Butt Welding Inspection And Defects Three-dimensional Imaging Using Ultrasonic Phased Array Technology

Weldment is made by welding processing technology. It is widely used in machinery manufacturing, transportation, nuclear power, aerospace and other industry. Compared with traditional riveting and casting process, it has the advantages of metal material saving, simple process, easy operation and short cycle of manufacturing. In the welding process, due to the structure properties, process design and artificial operation factors, there often exists some defects such as cracks, blowhole, slag inclusion, incomplete fusion, lack of penetration and so on. All kinds of welding defects have a great influence on quality of the weldment in service. The defects destroyed the contact of the welding parts, reduced the mechanical properties and mechanical strength of material, and caused failure mechanism easily, that seriously affects the service performance of the welded parts.As an advanced new technology of nondestructive testing, ultrasonic phased array detection technology has been used in detection of butt weld gradually with its dynamic focus and variable beam angle characteristic. However, the two-dimensional map gotten from the traditional ultrasonic phased array inspection exists such characteristic as the defects are nonintuitive, evaluation is influenced by many factors. In order to completely and accurately show the defect morphology and analysis defect characteristic, we fully consider the actual industry situation, combine ultrasonic phased array technology with three-dimensional visualization imaging technology and carry out research on ultrasonic phased array 3D imaging inspection of butt weld.This paper firstly described the transmitting and receiving beam technique and imaging principle, introduced three kinds of scanning methods, which are linear scanning, dynamic depth focusing and sector scanning. A linear array sound field mathematical model was built in this paper, which conducted the research on acoustic beam deflection and focusing characteristics using numerical simulation method. The study of the influence of array length and pitch shows that the array pitch has a great impact on grating lobes, and the change of array length has more effect on side lobe.Secondly, the data structure and imaging method of 3D visualization were studied, the visualization data has discreteness, regular or irregular structure and dimension and then listed four common structures, which are Image Data, rectilinear Grid, Structured Grid and Polygonal Data. Compared with the surface rendering and volume rendering technology, the hybrid rendering method based on region growing technique was used to realize the 3D reconstruction of defects.Furthermore, the whole scanning imaging and data transmission system was designed based on the secondary development module of Phascan ultrasonic phased array platform, Arduino Uno as the main control chip, OpenCV based on python language interface realized image median filtering, color mapping and contour extraction pretreatment, MIMICS platform is to complete three-dimensional reconstruction. It was proved that this system and imaging method are feasible and have good imaging resolution through three groups of artificial test blocks with different contrast defects which reflect depth, diameter, direction and other information.In this final installment, experiment research selected appropriate array probe parameters for butt weld specimen, clearly defined the principle and operation method of velocity calibration, delay calibration and sensitivity calibration(ACG correction) and TCG correction and got the faults 2D maps and 3D defects image through the 3D imaging scanning on butt weld.The characteristic of typical defects in butt weld was summarized through the analysis of 2D maps and 3D defects. The results, which compared with traditional A-scan ultrasonic testing and radiographic testing results, contrast experiment show that the 3D image of the defect is very intuitive, specific and accurate. The research methods and results can provide reference for the popularization and development of ultrasonic phased array 3D imaging detection technology.