Ultrasonic molds are designed for use with ultrasonic plastic welding machines, with the purpose of welding plastic products. Due to varying applications and welding materials, the size of the welds can differ, and so can the specifications of the machines. Their output power ranges from manual welding.

Two primary parameters of ultrasonic molds: ultrasonic frequency and amplitude.

Frequency: F ≥ 20 kHz

Power Density: p = Emitted Power (W) / Emitted Area (cm²); typically, p ≥ 0.3 W/cm².

Ultrasonic waves propagating through liquids can clean dirt from the surface of objects, which can be explained by the "cavitation" phenomenon.

When the sound pressure of ultrasound propagating in a liquid reaches one atmosphere, its power density is 0.35 W/cm2. At this point, the peak sound pressure of the ultrasound can reach a vacuum or negative pressure; however, there is actually no negative pressure present. Therefore, it generates a significant pressure in the liquid, pulling the liquid molecules apart to form cavities—hollow cavitation nuclei.

This cavity is very close to a vacuum, and it ruptures when the ultrasonic pressure reverses to its limit. The intense shockwave generated from the rupture knocks dirt off the surface of the object. This phenomenon of shockwaves produced by the bursting of countless tiny cavitation bubbles is called "cavitation."