Magnetic flux leakage testing method for Ferromagnetic workpiece with rough surface based on the ferromagnetic lift-off layer

Conventional leakage detection studies usually consider the surface of the workpiece to be smooth by default. The lifting medium between the sensor and the workpiece is often a non-ferromagnetic material such as air; however, the surface roughness of the latter often affects the sensitivity of leakage detection in practical applications. To address these problems, this study proposed a magnetic leakage detection method based on the influence of surface roughness on the leakage field of surface cracks on the workpiece. The influence of the characteristic parameters of magnetic media on the leakage field signal of rough surface cracks was analyzed through simulations, and subsequently verified via experiments. The experimental results confirmed that the magnetic flux leakage detection method based on magnetic lift-off layer improved the signal-to-noise ratio (SNR) of the magnetic flux leakage signal of cracks on a rough workpiece surface. An increase in thickness (0.5 mm) and permeability of the magnetic media layer also improved the SNR (by 2.2 dB) of the magnetic flux leakage detection signal. Thus, the proposed method can improve the SNR of the leakage detection signal in general, which is expected to provide a certain reference value for leakage detection of rough surface workpieces.