Effect of vibration transmission direction in ultrasonic thermoforming on the formability of micro-corrugations

The energy of ultrasonic vibrations has been used in various polymer fabrication processes owing to its rapid and energy-efficient heating capability. This study concerns ultrasonic thermoforming of micro-speaker diaphragms, especially investigating the effect of the direction of vibration transmission to improve the forming accuracy of micro-corrugations; direct and indirect ultrasonic thermoforming processes were compared thereby. Experimental comparison reveals that indirect ultrasonic thermoforming shows better heating capability and formability than direct ultrasonic thermoforming does. This indirect thermoforming was then further investigated to find optimal forming condition, with the aid of response surface analysis. By applying the optimal forming condition, the micro-speaker diaphragm could be successfully fabricated with an excellent forming ratio (> 90%), within 10 seconds cycle time. The sound quality of the developed diaphragm was as good as that of conventional diaphragms fabricated by the conventional thermoforming process, which required more than 100 seconds cycle time.