Numerical Simulation And Experimental Study On Ultrasonic Testing For Laser Cladding Remanufacturing Parts

Laser cladding, due to its technological advantages, has become one of the important means of green remanufacturing for old products. But practice shows that stress of laser cladding coating and flaw of rough products and laser cladding coating are key factors that affecting the service performance and life cycle of remanufacturing parts. The non-destructive evaluation of flaw and stress of Fe314 laser cladding remanufacturing parts and rough products were investigated in this paper. In order to achieve quantitative evaluation results and improve the reliability of non-destructive evaluation, the ultrasonic non-destructive testing technology was adopted. The study of this paper can not only provide theoretical and technical support for improving the quality of laser cladding remanufacturing parts, but also has important significance to the construction of source-saving and environment-friendly society.The non-destructive evaluation of flaw was discussed with the help of numerical simulation combined with experimental method. By using ultrasonic wave technology, the positioning, quantitative, qualitative evaluation of flaws in Fe314 laser cladding remanufacturing parts and rough products were discussed; Surface ultrasonic wave was used to evaluate stress of laser cladding coating; The inner and extraneous factors affecting the evaluation results of flaw and stress were discussed; Based on analysis of microstructure of coating, the reason of noise in ultrasonic wave signal was analyzed; the principle and method of signal de-nosing were discussed. The main contents and conclusions are as follows:The method of identifying the type of flaws in ultrasonic testing was discussed. The Finite Element Model of ultrasonic flaw testing was developed. The scattering ultrasonic fields of different types of flaws were simulated based on the model. By analyzing the characteristics of scattering ultrasonic fields and the corresponding Fourier spectrum diagrams of flaw echo signals, the method of identifying the type of flaws was proposedanalysis of dynamic Fourier spectrum diagrams of flaw echo signals. The accuracy of the provided method was verified by the experimental results.The influence of anisotropic laser cladding coating on the propagation behaviors of ultrasonic beam was analyzed. The propagation behaviors of ultrasonic beam in the laser cladding Fe314 alloy coating were investigated with the help of Rayleigh integral combined with pencil method. The simulation results show that the influence of anisotropic material on the incident field due to the value of slowness, the direction of beam steering is determined by the normal vector of slowness surface, the beam focusing and defocusing behavior is determined by the curvature of slowness surface. The radiated ultrasonic field maintains a uniform distribution relative to the axis of the incident beam, when the direction of incident beam is consistent with or perpendicular to the grain orientation of laser cladding coating, which the directivity of beam is preferably. The reason lies in the incident direction of ultrasonic wave is perpendicular to the isotropic plane of crystal. In the radiated field of transverse wave angle probe, the transverse wave splits and the beam steers, separates with the change of grain orientation. The fundamental reason that transverse wave splitting due to the anisotropy of the laser cladding coating.The reason that beam steering lies in that the direction of group velocity(the direction of normal vector of slowness surface) is inconsistent with that of phase velocity(the direction of transverse wave vector). The slowness surface of anisotropic laser cladding coating is irregular in shape, the beam will appear in other angles in addition to the main beam,when transverse wave refraction. An ultrasonic measurement model for the laser cladding remanufacturing parts was developed by combining the beam model with the scattering model based on Kirchhoff approximation and Born approximation theory. This model can be used to predict the testing signals from the flaws in laser cladding remanufacturing parts. The accuracy of the provided model was verified by comparisons of the simulation results with the experimental results, both the signal amplitude and phase were in good agreement. Numerical simulation results provide an important theoretical basis for rational design of the process scheme of ultrasonic testing for laser cladding remanufacturing parts.The method of positioning, quantitative and qualitative evaluation of flaws in laser cladding remanufacturing parts was discussed. The longitudinal wave technology was used to evaluate the flaw of this kind of parts. Positioning evaluation of flaw was realized by using the pulse reflection method based on the analysis of generalized related cepstrum. The quantitative evaluation of flaw was realized through establishing the curve between signal amplitude and flaw size. The qualitative evaluation of flaw based on analysis of dynamic Fourier spectrum of flaw echo signals was discussed. Based on analysis of microstructure of coating, the reason of noise in ultrasonic wave signal was analyzed. The de-nosing method based on optimal wavelet packet analysis and entropy theory was discussed. The experimental results show that this method has powerful capability to find small flaws and enhance SNR in ultrasonic flaw testing. The impact of testing distance and direction on evaluation results of flaws was discussed. Due to the attenuation of ultrasonic wave energy, the amplitude of flaw echo signal decreases gradually, as the testing distance increases. Because the existence of different interface and microstructure in laser cladding coating, the energy loss of ultrasonic wave is different in the process of wave reflection, scattering and mode conversion, so the evaluation result of flaw changes, as the testing direction changes.Surface ultrasonic wave was used to evaluate stress of laser cladding coating. Combined with the static load tensile test, the acoustoelastic formula for evaluation of stress of laser cladding Fe314 alloy coating was established. The inner and extraneous factors affecting the evaluation results of stress were discussed. The experimental results indicate that the anisotropy and residual stress of laser cladding Fe314 alloy coating can result in relative change of surface ultrasonic propagation speed. After the experimental results were calibrated by the initial stress calculated by acoustoelastic formula, the experimental results were more close to the actual load.In addition, due to the inhomogeneous deformation of anisotropic laser cladding coating during tensile process, the error of high stress stage was greater than that of low stress stage. A time delay estimation algorithm based on complex cepstrum was proposed in this paper, it was shown from the computer simulation and experimental results that the new algorithm has higher precision and certain anti-jamming capability in comparison with traditional correlation analysis method. During the process of loading, the deformation of material can influence the evaluation results of stress, so the time delay due to the deformation of material should be deducted from the experimental results. The experimental results showed that the error of stress evaluation results reduced significantly after adopting the above calibration method.