disclosed is an apparatus 10 and method of ultrasonic injection molding a plastic part including : providing plastic pellets 12 ; passing the pellets into a defined space 14 in an ultrasonic horn apparatus 16 ; applying ultrasonic energy to the horn thereby permitting flow of the melted plastic ; applying a force to a plunger 18 which forces the melted plastic into a mold 24 of a desired shape ; and recovering the desired part .