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Ultrasonic staking

Ultrasonic staking is an assembly method in which the controlled

melting and reforming of a plastic stud is used to capture or

lock two components together. This method employs the use of

a plastic stud on one part, which protrudes through a hole or slot

on the second part. The vibrational energy applied by the

ultrasonic horn is used to melt the plastic; the plastic is deformed

by pressure applied to the staking horn. After deforming, the

plastic quickly cools in its new position, locking the two parts

together.

Ultrasonic staking offers several advantages, including short

cycle times, good repeatability and control, tight locking, and

the ability to form multiple stakes at one time. This has been

proven as an acceptable method for joining parts manufactured

from Eastman

™

polymers to parts manufactured from other

materials, such as steel.

There are several acceptable ultrasonic horn head forms. Typical

dimensions and designs are shown in Figure 33.

Heat staking

Heat staking is similar to ultrasonic staking, offering several of

the same advantages. Heat staking has been shown to provide

equal or greater strength compared to ultrasonic staking when

proper staking guidelines are followed (Figure 33).

It is best to “dial-in” optimized conditions for each individual

application. A good starting temperature for Eastar

™

copolyesters

and DuraStar

™

polymers is 260°C (500°F). Raise the temperature

gradually until the polymer begins to stick to the horn, then

back off by 6°–8°C (10°–15°F). This is the optimum horn

temperature. The object is to melt the plastic post tips quickly

without burning the material.

The optimum pressure should also be “dialed-in.” Begin with

low pressure, gradually increasing until a complete and properly

shaped head is formed.

Figure 33 Ultrasonic/heat-staking methods

Welding similar materials

Ultrasonic and heat staking should be limited to applications

where parts made of Eastar

™

copolyesters and DuraStar

™

polymers are staked to parts composed of other materials.

We have found that when staking two Eastar

™

copolyesters or

two DuraStar

™

polymers together, a slight melt interface forms

where the deformed head pushes down against the mating

piece. This can form “melt microcracks,” which can propagate

under loading, forming a brittle joint. For best results, limit heat

and ultrasonic staking to applications in which the plastics have

a melting temperature difference of at least 22°C (40°F). We

suggest using alternative joining methods (permanent snap ﬁts,

ultrasonic welding with shear joints, hot plate welding, screws,

inserts, adhesives, etc.) in this situation.

Nonthermoplastic plate

2.1D

0.5D

Staking horn

Radius

1.6D

0.5D

Radius

at stud

base

required

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