Additive manufacturing (AM) is the fabrication of real three-dimensional objects from metals, ceramics, or plastics by adding material, usually as layers. There are several variants of AM; among them material extrusion (ME) is one of the most versatile and widely used. In MEAM, molten or viscous materials are pushed through an orifice and are selectively deposited as strands to form stacked layers and subsequently a three-dimensional object. The commonly used materials for MEAM are thermoplastic polymers and particulate composites; however, recently innovative formulations of highly-filled polymers (HP) with metals or ceramics have also been made available. MEAM with HP is an indirect process, which uses sacrificial polymeric binders to shape metallic and ceramic components. After removing the binder, the powder particles are fused together in a conventional sintering step. In this review the different types of MEAM techniques and relevant industrial approaches for the fabrication of metallic and ceramic components are described. The composition of certain HP binder systems and powders are presented; the methods of compounding and filament making HP are explained; the stages of shaping, debinding, and sintering are discussed; and finally a comparison of the parts produced via MEAM-HP with those produced via other manufacturing techniques is presented.

A major challenge in extrusion‐based additive manufacturing is the lack of commercially available materials compared to those in well‐established processes like injection molding or extrusion. This study aims at expanding the material database by evaluating the feasibility of polypropylene, which is one of the most common and technologically relevant semicrystalline polymers. Expanded‐perlite‐filled polypropylene and ternary blends with amorphous polyolefins are evaluated to establish an understanding of their processability and their printability. A detailed study on the shrinkage behavior, as well as on the thermal, mechanical, morphological, and warpage properties is performed. It is found that smaller sized fillers result in a tremendous warpage and shrinkage reduction and concurrently improved mechanical properties than compounds filled with bigger sized fillers. Based on the optimal properties profile, a ternary blend that can overcome the shrinkage and warpage of printed parts is suggested.

For parts produced by fused filament fabrication (FFF) the adhesion between the first printed layer and the printing bed is crucial, since it provides the foundation to the subsequent layers. Inadequate adhesion can result in poor printing quality or destroyed bed surfaces. This study aims at understanding and optimising the adhesion process for parts produced by FFF. The consequences of varying printing bed temperatures on the adhesion of two commonly used printing materials on two standard bed surfaces were investigated by means of an in-house built adhesion measurement device and complemented by contact angle measurements. This study shows a significant increase in adhesion forces, when printing parts at a bed temperature slightly above the glass transition temperature of the printing material.

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Polypropylene (PP) parts produced by extrusion‐based additive manufacturing (EB‐AM) suffer from warpage issues due to their high degree of crystallinity and orientations introduced during printing. These issues can be overcome by the addition of spherical fillers. However, the low aspect ratio of the filler and high filling degrees necessary for preventing warpage downgrade the mechanical properties, especially the toughness. This study aims at optimizing a PP‐compound containing spherical glass microspheres for the application in EB‐AM by maximizing the matrix–filler compatibility and therefore the printability, tensile properties and toughness, while still counteracting dimensional inaccuracies. A detailed study on the tensile, fracture, thermal, rheological, and impact properties of various compounds containing different glass types was conducted. It was shown that for EB‐AM applications, PP compounds based on borosilicate glass spheres outperform compounds filled with the conventionally used inorganic soda lime glass. The proposed optimized composite exhibits an exceptional interfacial adhesion between the microspheres and the matrix and a homogeneous filler distribution. It offers an improved processability and tensile properties up to the yield point comparable to those of neat PP. In a concluding impact test on printed composites, the optimized system exhibited impact energies 80% higher than compounds containing the conventionally used glass. POLYM. COMPOS., 40:638–651, 2019. © 2017 Society of Plastics Engineers