This study concerns the use of the fused filament fabrication technique to create models of the landing gear of an unmanned aircraft. These components are made of filament with short fibers (chopped fibers) of carbon fiber and fiberglass. In order to identify the material with the high mechanical strength, the designed models were subjected to a finite element analysis and to a three-point bending test, followed by a microscopic examination of the tested components. Following a comparative study, both the finite element analysis results and the three-point bending test results provided similar results, with a relative error of 2%, which is acceptable in the aviation field. After analyzing all the results, it was found that the carbon fiber-reinforced polymer material has the highest mechanical performance, with a bending strength of 1455 MPa. Among the fused filament fabricated landing gears, the one with the best mechanical performance was polyethylene terephthalate with short carbon fiber, which had a bending strength of 118 MPa. Microscopic analysis of the landing gear models, manufactured by the fused filament fabrication process, indicated the typical defects of composite filaments: voids and interlayer voids.

Fused Filament Fabrication (FFF) is one of the frequently used material extrusion (MEX) additive manufacturing processes due to its ability to manufacture functional components with complex geometry, but their properties depend on the process parameters. This paper focuses on studying the effects of process parameters, namely infill density (25%, 50%, 75%, and 100%), on the mechanical and thermal response of the samples made of poly(lactic acid) (PLA) reinforced with short glass fibers (GF) produced using FFF process. To perform a comprehensive analysis, tensile, flexural, compression, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA) tests were used. The paper also aims to manufacture by FFF process of composite structures of the fuselage section type, as structural elements of an unmanned aerial vehicle (UAV), and their testing to compression loads. The results showed that the tensile, flexural and compression strength of the additive manufactured (AMed) samples increased with the increase of infill density and therefore, the samples with 100% infill density provides the highest mechanical characteristics. The AMed samples with 50% and 75% infill density exhibited a higher toughness than samples with 100% infill. DSC analyses revealed that the glass transition (Tg), and melting (Tm) temperature increases slightly as the infill density increases. Thermogravimetric analyses (TGA) show that PLA-GF filament loses its thermal stability at a temperature of about 311 °C and the increase in fill density leads to a slight increase in thermal stability and the complete degradation temperature of the AMed material. The compression tests of the fuselage sections manufactured by FFF made of PLA-GF composite showed that their stiffening with stringers oriented at an angle of ±45° ensures a higher compression strength than the stiffening with longitudinal stringers.

Abstract. In this article are studied the possibilities of manufacturing human teeth using the Selective Laser Melting (SLM) process. The human teeth are a biological construction, and because of this, they have a very complex structure with external and internal complex surfaces, unique for each person. To manufacture such structures, even using additive technologies, it is important to find the right manufacturing strategy. In this study are presented three strategies to manufacture the first molar using a SLM process and ANSI 316 L stainless steel as the building material. The best strategy to manufacture the teeth is chosen, and once build they can be used to test dental tools.

This paper presents the stages taken to remanufacture a damaged part, for which no documentation is available, using the SLM additive technologies. A damaged part is scanned using the COMET L3D scanner and the points cloud is used to redesign and reconstruct the part as a 3D CAD model. Using the generated 3D CAD model the build job for the SLM is created by designing and adding the construction supports, the material type and the type of hatching strategy for each slice. The slices are used by the SLM250HL equipment and the new metallic part is manufactured. The manufactured part was scanned with the same 3D scanner and the data from the original part was compared with the new reading. The results can be used to reconstruct more complex parts, to redesign the broken parts and to improve the manufacturing process.

The application of fused filament fabrication processes is rapidly expanding in many domains such as aerospace, automotive, medical, and energy, mainly due to the flexibility of manufacturing structures with complex geometries in a short time. To improve the mechanical properties of lightweight sandwich structures, the polymer matrix can be strengthened with different materials, such as carbon fibers and glass fibers. In this study, fiber-reinforced composite sandwich structures were fabricated by FFF process and their mechanical properties were characterized. In order to conduct the mechanical tests for three-point bending, tensile strength, and impact behavior, two types of skins were produced from chopped carbon-fiber-reinforced skin using a core reinforced with chopped glass fiber at three infill densities of 100%, 60%, and 20%. Using microscopic analysis, the behavior of the breaking surfaces and the most common defects on fiber-reinforced composite sandwich structures were analyzed. The results of the mechanical tests indicated a significant influence of the filling density in the case of the three-point bending and impact tests. In contrast, the filling density does not decisively influence the structural performance of tensile tests of the fiber-reinforced composite sandwich structures. Composite sandwich structures, manufactured by fused filament fabrication process, were analyzed in terms of strength-to-mass ratio. Finite element analysis of the composite sandwich structures was performed to analyze the bending and tensile behavior.

In this paper is investigated the effect of building parts with different layer sizes using an additive manufacturing technique, from the statistical point of view. The paper is focused on the differences that appear at the stainless steel parts when the building layer is increased, this being done on the SLM 250 HL machine. This machine uses a fiber laser to melt fine powder on a layer-by-layer basis to create three-dimensional metallic parts from CAD files. The samples were constructed using two different layer thicknesses and then reprocess so that a micro hardness test could be employed. The micro hardness’s are compared using statistical methods. Overall, the obtained results indicate that the outcome influences the manufacturing strategy that it is chosen.

Nowadays Additive Manufacturing, and in particular Selective Laser Melting (SLM ), is being used more and more. The SLM manufacturing process has been subjects to a lot of studies in order to improve the manufacturing parameters. In this paper are presented some researches on the internal structure of the manufactured parts with two layer thickness: 30[μm] and 50[μm]. The internal structure of parts manufactured on SLM machine is obtained as images with a microscope. On the images each grain of the internal structures is painted in a different color and grouped according to its shape. All data about grains are analyzed by the means of statistical methods. The two manufacturing strategies, 30[μm] and 50[μm] layer thickness, generate parts that have slightly different internal structures. Thus, from the point of views of internal structure and manufacturing time, the strategy with 50[μm] layer thickness can be used because it generates a lowering in manufacturing costs and increases the overall productivity.

Additive manufacturing, through the process of thermoplastic extrusion of filament, allows the manufacture of complex composite sandwich structures in a short time with low costs. This paper presents the design and fabrication by Fused Filament Fabrication (FFF) of composite sandwich structures with short fibers, having three core types C, Z, and H, followed by mechanical performance testing of the structures for compression and bending in three points. Flatwise compression tests and three-point bending have clearly indicated the superior performance of H-core sandwich structures due to dense core structures. The main modes of failure of composite sandwich structures were analyzed microscopically, highlighting core shear buckling in compression tests and face indentation in three-point bending tests. The strength–mass ratio allowed the identification of the structures with the best performances considering the desire to reduce the mass, so: the H-core sandwich structures showed the best results in compression tests and the C-core sandwich structures in three-point bending tests. The feasibility of the FFF process and the three-point bending test of composite wing sections, which will be used on an unmanned aircraft, have also been demonstrated. The finite element analysis showed the distribution of equivalent stresses and reaction forces for the composite wing sections tested for bending, proving to validate the experimental results.