| Metal additive manufacturing is widely applied and plays an essential role in modern manufacturing technology.During the(process of)SLM,the gradient of temperature increases sharply due to the accumulation of thermal energy.When residual stress increases to a critical condition which the material cannot stand,it will generate a crack to release stress.Crack defects severely the mechanical performance of components as well as reduce the fatigue life of components.Thus,it’s of vital importance to locate cracks.Acoustic emission technology,a new type of dynamic non-destructive testing technology,is popular in complex industrial inspection.The traditional acoustic emission location method is not suitable for complex structures.For this,we introduced the time-reversal method into Acoustic emission technology and systematically research crack defect detection and positioning applied in metal additive manufacturing.(1)We studied the temporal and spatial focusing characteristics of the timereversal method and verified the feasibility of the time-reversal method to locate the crack defect in metal via finite element simulation.By analyzing the influence of array element density,carrier frequency,sound source spacing,noise level,and backplane structure on the positioning accuracy,we realized simulation verification on various typical structures in additive manufacturing.(2)An enhancement method with good anti-interference effect in the same direction is proposed,which can effectively suppress pseudo focus and assist in the identification of positioning points.(3)we propose a design idea for the backplane system and developed a special backplane for metal 3D printing.Acoustic sensor array embedded in the backplane,which can capture the acoustic signal generated in the component during the 3D printing process instantly.(4)Based on the backplane,we conduct a positioning experiment using analog sound on AL6061 and TC4.Finally,by conducting a line inspection experiment of crack defect,we successfully detected the artificial crack in the size of about 100 μ m in Aluminum alloy samples via subtracting noise from the signal obtained during the laser cladding process.Base on the smart backplane proposed in this thesis,we utilized time-reversal method to successfully locate acoustic emission signal during 3D printing,that provides an effective way for 3D printing online quality inspection.Besides,the smart backplane is verified to have the ability to detect surface crack defects. |
