In-Process Thread Orientation Monitoring in Additive Manufacturing

Additive manufacturing/3D printing (AM/3DP) has become a practical manufacturing modality in fabricating highly-complex/optimized parts, providing a form-free flexibility for the development of high-value/highperformance products. However, significant build-to-build variabilities in geometric tolerances and mechanical strength have often been reported as shortcomings. Currently, AM/3DP lacks a practical in situ/real-time quality monitoring utility. In fused filament fabrication, the quality of production in a uniform build depends on two fundamental parameters: the strength of each thread (an extruded line of filament material, created by the heated nozzle) and the nature/strength of thread-to-thread bonds in (in-plate) horizontal and (out-of-plane) vertical directions. In this study, we present an in situ/real-time monitoring approach, in which, instead of monitoring the actual build, the spectral characteristics of elastic wave propagation in a specially designed artifact having periodic internal structures are monitored. The design of an artifact is based on the geometric complexities of the actual build, and its internal structures amplify certain specified aspects of its AM/3DP process and materials. Furthermore, the artifact is substantially simpler and smaller than the actual build it represents, thus considerably easier to monitor. In this study, the artifact design consists of repeating biperiodic substructures of sparsely located threads. As a model problem, in this study we introduce and report a simple phononic crystal artifact design with varying thread-crossing angles and the effects of thread orientation and placement on the shifts of its pass and stop bands and/or the creation of stop bands. In current proof-of-concept study, an experimental setup and basic artifact designs are described, off-line monitoring data are presented, and the sensitivity of the approach is analyzed.