Effect of the Material Extrusion Process Parameters on the Compressive Properties of Additively Manufactured Foamed and Nonfoamed Polylactic Acid Structures

This work evaluates the potential for foamable polymer filaments to be used to make lightweight, energy-absorbing structures using additive manufacturing. To achieve this, a commercial, foamable polylactic acid filament was extruded using a material extrusion process to make parts for compression testing. It was found that a maximum foam expansion could be achieved at an extrusion nozzle temperature of 220°C, but that to achieve dimensional accuracy, the material flow rate through the nozzle had to be adjusted by decreasing the extrusion multiplier value. In a novel approach, accurate and faster builds could be achieved by decreasing the infill instead. When compared with porous structures achieved by using partial infilling instead or as well as foaming, all materials were found to follow the same power-law function of the solid fraction. These trends indicated that the mechanical response was, within experimental scatter, a function of the overall solid fraction and not influenced by whether the porosity was within or between the raster lines. Although there was no apparent benefit to the mechanical performance in introducing porosity into a polymer by foaming, foamable filaments are desirable if stiff, lightweight structures with low fractions of interconnected porosity are required and can be used in combination with infilling to produce low-density structures that would be highly suitable for cores in novel lightweight sandwich structures.