Feasibility Study on Neck Defect Inspection Technique for Press-formed Products by Using Structural Vibration Measurement

Abstract

If defects occur in a press-formed article, the mechanical properties change and the vibration characteristics may change. In particular, it is not difficult to prove a crack defect on the basis of structural vibration measurement. The purpose of this study was to develop a defect inspection technique that can quickly determine whether the neck of a press-formed article is defective by measuring the simple structural vibration of the neck, which indicates a defect of a fine press-molded product, rather than a crack. The press moldings used in the experiment were automobile front door panels; the structural vibration of the front door panels was measured with an impact hammer test. The frequency response function measured by the impact hammer test was obtained by the vibration frequency analysis program LMS Test.lab. With this method, we compared and analyzed whether there is a significant difference from a front door panel in which a defect is generated, on the basis of the natural frequency dispersion that many normal front door panels without defects have in the corresponding mode. A total of 10 normal front door panels and two necked defective front door panels were tested. The observable mode frequencies of the normal front door panel and the necked front door panel were shown in terms of sigma levels to determine if there is a significant natural frequency difference. In addition, normal door panels without necks were divided into two groups with a difference of approximately 9 months in production. SPSS software was used for the statistical validation t-test. From this experiment, the results will become the basic data of a test method to detect the defective necks of press-formed parts through natural frequency measurement.