In-process ultrasonic inspection of additive manufactured parts

Abstract

This project introduces an in-situ application of ultrasonic inspection techniques to fused deposition modeling (FDM) in order to detect defects as they are produced in a 3D printed plastic part. The growth of additive manufacturing into performance critical applications has revealed the need for precise quantitative evaluation of printed parts. Ultrasonic testing has been extensively demonstrated as a means of detecting small geometric defects in materials, but has not previously been applied in-process to thermoplastic FDM. This experiment used four piezoelectric transducers bonded to the build plate of an FDM machine printing Acrylonitrile Butadiene Styrene (ABS) to ultrasonically inspect parts periodically during the printing process. Every 30 s, the partially formed model is interrogated with an ultrasonic chirp signal and the response recorded. The normalized frequency response is then compared to an experimentally determined ideal response in order to detect faults in the most recently deposited layers. This analysis is based on the hypothesis that the frequency response of the part will be substantially altered if unexpected (defective) geometries are present. Due to the complexity added by low-density internal structures, this work investigates only parts with a solid fill and simple external geometries. However, with sufficient signal processing capabilities, it is feasible to extend this technique to more complicated part shapes and low-density fill patterns, as might be expected in a manufacturing setting.