A novel testing method to evaluate edge formability nondestructively with eddy current

Abstract

Eddy current (EC) testing is one of the most extensively used NDE techniques in the automotive industry for automatic in-line inspection of ferrous materials such as advanced high strength steels (AHSS). In addition, shearing is a very common forming operation in the automotive industry. With the increase of shearing clearance, the sheared-edge experiences significant work-hardening that normally decreases the formability of the sheared edge. This paper introduces a novel and real-time monitoring NDE method based on the EC sensor to characterize variations in shear edge quality for two different grade advanced high strength steels, DP780 and 980GEN3. The developed NDE method was applied to scan the edges sheared at various clearances between 5 and 25% of the material thickness. The NDE signal received was correlated with pre-straining introduced during the shearing process at various clearances. Microhardness measurements were taken to compare the trends obtained from the NDE tool with the hardness values. To evaluate the edge formability, half-specimen dome testing (HSDT) was conducted for the edges sheared at various clearances. A digital image correlation (DIC) system was used to measure failure strain during the HSDT. The failure strain of sheared edges was correlated with the NDE measurements for each clearance to assess the application of an NDE measurement in determining edge quality. The NDE method can potentially be used to inspect the sheared edge quality for sheet metal stamping process.