OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 4 2024 Fig. 6. Formation of the transfer fi lm a b Fig. 7. Eff ect of normal load (a) and speed (b) on PO1 wear which minimizes wear, so polymers are often chosen as a material for wearing parts. This is one of the important tribological phenomena. It is also known that when separation occurs inside the transfer fi lm, it occurs between the fi lm and the polymer rather than between the polymer and steel, so it acts as a protective layer that minimizes wear. The adhesive wear mechanism is one of the reasons for the development of the transfer fi lm in polymer. A schematic diagram of the transfer fi lm formation is shown in Fig. 6. PLA is one of the popular materials because of its non-toxicity, biodegradability, biocompatibility and eco-friendliness. Additionally, since it is a 3D printing material, it is highly appreciated in biomedical applications where there are relative motions between two surfaces (such as hip, knee and other joints). It has been reported in the literature that the printing orientation angle also plays an important role in the wear behavior of PLA material. In the present study, PO1, PO2 and PO3 pins were manufactured using additive technology with constant and optimized parameters reported in the literature so that the printing uniformity can be maintained. The eff ects of normal load and speed as well as printing angle on the wear behavior were studied. Figure 7, a and b show the eff ects of normal load and speed on the wear pattern of PO1 pin (print orientation angle 0°). A gradual increase in the wear was observed under normal load and variable speed. The minimum wear was recorded as 2,291 μm and the maximum was recorded as 2,523 μm. From Fig. 7, a and b, it can be seen that the slope of the wear versus speed graph increased by almost 43 % compared with that of the normal load versus wear graph. This indicates that the speed has a prominent eff ect on the wear pattern. This was also evident from the exponent values of the equation (PO1) given in Table 4. As the speed increases, the vibrations in the system increase, which is an unfavorable condition for forming a stable transfer fi lm. Fig. 8, a and b shows the eff ects of normal load and speed on the wear pattern for the PO2 pin (print orientation angle of 45°). The minimum wear of 2,948 μm and the maximum wear of 3,489 μm (Fig. 8, a and b) showed that the slope of the wear versus speed graph increased by almost 26 % compared to the slope of the wear versus normal load graph. The wear of PO2 is greater compared to PO1 in the considered cases. This was due to the improper bonding of the material at a printing otation angle of 45°. A similar fact was also reported in the literature.
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