Researchers fromETH Zurich，瑞士将3D打印与铸造方法融合在一起，以设计“蛋壳”混凝土3D打印过程。
Combining large-scale robotic Fused Deposition Modeling (FDM) 3D printing with the simultaneous casting of a fast-hardening, set-on-demand concrete, enabled the team to produce complex structures in a more material-efficient way. Moreover, casting the fast-hardening concrete within a continuous process minimized the lateral pressure on the material, allowing for the creation of printed concrete sculptures with complex geometries.
使用此技术，并与德国工程公司合作Basler & Hofmann, the Zurich team ‘planted’ a “future tree” in the courtyard of the company’s headquarters. This concrete model, in addition to others produced by the team, could indicate the potential of the process for mass customization and structural optimization within concrete architecture.
研究人员说：“这种新型的制造过程被称为“蛋壳”，允许制造非标准，结构优化的混凝土结构，同时能够整合标准加固并最大程度地减少模板浪费。”
“作为使用这种制造方法的第一个构建示例，它表明非标准的混凝土结构可以在经济上有效，经济和可持续性地进行制造。”
为什么需要一种新颖的混凝土3D打印过程？
Concrete is the most-used building material in the world. In order for concrete to be 3D printed in a construction setting though, it needs to be supported by formwork as it transitions from a fluid material into a solid. This can be expensive, constituting up to 50 percent of the material’s cost, or even 80 to 90 percent for non-standard elements.
结果，尽管理论上可以将混凝土变成几乎任何形式，但标准的正交结构仍然是规范。这意味着这种建筑物是使用比真正需要更多的材料建造的，从而为开发替代方法创造了机会。尽管FDM 3D打印在施工应用中显示出希望，但该方法的速度，规模和无法生产薄而脆弱的印刷结构以将新鲜的混凝土固定在适当的位置，这阻止了其广泛的采用。
Having been developed from “Contour Crafting” techniques, concrete 3D printing remains an area of constant study for many research institutions. Nonetheless, according to the Zurich team, these methods also have problems, as cold joints occur between the layers of printed concrete, and it remains difficult to integrate reinforcement within such printed structures. These issues have limited concrete 3D printing’s implementation to non-load-bearing structures or as lost formworks.
苏黎世研究人员在2014年开发的智能动态铸造（SDC）方法提供了另一种方法。通过使用数字铸造过程并控制混凝土的水合，移动模板出口处的材料能够承载上面的材料的负载。尽管此过程比以前的方法更快，但由于动态移动模板所需的复杂机械致动，它能够产生的几何形状范围仍然有限。
The Zurich eggshell methodology
Attempting to utilize the benefits of the SDC process while eliminating its drawbacks, the modern Zurich team devised their eggshell concept. The novel technique merges large-scale robotic FDM 3D printing with the set-on-demand digital casting system developed within SDC. This allows for the creation of more complicated structures using a thin, single-layered shell as formwork.
“通过印刷模板而不是工作as in SDC, a much wider range of geometries can be produced without losing the advantage of being able to include traditional reinforcement in structural building components,” explained the researchers. In addition, simultaneously 3D printing and filling the formwork means that the structure doesn’t need to be moved during fabrication, thus reducing any risk of damage caused during transit.
为了测试其新发掘的添加剂技术，苏黎世的研究人员生产了一个分支柱，扭曲的列和“未来树”概念。为了创建这些混凝土结构，该团队使用了由自定义开发的Python接口控制的机器人臂，以基于预编程的CAD文件来构建列。机器人在每个手臂的末端挥动一个自建造的丝挤出机，能够打印3D。
该过程的铸造元素使团队混合混凝土总共八个小时，并使用自定义加速器混合物即时激活它。一旦打印了3D打印的混合物，研究人员就会进行一系列溶液以支持其混凝土柱。其中包括增加混凝土矩阵，将钩纤维放在铸造层之间，并施加后安装的制造管道，但他们得出结论，只能通过结合这些方法来实现最佳结果。
3D printed concrete columns and “the future tree”
虽然发现所得的列在一个或两个小时内是自支撑的，但苏黎世团队发现，将结构再保留三天会带来更好的固化条件。在最终形式中，混凝土结构在其层之间没有冷接头，更复杂的扭曲柱证明了该过程制造更复杂的几何形状的能力。
除了混凝土柱外，该团队还创建了一个绰号为“未来树”的大型树状结构。研究人员与德国工程公司Basler＆Hofmann合作，使用其蛋壳过程和许多充当互惠框架的木材元素的组合来建造树。覆盖1,152平方英尺或107平方米以上，冠层由380个乙酰化的木材元件组成，并与螺钉连接在一起，螺钉连接到附近两侧的建筑物。这些由树的混凝土“茎”支撑，该混凝土的“茎”固定在两侧的附近建筑物上，并在对面的角落悬臂。
“Here, motivated by the frame’s structural behavior, the honeycomb pattern gradually transforms between a hexagonal and a triangular in order to achieve varying levels of flexural rigidity in different areas of the frame,” explained the tree’s designers. “The increasingly triangular configuration in the cantilevering corner makes this area stiffer and locally minimizes structural deformations.”
Overall, the Zurich team has conceded that a faster version of the method will need to be developed in order to prevent the joints of their creations from going dry. Additionally, the researchers are working towards automating the process and utilizing more recyclable materials within it, to make the method more sustainable and financially viable. Nonetheless, they remain confident that a more advanced version of their eggshell approach could be used within a wide range of building applications.
“As research progresses and the process is stabilized and streamlined, the range of building components produced could extend to beams, floor slabs, or connecting and transitional elements, paving the way toward sustainable mass customization in concrete architecture,” concluded the Zurich researchers.
Concrete construction and the 3D printing industry
混凝土3D打印已开始引起全球众多公司和研究设施的严重关注。新加坡科学家Nanyang Technological University（NTU）例如，已经开发了单机器人3D打印平台用于创建具体结构。通过采用印刷方法，该团队的机器人臂能够单独使用3D打印大型结构。
美国的混凝土专家QUIKRETE和Contour Crafting Corporation(CC Corp), meanwhile, have partnered up to3D print a range of concrete buildingsaround the United States. The goal of the project is to build low-income housing and disaster relief facilities.
工程师来自Purdue University,on the other hand, have begun working on a method of3D打印混凝土风力涡轮机零件for offshore use. The Purdue research aims to 3D print steel wind turbine anchors out of concrete, to reduce the associated shipping and production costs.
The researchers’ findings are detailed in their paper titled “Eggshell: Ultra-Thin Three-Dimensional Printed Formwork for Concrete Structures。”该报告由Joris Burger，Ena Lloret-Fritschi，Fabio Scotto，Thibault Demoulin，Lukas Gebhard，Jaime Mata Falcon，Fabio Gramazio，Matthias Kohler和Robert J. Flatt合着。
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特色图片显示了由苏黎世埃德（Eth Zurich）团队和德国公司Basler＆Hofmann的工程师建造的“未来树”。通过Eth Zurich的照片。
