Non-destructive Ultrasound Thickness Characterization of Parts Additively Manufactured by Fused Filament Fabrication

Abstract

Additive manufacturing is progressively gaining prominence as a manufacturing method within the industrial sector, owing to its distinctive capability to fabricate intricate and complex parts. Fused filament fabrication (FFF) is an extrusion based additive manufacturing method for fabrication of objects by depositing melted polymers layer-by-layer. Non-destructive thickness assessment assumes a pivotal role in ensuring the reliability and suitability of FFF parts, especially if they are exposed to harsher materials such as exposure to corrosive/abrasive chemicals or slurries. A-scan mode or time-amplitude scan ultrasound testing provides a one-dimensional representation of material interfaces. This method uses sound waves and converts them into spikes that correspond with material interfaces, and therefore is commonly used for parts manufactured with conventional manufacturing methods. However, ultrasound assessment of FFF additively manufactured parts can be challenging due to the layer-by-layer nature of the FFF process, which increases the likelihood of subpar interfaces. The goal of this thesis is to evaluate the use of A-scan ultrasound testing for measuring quality-related metrics of objects fabricated by FFF. The effect of different parameters on the ultrasound measurement such as infill patterns, infill densities as well as the presence of the top or bottom layers, are studied. Results show a limited ability of ultrasound to measure thickness beyond 5 mm for a 10 MHz contact ultrasound transducer. In addition, measurements of some infill patterns are sensitive to transducer orientation. However, the ultrasound results for samples fabricated with concentric infill patterns generally better match thickness measurements with calipers and are less sensitive to transducer orientation. Finally, this thesis investigates thickness monitoring of samples in real-time under the effect of simulated erosion to measure thickness reduction.