Abstract
White Polyamide 12 (PA12) is the most usable material for additive manufacturing. PA12 parts manufactured by Selective Laser Sintering (SLS) process are chemically stable, environmentally friendly, and have reasonable mechanical properties. As a result, PA12 powder has been used for rapid prototyping purposes and manufacturing of end-user products. Although, the mechanical properties of PA12 manufactured by SLS technology have been the focus of many investigations, so far, the effect of build orientation on the tribological properties PA12 parts have not received sufficient attention in previous research. Therefore, this study is devoted to investigating the dry sliding friction and wear characteristics of PA12 parts manufactured by SLS technique at three different orientations (X, Y, and Z). For this purpose, the coefficient of friction (COF) and the approximate contact temperature of PA12 pins loaded against a stainless steel disc are measured using a Pin-on-disc test apparatus. The experimental results revealed that under dry sliding conditions, the COF, frictional heat, and specific wear rate of PA12 specimens oriented along the Y-axis are significantly smaller than those oriented along X and Z axes. Furthermore, the transfer film observed on the steel disc surface acts to decrease the COF and wear rate of Y-oriented test specimens. On the other hand, the results showed that at the steady-state wear stage, PA12 specimens oriented along X and Z axes experienced a combination of abrasive wear, adhesive wear, and sometimes surface fatigue wear. The results from this study can help designers to orient the active rubbing surface of PA12 during SLS process in the proper way to reduce the COF, frictional heat, and wear rates of PA12 objects.

Key words: Polyamide 12 (PA12); Selective Laser Sintering; Tribological properties, build orientation