WHAT IS ULTRASONIC WELDING?

Ultrasonic welding technology uses high-frequency vibration (ultrasonic) to accurately seal two thermoplastic parts together in sub-second time. Under precise pressure, the connection is sealed in less than 0.2 seconds. 

Ultrasonic waves vibrate 100,000 times per second. This vibration is transmitted to the contact surface that is in direct contact with the plastic part. Since the boundary of the welding area has a large acoustic impedance, high temperature is generated. Plastic is a very poor conductor of heat and cannot emit heat until it changes its state from solid to liquid. With a little pressure applied, this causes the two parts to mix together as if they were a piece of plastic. Once the ultrasonic signal stops, the part will harden again. This is the magic of creating a clean and strong weld between two parts. The strength of the weld is close to the strength of the raw materials formed together in the injection molding process. 

THE BASICS OF ULTRASONIC WELDING

Step 1 - Parts in fixture

The two thermoplastic parts that need to be assembled are placed together, one on the top of the other, in a supportive nest called a fixture.

Step 2 - Horn contact

A titanium or aluminum component called a horn is brought into contact with the upper plastic part.

Step 3 - Pressure applied

A controlled pressure is applied to the parts, clamping them together against the fixture.

Step 4 - Weld time

The horn is vibrated vertically 20,000 (20 kHz) or 40,000 (40 kHz) times per second for a precise amount of time - also called the weld time. The various parts parts are precisely engineered so that the energy is directed to specific points of contact between the two parts.

The mechanical vibrations are transmitted through the thermoplastic materials to the joint interface to create frictional heat. When the temperature at the joint interface reaches the melting point, plastic melts and flows, and the vibration is stopped. This allows the melted plastic to begin cooling.

Step 5 - Hold time

The clamping force is maintained for a predetermined amount of time to allow the parts to fuse as the melted plastic cools and solidifies. This is known as hold time. Improved joint strength and hermetical sealing may be achieved by applying a higher force during the hold time. This is accomplished using dual pressure at various points in the hold time.

Step 6 - Horn retracts

Once the melted plastic has solidified, the clamp is removed and the horn is retracted. The two plastic parts are now joined as if molded together and are removed from the fixture as one part.

Ultrasonic welding for plastic assembly is a fast, clean, efficient, and repeatable process that consumes very little energy. No solvents, adhesives, mechanical fasteners, or other consumables are required, and finished assemblies are strong and clean.