Improving deposition quality at higher rates in material extrusion additive manufacturing

Abstract

Material Extrusion (ME) is one of the established processes in Additive Manufacturing (AM) realm. The process involves deposition of adjacent material strands that are bonded together in order to create successive layers that are stacked one upon the previous until the three-dimensional part is fabricated. One of the key factors for increased performance and part quality is the extrusion of strands that are uniformly deposited according to the designed trajectory, without defects and with minimal deviation from the intended strand shape and dimension. This objective becomes more challenging when ME subsystems must be optimally synchronized, in order to perform material deposition at higher rates, given the timely need to improve ME process efficiency. In this study, eight factors that control material flow and deposition from kinematic, rheological, and thermal aspects are investigated via a fraction factorial design of experiments. Machine vision methods are employed to evaluate factor contribution to the fabrication of simple linear segments, and to effectively measure the free form shape of the resulting strands. Analysis of the experimental results reveals the mechanisms that trigger Material Deposition Discontinuity (MDD) during part fabrication. In addition, Strand Width Deviation (SWD) along the linear path is minimized with special attention to the undesirable material overfills at the start and the end points of the strand. Two separate regression models are generated, describing the relationship between the investigated factors and the MDD and SWD criteria. The models are utilized as roadmaps towards continuous and uniform deposition in indicative case studies at normal (4.80 mm3/s) and increased (7.80 mm3/s) melt flow rate. Compared with non-optimized runs at similar flow rates, continuous and more uniform deposition is achieved for both normal and increased rates as indicated by a corresponding reduction of 34% and 19% of the measured strand width deviation.