The figure above shows the different types of stake designs.
The
general purpose stake is recommended for studs with a diameter between 1.6 and
4 mm (1/16-5/32 inch). The dome stake is recommended for small studs with a
diameter smaller than 1.6 mm (1/16 inch). The flush stake is used where a flat
surface is required. The hollow stake minimizes sink marks and shrinkage
voids, and is used where the stud has a diameter greater than 4 mm (5/32 inch).
Cold staking
In cold staking, the stud is deformed through the application of high
pressure. Cold flow subjects the stud region to high stresses and consequently
it is only suitable for use with the more malleable plastics.
Heat staking
In heat staking, the compression probe is heated so that less pressure is
required to form a head on the stud , giving lower residual stresses in the
head. This widens the application of staking to a broader spectrum of
thermoplastic materials than is possible with cold staking, including
glass-filled materials. The quality of the joint is dependent on the control
of the processing parameters: temperature, pressure and time. A typical cycle
time lies between 1 and 5 seconds. Heat staking has the advantage that parts
can be disassembled in many cases.
Hot air staking
In thermo-staking or hot air staking, heat is applied to the stud by means of
a stream of superheated air, delivered through a tube which surrounds the
stud. A cold probe is then lowered to compress the stud head.
Ultrasonic staking
In ultrasonic staking, the stud is melted using ultrasonic energy supplied
through a welding horn. During the continued pressure of the horn, the melted
stud material flows into the cavity within the horn to form the required head
design. Cycle times are typically less than two seconds and welds may be
performed with a hand-held welding head.
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