自第一次工业革命 (1760~1820) 以来, 制造业在大规模生产和减材制造领域蓬勃发展, 建筑实践也被简化为工厂里的基本工艺和工具。而工厂的条件也使得标准化和大规模生产出来的都是重复、线性的建筑构件, 这些构件再被一件件地组装起来^[1]。

　　 传统的材料工艺通常采用减材方法, 如对标准件进行切割、铣削以生产某种形态的构件^[2], 采用这种方法生产的材料利用效率低下且难以生产出定制的形状。再现手工艺品中复杂几何形态的困难, 以及使用标准化的现成工具来定制形体的困难^[3], 都表明传统的制造工艺必须有所转变。3D打印可进行任意数字模型的生成, 且在不必要的地方不消耗材料, 可大大减少材料的使用和浪费^[4]。

　　 本文讨论的设计框架和制造方法由一种椅子的设计原型——The Claw (利爪) (图1) 来说明。该椅子获得了2016年VMODERN家具大赛荣誉奖, 由有机和可回收的PLA (聚乳酸) 材料制成。该设计由人体工程学获得人体斜倚时的曲线, 并对曲线进行扫描生成形体。它的光滑和表皮上不均匀的细胞形态, 都体现出3D打印的高还原度。无需传统正投影图一类的交互, 这个产品从设计到生产的流畅转化, 达到了几何图形复杂度和还原度的新层次。

　　 数字设计框架 (图2) 有三种尺度:整体、局部和细胞。椅子的整体形状由三条曲线构成:一条中间曲线、两条对称的外部曲线, 三者通过Loft (放样) 生成一个可用于设计深化和结构优化的表皮。

　　 在局部尺度上可以看出表皮的细节。这部分我们通过Grasshopper的可视化编程, 对椅子的性能和美观两方面进行优化。我们随机在放样的表皮上填充1 900个点, 作为用于初始结构分析的点云。添加应力荷载后, 点的位置被重新分配, 使得应力高的地方点分布更密集。其余点分布在顶部 (25个) 、靠背 (280个) 、椅脊处以及椅脊的边缘、座位边缘 (各有50个) 、椅脚处 (35个) , 全部共计2 540个。随后这些点转化为优化过的三维Voronoi (泰森多边形) 细胞。

　　 通过使用2 540个点来产生三维的泰森多边形图形, 我们创造出椅子上的多细胞表皮。而椅子有的地方需要增加刚度, 有的地方需要增加柔度, 为了改变形态以优化结构, 我们对细胞空隙的位置进行偏移, 这一做法也提高了细胞空隙的表现力。为使3D打印可以平滑地进行, 表皮上的细胞都通过Weaverbird¹ (织巢鸟) 的Catmull Clark Mesh²细分曲面来进行深化设计 (图3) 。

　　 椅子的厚度为3mm, 采用1.75mm的蓝色PLA细丝打印, 可在黑暗中发光。使用了闪铸科技引领者 (FlashForge Guider) 打印机, 其打印空间为250mm×250mm×200mm, 因此椅子被分为18个部件进行打印。每个部件由筏状和树状结构³支撑, 以承受弯曲悬臂所引起的力矩。也因此, 通过逐层沉积材料, 它得以在物理上建造出数字形体^[5]。

　　 3D打印的工作方式类似于在施工过程中移除脚手架;它先是生产出带有筏状结构和支撑结构的“原始”输出, 然后再把这些多余的结构去除掉。打印过程耗时一周, 之后是18块部件的组装。总而言之, 设计师通过与数字指令的交互, 创造出高度定制化的几何形体, 同时确保材料得到高效利用, 设计兼具高经济性与高复杂度。

　　 一定程度上, 3D打印实现了传统的绘图—建造过程无法企及的高还原度。由于打印机可以根据生成代码 (G-Code) 产出数字模型的一个精确复制品, 建造、装配的过程就不再需要图纸了。本文通过制造一个人类手工尺度难以达到的复杂设计, 探讨了数字和物理/材料之间的直接联系。

　　 The Claw (利爪) 超越了一般的标准化生产, 展示了大规模生产的一种转向。本文概述了数字增材制造技术的影响, 而更多创新将与这种高效益的深化设计一同持续出现。去掉了复杂的产品供应链, 在今天, 3D打印提供了即便是普通用户也可以享受的定制化服务^[6]。随着打印的精度达到0.1mm^[7], 增材技术的进步将使得3D打印的前景更加开阔。

　　 20世纪60年代的Panton椅是第一把单一连续形态的塑料椅子^[8], 它突破了传统木制家具的设计方法。3D打印则对成型方法进一步突破, 使得仅通过一种操作, 即可生成优化的造型产品。譬如建筑师Zaha Hadid的3D打印椅 (2014) , 她根据结构需要使用了不同品类的塑料。虽然Panton椅已实现通过控制厚度来完成结构支撑, 但3D打印椅还要更进一步, 可通过材料优化来迭代测试结构强度^[9]。

　　 最近, 3D打印的材料选择范围得到扩展, 金属和碳也可用于沉积打印^[10]。越来越多大型建筑的原型研究使用3D打印进行, 如2016年Joris Laarman的Gradient (梯度) 椅。它是MX3D桥的原型, 用打印铝材来试验桥的结构和孔隙是否合理。因此, 在原型研究中打印大一些的、具有特定设计特征的部件, 可以帮助我们理解建筑尺度上材料属性是如何起作用的。

　　 在工业层面, 通过配备机器臂和挤出材料的喷头, 我们可以为增材建造扩展工作空间。有了更大的打印空间和额外的自由度以后, 我们可以以1:1的比例进行更大的3D打印^[11]。吸取热塑性材料 (如PLA) 的经验, 并用于适合建筑的材料 (如混凝土) , 我们可以进一步探索3D打印与工业的关联。本文是某大型研究的一部分, 该研究涉及混凝土建筑和施工的增材建造, 尤其是使用热塑性材料为自由形态的薄壳混凝土构建模板。

　　 建造往往涉及分段部件的组装, 而3D打印技术使得角接头的粘合存在一些限制。这些限制由观察到的两个因素引起:1) 由于交接面的倾斜, 顶部构件与底部表面略微脱开, 使得组装和粘合两个角接头存在困难;2) 材料挤出过程中会发生收缩, 导致3D打印不精确。The Claw (利爪) 的下一阶段将使用六轴机械臂, 把椅子打印为无需分割的几何形体, 以此去掉零件装配的环节。尽管商用3D打印机仍存在局限性, 它依然可以面向兼具经济性和复杂度的形体, 进行快速实验探究。未来的工作还将实现多材料混合的3D打印, 以实现最佳设计和提高整体强度。使用Scan-and-Solve进行的应力模拟测试, 可为几何形体提供可视化的应力分析, 而其中高位移的区域需考虑使用更强的材料。多品类的塑料以及其他材料, 都为3D打印的多喷头挤出提供了新的可能性。

　　 本文介绍的项目展示了使用3D打印定制化生产的设计产品在几何复杂度上的可能性。通过将增材技术与家具设计相结合, 3D打印开辟了新的制造方式。参数化找形的引入, 使我们可以通过快速数字设计产出定制化的产品、构件, 提高了工作效率。因此, The Claw (利爪) 展示的是家具设计从大规模标准化生产, 向大规模定制化生产转向的未来, 并丢掉了定制化生产“价格高昂”的标签。在数字化和材料技术方面, 它可以作为试验复杂想法和过程的有效原型, 以寻求建筑的更多可能性。

　　 Since the First Industrial Revolution (1760-1820) , the current state of manu-facturing has thrived on mass production and subtractive fabrication, refining construction practices to basic crafting skills and tools within a factory setting.These limitations have resulted in the standardisation and mass production of repeated, linear architectural elements, usually with part-to-part assembly (Castaneda et al.2015, p.3) .

　　 Conventional material processes typically employ subtractive methods such as cutting or milling away from standard blocks to achieve form (Aydin, 2015, p.590) , materially inefficient and impossible to produce bespoke forms.The difficulty to represent complex geometries for the manual craftsman to fabricate, and the use of standard off-the-shelf tool-ends to fab-ricate bespoke forms, (Onuh, Yusuf, 1999, p.309) has prompted a necessary shift from conventional fabrication processes.Alternatively, 3D printing al-lows the formation of any digital object, depositing material only where needed, essentially reducing material use and wastage (Pirjan, Petrosanu, 2013, p.3) .

　　 The design framework and fabrication methods discussed in this paper is demonstrated through a chair prototype-The Claw (Figure 1) , undertaken for the VMODERN Furniture Competition 2016, and awarded an Honourable Mention.It is made from PLA (polylactic acid) , an organic and recyclable material.The design implements a sweep curve in reference to ergonomic requirements of a reclining human body.Its sleekness, cellularity, and multi-density of cells, are all demonstrators of the fidelity that 3D printing offers.Here, the streamlining of translation from design to production enables new orders of geometric complexity and fidelity through the elimination of tradi-tional forms of communication through orthographic drawings.

　　 3.1.1 Global:Parametric form finding

　　 The digital framework (Figure 2) operates in three scales:global, local and cellular.Three curvilinear profiles drive the form of the global shape, con-sisting of one middle profile and two symmetrical exterior profiles, ‘lofted’together to produce a generic surface for detailing and structural optimisa-tion.

　　 3.1.2 Local:Surface detailing for structural optimisation

　　 Surface detailing occurs on a local scale, within the visual programming en-vironment of Grasshopper for optimised performance of the chair and aes-thetics.The lofted surface is populated randomly with 1900 points, produc-ing a point cloud for primitive structural analysis.Stress loads are located, and a redistribution of points densifies areas with high stress levels.Addi-tional points are distributed in the top rest area (25) , the back rest (280) , the chair spine as well as the spine edges and seat edges (50 each) and the foot of the chair (35) , resulting in 2540 points in total.The points are then con-verted into an optimised, multi-cellular distribution of 3D Voronoi cells.

　　 3.1.3 Cellular:Performative cell openings

　　 The chair implements a 3D Voronoi diagram to produce a multi-cellular sur-face using all 2540 points.Each cell opening is offset to generate performa-tive openings of varied porosity, functioning to structurally optimise the form, assigning rigidity and flexibility where needed.Surface cell detailing uses Weaverbird’s Catmull Clark mesh subdivision to ensure a smoothened 3D print finish.

　　 The chair has a thickness of 3mm, printed using blue 1.75mm PLA filament, which glows in the dark.With a250x250x200mm print space using a Flash-Forge Guider, the chair is 3D printed in eighteen pieces.Each piece prints with a raft and tree-structure supports to permit geometric moments of canti-levered curvature.Thus, via a layer-by-layer deposition of material, it has the capacity to physically realise the digital (2013, Strauss, p.31) .3D printing works in a similar manner to the removal of scaffolding in construction;it produces‘raw’outputs where the raft and structural supports need to be removed from the geometry.The printing process took a week to complete, followed by the assemblage of eighteen parts.In conclusion, the designers interaction with digital instruction allow for the additive deposition of a highly customised geometry implementing efficient material processes and cost-effective design complexities.

　　 3D printing offers a degree of fidelity unseen in the traditional drawing-to-fabrication process.No drawings are required to communicate fabrication or assembly but rather the printer produces an exact replica of the digital model via generated code (G-Code) .This paper explores the direct connection be-tween digital and physical/material, fabricating a complex design that is im-possible to produce at the human scale.

　　 The Claw demonstrates the overcoming of standardisation and a shift to-wards mass customisation.Ultimately, the impact of digital additive manu-facturing technologies outlined in this paper give rise to innovation accom-panied with cost effective detailing.3D printing offers customisation using material that is today accessible even to the regular user while eliminating the supply chain (Berman, B.2012, p.156) .With the precision of 3D print-ing already at one-tenth of a millimetre (“Print Me a Stradivarius”, 2011) , its future prospects are to develop even further as additive technologies advance.

　　 The Panton Chair in the 1960’s was the first plastic chair to be casted into a single continuous form (Kessler, van Oosten, van Keulen, 2004, p.86) , breaking away from traditional methods of timber furniture design.3D print-ing has disrupted forming methods allowing for a singular operation of op-timised form production, such as Zaha Hadid Architect’s 3D Printed chair (2014) , using different grades of plastic where structurally needed.While the Panton Chair demonstrates controlled thickness of form to achieve structural support, the 3D Printed chair takes this a step further, iteratively testing structure via material optimisation (Bhooshan, 2016, p.51) .

　　 More recently 3D printing has expanded the material palette, allowing the deposition of metal and carbon (Bhandari, Regina, 2014, p.378) .It is in-creasingly being adopted for prototyping structures at larger building scales as seen in Joris Laarman’s Gradient Chair (2016) a prototype for the MX3D Bridge, experimenting with structure and porosity with aluminium.Thus, printing larger objects with specific design features as prototypes assist in understanding how material properties can function at a construction scale.

　　 At an industrial level, we can extend a workspace for additive fabrication by equipping a robotic arm with a material extruding endeffector.The print space expands and offers additional degrees of freedom, allowing 3D print-ing of larger geometries at a 1:1 scale (Lipson, 2013, p.22) .Learning from thermoplastics (PLA) and shifting to suitable building materials (concrete) , an industrial relevance could be explored.This paper is part of a larger re-search that involves additive fabrication in concrete architecture and con-struction, specifically thermoplastics as formwork for free-form, thin shell concrete geometries.

　　 Fabrication involved segmented elements requiring part-to-part assembly.The bonding of angular joints became a limitation associated with 3D print-ing for two observed reasons:i.difficulty arises when assembling and gluing two angular joints, where the top piece detaches from the bottom surface be-cause of sloped bonding surfaces, and ii.The inaccuracy of 3D printing due to material shrinkage during material extrusion.The next stage of The Claw will eliminate part-to-part assembly, where a six-axis robotic arm could print the chair as an uncut geometry.The limitations of a commercial 3D printer however, offers quick experimental exploration of cost-effective complex forms.Future work will also implement multi-material 3D printing for opti-mal design and strength integrity.A simulation of a stress test using Scan-and-Solve visually provided a stress analysis of the geometry where areas of high displacement requires the consideration of a stronger material.The mul-ti-grading of plastics, or another material, are new possibilities of 3D printing technologies using multi-head extrusions.

　　 The project presented in this paper demonstrates the possibly to include ge-ometric complexities for bespoke design outcomes using 3D printing.By familiarising additive technologies with furniture design, 3D printing opens up new ways of manufacturing.The introduction of parametric form finding, allows quick digital design changes in order to customise products or objects, permitting a more efficient workflow.Hence, The Claw exhibits the future of furniture design shifting away from mass-standardised products and towards mass-customisation without the hefty price tag attached.When accompanied with a digital and material framework, it can be an effective way to experi-ment with complex ideas and processes at a prototype scale for larger archi-tectural possibilities.