Processing of Highly Filled Polymer-Metal Feedstocks for Fused Filament Fabrication and the Production of Metallic Implants

New Partially Water-Soluble Feedstocks for Additive Manufacturing of Ti6Al4V Parts by Material Extrusion

In this work, a process chain for the realization of dense Ti6Al4V parts via different material extrusion methods will be introduced applying eco-friendly partially water-soluble binder systems. In continuation of earlier research, polyethylene glycol (PEG) as a low molecular weight binder component was combined either with poly(vinylbutyral) (PVB) or with poly(methylmethacrylat) (PMMA) as a high molecular weight polymer and investigated with respect to their usability in FFF and FFD. The additional investigation of different surfactants' impact on the rheological behaviour applying shear and oscillation rheology allowed for a final solid Ti6Al4V content of 60 vol%, which is sufficient to achieve after printing, debinding and thermal densification parts with densities better than 99% of the theoretical value. The requirements for usage in medical applications according to ASTM F2885-17 can be fulfilled depending on the processing conditions.

Feedstock Development for Material Extrusion-Based Printing of Ti6Al4V Parts

In this work, a holistic approach for the fabrication of dense Ti6Al4V parts via material extrusion methods (MEX), such as fused filament fabrication (FFF) or fused feedstock deposition (FFD), will be presented. With respect to the requirements of the printing process, a comprehensive investigation of the feedstock development will be described. This covers mainly the amount ratio variation of the main binder components LDPE (low-density polyethylene), HDPE (high-density polyethylene), and wax, characterized by shear and oscillation rheology. Solid content of 60 vol% allowed the 3D printing of even more complex small parts in a reproducible manner. In some cases, the pellet-based FFD seems to be superior to the established FFF. After sintering, a density of 96.6% of theory could be achieved, an additional hot isostatic pressing delivered density values better than 99% of theory. The requirements (mechanical properties, carbon, and oxygen content) for the usage of medical implants (following ASTM F2885-17) were partially fulfilled or shortly missed.

Experimental Study on Metal Parts under Variable 3D Printing and Sintering Orientations Using Bronze/PLA Hybrid Filament Coupled with Fused Filament Fabrication

Producing metal parts from Fused Filament Fabrication (FFF) 3D printing coupled with a metal/polymer hybrid filament, considering the advantages of high-performance and low cost, has generated considerable research interest recently. This paper addresses the studied relationship between variable printing/sintering directions and the properties of the sintered metal parts. It was shown that the printing directions played a significant role in determining the properties of final products, such as shrinkage, tensile stress, and porosity. The shrinkage in the layer direction because of anisotropic behavior is more minor than in the other dimensions. The microstructural analysis indicated that the printing directions had influenced the form and position of porosity on the produced metal parts. Most porosities occurred on the surfaces printed parallel to the printing bed. Furthermore, the sintering orientations had no possible benefits for dimension shrinkage, weight shrinkage, density, and porosity position of produced metal parts. However, the sintering direction “upright” resulted in parting lines inside the sintered tensile samples and made them fragile. The best printing-sintering combination was “on-edge-flat”.

Mechanical, Electrical, and Thermal Characterization of Pure Copper Parts Manufactured via Material Extrusion Additive Manufacturing

Material Extrusion Additive Manufacturing (MEAM) is a novel technology to produce polymeric, metallic, and ceramic complex components. Filaments composed of a high-volume content of metal powder and a suitable binder system are needed to obtain metallic parts. Thermal and energetic controversies do not affect MEAM technology, although common in other additive manufacturing (AM) techniques. High thermal conductivity and reflectivity of copper to high-energy beams are the most challenging properties. A material extrusion technique to produce high density and quality copper parts is deeply studied in this research. Characterization of the filament, printed parts, brown parts and final sintered parts is provided. The sintering stage is evaluated through density analysis of the sintered copper parts, as well as their dimensional accuracy after part shrinkage inherent to the sintering process. The mechanical behavior of sintered parts is assessed through tensile, hardness and impact toughness tests. In addition, the measured electrical and thermal conductivities are compared to those obtained by other AM technologies. High-density components, with 95% of relative density, were successfully manufactured using MEAM technology. Similar or even superior mechanical, thermal and electrical properties than those achieved by other 3D printing processes such as Electron Beam Melting, Selective Laser Melting and Binder Jetting were obtained.

Printing of Zirconia Parts via Fused Filament Fabrication

In this work, a process chain for the fabrication of dense zirconia parts will be presented covering the individual steps feedstock compounding, 3D printing via Fused Filament Fabrication (FFF) and thermal postprocessing including debinding and sintering. A special focus was set on the comprehensive rheological characterization of the feedstock systems applying high-pressure capillary and oscillation rheometry. The latter allowed the representation of the flow situation especially in the nozzle of the print head with the occurring low-shear stress. Oscillation rheometry enabled the clarification of the surfactant’s concentration, here stearic acid, or more general, the feedstocks composition influence on the resulting feedstock flow behavior. Finally, dense ceramic parts (best values around 99 % of theory) were realized with structural details smaller than 100 µm.

Bending Properties of Lightweight Copper Specimens with Different Infill Patterns Produced by Material Extrusion Additive Manufacturing, Solvent Debinding and Sintering

Material extrusion additive manufacturing (MEX) is a versatile technology for producing complex specimens of polymers, ceramics and metals. Highly-filled filaments composed of a binder system and a high-volume content of sinterable powders are needed to produce ceramic or metal parts. After shaping the parts via MEX, the binder is removed and the specimens are sintered to obtain a dense part of the sintered filler particles. In this article, the applicability of this additive manufacturing process to produce copper specimens is demonstrated. The particular emphasis is on investigating the production of lightweight specimens that retain mechanical properties without increasing their weight. The effect of infill grades and the cover presence on the debinding process and the flexural properties of the sintered parts was studied. It was observed that covers could provide the same flexural strength with a maximum weight reduction of approximately 23%. However, a cover on specimens with less than 100% infill significantly slows down the debinding process. The results demonstrate the applicability of MEX to produce lightweight copper specimens.