Eddy Current Detection Of Surface And Subsurface Defects By Laser Melting Deposition

Laser fusion deposited parts are prone to defects in the manufacturing and use process,eddy current non-destructive testing for surface and sub-surface defects identification sensitivity,easy to achieve automatic detection,is to ensure the quality of laser fusion deposited parts reliable and effective detection method.In view of the difficulty of interpreting and quantifying the eddy current signals of defects in laser melting deposited parts,this paper uses eddy current inspection to detect artificial defects in laser melting deposited titanium alloy parts,and studies the theoretical basis of the influence of defect characteristic values on eddy current signals through finite element model simulation calculations and artificial prefabricated defect test blocks,and studies the quantitative assessment of defects in laser melting deposited samples based on the quantitative method of field magnitude.The main research contents of this paper are as follows:(1)Based on ANSYS Maxwell finite element simulation software to establish the probe and defect-free test block simulation model,field volume calculation,finite element calculation of the electric field and eddy current field distribution inside the test block,through the calculation results to analyze the change law of magnetic induction intensity and eddy current density inside the defect-free test block.The influence of different excitation frequencies and different lifting amounts on the changes of electromagnetic field distribution at different depths in the test block is studied.(2)Set up an automated eddy current inspection experimental equipment to improve the inspection efficiency and keep the lift-off amount constant by robot clamping the inspection probe.The Ti-6Al-4V specimens with subsurface defects were prepared,and the signal variations caused by different inspection parameters were studied and analyzed.The correctness of the probe-defect-free specimen simulation model is verified,and artificial defect specimens with different depths,widths and lengths are prepared for eddy current inspection and the eddy current signal gain variation law is summarized.(3)Establish the probe-defective test block simulation model,by comparing the change of eddy current density distribution in the test block with and without defects,to explain the reasons for the change of eddy current signal caused by defects.Calculation of the detection probe in the process of moving above the test block,different sizes of defects caused by the characteristic value of the magnetic induction intensity change law.Comparison of simulation results magnetic induction intensity amplitude change trend and eddy current detection of artificial prefabricated defects of the same trend of vertical gain change,proving the correctness of the finite element simulation results,analysis of the impact of defect characteristics on the magnetic induction intensity amplitude and thus provide a theoretical basis for the amplitude of eddy current signal change.(4)The method of defect quantification is proposed,and based on the finite element simulation results,the relationship equation between the variation of magnetic induction intensity and the volume of microcrack defects is calculated by fitting,and the calculation results are in accordance with the permissible range of fitting error to achieve the quantitative evaluation of microcrack defects in the volume range of 0.875 mm~3-7.875 mm~3in the case of depth less than 1 mm.