Publikace

New types of filaments were formed by adding various fillers into polymers during the fabrication. We designed two new composites in cooperation with a filament producer. Biodegradable thermoplastic polyester polylactic acid (PLA) was filled with carbon black. Carbon black (CB) formed 30 wt.% of in the final mixture. The second composite was made by compounding the polyethylene terephthalate glycol-modified (PET-G) with titanium dioxide. Two different contents of TiO2, namely 10 and 20 wt.%, were selected for filament preparation. The goal of the testing was to evaluate the change of mechanical and thermomechanical properties in contrast to pure filaments. The testing specimens were prepared by Fused Deposition Modeling (FDM), which belongs to 3D printings techniques. The printed samples were subjected to mechanical tensile testing and to microhardness measurement by the Vickers method. Thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) were performed too. In particular, glass transition temperature, coefficient of thermal expansion (CTE), and storage modulus were analyzed. All composites showed a lower ultimate tensile strength than the neat polymer. Notable changes in thermomechanical behavior were also detected. The most significant difference was the drop in CTE above the glass transition in the case of filled PLA samples.

This work presented an FEM (finite element method) mathematical model that describes the temperature distribution in different parts of a 3D printer based on additive manufacturing process using filament extrusion during its operation. Variation in properties also originate from inconsistent choices of process parameters employed by individual manufacturers. Therefore, a mathematical model that calculates temperature changes in the filament (and the resulting print) during an FFF (fused filament fabrication) process was deemed useful, as it can estimate otherwise immeasurable properties (such as the internal temperature of the filament during the printing). Two variants of the model (both static and dynamic) were presented in this work. They can provide the user with the material’s thermal history during the print. Such knowledge may be used in further analyses of the resulting prints. Thanks to the dynamic model, the cooling of the material on the printing bed can be traced for various printing speeds. Both variants simulate the printing of a PLA (Polylactic acid) filament with the nozzle temperature of 220 °C, bed temperature of 60 °C, and printing speed of 5, 10, and 15 m/s, respectively.

This work focuses on evaluating the anisotropy of the structures manufactured by two 3D printing technologies, Fused Filament Fabrication (FFF) and Stereolithography (SLA). According to the manufacturing process, printed structures are expected to have some level of anisotropy. It is essential to consider it while designing a model for 3D printing. Printed specimens were subjected to tensile testing, thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). Measurements were based on the ASTM D638, E1545 and D4065 standards. The specimens were printed in three different orientations for tensile tests and DMA, respectively in four orientations for TMA. The FFF specimens were prepared from poly-lactic acid (PLA) with different extruder temperatures, 210°C and 240°C. In the case of SLA specimens, photopolymer based on epoxy resin was used, the process differed in curing time (8 s and 16 s). The results clearly showed a higher level of anisotropy of the FFF specimens compared to SLA specimens. The FFF specimens show in the orientation XZ 1,5 times lower tensile strength than in the other two orientations, compared to SLA, where the tensile strength was similar. The anisotropy of the thermomechanical properties was high for FFF specimens; in contrast, the SLA specimens showed no difference in thermal expansion for different printing orientations.

Although stereolithography (SLA) is the oldest 3D printing method, only a few works have been published about the complex electrical properties of objects printed from unfilled photopolymerizable resins. In this paper, we describe how the dielectric constant, loss factor, dielectric strength, and volume resistivity of printed objects are influenced by the type of resin and the thickness of the sample. Two commercial resins were used - acrylate/epoxy "blue" resin and acrylate "orange" resin. The electrical properties were mostly dependent on the type of resin and thickness of the sample. Thicker blue samples showed the highest polarizability among all tested materials. Volume resistivity of orange samples was one order of magnitude higher than the one of blue samples. Dielectric strength was not dependent on the type of the resin but rather on the thickness of the samples. Our results contribute to the current knowledge about the electrical behavior of SLA-printed objects.

The aim of this work was to evaluate the mechanical and thermomechanical properties of structures prepared by 3D printing from biodegradable thermoplastic polyester PLA (Polylactic Acid). PLA structures and their manufacture by 3D printing can be a cost-saving and ecological alternative to the current production of insulation systems, e.g. condenser bushings or substrates for printed circuit boards. For further practical application, the knowledge of the change of mechanical and thermal properties in dependence on process parameters is necessary. In this research, PLA test samples were first prepared at different printing speeds and nozzle temperatures. Then, they were characterized by thermomechanical analysis (TMA), dynamic mechanical analysis (DMA), and tensile tests. The data showed that the decrease of printing temperature remarkably increased the dimension change evaluated from TMA measurement of 3D printed structures. On the other hand, no significant differences were found between samples printed with different printing speeds. Our results should lead to a better understanding of how to set up the 3D printing process properly.

The degradation of plastic materials induced by solar radiation can limit their use in outdoor applications. Therefore, we aimed to find a relationship between the photodegradation of 3D printed polylactic acid (PLA) and its electrical and thermomechanical properties. In the first stage, the printing settings were optimized with regard to the dielectric strength of samples. Afterward, the sets of printed specimens were exposed to UV light of different spectrum and duration. UV gas-discharge lamps with spectral peaks at 254 and 385 nm were used as intense UV light sources; the individual exposure times were chosen as 6, 12, 24, 48, and 96 hours. Subsequently, the dielectric strength of each set was evaluated, and thermomechanical analyses were performed. Although the irradiation at 254 nm caused substantial degradation of PLA, it did not remarkably affect its dielectric strength. Nonetheless, both sources of UV light caused a considerable brittleness that might be the limiting factor for the outdoor application of PLA.

The aim of this work was to evaluate the use of FFF (Fused Filament Fabrication) technology in high and medium voltage applications. The research is based on previous work, where the dependence of dielectric strength of 3D printed objects on printing resolution (the thickness of one layer) was examined. Four polymer materials designated for FFF were chosen for the experiments - ABS (acrylonitrile butadiene styrene), PET-G (polyethylene terephthalate - glycol modified), ASA (acrilonitrile styren acrylate) and PP (polypropylene). The following tests of the printed samples from such materials were conducted - atmospheric impulse test with positive polarity, short-term AC and DC breakdown strength tests and measurement of partial discharges. Based on acquired results, the optimal material for unipolar stresses (DC and impulse) is PP, whereas for bipolar stresses it is a close match between ABS and PET-G. For systems in which all three types of stresses occur, ASA seems to be the best compromise. Although the dielectric strength of the examined 3D structures is sufficient, an improvement of these materials would be proper, for example by adding admixtures to the base materials or better printing quality.

Fused Deposition Modelling (FDM) is one of the most common methods of 3D printing used in many fields of industry, especially in development departments. Since plastics are fundamental materials for electronics industry, the aim of this work is to examine dielectric properties of objects printed from such materials. This work’s contribution is the evaluation of the dependency of the printed objects properties on printing quality and the use of 3D printed plastic components in electronics. For the experiment, three commonly used materials in FDM were chosen – PLA, ABS and PET-G. The materials were pure without any additional admixtures and the relevant test samples were printed with different printing resolution (height of one layer). The following properties were examined – permittivity, dissipation factor and dielectric strength. The results showed that permittivity slightly decreased with increasing height of one layer. Dissipation factor varied significantly in the measured range and there was no apparent dependency on the printing resolution. Rather, it was an indicator of the printing quality. Dielectric strength also slightly decreased with the decreasing resolution; however this parameter was governed primarily by the employed material. Generally, an improvement of the dielectric properties of these materials is required due to a relatively small dielectric strength, for example by adding admixtures to the base material or better printing quality.