Ultrasonic staking is an excellent method of joining assemblies that are large or comprised of dissimilar materials. The typical AMS ultrasonic staking machine includes a number of important features that are essential to achieving consistent, repeatable welds cycle after cycle.
Using ultrasonic welding technology to stake plastic bosses is often cost prohibitive. However, AMS machines utilize the common sense approach of sequencing so that a few power supplies can operate a large number of actuators. This approach brings the cost of ultrasonics in line with expectations for staking applications. Additionally, AMS uses solid, wear resistant ultrasonic horns that last dramatically longer than carbide coated titanium horns. This further improves the cost effectiveness of ultrasonic staking.
30 kHz Ultrasonic Staking Machine for Washer/Dryer Door
The 30 kHz staking machine shown in the pictures above processed a three piece washer/dryer door assembly that included 15 hollow bosses. 30 kHz was chosen to protect the Class A surface from weld read-through often experienced with 20 kHz systems and for its powerful ability to weld and form fully chromed bosses. Thermal and hot-air staking cannot form chromed bosses.
One dedicated actuator (with ultrasonic stack) is positioned over each boss. Each actuator includes a mechanical stop, individual pressure regulator, and weld by distance capability. This approach provides maximum weld repeatability and ensures that bosses are fully welded and formed, but not over-welded.
Rigid part hold-down clamps provide a fully compressed and tight after-weld assembly. Other features, such as the programmed ability to sequence from fewer ultrasonic power supplies thus decreasing costly spares, make for a reliable machine that exemplifies the knowledgeable approach AMS applies to each application.
Ultrasonic Staking with Fully Chromed Bosses
Image of ultrasonically staked, chrome plated hollow boss. The gap seen is due to a drain path slot in the original boss (i.e., prior to ultrasonically staking) which is required in the chroming process.
The mechanical scrubbing action in ultrasonic welding is able to penetrate through the chromed boss. Thus, it is not necessary to mask each boss prior to the chroming process as is required for thermal or hot air staking. This saves significant costs in the chroming process.
Special Wear Resistant Horns
Titanium ultrasonic horns often wear faster than desired when used for ultrasonic staking, especially against chromed bosses. This leads to high consumable tooling and tool change costs. Plus, worn horns cannot form the plastic boss correctly.
Traditionally, carbide coatings were applied to horns or threaded tips to increase their wear resistance. However, carbide coatings are expensive and tips are unreliable in production. Today, AMS uses affordable, solid, wear restant horns that last dramatically longer than carbide coated horns.
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