Parametric optimization of intra- and inter-layer strengths in parts produced by extrusion-based additive manufacturing of poly(lactic acid)

Parts produced by extrusion-based additive manufacturing experience the disadvantage of consisting of many weld-lines, which consequently downgrade their mechanical properties. This work aims at maximizing the strength of printed parts by considering and improving the intra- and inter-layer cohesion between adjacent strands. Therefore, printed poly(lactic acid) specimens were characterized by means of a particular tensile test setup, and the inter-layer cohesion of printed specimens was evaluated by means of the double cantilever beam test. A detailed parametric statistical evaluation, which included printing temperatures, layer thicknesses, and layer-designs, was complemented by the material's viscosity data and the analysis of the specimens' fracture surfaces and cross-sections. An optimal layer-design was found to be a key parameter in the optimization of strength with regard to different loading directions. Additionally, the maximization of the cohesion leads to a tremendous improvement in the mechanical performance of the printed parts, resulting in strengths of roughly 90% of those of compression-molded parts. (C) 2017 Wiley Periodicals, Inc.