Experimental study on the effect of filament-extrusion rate on the structural, mechanical and thermal properties of material extrusion 3D-printed polylactic acid (PLA) products

Material extrusion (MEX), also commonly referred to as fused deposition modeling (FDM) or fused filament fabrication (FFF) is currently one of the most commonly used additive manufacturing techniques. The quality of the 3D-printed objects fabricated by MEX methods highly relies on various printing parameters, one of which is the so-called filament extrusion multiplier ( k ). In this study, 3D-printed parts were prepared by MEX technique during which the material feeding rate was adjusted by varying the extrusion multiplier in the range of 97–105% ( k = 0.97–1.05). The fabricated parts were tested for their geometrical, structural, mechanical, and thermal conductivity properties. Based on computed tomographic analysis and scanning electron microscopic images, increasing the k parameter resulted in smaller voids, along with gradually decreasing porosity (from 5.82 to 0.05%). Parallel to the decreasing defects, the thermal conductivity of the parts improved from 0.157 to 0.188 W/mK as determined by light-flash analysis technique. On the other hand, when k was set to ≥ 1.03 the geometrical accuracy declined, the size of the specimens considerably increased relative to the nominal values, especially in the X–Y directions due to excess material getting “squeezed” on the sides of the specimens. This latter phenomenon also resulted in the formation of a number of stress concentration sites, which manifested in the decrease of mechanical properties. Accordingly, the tensile, flexural, and impact strength of the samples improved up to k = 1.03; however, above that it dropped considerably.