Evaluation of the influence of ultrasonic vibration on physical, tensile, and morphological properties of fused deposition modeled specimens

Abstract

The use of fused deposition modeling (FDM) in printing polymers for various applications has been ever increasing. However, its utilization in printing polymers for high-strength and superior surface finish applications is still a challenge, primarily due to process intrinsic defects, i.e., voids between the layers and the rough exterior arising from unrestrained deposition of molten polymer. This research hypothesizes that application of ultrasonic vibration (USV) post-fabrication could minimize these shortcomings. For this investigation, ASTM D638 Type IV samples were FDM-printed using poly(lactic) acid (PLA). Through screening experiments, an optimized set of ultrasonic parameters was determined. Then, the effect of both-sided ultrasonic application was characterized. Subsequently, the impact of USV on the samples’ physical, tensile, and morphological properties was examined by varying the layer height, infill patterns, and % infill density. Up to 70% roughness reduction was observed as a result of post-FDM ultrasonic application. Additionally, the tensile strength of the samples increased by up to 15.31%. Moreover, for some lower % infill samples, post-ultrasonic tensile strengths were higher than 100% infill control samples. Analysis of scanning electron microscopy (SEM) and X-ray computed tomography (CT) imagery indicated enhanced layer consolidation and reduced void presence in samples treated with ultrasonic. The combination of ultrasonic-generated heat and downward pressure promoted a synergistic squeeze flow and intermolecular diffusion across consecutive layers of polymers. As a result, increased tensile strength and surface finish were achieved while dimensional change was marginal.