- Nugget Profiler
The Nugget Profiler is a non-destructive inspection device that evaluates the magnetic and electrical properties of materials, particularly steel sheets, by utilizing electromagnetic induction.
Sensor Structure and Data Acquisition
The system consists of two coils: an excitation coil and a detection coil. The excitation coil generates magnetic flux (Φ), while the detection coil—positioned perpendicularly—detects the induced electromotive force (e) based on Faraday’s Law of Electromagnetic Induction. According to this law, the induced voltage is proportional to the rate of change in magnetic flux through the circuit.
Effect of Magnetic and Electrical Resistance
Even with a constant voltage applied to the excitation coil, the resulting magnetic flux varies depending on the specimen’s characteristics. A material with lower magnetic resistance (higher permeability) allows more magnetic flux to pass through. Conversely, lower electrical resistance causes eddy currents to form within the specimen, which slow down changes in magnetic flux. These changes directly affect the induced voltage, enabling the profiler to measure both magnetic and electrical properties of the material.
Impact of Heat Treatment on Steel Sheets
Heat treatment alters the mechanical properties of steel sheets, which in turn affect the detected magnetic and electrical signals. Tests on ultra-high-strength steel sheets (approximately 980 MPa tensile strength) showed that different heat treatment conditions led to observable changes in magnetic characteristics. These changes closely correlate with variations in mechanical properties. For spot-welded high-strength steel, the mechanical condition typically corresponds to the heat treatment pattern labeled “WQ.”
This inspection method provides a valuable, non-destructive means to assess weld quality and material properties in steel manufacturing and automotive applications.
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