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Digital Fabrication: Manufacturing Architecturein the Information Age

Branko KolarevicUniversity of Pennsylvania, USA

AbstractThis paper addresses the recent digital technological advances in design andfabrication and the unprecedented opportunities they created for architecturaldesign and production practices. It investigates the implications of new digitaldesign and fabrication processes enabled by the use of rapid prototyping (RP)and computer-aided manufacturing (CAM) technologies, which offer the pro-duction of small-scale models and full-scale building components directly from3D digital models. It also addresses the development of repetitive non-stan-dardized building systems through digitally controlled variation and serial dif-ferentiation, i.e. mass-customization, in contrast to the industrial-age para-digms of prefabrication and mass production.

The paper also examines the implications of the recent developments in thearchitectural application of the latest digital design and fabrication technolo-gies, which offer alternatives to the established understandings of architecturaldesign and production processes and their material and economic constraints.Such critical examination should lead to a revised understanding of the historicrelationship between architecture and its means of production.

KeywordsDigital Fabrication, Computer-Aided Manufacturing, Digital Construction

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1 Introduction“Integrating computer-aided design with computer-aidedfabrication and construction [...] fundamentally redefinesthe relationship between designing and producing. It elimi-nates many geometric constraints imposed by traditionaldrawing and production processes—making complex curvedshapes much easier to handle, for example, and reducingdependence on standard, mass-produced components. [...] Itbridges the gap between designing and producing that openedup when designers began to make drawings.”

- W. Mitchell and M. McCullough in Digital Design Media

The Information Age, like the Industrial Age be-fore it, is challenging not only how we designbuildings, but also how we manufacture and con-struct them. In the conceptual realm computa-tional, digital architectures of topological, non-Euclidean geometric space, kinetic and dynamicsystems, and genetic algorithms, are supplantingtechnological architectures. Digitally driven de-sign processes characterized by dynamic, open-ended and unpredictable but consistent transfor-mations of three-dimensional structures are giv-ing rise to new architectonic possibilities(Kolarevic 2000). The generative and creativepotential of digital media, together with manu-facturing advances already attained in automotiveand airplane industries, is opening up new dimen-sions in architectural design. The implications arevast, as “architecture is recasting itself, becomingin part an experimental investigation of topologi-cal geometries, partly a computational orchestra-tion of robotic material production and partly agenerative, kinematic sculpting of space,” as ob-served by Peter Zellner in “Hybrid Space” (1999).

It was only within the last few years that the ad-vances in computer-aided design (CAD) and com-puter-aided manufacturing (CAM) technologieshave started to have an impact on building designand construction practices. They opened up newopportunities by allowing production and con-struction of very complex forms that were untilrecently very difficult and expensive to design,produce, and assemble using traditional construc-tion technologies. The consequences will be pro-found, as new digitally driven processes of design,fabrication and construction are increasingly chal-lenging the historic relationship between archi-tecture and its means of production.

2 FabricationThe continuous, highly curvilinear surfaces thatfeature prominently in contemporary architecturebrought to the front the question of how to workout the spatial and tectonic ramifications of suchnon-Euclidean forms. For many architects,trained in the certainties of the Euclidean geom-etry, it was the issue of constructability that broughtinto question the credibility of spatial complexi-ties introduced by the new “digital” avantgarde.However, the fact that the topological geometriesare precisely described as NURBS (Non-Uni-form Rational B-Splines) and thuscomputationally possible also means that theirconstruction is perfectly attainable by means ofcomputer numerically controlled (CNC) fabrica-tion processes, such as cutting, subtractive, addi-tive, and formative fabrication, which are describedin more detail in this section.

2.1 2D FabricationCNC cutting, or 2D fabrication, is the most com-monly used fabrication technique. Various cut-ting technologies, such as plasma-arc, laser-beam,or water-jet, involve two-axis motion of the sheetmaterial relative to the cutting head and are imple-mented as a moving cutting head, a moving bed,or a combination of the two. In plasma-arc cut-ting an electric arc is passed through a compressedgas jet in the cutting nozzle, heating the gas intoplasma with a very high temperature (25,000F),which converts back into gas as it passes the heatto the cutting zone (Figure 1). In water-jets, astheir name suggests, a jet of highly pressurizedwater is mixed with solid abrasive particles and isforced through a tiny nozzle in a highly focusedstream, causing the rapid erosion of the materialin its path and producing very clean and accuratecuts (Figure 2). Laser-cutters use a high-intensityfocused beam of infrared light in combinationwith a jet of highly pressurized gas (carbon diox-ide) to melt or burn the material that is being cut.There are, however, large differences betweenthese technologies in the kinds of materials ormaximum thicknesses that could be cut. Whilelaser-cutters can cut only materials that can ab-sorb light energy; water-jets can cut almost anymaterial. Laser-cutters can cost-effectively cutmaterial up to 5/8”, while water-jets can cut much

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thicker materials, for example, up to 15” thick ti-tanium.

The production strategies used in 2D fabricationoften include contouring, triangulation (or polygo-nal tessellation), use of ruled, developable surfaces, andunfolding. They all involve extraction of two-di-mensional, planar components from geometricallycomplex surfaces or solids comprising thebuilding’s form. Which of these strategies is useddepends on what is being defined tectonically:structure, envelope, a combination of the two, etc.

In contouring, a sequence of planar sections, oftenparallel to each other and placed at regular inter-

vals, are produced automatically by modeling soft-ware from a given form and can be used directlyto articulate structural components of the build-ing, as was the case in a number of recently com-pleted projects (Figures 3 and 4).

Complex, curvilinear surface envelopes are oftenproduced by either triangulation (or some otherplanar tessellation) or conversion of double-curved intoruled surfaces, generated by linear interpolationbetween two curves (Figures 5 and 6). Triangu-lated or ruled surfaces are then unfolded into pla-nar strips, which are laid out in some optimal fash-ion as two-dimensional shapes on a sheet (in aprocess called nesting), which is then used to cutthe corresponding pieces of the sheet materialusing one of the CNC cutting technologies. Forexample, Frank Gehry’s office used CATIA soft-ware in the Experience Music Project in Seattleto “rationalize” the double-curved surfaces by

Figure 1. Plasma-arc CNC cutting of steel supports for masonrywalls in Frank Gehry’s Zollhoff Towers in Dusseldorf, Germany(Rempen 1999).

Figure 2. Aluminum space frame for ABB Architects’ BMWPavilion is cut directly from digital data using CNC water-jettechnology.

Figure 3. Structural frames in Frank Gehry’s Experience MusicProject in Seattle, produced by contouring.

Figure 4. Structural framework for Bernard Franken’s BMWPavilion produced by bi-directional contouring.

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converting them into “rule-developable” surfaces,which were then unfolded and fabricated out offlat sheets of metal (Linn 2000).

The surface data could be also used to directlygenerate a wireframe abstraction of the building’sstructural framework, which could be then pro-cessed by the structural analysis software to gen-erate the precise definition of all structural mem-bers. In Gehry’s Bilbao project the contractor useda software program from Germany called Bocadto automatically generate a comprehensive digi-tal model of the structural steel, including thebrace-framed and secondary steel structures forthe museum (Stephens 1999). More importantly,that same program was used to automatically pro-duce the fabrication drawings or CNC data toprecisely cut and pre-assemble the various com-ponents (LeCuyer 1997).

The surface model could be also used to design,analyze, and fabricate the envelope componentsfrom sheet material. In designing theGuggenheim Museum in Bilbao, Gehry’s officeused the Gaussian analysis to determine the areas

of excessive curvature as there are limits as to howmuch the sheets of metal could be bent in twodirections; the same technique was used on otherprojects by Gehry (Linn 2000). The analysis pro-duced a colored image that indicated through vari-ous colors the extent of the surface curvature (Fig-ure 7).

2.2 Subtractive FabricationSubtractive fabrication involves removal of speci-fied volume of material from solids (hence thename) using multi-axis milling. In CNC (Com-puter Numerical Control) milling a dedicatedcomputer system performs the basic controllingfunctions over the movement of a machine toolusing a set of coded instructions (McMahon andBrowne 1998).

Early experiments in using CNC milling ma-chines to produce architectural models were car-ried out in early 1970s in the United Kingdom.Large architectural firms in the United States,such as Skidmore Owens Merrill’s office in Chi-cago, have used CNC milling machines and lasercutters extensively in the production of architec-tural models and studies of construction assem-blies. Automated milling machines were used inlate 1980s and 1990s to produce constructioncomponents (Mitchell and McCullough 1995),such as stones for New York’s Cathedral of SaintJohn the Divine and columns for Sagrada FamiliaChurch in Barcelona. Frank Gehry’s project forDisney Concert Hall in Los Angeles representsthe first comprehensive use of CAD/CAM to pro-

Figure 5. Triangulated complex surfaces in Frank Gehry’s DGBank Building in Parizer Platz, Berlin, Germany.

Figure 6. Use of ruled surfaces in the Water Pavilion by NOX inthe Netherlands. Figure 7. Gaussian analysis of the surface curvature.

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duce architectural stonework: for the initial 1:1scale model the stone panels with double-curvedgeometry were CNC milled in Italy and thenshipped to Los Angeles, where they were posi-tioned and fixed in place on steel frames (Mitchelland McCullough 1995). Gehry’s office used thissame fabrication technique for the stone claddingin the Bilbao project.

The CNC milling has recently been applied innew ways in building industry – to produce theformwork (molds) for the off-site and on-site cast-ing of concrete elements with double-curved ge-ometry, as in one of the Gehry’s office buildingsin Dusseldorf, Germany, and for the productionof the laminated glass panels with complex curvi-linear surfaces, as in Gehry’s Conde Nast Cafete-ria project and Bernard Franken’s BMW pavilion(Figure 8).

In Gehry’s project in Dusseldorf (Zollhof tow-ers) the undulated forms of the load-bearing ex-ternal wall panels, made of reinforced concrete,were produced using blocks of lightweight poly-styrene (Styrofoam), which were shaped in CATIAand CNC milled (Figure 9) to produce 355 dif-ferent curved molds that became the forms forthe casting of the concrete (Rempen 1999, Slessor2000).

2.3 Additive FabricationAdditive fabrication involved incremental formingby adding material in a layer-by-layer fashion, ina process converse of milling. It is often referredto as layered manufacturing, solid freeform fabrica-tion, rapid prototyping, or desktop manufacturing. Alladditive fabrication technologies share the sameprinciple in that the digital (solid) model is slicedinto two-dimensional layers. The information ofeach layer is then transferred to the processinghead of the manufacturing machine and the physi-cal product is incrementally generated in a layer-by-layer fashion (Jacobs 1992).

Since the first commercial system based onstereolithography was introduced by 3D Systemsin 1988, a number of competing technologies nowexist on the market, utilizing a variety of materi-als and a range of curing processes based on light,heat, or chemicals (Kochan 1993, Chua andLeong 1997). Stereolithography (SLA) is based onliquid polymers that solidify when exposed to la-ser light. In Selective Laser Sintering (SLS) laserbeam melts a layer by layer of metal powder tocreate solid objects. In 3D Printing (3DP) layersof ceramic powder are glued to form objects.Sheets of material (paper, plastic), either precutor on a roll, are glued (laminated) together andlaser cut in the Laminated Object Manufacture(LOM) process. In Fused Deposition Modeling(FDM) each cross section is produced by melting

Figure 8. Milling of molds for the production of double-curvedacrylic glass panels for Bernard Franken’s BMW pavilion.

Figure 9. Milling of Styrofoam molds for the casting of rein-forced concrete panels for Gehry’s Zollhof Towers in Dusseldorf,Germany (Rempen 1999).

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a plastic filament that solidifies upon cooling.Multi-jet manufacture (MJM) uses a modifiedprinting head to deposit melted thermoplastic/wax material in very thin layers, one layer at atime, to create three-dimensional solids.

Because of the limited size of the objects that couldbe produced, costly equipment, and lengthy pro-duction times, the additive fabrication processeshave a rather limited application in building de-sign and production. In design they are mainlyused for the fabrication of (massing) models withcomplex, curvilinear geometries (Novitski 2000).In construction, they are used to produce com-ponents in series, such as steel elements in lighttruss structures, by creating patterns that are thenused in investment casting (Figure 10). Recently,however, several experimental techniques basedon sprayed concrete were introduced to manu-facture large-scale building components directlyfrom digital data (Khoshnevis 1998).

2.4 Formative FabricationIn formative fabrication mechanical forces, restrict-ing forms, heat, or steam are applied on a mate-rial so as to form it into the desired shape throughreshaping or deformation, which can be axiallyor surface constrained. For example, the reshapedmaterial may be deformed permanently by suchprocesses as stressing metal past the elastic limit,heating metal then bending it while it is in a soft-ened state, steam-bending boards, etc. Double-curved, compound surfaces can be approximatedby arrays of height-adjustable, numerically-con-trolled pins, which could be used for the produc-tion of molded glass and plastic sheets and forcurved stamped metal. Plane curves can be fabri-cated by numerically-controlled bending of thinrods, tubes, or strips of elastic material, such assteel or wood, as was done for one of the exhibi-

tion pavilions designed by Bernhard Franken(ABB Architekten) for BMW.

2.5 AssemblyAfter the components are digitally fabricated, theirassembly on site can be augmented with digitaltechnology. Digital three-dimensional models canbe used to determine the location of each com-ponent, to move each component to its location,and finally, to fix each component in its properplace.

Traditionally, builders took dimensions and co-ordinates from paper drawings and used tapemeasures, plumb-bobs, and other devices to lo-cate the building components on site. New digi-tally-driven technologies, such as electronic survey-ing and laser positioning, are increasingly being usedon construction sites around the world to pre-cisely determine the location of building compo-nents. For example, as described by AnnetteLeCuyer (1997), Frank Gehry’s GuggenheimMuseum in Bilbao “was built without any tapemeasures. During fabrication, each structuralcomponent was bar coded and marked with thenodes of intersection with adjacent layers of struc-ture. On site bar codes were swiped to reveal thecoordinates of each piece in the CATIA model.Laser surveying equipment linked to CATIA en-abled each piece to be precisely placed in its posi-tion as defined by the computer model.” Similarprocesses were used on Gehry’s project in Seattle(Figure 11). As LeCuyer notes in her article, thisprocesses are common practice in the aerospaceindustry, but relatively new to building.

Figure 10. Trypiramid, a fabricator in New York, used rapidprototyping to manufacture truss elements for Polshek’s Rose Cen-ter for Earth and Sciences in New York.

Figure 11. Global Positioning System (GPS) technology was usedon Gehry’s Experience Music Project in Seattle to verify the loca-tion of components (Linn 2000).

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In Japan, a number of robotic devices for movingand fixing of components was developed, such asShimizu’s Mighty Jack for heavy steel beam posi-tioning, Kajima’s Reinforcing Bar Arranging Ro-bot, Obayashi-Gumi’s Concrete Placer for pouringconcrete into forms, Takenaka’s Self-Climbing In-spection Machine, Taisei’s Pillar Coating Robot forpainting, and Shimizu’s Insulation Spray Robot.

3 ImplicationsThe digital design and production techniquesbased on CAD/CAM technologies were widelyadopted over the past two decades in many fields,such as product design, automotive, aerospace andshipbuilding industries. The impact was profound– there was a complete reinvention of how prod-ucts in those respective industries were designedand made. Boeing 777, “the first 100% digitallydesigned aircraft,” is probably one of the best-known examples.

While the CAD/CAM technological advances andthe resulting changes in design and productiontechniques had an enormous impact on other in-dustries, there has yet to be a similarly significantand industry-wide impact in the world of build-ing design and construction. The opportunitiesfor the architecture, engineering, and construc-tion (AEC) industries are there and the benefitswere already manifested in related fields.

By integrating design, analysis, manufacture andassembly of buildings around digital technologies,architects, engineers, and builders have the op-portunity to reinvent the role of a “master-builder” and reintegrate the currently separatedisciplines of architecture, engineering and con-struction into a relatively seamless digital collabo-rative enterprise, thus bridging “the gap betweendesigning and producing that opened up whendesigners began to make drawings,” as observedby Mitchell and McCullough (1995).

The legal framework within which AEC profes-sionals operate still requires drawings, often tensof thousands of them for a project of medium sizeand complexity. As new synergies in architecture,engineering, and construction are emerging, theneed to externalize representations of design, i.e.,produce drawings, is bound to wane. As produc-tion of (unnecessary) drawings declines, i.e., as

digital data is increasingly passed directly froman architect to a fabricator, so will the buildingdesign and construction processes become moreefficient. By some estimates, there is a potentialfor building construction to become 28–40 per-cent more efficient through better (digital) infor-mation and coordination (Cramer 2000). But forthat process to begin, the AEC legal framework,in which the drawings establish the grounds ofliability, would have to change. In other words,the 19th century AEC practices would have tochange for architects to work directly with fabri-cators, i.e., subcontractors; this“disintermediation” (Cramer 2000) should bringnew efficiencies. As observed by James Cramer,Chairman/CEO of Greenway Consulting, “de-signers and contractors will no longer be the cus-todians of traditional assets but the creators of newvalue in a new industry.” According to Cramer,architects will find themselves “moving from lin-ear to non-linear changes – from information thatis shared by teams, rather than individuals, andcommunication that is continuous, rather thanformal and fragmented.”

3.1 New MaterialityAs new digital processes of conception and pro-duction begin to permeate building design andproduction, there is an increasing interest in“new” materials, well known in other productionfields and only recently discovered by architects.

Much of the interest among architects in newmaterials stems from the new geometric complexi-ties. In dealing with tectonic ramifications of non-Euclidean forms a particular challenge is how toavoid the usual translation into structural bays,often done by contouring, described in the pre-vious section. This had lead to a renewed interestin surface or shell structures, or monocoque or semi-monocoque constructions in which the skin absorbsall or most of the stresses. The principal idea is toconflate the structure and the skin into one ele-ment thus creating self-supporting forms that re-quire no armature. That in turn prompted a searchfor “new” materials, such as high-temperaturefoams, rubbers, plastics, and composites, whichwere until recently rarely used in building indus-try. As observed by Giovannini (2000b), “the ideaof a structural skin not only implies a new mate-

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rial, but also geometries, such as curves and foldsthat would enable the continuous skin to act struc-turally, obviating an independent static system:The skin alone does the heavy lifting.” Thus aninteresting reciprocal relationship is establishedbetween the new geometries and new materiali-ties: new geometries opened up a quest for newmaterials and vice versa. Kolatan and MacDonald’shouse addition project in Connecticut nicely il-lustrates that reciprocity: the building is made ofpolyurethane foam sprayed over an egg-crate ply-wood armature that was CNC-cut, thus forminga monocoque structure that is structurally self-sufficient without the egg-crate, which will re-main captured within the monocoque form (Fig-ure 12).

The implications of the “new” materiality are sig-nificant, as noted by Giovannini (2000b), as “new”materiality promises a radical departure fromModernism’s ideals:

“In some ways the search for a material and formthat unifies structure and skin is a counterrevolu-tion to Le Corbusier’s Domino House, in whichthe master separated structure from skin. The newconflation is a return to the bearing wall, but onewith freedoms that Corb never imagined possible.Architects could build many more exciting build-ings on the Statue of Liberty paradigm, but com-plex surfaces with integrated structures promise aquantum leap of engineering elegance and intel-lectual satisfaction.”

3.2 Mass CustomizationThe ability to mass-produce irregular buildingcomponents with the same facility as standard-ized parts introduced the notion of mass-customization into building design and production(it is just as easy and cost-effective for a CNCmilling machine to produce 1000 unique objects

as to produce 1000 identical ones). Mass-customization, sometimes referred to as system-atic customization, can be defined as mass produc-tion of individually customized goods and services(Pine 1993), thus offering a tremendous increasein variety and customization without a corre-sponding increase in costs. It was anticipated as atechnological capability in 1970 by Alvin Tofflerin Future Shock and delineated (as well as named)in 1987 by Stan Davis in Future Perfect (Pine 1993).

In addition to “mass-customization,” the CNC-driven production processes, which afford the fab-rication of non-standardized repetitive compo-nents directly from digital data, have also intro-duced into architectural discourse the new “log-ics of seriality,” i.e., the local variation and differ-entiation in series. It is now possible to produce“series-manufactured, mathematically coherentbut differentiated objects, as well as elaborate,precise and relatively cheap one-off components,”according to Peter Zellner (1999), who argues thatin the process the “architecture is becoming like‘firmware,’ the digital building of software spaceinscribed in the hardwares of construction.” Thatis precisely what Greg Lynn’s “EmbryologicHouses” manifest: “mass-customized” individualhouse designs produced by differentiationachieved through parametric variation in non-lin-ear dynamic processes.

The implications of mass-customization are pro-found. As Catherine Slessor (1997) observed, “thenotion that uniqueness is now as economic andeasy to achieve as repetition, challenges the sim-plifying assumptions of Modernism and suggeststhe potential of a new, post-industrial paradigmbased on the enhanced, creative capabilities ofelectronics rather than mechanics.” In the Mod-ernist aesthetic, the house was to be considered amanufactured item (“machine for living”), draw-ing upon the engineering logic for the design tobe clarified and reduced to the essential. Massproduction of the house would bring the best toa wide market and design would not cater to theelite (Le Corbusier 1931). At the start of thetwenty-first century the goal remains, althoughreinterpreted, with the process inverted. Nolonger does factory production mean mass pro-duction of a standard item to fit all purposes, i.e.,Figure 12. Kolatan and Macdonald’s house addition in Connecti-

cut.

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one size fits all. Instead, we now strive for masscustomization, bringing the benefits of factoryproduction to the creation of a unique compo-nent or series of similar elements differentiatedthrough digitally controlled variation (Kvan andKolarevic 2001).

4 ConclusionsThe paradigm shifts currently at play in contem-porary architectural design are fundamental andinevitable, displacing many of the well-establishedconventions. In a digitally-mediated design, asmanifested in Gehry’s buildings and projects ofthe “digital avantgarde,” the practices of the pastsuddenly appear irrational. Models of design ca-pable of consistent, continual and dynamic trans-formation are replacing the static norms of con-ventional processes. The predictable relationshipsbetween the design and representations are aban-doned in favor of computationally generated com-plexities. The topological, curvilinear geometriesare produced with the same ease as Euclideangeometries of planar shapes and cylindrical,spherical, or conical forms. Plan no longer “gen-erates” the design; sections attain a purely ana-lytical role. Grids, repetitions, and symmetries losetheir past raison d’etre as infinite variability be-comes as feasible as modularity and as mass-customization offers alternatives to mass-produc-tion.

As architects find themselves increasingly work-ing across the disciplines of architecture, mate-rial science, and computer-aided manufacturing,the historic relationship between architecture andits means of production is increasingly being chal-lenged by the emerging digitally driven processesof design, fabrication and construction. The amal-gamation of what were until recently separateenterprises has already transformed other indus-tries such as aerospace, automotive, and shipbuilding, but there has yet to be a similarly sig-nificant and industry-wide impact in the world ofbuilding design and construction. That change,however, has already started, and is inevitable andunavoidable.

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