Manufacturing of gypsum–sisal fiber composites using binder jetting

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Among additive manufacturing (AM) technologies, binder jetting (BJ) produces workpieces that could be used in a great variety of applications, such as decorative parts, prototypes, foundry molds, bone implants, and others. This technique includes the powder deposition to form the layers, binder application, and post-processing to enhance mechanical properties. Fibers can be mixed with traditional raw material powder in order to produce composite parts that are stronger. Sisal fibers are considered to be a promising reinforcement in composites because of their low cost, high strength, and lack of risk to human health. In Brazil, sisal fibers are abundant and there has been no previous study on the application of this fiber in binder jetting. This article proposes the production of gypsum–sisal fiber parts using BJ and the analysis of the effects of some manufacturing parameters, such as the presence of fiber, printing orientation, and post-processing. A material characterization is performed on raw materials and printed parts in the form of thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A complete 24 factorial design for analysis of variance was performed to evaluate the mechanical strength and porosity of the manufactured parts. It was observed that the fibers had a positive influence on the mechanical strength of the infiltrated parts, but a loss of strength was verified on the green parts. The reason for a loss of mechanical strength correlated with the increase in porosity caused by the fiber during the printing process; however, this increased porosity contributed to a more efficient infiltration post-processing.