The Research On Electromagnetic Ultrasonic Online Defect Detection System In Additive Manufacturing Process

In the additive manufacturing process,cracks,pores and other welding defects are prone to occur inside the specimen,and the single non-destructive testing technologies such as eddy current and ultrasonic are affected by skin effect,high temperature,coupling medium and other factors,so the online detection of internal defects cannot be realized.Based on maxwell's theorem,electromagnetic ultrasound excites ultrasonic waves by using eddy current to make particles vibrate on the surface and inside of the specimen under the action of bias magnetic field,so as to locate defects,which makes it possible to detect non-contact detection and internal defects at high temperature and high speed.This paper focuses on the electromagnetic ultrasonic testing model for the defects of non-ferromagnetic materials titanium alloy and aluminum alloy in the additive manufacturing process,and designs an electromagnetic ultrasonic testing system.Based on the demand analysis,the theoretical model of the detection process is established,and the detection waveform and detection method are determined.Based on the theoretical model,the electromagnetic ultrasonic detection system and the system parameters are designed.Based on the theoretical model and system structure,the probe of electromagnetic ultrasonic transducer is designed and simulated,and the corresponding acoustic wave simulation model is established.Based on simulation,establish design parameters of hardware circuit such as power,voltage,etc.The hardware circuit of the system is divided into modules,the detection center frequency and system gain of the corresponding materials are calculated,and the main control system and the high-power pulse module are designed.Based on the corresponding material dispersion coefficient,the echo signal bandwidth,sampling frequency and transmission rate are determined,and chip selection,multi-stage filtering module and data acquisition module design are performed.The working mode and firmware system based on "MUC-CPLD" dual control system are designed in detail,and the finite state machine working conversion method is adopted to satisfy parameter configuration,user control,signal conversion,data storage,data transmission and CPLD combined sequential logic control.By debugging the detection system and conducting online testing experiments,the defects of about 5mm depth and 0.5mm size can be detected.