What is Ultrasonic Welding?
Ultrasonic plastic welding is the joining or reforming of thermoplastics through the use of heat generated from high-frequency mechanical motion. It is accomplished by converting high-frequency electrical energy into high-frequency mechanical motion. That mechanical motion, along with applied force, creates frictional heat at the plastic components' mating surfaces (joint area) so the plastic material will melt and form a molecular bond between the parts. The following drawings illustrate the basic principle of ultrasonic welding.
The basic principle of ultrasonic welding
Step 1 - Parts in fixture
The two thermoplastic parts to be assembled are placed together, one on 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, at distances measured in thousandths of an inch (microns), for a predetermined amount of time called weld time. Through careful part design, this vibratory mechanical energy is directed to limited 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. (Note: Improved joint strength and hermeticity may be achieved by applying a higher force during the hold time. This is accomplished using dual pressure.)
Step 6 - Horn retracts
Once the melted plastic has solidified, the clamping force 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.
Plastics 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.