Research On The Surface Defect Detection Of Molybdenum Wire Based On The Encircling Eddy Current Sensor

As a key part of Wire Electrical Discharge Machining,molybdenum wire runs in a high precision environment,and its surface quality directly affects the quality and precision of machined parts.At present,the precision and reliability of the molybdenum wire detection equipment used in the factory are low,which mainly focuses on the offline detection after the drawing and forming of molybdenum wire,greatly affecting the detection efficiency.In this paper,based on the optimized design of the size and structure of the sensor framework,the defect detection of molybdenum wire by EER is studied by simulation analysis and experimental detection.Based on the theory of electromagnetics and the principle of eddy current testing,a three-dimensional encircling eddy current testing model is established.Based on the characteristics of eddy current distribution on the surface of molybdenum wire,the parameters that affect the distribution of eddy current on the surface of molybdenum wire are analyzed.According to the no-load impedance characteristics and detection depth of the encirling eddy current detection,the influence of coil parameters on the field strength is discussed.The coil adopts a self retracting cylindrical structure,and the control variable method is used to study the influence of different coil size parameters on the detection of molybdenum wire surface by the encircling coil eddy current sensor from the height,inner diameter and outer diameter of the coil.The optimal design size of the encircling coil sensor probe is obtained.On the basis of theoretical research,the on-line eddy current testing test-bed is built.Taking the encircling coil probe as the core,the structure frame of the experimental platform and the working principle of each component module are analyzed in detail.The detachable probe support is designed to facilitate the removal and replacement of the winding probe coil.The screw rod and nut are used to coordinate with each other to adapt to the adjustment of the height and position of the probe frame,so as to realize the detection ability of small crack defects and improve the detection efficiency of the detection system.The field strength is simulated with Maxwell finite element method.Through the research and analysis of crack direction,the sensitivity and resolution of the designed coil to detect axial and circumferential cracks are verified.Based on the distribution of the magnetic induction intensity of the coil to the axial and circumferential cracks,the response relationship between the change of the coil parameters of the sensor and the crack direction of the molybdenum wire was studied by means of the parametric scanning.Combined with the obtained magnetic field strength curve,the change rule of peak and valley is analyzed,and the optimal size of the sensor probe matching the crack direction is explored,which provides a reference for the design of the sensor coil.Combined with the experiment,the structure of the coil is optimized,and the encircling coil framework with step groove is designed.The optimal parameters of the coil obtained from the simulation are verified,and it is determined that the designed coil has high sensitivity to each crack direction.To sum up,I have done in-depth research on the structure design and performance test of EER probe.On the one hand,based on the existing eddy current testing theory and experience,the coil structure is innovated to ensure the lift off height and coaxiality between the coil and the test piece.On the other hand,on the basis of experimental detection,combined with simulation analysis software,the parametric scanning and experimental results are compared and analyzed,and the corresponding relationship between crack direction and eddy current signal value is studied.Finally,using data acquisition card,the feasibility of the designed upper computer software to test EER detection signal is verified.