Study On The Laser Unltasonic In-situ Detection Technology Of Defects In DED Additive Manufacturing

The Directed Energy Deposition(DED)method of the metal Additive Manufacturing(AM)has attracted more attention in the field of scientific research and industrial production,due to its high manufacturing speed,excellent formability,great material utilization rate and design freedom.However,resulting from the point-layer processing principle of AM,defects such as porosity,poor fusion and cracks inevitably occur in the production process,which are seriously harm to the quality and pose threat to service safety of products.The off-line detection techniques are widely used after producing,but cannot detect the defects in real time or guide the defect repair process.Laser ultrasonic testing(LUT)technology,which has the advantages of high sensitivity,high degree of freedom,long-distance non-contact characteristic and resistance to harsh environment,are potential in the field of DED detection,and may become the key to break through the technical problems of online detection and improve the forming quality.In this paper,the LUT technology of DED defects was studied.Firstly,a finite element simulation model was established to explore the laser ultrasonic characteristics and the interaction between ultrasonic and defects.On this basis,a LUT platform was established to compare and analyze two DED on-line defection methods’ effects and applicability.Finally,an on-line inspection system for AM was designed and integrated.The main research results are as follows:(1)The finite element model of laser ultrasonic was established to simulate the process of laser inducing and receiving ultrasonic on the surface of 316 L sample.The influence of laser parameters on the ultrasonic was studied.The interaction between surface defects with surface waves as well as internal defects and P-Wave and S-wave were summarized.It provides a theoretical basis for LUT of AM defects.(2)Combining with the DED forming characteristics,"melting scanning imaging detection" and "molten pool fast track detection" were designed and respectively used to detect the preset surface defects and internal defects.Comparing the analyzing the effects,the accurate detection of surface detects(0.05 mm diameter)and positioning detection of internal defects(0.5mm diameter and 0.5mm depth)are realized.(3)The LUT system and testing plan for DED metal AM on-line detection were design.After finishing the hardware processing,the software programming and the optical devices adjusting,the LUT on-line detection equipment was integrated on the plasma arc-wire feeding AM machine.The universality and detection effect of the system were verified.