China: Enhancing Strength in 3D Prints via Bioinspired Tool Paths

In the recently published ‘Strength and toughness enhancement in 3D printing via bioinspired tool path,’ Chinese researchers delve further into challenges with mechanical properties, especially issues with strength, toughness, and anisotropy. While these properties may be attainable, that is often not the case simultaneously. In this study, the team offers a bioinspired parallel-scan path for increasing strength and toughness with in-plane isotropy.

Both contour-parallel path and parallel-scan are the most used types of filling paths, with the first offering excellence in accuracy, but deficiencies otherwise, and the second offering speed but lack of accuracy. To solve these discrepancies, many researchers use a hybrid path strategy.

Bioinspired structural materials are also employed to offer simultaneous strength, toughness, stiffness, and low density. Taking inspiration from nature as is so often the case, the researchers looked to natural organisms to solve deficiencies in material properties.

Materials like honeycomb, nacre, and conch have been used to refine mechanical properties previously, but Bouligand structures present added flexibility, and are now being used in SLA 3D printing for enhancing strength. As the researchers point out though, these methods usually require ‘two materials arranged into a hierarchical fashion’ and can be both complex and expensive.

Here, the researchers developed a new parallel scan path meant to increase mechanical properties:

“With this method, both the strength and toughness can be improved remarkably only through adjusting the rotation angles in printing tool path, and no special equipment or complicated material treatment are required. This may offer a very applicable, low-cost and widely extendable strategy to improve mechanical properties in 3D printing,” explain the researchers.

Bioinspired Bouligand structure (a) the path generation strategy inspired by Bouligand structure and (b) hierarchical structure in Homarus americanus (American lobster).

During the study, samples were 3D printed at the desktop level with a JGAURORA A3S FDM 3D printer, using PLA filament from JGAURORA (China, founded in 2008). The researchers worked with the following details:

• Layer thickness of 0.1 mm
• Printing speed of 30mm/s, continually
• Nozzle temperature of 200 °C
• Heat bed temperature of 60 °C

Samples were evaluated for strength, stiffness, toughness, and behavior regarding various parallel-scan paths.

“Since the influence of Bouligand structure on mechanical properties mainly occurs in x-y plane, the building orientation of all specimens are parallel to the platform,” stated the researchers.

Specimen preparation and test (a) specimen fabrication on the FDM printer platform and its dimensions, (b) parallel-scan paths design for tensile tests and (c) tensile tests implementation.

During tensile testing, the researchers confirmed that both strength and toughness were increased—in comparison with samples created via conventional path designs. They were improved by 12.1 percent and 101 percent with the ‘influence of critical design’ displayed showing an increase with the decrease of α, and toughness peaking with α at approximately 15°.

“Results show that the largest fracture surface area appears at α = 15° and the stress distribution changes with the decrease of α. This result indicates that both of the two important factors contribute to the optimal mechanical properties, and an appropriate rotational angle α can be determined with the consideration of these two factors at different processing conditions,” concluded the researchers.

Problems with mechanical properties continue for researchers relying on 3D printing, often motivated by need to innovate with hardware, software, and materials. Because of this, while many users opt to make parts and experiment with ABS or PLA, today we also see many new materials including composites, and ongoing experiments in 3D (and 4D) printing overall regarding better choices for color, shape memory, and more.

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Tensile test results (a) ultimate tensile strength and (b) toughness with different parallel-scan paths design