Application of Ultrasonic Vibration to Injection Molding. Experimental Study of the Fluidity of Molding Materials.

The effects of ultrasonic vibration on injection molding were investigated. An ultrasonic injection molding (UIM) machine in which the mold resonated under ultrasonic vibration was developed. The resonance in the mold occurred at n wavelengths, where n=0.5N and N is a positive integer. A transducer was placed on the movable mold through a directional converter of vibration. The fluidity of the molding materials and the molecular orientation of products were evaluated by the UIM machine. This evaluation allowed the improvement of the apparent fluidity of the molding materials compared to the case without ultrasonic vibration. Consequently, the molecular orientation caused by the flow was decreased. Wall slip was observed between the resin and wall surface with ultrasonic vibration in flow visualization experiments. It was found that the fluidity was improved by the action of sound pressure and the reduction of apparent friction between the wall surface in a cavity and the molding material by ultrasonic waves.