Materials for Additive Manufacturing

Additive manufacturing, also known as 3D printing, was developed to aid in rapid prototyping for industrial applications. Initially, the only material that could be printed using this technology was polymer based. In the years since the development of this novel approach to manufacturing, several different processes have been conceived that allow materials that are either composites incorporating polymers or materials that are polymer free such as Inconel and titanium alloys to be used. One drawback to using metals for additive manufacturing is the high cost of both the instrument and the stock. Most printers, especially those used to produce metallic structures, are optimized to use one type of material. One goal of the research being carried out by our research group is to explore how to combine materials with the aim being to combine materials for prototype applications and to explore additive manufacturing of structures composed of functionally graded materials. It is a fundamental property of the additive manufacturing technology that materials are deposited layer by layer; the desire is to vary the composition in the same timeframe. This manufacturing approach has the potential be a particularly efficient and precise way to produce structures using complex functionally graded materials.

The machine that is being used for this research is a Lulzbot TAZ5 fused-filament fabrication (FFF) 3D printer. This printer was chosen because it offers considerable flexibility in using and combining filaments. Because the printer is FFF, filament must be fed to the printhead. At the printhead, the filament is melted and the printer begins printing layer by layer. The printhead moves in the positive z direction as the build plate adjusts in the y direction for each layer. One motivation for this research is to review critically current metallic powder-loaded filaments that may be used to form functionally graded structures upon printing. A variety of materials are commercially available for relatively conventional and quite unique manufacturing; in addition, different binders can be selected in order to make a new powder-loaded filament.

PLA and ABS are the two polymer filaments commonly used in FFF printing. In addition, a bio-compatible polymer* is being considered for biomedical applications. These three materials are each being considered as potential binders in this study. Stainless Steel PLA manufactured by ProtoPasta and Copper PLAmanufactured by ColorFabb are metal-powder-loaded filaments that are being studied to understand the current state of this technology. These materials are being characterized using several complementary techniques before and after they are used in printing. The metal-powder-loaded filament is also being analyzed once the polymer binder has been baked out. Visible light microscope (VLM) and scanning electron microscope (SEM) images are being used to examine microstructural and chemical variations such as composition, grain structure, porosity, and phase morphology. Initial results of uniaxial tensile tests for determining mechanical properties will be reported. The aim of this analysis is to connect the structural features of these materials to mechanical properties measured. This data should provide insights into the synthesis of powder-loaded filaments and possibly offer alternative binder materials to PLA.

*Material provided by Prof. S. Kumbar.