International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Three-dimensional (3D) printing technologies have been developed for prototype purposes. However, it has become possible to manufacture various functional parts with improving mechanical properties of 3D printing materials. Although polylactic acid (PLA) is the most widely used 3D printing material, the mechanical properties required for functional parts are not sufficient. For this reason, carbon fibre reinforced PLA composites are preferred as 3D printing material to advance the mechanical properties of the fabricated parts. However, for 3D printed parts, it is known that the layer thickness and printing orientation angles affect the mechanical properties. In this study, unreinforced PLA and 15% carbon fibre reinforced PLA composite tensile specimens were 3D printed using fused deposition modeling (FDM) technique. The effects of printing orientation angle and layer thickness on modulus of elasticity and tensile strength are investigated. 3D printed unreinforced PLA samples exhibited better tensile performance as compared to carbon fibre reinforced PLA composite samples.

Three-dimensional (3D) printing technologies are the most promising method in the production of functional parts. Although 3D printing technology includes various methods, fused deposition modelling (FDM) is the most widely used one. In FDM, generally polylactic acid (PLA) filaments are used to fabricate 3D geometry by stacking individual layers. In fact, FDM is a complicated process with numerous parameters that affect printing quality. Printing parameters such as printing orientation, layer thickness, printing orientation angle, filling ratio, filament feed rate, etc. have significant impact on the quality and performance of FDM printed parts. Since the mechanical properties are very important for functional parts, the effect of these parameters on the mechanical properties of the PLA specimens has been extensively studied. However, there is no sufficient data in the surface characterization literature of these parameters. In this study, the effect of layer thickness and printing temperature on the surface properties of PLA specimens printed using FDM was investigated.

Dry sliding wear behaviour of unreinforced Al4%Cu and Al4%Cu – SiC composites was investigated. Composites containing 10-50 vol.% SiC were obtained via hot press by using Al, Cu and SiC starting powders. Wear tests were conducted by an oscillating tribometer having a 6 mm diameter alumina ball. 2 N load was employed and sliding span was 5 mm with a total test distance of 6 m. Wear tracks were examined by an optical microscope, track cross sectional areas were determined by a profilometer and wear rates were calculated. It was seen that the wear track formed on the unreinforced sample was much larger and deeper than the ones on the composite samples. Wear mechanism was suggested to be initially adhesive and then adhesive and abrasive. The wear rate of unreinforced sample was about 11×10^-3 mm³/N.m. Wear rate was seen to decrease abruptly with the addition of SiC particles into the matrix alloy. When 10 vol.% SiC was used, wear rate decreased to 1.5×10^-3 mm³/N.m. The lowest wear rate was achieved in the sample containing 30 vol.% SiC, 0.5×10^-3 mm³/N.m.

Metal matrix composites, containing Al (4 wt.% Cu) as the matrix material and SiC particles as the reinforcement, were produced by hot pressing. SiC(p) content of the composites were in 10 – 50 vol.% range. Appropriate amounts of Al, Cu and SiC powder were dry mixed and pressed at 25MPa at 525 and 550^oC. Obtained composites were subjected to density and hardness measurements, 3 point bending tests and optical microscope investigations. Hardness was seen to increase continuously with the increase in the amount of SiC(p) from 54HB10 (unreinforced matrix) to 148HB10 (50 vol.% SiC). On the other hand, bending strength values of the composites first showed an increase up to 20 vol.% SiC and then decreased. Strain values decreased considerably, with the addition of SiC into the unreinforced matrix and the composites containing 40 and 50 vol.% SiC did not show plastic deformation before fracture. Yield strength and elastic moduli of the composites increased with the increase in the SiC amount. It was seen that the properties of Al%4Cu-SiC(p) composites, such as strength and hardness, can be adjusted by varying their SiC contents.

Formation of TiB₂ , TiN and Al₂O₃ powder mixtures were obtained through self-propagating high-temperature synthesis (SHS), starting from TiO₂ + BN + Al mixtures. As a diluent, NaCl was added in 0-40 wt% range to the starting mixture in order to refine the size of the formed particles. Thermochemical calculations were performed by Factsage software. The products were subjected to XRD, SEM and particle size analyses. Intended reaction products were obtained in the TiB₂, TiN and Al₂O₃ system according to XRD analyses, with no cross reaction products. The crystallite size of the products decreased with the increasing amount of NaCl according to the broadening of the peaks on the XRD patterns of the products. Particle size measurements revealed that near-nano size particles were formed. A decrease in the adiabatic temperature was calculated, a decrease in the velocity of the SHS wave front was observed and a decrease in the particle size of the obtained products was measured as a result of the increase in the diluent amount.