Design and analysis of ultrasonic horn for polymer sheet forming

The present work proposes to use ultrasonic vibration energy for polymer sheet forming. Polymer sheets are usually formed by the thermoforming process, in which a polymer sheet is heated and softened in order to be shaped into desired part. In this work, instead of the thermal energy used in the conventional thermoforming process, the energy of ultrasonic vibration was used to soften a polymer sheet. For this purpose, an ultrasonic horn was designed with a number of convex features to be used in the sheet forming. Finite element modal analyses were performed to ensure the desired vibration characteristics: the horn should resonate at a specific frequency and should vibrate along its longitudinal axis. The ultrasonic horn was fabricated based on the results from modal analysis, and then was applied to the thermoforming of a 1.0-mm thick thermoplastic poly-urethane sheet. Considering that this process required only 1.1 s vibration time and 10 s holding time, the proposed ultrasonic sheet forming process is much superior to the conventional thermoforming process in its cycle time.