Magnetic flux leakage inspection of tailor-welded blanks

A feasibility study was conducted on the application of magnetic flux leakage (MFL) inspection to the evaluation of weld quality in automotive tailor-welded blanks (TWB). Using a permanent magnet configuration, magnetic flux was directed through the weld region of a TWB. A Hall effect sensor was coupled to the movement of a digital plotter and was, thereby, scanned around the weld region. Signals from the Hall effect sensor were processed and correlated with defects to determine corresponding, MFL signatures. Simulated through-hole defects as small as 0.34 mm in diameter were readily detected. Furthermore, there was a reasonably linear relationship between the MFL signals associated with these defects and the diameter of the defect hole. Preliminary tests with specimens having naturally occurring defects such as concavity, pinholes, and undercutting, indicate that the MFL technique has excellent potential as an inspection method in this application.