Evaluation of Periodic Wrinkle during Sheet Press Forming Utilizing Frequency Characteristic of Ultrasonic Wave

This study suggests a novel method to detect wrinkles using the frequency characteristic of reflected ultrasonic wave. The experimental apparatus was manufactured to simulate the press forming. A plate specimen possessing periodic wrinkles in a trapezoidal shape was also prepared to simulate actual wrinkles during the press forming process. These wrinkles affected the reflected wave of ultrasonic wave. The power spectrum of reflected wave at a frequency of 0.8 MHz was changed by the occurrence of wrinkles. The comparison of the frequency characteristics provided obvious difference between wrinkled and flat specimens. As a result, the present work confirmed that the frequency characteristic of reflected wave would detect the formation of wrinkles.