Filter
Top Products
Dukane Manual Part No. 403-570-01
Page 59
Section 7 - Optimizing Performance
.
Spin Welding Process
The formal denition of spin welding is “An assembly
process in which thermoplastic parts with rotationally–
symmetric mating surfaces are joined together under
pressure using unidirectional circular motion. The heat
generated during the rotational contact melts the plastic in
the heat–affected zone forming a weld upon cooling.” Note
that the parts themselves can be any shape, only the mating
surfaces to be welded need to be circular.
The spin welding process is divided into ve distinct
phases. In Phase I, the rotational friction generates heat.
Frictional heating is intensied with both axial (press
vertical) and joint surface velocities. In Phase II, the
friction results in abrasive forces which strip off surface
roughness, generating wear particles causing the surfaces
of the polymer to begin to melt. As the polymer reaches
its crystalline melting point or glass transition temperature,
it enters Phase III, where heat starts to be generated by
internal friction within the molten region. This continues in
Phase IV, where the temperature of the molten layer remains
relatively constant. Because plastics are poor conductors of
heat, the surface heat is transferred slowly to the interior
and much of it remains localized. At this point, the rotation
is stopped and we enter Phase V where the molten material
is allowed to cool under pressure for a short period called
the Hold Time.
Material Considerations
Materials that can be friction (i.e. vibration) welded can
also be joined with by spin welding. The semicrystalline
thermoplastics are more readily joined using spin welding
than ultrasonics. Using compatible polymers, spin welding
is capable of making reliable hermetic seals. Far–eld
welding is easier with spin welding than with ultrasonic
welding. Additional parts can be entrapped between the
upper and lower pieces during spin welding.
Joining of dissimilar polymers is possible using the spin
weld process although it generally produces lower strength
weld joints. By designing the weld joint with an undercut,
the polymer with the lower melting temperature will ow
into the undercut, creating a mechanical union.