COMPUTERIZED MAGNETIC FLUX LEAKAGE TESTING SYSTEM USED FOR GRAY CAST IRON COMPONENT OF AUTOMOBILE
Li Luming Zhang Jiajun Li Zhenxing NDT Lab. Mechanical Department, Tsinghua University Beijing, P. R. China
Keywords: Signal processing, Computer, Magnetic flux leakage testing (MfL), Gray cast iron, Reliability
ABSTRACT
For some reasons, especially human factor, some gear-box lids of automobile with cracks have been failed to find using magnetic particle method in one automobile corporation in China. A computerized magnetic flux leakage testing system, which can get rid of the human factor, is developed to inspect this component in order to increase the testing reliability. The material of the lid is gray cast iron. Central conductor method is used to magnetize the lid. The distribution of the magnetic field is computed using finite element method (FEM) to optimize the magnetic field in the testing zone. Hall probe is chosen as the sensor in this testing system and differential Hall probes are used to decrease the influence of common-mode noise. Signal processing is the most important part in the testing system. Based on the signal spectrum analysis, the signal after A/D is processed using particular program filter method by computer. The waveforms before and after processing are given. And the comparison shows that the S/N is greatly increased more than 20 dB. After complex intelligent judgment, the computer tells the operator the result that the lid is perfect or with defect. The testing sensitivity is very high--the lids with cracks which are failed to find using magnetic particle can be all found by this method.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.full paper not received Publisher:Ashgate Publishing Company
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