Abstract
The properties of 3-D printed polymeric parts depend significantly on the processing conditions under which they are fabricated. This study aims to determine how the use of low-pressure additive manufacturing (AM) processing conditions, influences the mechanical performance of printed polymeric parts. This polymer material extrusion (PME) study was carried out using an open-source desktop printer, under both low pressure (1 Pa) and at atmospheric pressure. The printing study was carried out using acrylonitrile butadiene styrene (ABS), polylactic acid (PLA) and a nylon co-polymer (PA6). The resultant polymer parts were compared based on their printed mass, density, volume, porosity, surface energy, ATR-IR analysis and thermal properties (DSC). As expected only minor differences in chemical functionality were observed between parts printed under the two processing pressures. Under low-pressure printing conditions, the polymer parts exhibited some physical changes, when compared to those, printed under atmospheric conditions, such as an increase in density and a decrease in porosity. This was observed in particular with the low-pressure printing of PA6 parts, which exhibited an increase in density from 1.095 to 1.113 g/cm3 and a decrease in porosity by 8%. Comparing low-pressure printed type V dog bones (ASTM D-638), with those printed at atmospheric pressure, it was observed that the ABS, PLA and PA6 exhibited an increase in Ultimate Tensile Strength of 9%, 13% and 42% respectively. It is proposed that the superior mechanical properties obtained for polymers printed under low pressure conditions, may be due to a combination of two factors. These are the reduction in porosity of the printed part and the reduction in heat loss at the printed polymer surface, yielding enhanced bonding between the polymer layers. In a further printing study carried out at atmospheric pressure in a nitrogen atmosphere, it was also demonstrated that any oxidation of the polymer layers during printing, did not significantly influence the mechanical properties of the resultant printed parts.
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