Denoising Of Hammer Signal And Research On The Process Of Laser Cladding In Die Repair

Hot work dies are exposed to alternating thermal load and repeated contacts with high temperature medium in service,making it prone to produce fatigue cracks and corrosion failure on the surface of die parts,and leading to the result of lifespan reduction and an increased cost of production.The laser cladding process is a new surface modification technology.Therefore,it can prolong the life of dies by preparing a coating of good wear-resistance and high temperature resistance on the failure surface of dies.However,a large welding residual stress developed in the cladding layer induced by the quickly cooled in laser cladding.It will promote the initiation and propagation of cracks in the region of die repair,when the welding residual stress acted as tensile stress and superimposed with the external load.As an effective method for residual stress relief,hammer peening can be used to eliminate the stress in cladding layer.Nonetheless,the hammer parameter lacks an effective standard,limiting its extensive application in the die repair.In this study,a device and the software of Lab VIEW were used to collect the hammer signal and achieve quantitative disposal by compiling program and setting the parameter.In order to solve the problem that the noise of the hammer power signal in mold repair is higher,the db N wavelet(abbreviation of Daubechies,N is the wavelet order)is used to reconstruct the hammer force signal according to the obtained low frequency coefficient,the low-frequency coefficients of the signal are reserved,the high-frequency coefficients are discarded,the signal-to-noise ratio after noise reduction is 10.0778,and the mean square error is 0.6633,ultimately the noise reduction of hammer power signal in mold repair is initially achieved.Simultaneously,the thresholding is done on the basis of db N wavelet decomposition.The noise reduction effect of hammer force signal under four threshold selection principles is compared.And the noise reduction effect between soft threshold and hard threshold is also compared.Experimental results show that the ‘minimaxi' principle has the best noise reduction effect,and soft threshold noise reduction is better than hard threshold.Comprehensive the macro-waveform characteristics and the noise reduction parameters,the result indicated that the two methods can achieve noise filtering of hammering force signal.But the soft threshold method has a greater degree of reduction for the original signal.The db N wavelet method produced the phenomenon of signal distortion.Besides,the soft threshold method has a greater degree in restoring the details of the original signal,avoid the signal distortion,and ensure that the subsequent calculation accuracy of hammering force signal in mold repair.In this paper,based on the denoising and quantitative disposal of hammer force,Si C ceramics were used to prepare the cladding layer on the surface of H13 steel in preliminary experiment to study the process of laser cladding for welding residual stress relieving by hammer peening.Then the macroscopic feature,microstructure and composition were observed by the metalloscope,scanning electron microscope and energy depressive spectroscopy.The experimental results indicated that the cross sections of the cladding sample are markedly divisional.The microstructure of cladding layer is non-directional and compact,without obvious crack and porosity,and with good performance;the microstructure of bonding layer is homogeneous and with small grain.And the cladding layer has good metallurgical bonding with the substrate.