Effect of Infill Pattern, Density, and Orientation on the Mechanical and Surface Characteristics of MEX-Printed PLA Samples for Casting-Pattern Applications

Material extrusion (MEX) enables rapid fabrication of single-use polymer casting patterns for foundry and mechanical engineering applications, where handling strength and surface texture are critical. This study examines how infill pattern, density, and orientation affect the mechanical and surface properties of samples printed from ELEGOO PLA on a Bambu Lab A1 using Bambu Studio 2.5.0. Two infill types (triangle, grid), two densities (50%, 70%), and five orientations were evaluated via uniaxial tension, fixed-deflection three-point bending, line-profile and areal surface texture measurements, and SEM fracture analysis. Tensile strength ranged from 23.60 to 29.19 MPa. Raising infill density from 50% to 70% increased mean tensile strength from 24.62 to 27.65 MPa. The highest tensile strength, 29.19 MPa, occurred for a 70% grid infill at 75° orientation; the highest bending load at 4 mm midspan deflection, 107.97 N, occurred for a 70% grid infill at 15°. Across the descriptive surface dataset, differences among the top, side, and bottom surfaces were greater than the variations associated with infill orientation. Top, side, and bottom surfaces formed via different mechanisms; the relatively high bottom-surface roughness arose from replication of the textured PEI build plate. The selected lower-density fracture surfaces exhibited more pronounced visible gaps and inter-bead discontinuities in the SEM images. Within the tested range, the 70% grid infill produced the best overall mechanical performance. These findings are specific to the ELEGOO PLA–Bambu Lab A1–Bambu Studio 2.5.0 system and should not be interpreted as intrinsic PLA properties, used for direct cross-material benchmarking, or assumed to represent behavior under industrial foundry conditions. Instead, they provide system-specific screening data for selecting candidate infill configurations and for the subsequent evaluation of this commercial MEX printing platform for producing single-use polymer casting patterns for complex-geometry components in mechanical engineering under representative foundry conditions.