Research On Ultrasonic Testing Method Of Hardened Layer

Surface hardening can produce hardened surface hardened layer with high hardness and high wear resistance while the heart still maintains good toughness,which is mainly used to strengthen the surface properties of machine tool spindle,rotary support raceway and gear rack..The thickness of the hardened layer is one of the important indexes to measure the surface quenching technology.The traditional hardened layer thickness detection methods need to destroy the hardened material,which leads to the increase of the cost and the decrease of the efficiency.Ultrasonic backscattering method can realize the nondestructive testing of hardened layer thickness,which has high research value.Therefore,the ultrasonic backscattering detection method of hardened layer thickness is studied in this subject.This paper mainly studies the basic theory of ultrasonic testing of the thickness of hardened layer,and uses COMSOL Multiphysics finite element simulation software to simulate the ultrasonic testing system of hardened layer thickness.On this basis,the ultrasonic testing system of hardened layer thickness is set up,and the standard test blocks of 45 steel and 42 Crmo steel are tested.Three kinds of hardened layer thickness are selected and ultrasonic testing results are processed by data processing method.In order to analyze the propagation law of ultrasonic in the hardened material and the ultrasonic testing result,the relationship between the scattering and attenuation of ultrasonic in the quenching material and the frequency of ultrasonic wave,and the relationship between the propagation speed and the waveform are analyzed.In this paper,the COMSOL Multiphysics finite element simulation software is used to simulate the ultrasonic testing system.In the simulation,the effects of four different frequency ultrasonic excitation signals and three probe wafer sizes on ultrasonic backscatter echo are compared.The simulation results provide theoretical guidance for the construction of the experimental system;In order to select the appropriate double crystal direct probe parameters in the ultrasonic testing system,three kinds of frequencies,three focal length and two kinds of chip sizes are used to compare detection result,and the experiment is carried out on the 45 steel and 42 Crmo steel which includes three hardened layer thickness in each material;In order to make the hardened layer thickness of ultrasonic testing more accurate,the paper uses envelope extraction and denoising method to deal with the original experimental data of 45 steel and 42 Crmo steel.The results of multi group experiments show that the double crystal direct probe with the frequency of 5M,the focal length of 10 mm and the wafer size of 14 mm has a good effect on the ultrasonic scattering echo,which is helpful to improve the accuracy of the detection results.The hardened layer thickness detection system built in this paper is accurate to the test block with the thickness of the hardened layer of 3.5~4.5mm.The test accuracy of hardened layer with thickness of 0.81 mm is lower;Data processing results show that the Hilbert transform envelope extraction method does not improve the accuracy of the original experimental results.Compared with the sliding average denoising and Savitzky-Golay filtering de-noising,the denoising effect of the wavelet threshold denoising method is obvious,and the scattering echo signal can be highlighted,which is beneficial to the location of the scattering echo.