Research On Key Technology Of Engine Valve Hardness Sorting Based On Eddy Current Testing

Valves are an essential component of the valve mechanism of an aviation piston engine.The hardness test of the valve can reflect its ability to resist external elastic deformation,plastic deformation and anti-damage,and the comprehensive mechanical properties of the valve can be estimated,which is helpful to reduce the failure probability of the valve mechanism and the engine in operation.Based on the analysis of the current research status of eddy current hardness separation technology,combined with the high-level innovative talent program of Guizhou Province and the horizontal project of an enterprise,this paper carried out the research on the key technology of engine valve hardness separation based on eddy current testing.The main work of this paper is as follows:(1)Taking the electric bridge type eddy current sorting system as the research object,the forward and inverse problems of eddy current testing are studied.In the forward problem,based on axisymmetric time-harmonic magnetic field,the finite element discretization method of eddy current differential equation is presented,and the mathematical model of impedance variation of differential detection coil used in eddy current separation of valve hardness is deduced.The influence of main electromagnetic parameters of valve and temperature variation on eddy current impedance is analyzed.In the study of reverse problem,the principal component analysis method is used to preprocess the eddy current impedance signal,which simplifies the regression analysis process of eddy current impedance signal and hardness,and the inversion model is established based on the support vector regression method and the inversion calculation is carried out.(2)The processing method and technology of eddy current response signal of valve hardness are studied.Based on the cross-correlation function,a positive interactive correlation algorithm was proposed to extract,process and reconstruct the eddy current response signals.The sampled eddy current signals were simulated and analyzed by MATLAB,and compared with the eddy current signals reconstructed by wavelet transform and Hilbert-Huang transform,respectively,and the advantages of the algorithm were verified.The technical work of the positive interaction correlation algorithm is realized based on FPGA device,and the positive interaction correlation detector is designed,and the extraction effect of the detector is verified by experiments.(3)The method and technology of eddy current hardness separation are studied.In the comparative study of traditional impedance matching method,the logistic regression method and Support vector machine(SVM)based on sorting examples,puts forward the Increment and decrement support vector machine(ID-SVM)separation method,based on the FPGA device to create static and dynamic classifier,the hardness and several typical testing conditions for the actual effect of the separation test,verify the feasibility and applicability of technology.(4)A set of eddy current hardness sorting device was developed and applied in the Precision Measurement Co.,Ltd by hardware and software integration of the above key technologies.