OBRABOTKAMETALLOV Vol. 26 No. 4 2024 TECHNOLOGY respectively. The graphs are based on varying two process parameters while keeping the third parameter constant. The study revealed the infl uence of the interaction of process parameters and the printing orientation angle on the wear rate of PLA in a friction pair with SS 316 stainless steel. It is seen that the wear increases with the increase of speed and normal load. However, the increase in wear will become more noticeable at higher process parameters. The speed followed by normal load can be seen as most signifi cant parameters aff ecting wear. This can also be confi rmed by the higher exponent value for the speed followed by for load Table 4. This study fi nds that wear is prominently aff ected by speed, especially at higher values of normal load. Grey relational analysis is the multi response optimization method that has been applied in the performance evaluation of various complex applications with limited information. It is widely used to measure the degree of relationship between sequences using gray relational grade. The procedure for GRA is explained above in the methodology. In the present study, the input factors were normal load and speed whereas GRA was conducted for the wear of PO1, PO2 and PO3 materials. The linear normalization of the experimental results for wear was based on the smaller-the-better approach. The experiments were conducted for diff erent input parameters according to Table 1 for PO1, PO2 and PO3 specimen. A total of 39 experiments were conducted, of which 1–13 experiments were for PO1, 14–26 for PO2 and the rest were for PO3. According to the procedure of GRA normalization of response (xi∙(k)), the deviation sequence (Δ0i) and the gray relation coeffi cient (GRC) for wear were determined. The values of xi∙(k), Δ0i and GRC for wear are shown in Table 5. A higher GRC indicates that the corresponding experimental conditions are optimal. Overall, PO1 material showed excellent performance compared with PO2 and PO3. However, PO2 showed poor performance. The optimal values of normal load and speed were found to be 600 N and 451 rpm. PLA Fig. 12. 3-D graphs showing the change in wear depending on the normal load and rotation speed for: a – PO1; b – PO2 and c – PO3
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