DETECTION AND CHARACTERIZATION OF SURFACE CRACKING IN SHEET METAL HEMMING USING OPTICAL METHOD

摘要

A new method and optical system have been developed to detect crack initiation during bending and hemming, and to characterize the surface quality on the bent/hemmed region. To detect the initiation of cracking during hemming, the cumulative lengths of micro-cracks are plotted against the total numbers of micro-cracks. The maximum number of micro-cracks is used to detect the initiation of cracking as the micro-cracks merge to form macro-cracks. The average length of the micro-cracks from each captured image of the hemline surface is used as an index for surface quality evaluation. Experimental results on the hemmed surface of an AA6111-T4 sheet demonstrate the validity of the proposed method. Furthermore, the average lengths of micro-cracks corresponding to cracking are found to be nearly constant, regardless of hemming process conditions.