General Design Principles for DuPont Engineering Polymers - Module

• After a certain period (controlled by a timer) the
clutch disengages, but pressure continues to be
applied for a further period (depending on the type
of plastic).
• The spindle is raised and the welded article ejected
(or the turntable switched to the next position).
In suitable cases, a tooth crown may be employed to
grip the part (see Figure 11.16). Alternatively,
projections on the part such as ribs, pins, etc., can be
employed for driving, because the spindle is not
engaged until after the part has been gripped.
Figure 11.05 shows an example of a part with four
ribs gripped by claws. Thin-walled parts need a bead a
to ensure even pressure around the entire weld circumference.
The claws do not, in fact, apply any pressure,
but transmit the welding torque.
Figure 11.05 Drill spindle with claws
a
It is sometimes not possible to use this method. For
instance, the cap with a tube at the side, shown in
Figure 11.06, must be fitted by hand into the top jig
before the spindle is lowered. This process cannot of
course easily be made automatic.
Another possibility is for the spindle to be kept
stationary, as shown in Figure 11.07, and for the
bottom jig to be placed on top of the compressed-air
cylinder. This simplifies the mechanical construction,
but it is impossible to fit a turntable and thus automate
the process.
One of the disadvantages of the methods described,
compared to inertia machines, is that more powerful
motors are required, especially for large diameters and
joint areas.
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Figure 11.06 Special drill spindle
Figure 11.07 Pivot welding with stationary spindle