Kumar Ajeet, Verma Saurav, Jeng Jeng-Ywan
High Speed 3D Printing Research Center, National Taiwan University of Science and Technology, Taipei, Taiwan.
Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
3D Print Addit Manuf. 2020 Apr 1;7(2):85-96. doi: 10.1089/3dp.2019.0089. Epub 2020 Apr 16.
Additively manufactured cellular structures represent a promising engineering design concept for making customized products where user-specific mechanical properties are required. One of the major challenges in the additive manufacturing (AM) process is removal of unwanted support structures from the lattice. The support structure consumes extra material, printing time, and energy for manufacturing. Postprinting, it needs extensive postprocessing work to remove it from the lattice structure chemically or mechanically. In the case of flexible materials such as thermoplastic polyurethane (TPU), removing the support structure from the lattice is very difficult with the material extrusion process. In this article, a new type of a shell-shaped lattice structure inspired by sea urchin (SU) morphology is designed. This lattice can be additively manufactured by material extrusion processes such as fused deposition modeling (FDM) without requiring any support structures. The mechanical properties of the proposed structure, such as stiffness and energy absorption during loading and unloading, have been evaluated as they are important for cushioning. The compressive results indicate that the stiffness property is almost twice as high compared with the benchmarked, bending-dominated, body-centered cubic (BCC) lattice structure of the same relative density and ethylene vinyl acetate (EVA) foam. Energy absorption is almost equal to the BCC lattice and 20% better than EVA foam. Last, a predictive model on stiffness behavior and energy return was developed to facilitate a systematic way to select optimal densities of the SU lattice structure for energy-absorbing applications. Visual inspection has also revealed that there is no sagging or failure of the lattice, which reduced the manufacturing time and postprocessing time, saving a significant amount of material without compromising on quality. Supportless lattice printing was also validated by printing the specimen with a different FDM printer and TPU filament. A possible application for supportless lattice structures can be for AM of customized shoe midsoles at low cost, ski boots, tires, automotive crush boxes, or any other energy-absorbing structures.
增材制造的多孔结构是一种很有前景的工程设计理念，可用于制造需要特定用户机械性能的定制产品。增材制造（AM）过程中的主要挑战之一是从晶格中去除不需要的支撑结构。支撑结构会消耗额外的材料、打印时间和制造能量。打印后，需要大量的后处理工作才能通过化学或机械方法从晶格结构中去除它。对于热塑性聚氨酯（TPU）等柔性材料，通过材料挤出工艺从晶格中去除支撑结构非常困难。在本文中，设计了一种受海胆（SU）形态启发的新型壳状晶格结构。这种晶格可以通过诸如熔融沉积建模（FDM）等材料挤出工艺进行增材制造，而无需任何支撑结构。所提出结构的机械性能，如加载和卸载过程中的刚度和能量吸收，因其对缓冲很重要而进行了评估。压缩结果表明，与具有相同相对密度的基准弯曲主导的体心立方（BCC）晶格结构和乙烯醋酸乙烯酯（EVA）泡沫相比，刚度性能几乎高出一倍。能量吸收几乎与BCC晶格相等，比EVA泡沫好20%。最后，开发了一个关于刚度行为和能量回返的预测模型，以促进一种系统的方法来选择用于能量吸收应用的SU晶格结构的最佳密度。目视检查还表明，晶格没有下垂或失效，这减少了制造时间和后处理时间，在不影响质量的情况下节省了大量材料。通过使用不同的FDM打印机和TPU细丝打印试样，也验证了无支撑晶格打印。无支撑晶格结构的一个可能应用是低成本定制鞋中底、滑雪靴、轮胎、汽车防撞箱或任何其他能量吸收结构的增材制造。
