Influence of wrinkles in sheet metal forming on ultrasonic reflection characteristics of angled beam

Abstract

In this paper, the relationships between wrinkles in sheet press forming and the ultrasonic reflection characteristics of an angled beam are shown. An angled probe was used assuming a case in which a vertical probe cannot be placed directly above defects. The wrinkles were evaluated using an apparatus that reproduced the die–workpiece contact situation of press forming. Model specimens used in the experiments had trapezoidal wrinkles similar to the wrinkle shape in press forming. The workpiece was sandwiched by dies in the apparatus. The apparatus was connected to an ultrasonic flaw detector. The relationship between the wrinkle shape and the irradiation position of ultrasonic waves was accurately obtained using the apparatus. Wrinkling was detected from the change in reflection intensity, i.e., the maximum amplitude of reflected waves. The reflection intensity varied with the wrinkle shape for a single wrinkle or periodic wrinkle with a wrinkle wavelength of 8 mm or more. This tendency was also observed for a vertical probe. The wrinkle evaluation using the angled probe was as effective as that using a vertical probe.