Fundamentals of Ultrasonics - PLASTICS


Variations of Joint Designs or Energy Directors

For the design of plastic parts for assembly with ultrasonic energy, many recommendations exist to save time, energy and tooling modifications. The first step for a designer is to determine the most suitable joining technique. The following variations are possible:

  • Ultrasonic Welding

  • Ultrasonic Swaging, Staking, Spot-Welding

  • Ultrasonic Insertion



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Ultrasonic Welding

The molten material builds at the contact area of the energy director between the to be welded parts. The ultrasonic waves are transferred through the part to the joint area. Common "standard" joint designs include:

  • Basic 90 Degree Energy Director

  • 90 Degree Energy Director Step Joint

  • 90 Degree Energy Director Tongue & Groove

  • Herrmann Ultrasonics Mash Joint

  • Double V-Point Tongue & Groove

The recommended process examples listed above can be varied with inserted gaskets or in-molded 2K injection molded gaskets.

Ultrasonic Swaging, Staking, Spot-Welding



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In addition to conventional types of joint design for bonding injection molded plastic parts, ultrasonic welding can be used in a verity of forms to accomplish a mechanical bond when only one part is of thermoplastic material. Common applications include:

  • Swaging, for deforming or bending an area of a plastic piece to trap the other part (of different plastic or other materials). Through swaging, different kinds of plastic parts can be joined with each other or in combination with materials that do not belong to the plastics family. Depending on the application, the bottom of the weld horn must be contoured or structured to enable the plastification and shaping of edges or pins to be swaged to retain the secondary part or insert.

  • Staking, for joining thermoplastic parts with parts of different materials.

  • Spot-welding, for permanently connecting large and bulky parts without an integrated joint design.


Ultrasonic Insertion

Ultrasonic Insertion is a very common technique in Ultrasonic Welding in which metal threaded inserts are embedded into plastic parts. Components that can be ultrasonically inserted include:
  • Threaded inserts or studs
  • Metallic webs or grills (speaker covers, etc.)
  • Permanent magnets
  • Electric contacts
The Weld Horn couples directly with either the insert or the thermoplastic part.
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