Study On Laser Opto-Ultrasonic Dual Detection And Its Application Of Wire+ Arc Additive Manufacturing Component

Additive manufacturing,different from the conventional subtractive manufacturing,is a potentially disruptive technology across multiple industries.With the significant advantages of high deposition rates,low costs and good structural integrity,wire + arc additive manufacturing(WAAM)has been widely concerned and applied in the key components manufacturing of aerospace,automotive,shipbuilding industry and so on.However,the problems of WAAM components,such as element segregation,defects,stress-strain,and grain abnormality,seriously affect the popularization and application of WAAM.With several weakness,the conventional technology cannot complete the detection demands of manufacturing components.Therefore,we investigated laser opto-ultrasonic dual(LOUD)detection method for the first time,which combines laser-induced breakdown spectroscopy(LIBS)and laser ultrasonic(LU)technology.The optical emission and ultrasound wave were generated when the single laser ablated the surface of the samples in the LOUD detection.The multi-modal detection of element composition and structural properties can be simultaneously obtained with the detection and analysis of spectral and ultrasonic signals.In this thesis,the mechanism of LOUD detection was studied firstly.On this basis,a LOUD detection system was established,which realized the simultaneous acquisition and analysis of spectral signals and ultrasonic signals.Then the evolution of opto-ultrasonic signals was explored and summarized through the simulation and experimental work.Finally,the LOUD detection was successfully applied to the detection of element composition,defects,residual stress,and grain size distribution of WAAM components.The main innovations obtained and research results in this paper are as follows:(1)The mechanism analysis and system construction of LOUD detection.A LOUD detection theory was proposed for the first time to satisfy the demands of composite detection in additive manufacturing.LIBS and LU were organically integrated to realize the LOUD detection of spectral signals and ultrasonic signals excited by a single laser at the same time through the in-depth analysis.Finally,an experimental system of LOUD detection was established,while the hardware equipment and software algorithm were developed and verified.(2)Study of acoustic and optical parameter optimization for LOUD detection.Based on mechanism analysis,the deeply studied from two aspects of acoustic and optical parameter optimization were completed.On the one hand,the COMSOL simulation model of ablation mechanism laser ultrasonic excitation and propagation was established to study the propagation and characteristics in defect and complete models,and verified by experiments.On the other hand,the mechanism and influence of key optical parameter such as laser wavelength and energy intensity on opto-ultrasonic signals were studied and optimized.The results showed that the opto-ultrasonic signals excited by the 355 nm laser made the best effect in terms of intensity,signal-to-noise ratio,and stability.With the improved parameters for experiments,the determination coefficients of quantitative analysis of Cu and Si elements in aluminium alloy can be 0.999,and the average relative error was less than 2.5% in the LOUD detection.As for the ultrasonic testing,LOUD detection realized the 0.55 mm defect detection of WAAM sample,and the average relative error is only 5.59%.(3)Study on the application of LOUD detection for simultaneous compositional,structural,and residual stress analyses of WAAM components.Firstly,the calibration curve of stress and ultrasonic time-of-flight delay,with average determination coefficients of 0.982,was established to realize the residual stress detection by the study of the acoustroelasticity theory.Moreover,the simultaneous detection of Si element,artificial defect and welding residual stress of typical laser welded sample was realized due to the synchronous acquisition of spectral and ultrasonic signals.Finally,the LOUD detection was applied to detect Cu element,defects,and residual stresses in the WAAM components,and the average relative error of results was less than 9% compared with that of conventional detections such as electron-probe micro analysis detection,digital X-ray detection and ultrasonic testing detection.(4)Study on the application of LOUD detection for element composition and grain size distribution of WAAM components.Based on the theory of ultrasonic attenuation in polycrystalline metals,a model for evaluating grain size by laser ultrasonic was established,which realized the rapid and large area detection of grain size of WAAM components.As a result,the LOUD detection was consistent with the electron backscatter diffraction detection,with the average relative error of 2.56 %.On this basis,the simultaneous detections of element composition and grain size distribution were obtained with the advantage of synchronous detection of spectral and ultrasonic signals,which verified and explored the relationship between macrosegregation of alloy-elements and grain size distribution.The results showed that the induction factors of the uneven grain distribution inside can be revealed by the element distribution on the surface of the component,which was of great significance for the material analysis.Based on the urgent requirements of WAAM detection,a LOUD detection was proposed in this thesis.With the mechanism and application were studied systematically,a LOUD detection system was established to realize the rapid,efficient and high-precision multimodal detection of element compositions and structural properties for WAAM components,which has broad application prospects in the advanced manufacturing detection.