[4A1] Optimisation of transducer assembly for the phased array ultrasound roller-probe inspection of wire + arc additive manufactured components
M Rizwan, R Zimermann, E Mohseni, R Vithanage, D Lines, C MacLeod, S G Pierce and
A Gachagan
University of Strathclyde, UK
Wire + arc additive manufacturing (WAAM) has been shown to offer reduced lead times for the manufacturing of large metal components due to its high deposition rates. The arc-based layer-by-layer deposition manufacturing is preferred over the traditional subtractive methods for high throughput, reduced material wastage and the ability to manufacture complex-geometry metallic components. However, as with other manufacturing processes, the quality of a WAAM component is hindered by the possibility of inherent defects, mainly lack of fusion, porosity and inclusions, which arise from poor process parameters and contaminated wire feedback. Hence, to ensure defect-free component manufacturing and at the same time reduce the material scrappage and rework resources, a robust in-process non-destructive testing (NDT) approach is required. Ultrasonic phased array imaging is widely adopted for volumetric inspection of metallic components; however, commercial ultrasound transducers cannot maintain direct contact with the high-temperature (ie more than 300°C) WAAM component. Therefore, a novel phased array ultrasonic testing (PAUT) roller probe, specially designed for in-process weld and manufacturing, cannot only withstand the elevated temperature but can be deployed using a robot for automatic NDT inspections.
On the other hand, the unmachined surface of a built component poses multiple challenges for the dry-coupled contact of the PAUT roller probe. First, the sensitivity of the ultrasound transducer is reduced by the multi-interface assembly of the probe. Secondly, the surface curvature of the WAAM wall produces a non-uniform contact of a linear array transducer used in the roller probe. The former is addressed by introducing a high dynamic range preamplifier in the system for signal acquisition, where the lower amplitude signals (reflected from the defects in particular) are amplified with a larger gain compared to the high-amplitude reflections from the interface surfaces. In addition, the latter is addressed by modifying the physical shape of the phased array transducer. In fact, an elevation-focused linear array transducer, where its radius of curvature is optimised for the roller probe assembly and for the in-process inspection of WAAM components, is expected to provide a better collimated and high-amplitude acoustic beam at the target location in the component.
On the other hand, the unmachined surface of a built component poses multiple challenges for the dry-coupled contact of the PAUT roller probe. First, the sensitivity of the ultrasound transducer is reduced by the multi-interface assembly of the probe. Secondly, the surface curvature of the WAAM wall produces a non-uniform contact of a linear array transducer used in the roller probe. The former is addressed by introducing a high dynamic range preamplifier in the system for signal acquisition, where the lower amplitude signals (reflected from the defects in particular) are amplified with a larger gain compared to the high-amplitude reflections from the interface surfaces. In addition, the latter is addressed by modifying the physical shape of the phased array transducer. In fact, an elevation-focused linear array transducer, where its radius of curvature is optimised for the roller probe assembly and for the in-process inspection of WAAM components, is expected to provide a better collimated and high-amplitude acoustic beam at the target location in the component.
