An ultrasonic welding process uses high-frequency ultrasonic acoustic vibrations to create a solid-state weld between two materials. Mating parts are held together under pressure and subjected to ultrasonic vibrations usually in the range of 20-40 kHz. The vibrations generate frictional heat at the interface of the parts, which causes the material to soften or melt and form a bond. The process is efficient and a permanent bond is typically formed in less than 1 second.

Ultrasonic welding is commonly used in a variety of industries including automotive, medical, and electronics manufacturing, for tasks such as assembling plastic components, sealing containers, or joining wiring.

However, ultrasonic welding does have limitations. It is best suited for small to medium-sized parts and may not be as effective for larger, more complex assemblies. It also requires specific joint designs to direct the ultrasonic energy properly, and the materials being welded must be compatible with the process.

Most ultrasonic welding applications require custom tooling in the form of a nest (holding fixture to align the mating parts during welding) and a horn (the acoustically tuned tool that ultimately transfers the energy from the welder to a workpiece).  While this combination is generally less expensive than other types of custom tooling, it is significant enough to mention here, and can take many weeks to produce.

While ultrasonic welding is a precise and efficient method for joining materials, its effectiveness can depend on the specific application, material compatibility, and the skill level of the operators. Some of the pros and cons of the process are detailed below.

Pros:

• The process typically takes less than a second, making it ideal for high-volume production.
• It can join a wide range of thermoplastics.
• Ultrasonic welding is an energy efficient process because it generates heat directly at the material's interface.
• There are no adhesives, solvents, or other consumables involved in the process.

Cons:

• The method is best suited for small to medium-sized parts and requires specific joint designs to direct the ultrasonic energy properly.
• Careful planning during the design phase is required to preserve part aesthetics, especially when "A" surfaces are concerned.
• Not all materials are suitable for ultrasonic welding, and it may not be effective for certain combinations of materials.

We would be happy to discuss ultrasonic welding's suitability for your application.

A well thought-out and implemented joint design is the foundation all successful welds are built on. The configuration of the components to be joined determines how the energy will be directed, how the parts will align, and ultimately, the strength and appearance of the resultant weld. Most joint designs incorporate an energy director - a strategically placed (usually triangular) feature that concentrates the ultrasonic energy:

• Butt Joint: This is the most basic design where two parts are aligned flat against each other. Energy is directed to the interface and creates melting at the contact point. In general, butt joints don't typically utilize an energy director due to their flat alignment. If deemed necessary, a slight energy director can be integrated on one of the surfaces to help initiate the melting process.
• Tongue and Groove Joint: In this design, a protruding feature (tongue) on one part fits snugly into a depression (groove) on the mating part, channeling the energy toward the joint interface and aiding in alignment. To ensure the initiation of the melting process at the joint's interface, the energy director can often be integrated into the groove or on the tip of the tongue.
• Shear Joint: Here, one part overlays the other, directing the ultrasonic energy into the interface between the overlapping sections. To instigate melting at the joint's interface, the energy director is commonly located at the edge of one or both overlapping parts.
• Step Joint: Featuring a design where one part has a step that meshes into a corresponding step in the other part, it offers both a larger weld area and an aid in alignment. The top of the step in one of the parts is often the location of the energy director. As the steps of the two components come together, this ensures that the melting process is initiated right at the interface.

Butt Joint	Tongue and Groove Joint
Shear Joint	Step Joint

When an ultrasonic welding joint is designed correctly, ultrasonic energy is concentrated where it's needed most, guaranteeing the initiation of the melting process and the formation of a robust, consistent weld. While it's important to identify and incorporate the right joint early in the design phase, we have been very successful retroactively incorporating joints into existing parts.

If you're struggling to get the welding results you need, or if you're still trying to determine the best joint for your parts, please give us a call to discuss - (416) 292-7765.