Abstract
The recent rapid development of industrial cameras and machine learning has brought new vitality to the very traditional flaw detection method, namely, magnetic particle inspection (MPI). To fully develop automatic fluorescent MPI technology, two main issues need to be solved urgently—the lack of theoretical analysis on the formation of the crack indications, and quantitative characterization methods to determine the crack indications. Here, we carry out a theoretical analysis and an experimental approach to address these issues. Theoretical models of the acting force of the leakage magnetic field were established. Subsequently, the impacts of different magnetic field strengths (1000–9000 A/m) and magnetic particle concentrations (0.5–30 mL/L) on the adsorption critical distance were analyzed. The models were solved by numerical calculations in MATLAB. In addition, a single variable control experiment was conducted to study the effects of crack images. In order to determine the quality of the crack image, three characteristic parameters were investigated, such as indication gray scale, background gray scale, and contrast ratio, were provided. The theoretical magnetic particle concentration range provided a guidance value for automated fluorescent MPI. Experimental results revealed that the optimal magnetic particle concentration was 3–4 mL/L, and, under this condition, the contrast between the crack indications and the background of crack images was obvious.
Highlights
Fluorescent magnetic particle inspection (MPI) is one of the most widely used nondestructive testing (NDT) technologies for the detection of surface cracks on ferromagnetic material workpieces, due to its simple operation and high sensitivity [1,2]
With the unprecedented applications of industrial cameras and machine learning, the automated fluorescent MPI technology based on machine vision has attracted tremendous attention in comparison to manual fluorescent MPI based on human vision, due to its high efficiency [3,4]
By using a single variable control experiment, we investigated the crack images and analyzed three characteristic parameters
Summary
Fluorescent magnetic particle inspection (MPI) is one of the most widely used nondestructive testing (NDT) technologies for the detection of surface cracks on ferromagnetic material workpieces, due to its simple operation and high sensitivity [1,2]. Sci. 2020, 10, 6805 hardware of fluorescent MPI equipment. This process still does not involve automatic detection technology, such as computer image processing algorithms [5], charge-coupled device (CCD). Indication gray scale gray scale gray gray scale scale gray scale gray scale gray scale gray scale gray scale gray scale gray gray scale scale gray scale Contrast ratio Contrast. When the magnetic particle concentration in suspension was low When the magnetic particle concentration in the suspension
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