3D Printing in Indonesia: Researching PLA Infill Pattern & Density

In the recently published ‘Infill pattern and density effects on the tensile properties of 3D printed PLA material,’ researchers from Indonesia delve further into the details of fabrication with polylactic acid (PLA) material, working with three different infill densities and patterns.

While both acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) are commonly used in 3D printing, for this study the researchers focused on PLA—often chosen due to affordability, accessibility, and potential for producing innovative, lightweight prototypes and parts. Not only that, because of its plant-based nature, PLA is biodegradable and more environmentally friendly.

Mainly investigating infill density and infill pattern, the research team used tensile tests to reveal material properties, varying parameters to test properties such as tensile strength, yield strength, and ultimate strength.

The following infill densities were chosen:

• 25 percent
• 50 percent
• 75 percent

Three infill patterns were used:

• Grid
• Tri-hexagon
• Concentric

Five samples were used per each combination, resulting in 45 specimens overall. The researchers used 1.75mm PLA, printing melting temperatures of approximately 190°C – 230°C. For 3D printing specimens, the research team used a temperature setting of 210°C.

The dimension of ASTM D638 – type I test specimen in mm

Infill patterns were printed as follows:

• Grid pattern printing object layers in 90-degree crossing paths
• Tri-hexagonal patterns printing object layers in three path directions, each varying by 120 degrees of the other
• Lowest path angle (in terms of specimen axial axis) of 30 degrees
• Concentric pattern printing in direction of specimen axial axis

Infill patterns: (a) grid, (b) tri-hexagonal, and (c) concentric. Grid pattern infill densities: (d) 25%, (e) 50%, and (f) 75%

Tensile properties of the PLA Specimens

Overall, the study showed that as tensile properties increase, the infill density increases—with the exclusion of the concentric pattern at 75 percent infill density.

Stress-strain plots: (a) grid pattern with varied infill densities, (b) 50% infill density with varied infill patterns.

“Based on the result, the highest tensile properties corresponded to concentric pattern with 75% of infill density, where it has 42.2 MPa of ultimate strength, 3.89 GPa of Young’s modulus, and 40.98 MPa of yield strength. In addition, grid pattern with 100% infill density was tested and it was recorded that the Young’s modulus and yield strength were 3.6 GPa and 48.2 MPa, respectively. For 100% infill density, the effect of infill pattern on mechanical properties is negligible,” concluded the researchers.

“The results can be used as reference data for creating finite element model (FEM) and predicting the optimum tensile properties with respect to the selection of the printing parameters. Comprehensive investigation on the effect of infill pattern on the tensile properties is suggested for future study.”

Research continues regarding PLA, from experimenting with composite materials in medical applications to the influence of color, additives like antioxidants, and more.

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