Ultrasonic Horns for Joining of Thermoplastics

Ultrasonic joining is a process whereby high frequency vibrations are imparted into two thermoplastic materials. The vehicle for importing the energy into the plastics is a resonant metal mass, commonly termed a horn. A booster horn usually amplifies the mechanical output from the ultrasonic system. This amplitude increase is a variable and depends upon the horn type and plastic assembly utilized. Various metals used for horns are selected based upon their acoustical properties. Titanium and aluminum exhibit excellent properties, whereas steel has a relatively high acoustic impedance and may be inefficient at ultrasonic frequencies. The limitations of the horn are physical size as well as material selected. Ganged horns may be used to increase the welding area beyond the limitations of a single horn. Replaceable horn tips may be utilized when joining reinforced plastics that may cause considerable wear on the horn surface.