controlled by a
sequence controller, which can be set according to the weld schedule
established for the parts to be joined.
Normally, one of the parts to be welded is
round in cross section. This is not an absolute necessity. Visual
inspection of weld quality can be based on the flash, which occurs
around the outside perimeter of the weld. This flash will usually extend
beyond the outside diameter of the parts and will curl around back
toward the part but will have the joint extending beyond the outside
diameter of the part.
If the flash sticks out relatively straight from the joint, it
indicates that the welding time was was too short, the pressure was too
low, or the speed too high. These joints may crack.
If the flash curls too far back on the outside diameter, it
indicates that the time was too long and the pressure was too high.
Between these extremes is the correct flash shape. The flash is normally removed after welding.
Friction Welding Process - Figure 10-79
Time for heating
Time for braking
Time for forging
Types of Friction Welding
Spin Welding Video
Spin welding involves a rotating chuck along with a flywheel. After reaching the required speed the motor disengages with the flywheel.
Linear Friction Welding
Linear Friction Welding Video
Linear Friction Welding
In linear friction welding an oscillating chuck is used. It is applied to non-round shapes as compared to spin welding. The material welded has to have high shear strength.
Friction surfacing is a surface coating process. The coating material is Mechtrode, which is rotated under pressure over the substrate.
Friction Stir Welding
Friction Stir Welding Diagram
Friction stir welding is a cylindrical shouldered tool with a profiled probe. A pin or nib is used. Friction is created between the metal being worked, the nib and the shoulder.
There are a wide variety of metals that can be joined. The process can also be used to join different metals.
Can produce high quality welds in a short cycle time.
No filler metal is required and flux is not used.
The process is capable of welding most of the common metals. It
can also be used to join many combinations of dissimilar metals.
Friction welding requires relatively expensive apparatus similar to a
Easy to operate equipment
Not time consuming
Low levels of oxide films and surface impurities
When compared to resistance butt welding creates better welds at lower cost and higher speed, lower levels of electric current are required
Small heat affected zone when comparing the process to conventional flash welding.
When compared to flash butt welding, less shortening of the component.
No need to use gas, filler metal or flux. No slag that can cause weld imperfections.
Process limited to angular and flat butt welds.
Only used for smaller parts.
Complicated when used for tube welding.
Hard to remove flash when working with high carbon steel.
Requires a heavy rigid machine in order to create high thrust pressure.