Ultrasonic welding
- Permanent, sealed joint
- No extra fasteners or cure time
- Parts cannot be opened without damage
Secondary operation
Ultrasonic Welding of Molded Plastic Parts: Joint Design and Resin Fit
Ultrasonic welding uses high frequency vibration to melt a small joint between two molded parts. The joint fuses in seconds with no adhesive, screws, or cure time.
How it works
Friction heat at the joint, not the whole part
Ultrasonic welding is a common way to close housings and join molded halves.
A horn presses the parts together and vibrates at ultrasonic frequency. Friction at a small feature called an energy director melts a thin layer of resin, which flows and solidifies into a weld once the vibration stops.
NetProto offers ultrasonic welding as a secondary operation, so the joint design is reviewed with the molded parts during DFM rather than after the tool is built.
Fit check
What welds well and what needs a closer look
Qualitative guidance. The joint is confirmed in DFM review.
| Factor | Tends to weld well | Needs a closer look |
|---|---|---|
| Resin family | Amorphous resins such as ABS and polycarbonate | Semi-crystalline resins such as nylon and acetal |
| Resin pairing | Same resin on both parts | Dissimilar resins |
| Joint | Energy director or shear joint designed in | Flat faces with no joint feature |
| Moisture | Dried, stable parts | Hygroscopic resins that absorb water |
Design notes
Design the joint into the molded parts
Weld quality is decided when the parts are designed, not at the welder.
Add an energy director or shear joint on the mating edge
Keep the horn contact face flat and close to the joint
Leave space around the joint for flash, or add a flash trap
Keep fragile features and electronics away from the joint area
Side by side
Ultrasonic welding versus snap fits
Both avoid adhesives. Serviceability usually decides.
Snap fits
- Can be designed to open for service
- No welding step after molding
- Seal needs a gasket or overmold
Continue exploring
Related guides
Sibling processes and supporting references.
Processes hub
All specialty processes and secondary operations.
Processes hubPad printing
Ink transferred by a silicone pad onto curved and recessed surfaces.
Pad printingHot stamping
Heated die and foil for metallic or solid color marks.
Hot stampingSecondary operations
Every post mold operation quoted with the part.
Secondary operationsUltrasonic welding vs adhesive
Choosing a joint for molded halves.
Ultrasonic welding vs adhesiveAssembly features
Locators, snaps, and joints designed into the part.
Assembly featuresFAQ
Common questions
Can ultrasonic welding make a watertight joint?
It can, when the joint is designed for sealing and the resins weld well. Sealing requirements should be stated in the quote so the joint is reviewed in DFM.
What should I send to quote a welded assembly?
Send CAD for both parts, the resin for each, and any sealing or strength requirement. List ultrasonic welding as a secondary operation in the quote request.
Next step
Quote the molded parts and the weld together
Upload CAD and list the operation in your quote request. NetProto manufacturing is ISO 9001 certified.