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.
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
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
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.
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.