Ultrasonic waves are effective in examining the contact state between the die and the material during sheet metal forming. In this study, ultrasonic measurements were performed on wrinkles and contaminant in press forming. A model specimen simulating wrinkles was used in the measurement of wrinkles. The contaminant was placed on a flat specimen and sandwiched between dies in the ultrasonic measurement of contaminant. The reflection intensity of 2.25 MHz ultrasonic waves irradiated to the convex part of the wrinkle decreased as the number of wrinkles with a wrinkle wavelength of 4 mm increased. However, the ultrasonic reflection intensity at the convex part of the wrinkles was not related to the number of wrinkles in 5 MHz ultrasonic waves. The contaminant changed the reflection characteristics of ultrasonic waves. The frequency characteristics of the reflected wave changed markedly at a specific frequency because of wrinkling and contamination. 2.25 MHz and 5 MHz ultrasonic waves were able to detect contaminants of the size occurring at the production site and wrinkles with a wrinkle height of 0.01 mm not only from the ultrasonic reflection intensity but also from the frequency characteristics.
