Quantitative analysis of surface deflections in the automobile exterior panel based on a curvature-deviation method

Abstract

A major problem with the evaluation of surface deflection is that panels are evaluated manually and to a great extent subjectivity is involved. For further study on surface deflections such as process optimization, it is necessary to evaluate the defect objectively and quantitatively. In this paper, quantitative analysis of surface deflections in the automobile exterior panel is carried out based on a curvature-deviation method. The curvature-deviation method uses the deviation-based indicators to quantify the surface deflection and uses the local curvature information to filter defect points in evaluation algorithm. In order to verify the effectiveness of the proposed evaluation method, sample panels with a door handle feature are stamped and measured in experiment. The sample panels are made of different materials and are formed under various blank holder forces. A stylus instrument is used to measure eight representative sections in the sample panel. The measurement result is analyzed in a program based on the curvature-deviation method. We also use the oil stoning method to make a subjective evaluation on surface deflection in the sample panel. By analyzing some verification curves and comparing the evaluation results based on the curvature-deviation method with the experimental oil stoning results, it is verified that the proposed curvature-deviation method can analyze the surface deflection accurately and has a good consistency with the stoning-based subjective evaluation method. In addition, the proposed method is applied to analyze the critical values of surface deflection and the influence of blank holder force on surface deflection. The proposed method to quantify surface deflections is beneficial to process optimization, material selection and tool design for automobile exterior panels.