15 research outputs found
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
Material Extrusion 3D Printing of PEEK-Based Composites
High-performance thermoplastics like polyetheretherketone (PEEK), with their outstanding
thermal stability, mechanical properties and chemical stability, have great potential for various structural
applications. Combining with additive manufacturing methods extends further PEEK usage,
e.g., as a mold insert material in polymer melt processing like injection molding. Mold inserts must
possess a certain mechanical stability, a low surface roughness as well as a good thermal conductivity
for the temperature control during the molding process. With this in mind, the commercially available
high-performance thermoplastic PEEK was doped with small amounts of carbon nanotubes (CNT,
6 wt%) and copper particles (10 wt%) targeting enhanced thermomechanical properties and a higher
thermal conductivity. The composites were realized by a commercial combined compounder and
filament maker for the usage in a material extrusion (MEX)-based 3D-printer following the fused filament
fabrication (FFF) principle. Commercial filaments made from PEEK and carbon fiber reinforced
PEEK were used as reference systems. The impact of the filler and the MEX printing conditions like
printing temperature, printing speed and infill orientation on the PEEK properties were characterized
comprehensively by tensile testing, fracture imaging and surface roughness measurements. In
addition, the thermal conductivity was determined by the laser-flash method in combination with
differential scanning calorimetry and Archimedes density measurement. The addition of fillers did
not alter the measured tensile strength in comparison to pure PEEK significantly. The fracture images
showed a good printing quality without the MEX-typical voids between and within the deposited
layers. Higher printing temperatures caused a reduction of the surface roughness and, in some cases,
an enhanced ductile behavior. The thermal conductivity could be increased by the addition of the
CNTs. Following the given results, the most critical process step is the compounding procedure,
because for a reliable process–parameter–property relationship, a homogeneous particle distribution
in the polymer matrix yielding a reliable filament quality is essential
Manufacturing of W/steel composites using electro-discharge sintering process
Tungsten-steel metal matrix composites are consolidated using electro-discharge sintering. At first steel and tungsten powders are sintered separately and then 25 vol% W, 50 vol% W and 75 vol% W mixed powders are sintered. A thorough process parametric study is carried out involving analysis of the influence of particle size distribution, sintering pressure, and discharge energy on the maximum discharge current and obtained residual porosity. Thermal expansion coefficient and the specific heat capacity of the optimized sintered composites are almost same as their theoretical values, however the thermal conductivities and the mechanical properties are lower than the expected values
Material Extrusion 3D Printing of PEEK-Based Composites
High-performance thermoplastics like polyetheretherketone (PEEK), with their outstanding thermal stability, mechanical properties and chemical stability, have great potential for various structural applications. Combining with additive manufacturing methods extends further PEEK usage, e.g., as a mold insert material in polymer melt processing like injection molding. Mold inserts must possess a certain mechanical stability, a low surface roughness as well as a good thermal conductivity for the temperature control during the molding process. With this in mind, the commercially available high-performance thermoplastic PEEK was doped with small amounts of carbon nanotubes (CNT, 6 wt%) and copper particles (10 wt%) targeting enhanced thermomechanical properties and a higher thermal conductivity. The composites were realized by a commercial combined compounder and filament maker for the usage in a material extrusion (MEX)-based 3D-printer following the fused filament fabrication (FFF) principle. Commercial filaments made from PEEK and carbon fiber reinforced PEEK were used as reference systems. The impact of the filler and the MEX printing conditions like printing temperature, printing speed and infill orientation on the PEEK properties were characterized comprehensively by tensile testing, fracture imaging and surface roughness measurements. In addition, the thermal conductivity was determined by the laser-flash method in combination with differential scanning calorimetry and Archimedes density measurement. The addition of fillers did not alter the measured tensile strength in comparison to pure PEEK significantly. The fracture images showed a good printing quality without the MEX-typical voids between and within the deposited layers. Higher printing temperatures caused a reduction of the surface roughness and, in some cases, an enhanced ductile behavior. The thermal conductivity could be increased by the addition of the CNTs. Following the given results, the most critical process step is the compounding procedure, because for a reliable process–parameter–property relationship, a homogeneous particle distribution in the polymer matrix yielding a reliable filament quality is essential
Lack of interferon-beta leads to accelerated remyelination in a toxic model of central nervous system demyelination.
Interferon-beta (IFN-beta) is a pleiotropic cytokine that is known to modulate the immune response in multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system (CNS). Spontaneous remyelination and repair mechanisms in MS are mostly insufficient and contribute to clinical disability. Here, we investigated whether IFN-beta has a potential in modifying the extent of de- and remyelination in a toxic model of CNS demyelination induced by the copper chelator cuprizone. IFN-beta deficient (k/o) mice showed an accelerated spontaneous remyelination. However, the amount of remyelination after 6 weeks did not differ between the two groups. Demyelination in IFN-beta k/o mice was paralleled by a diminished astrocytic and microglia response as compared with wildtype controls, whereas the accelerated remyelination was paralleled by an increased number of oligodendrocyte precursor cells (OPC) within the demyelinated lesion at the beginning of the remyelination phase. We hypothesize that the absence of IFN-beta leads to more efficient recruitment and proliferation of OPC already during demyelination, thus allowing early remyelination. These results demonstrate that IFN-beta is able to alter remyelination in the absence of an immune-mediated demyelination