Mechanical Property Optimization of FDM PLA in Shear with Multiple Objectives

This study presents the influences of key processing parameters on the resulting material properties of fused-deposition-modeled (FDM) polylactic acid (PLA) components tested in torsion. A reduced experimental matrix was produced through the use of a Taguchi L9 orthogonal array with three parameters at three levels each. The processing parameters included the layer thickness, infill density, and postprocessing heat-treatment time at 100°C. Testing of components at varying times is conducted to facilitate heat-treatment time testing range and show the effects of prolonged heating. The layer thickness and infill are tested across the entire useful range available for the FDM machine used. Shear stress–strain response curves are acquired and average ultimate shear strength, 0.2% yield strength, proportional limit, shear modulus, and fracture strain are calculated for each run. An analysis of results via regression analysis is used to determine influences levels of parameters of the mechanical properties. The layer thickness and infill density are shown to be of high importance when optimizing for strength, with heat-treatment implementation slightly improving the resulting properties. Ductility is mainly affected by infill and heat treatment, with layer thickness having only a slight effect on the fracture strain achieved. Recommendations are made based on results of a method to optimize for either strength or ductility and how to compromise between recommended settings when a balance between the two is desired. The ability to produce parts with mechanical properties at or near those of bulk PLA is shown.