Research On Eddy Current Detection Of Defects For Additive/subtractive Hybrid Manufacturing

Additive/subtractive hybrid manufacturing(ASHM),which combines the advantages of both additive manufacturing(AM)and subtractive manufacturing(SM),can eliminate the “stair effect” formed by AM to improve the surface quality and dimensional accuracy of parts.But for internal defects such as cracks and pores induced by AM,it is necessary to combine ASHM with non-destructive testing technologies for on-line detection and defect removal,in order to improve the mechanical properties of parts.This study combining the characteristics of ASHM and eddy current detection(ECD)focused on the subsurface defects detection of ASHMed parts by experimental analysis,an analytical model and a finite element model of eddy current distribution.The main research contents are as follows:(1)An ASHM specimen with subsurface defects was fabricated by varying the hatch spacing in AM.The effects of excitation frequencies,lift-off distances and defect sizes on ECD signals were studied.In addition,the results of X-ray computed tomography(XCT)and optical observation for the specimen were compared with ECD signals to verify the feasibility of ASHM combined with ECD.A finite element simulation model was established to study the effect of defect size on the eddy current distribution in the specimen.(2)An ASHM spescimen with different depths and sizes of subsurface defects was fabricated.Under different excitation frequencies and different lift-off distances,the effects of defect depth on ECD signals was studied respectively,and thus the effective detection depth was determined.(3)A specimen with subsurface defects located in the edge area was fabricated.Based on the results of ECD experiments and finite element simulations,the influence of edge effect on ECD was studied.In order to eliminate the edge effect,a detection method suitable for ASHM was proposed to ensure the detection of the whole parts.