Ultrasonic staking is an assembly method that uses the controlled melting and reforming of a plastic stud or boss to capture or lock another component of an assembly in place. The plastic stud protrudes through a hole in the component to be locked in place. High frequency ultrasonic activity from the horn is imparted to the top of the stud, which melts and fills the volume of the horn cavity to produce a head, locking the component in place. The progressive melting of plastic under continuous but generally light pressure forms the head.
The advantages of ultrasonic staking include:
• Short cycle time (generally less than one second)
• Tight assemblies with virtually no tendency for recovery (memory)
• Minimal stress in the formed plastic
• The elimination of consumables such as screws and rivets.
• The ability to perform multiple stakes with one horn
• Repeatability and control over the process (consistent results)
• Design simplicity
In many cases, more than one stud may be staked in a single operation. The feasibility of multiple staking is determined by the abiity to design a horn that will function properly. The horn used for multiple staking can be half-wavelength or composite in design. If the studs are on the same
plane and within 1/2 inch (12.7 mm) of each other, a half-wave horn is recommended. Large parts having studs widely spaced on the same
plane would require a full-wave composite horn to provide the necessary amplitude for staking.
Two methods are recommended for staking, depending upon the material and staking requirements: the conventional method, which is most frequently used, and the high-pressure method. Both methods of staking require the stud to be properly located and rigidly supported directly below to ensure correct alignment with the horn cavity, and that energy will be expended at the horn/stud interface rather than exciting the entire plastic assembly and fixture.