Page T2.2 . 01 November 2000                     
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  • Manufacturing Freeform Architecture

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    Manufacturing Freeform Architecture


    Implications for Architecture

    This digitally based convergence of representation and production represents one of the most important opportunities now facing the profession. The modern movement began as a response to industrialization and called for architects to master the means of production in an attempt to remain engaged in the qualitative aspects of crafting buildings. New means of production have emerged that can enable new aesthetics in post-industrial digital societies.

    CAD/CAM technologies enable us both to avoid traditional manufacturing costs and to design and produce complex freeform components that were previously either impossible or prohibitively expensive.

    Custom, digitally crafted architectural components can now be directly or indirectly manufactured without expensive reusable tooling, and mass customization is possible because manufacturing efficiencies are no longer compromised by variations in what is being produced.

    Prototyping Freeform Architecture

    The Computer-Aided Design and Manufacturing Laboratory at the Harvard Design School is the most extensive facility of its kind in an architecture school. Advanced research into the design and manufacture of freeform architectural components and surface structures has been ongoing for several years. These investigations include the creation of prototypes and tooling for structures made of reinforced concrete, metal, wood, and advanced composites.

    Harvard's CAD/CAM facilities include several rapid prototyping machines, a large CNC milling machine (3-axis router), a smaller milling machine, several CNC lasers, reverse-engineering equipment, a vacuum forming machine, and a broad range of traditional equipment and manufacturing tools. The school has licenses for SolidWorks, SurfaceWorks, other solid and surface modelers such as ProEngineer, Alias/Wavefront, and Maya, and MasterCAM, a leading CNC machining program.

    The Harvard Design School is also sponsoring the First International Symposium on the Application of Computer-Aided Design and Manufacturing in Architecture and Design in late October.

    Freeform Metal Frame Structures

    My own research at Harvard has focused on how CAD/CAM technologies can enable the design and production of freeform metal structural frames. (See Scale Models from Thin Air.)

    Architects began exploring the possibility of freeform metal frames at the turn of the last century in the Art Nouveau movement. The scale of their achievements, however, was limited by then-available casting technology and representational methods. The largest cast Art Nouveau structures are the Paris Metro stations designed by Hector Guimard.

    The design of larger freeform metal frames requires that components be optimized as hollow tubes. I identified manufacturing processes developed in other industries that might have the capacity to manufacture freeform tubes(TM), and categorized them as a) processes that would be applicable and economically viable in current professional practice; b) processes with emerging professional viability, and; c) emerging additive technologies for directly manufacturing metal components. This last category of technologies is still under research and development and is only in the initial stages of commercialization.

    Ceramic mold casting processes are the most practical and accurate methods for making architectural freeform tubes. Ceramic molds are made by incrementally investing an expendable pattern with alternate coats of ceramic slurry and dry stucco, and then, when the ceramic shell is thick enough, burning out the pattern in a furnace.

    These processes are generally referred to as investment casting technologies. Investment casting with CNC-milled expendable foam patterns is the least expensive method. Making freeform architectural tubes from additively formed expendable patterns is likely to become affordable as rapid prototyping technologies mature.

    I designed prototyping experiments to test the application of these processes to the problem of manufacturing freeform tubes for metal architectural structures.

    Prototyping Freeform Tubes

    With ProEngineer I designed a six-foot-long freeform tubular column with an integral secondary branching component. In collaboration with the foundry I analyzed it using MAGMASoft, a computer program for predicting the behavior of molten alloys during casting. This analysis indicated the need to change some variations in wall thickness to ensure proper solidification and casting integrity.

    Making such changes to a solid model is easy with advanced feature-based parametric modelers, because simple editing of the dimensions or equations used to create the model results in automatic recreation and regeneration of the form.

    I then divided the solid model into two interlocking components in order to accommodate locally available casting equipment. Then each of these components was subdivided into interlocking, self-registering pattern halves that were later glued together.

    The ProEngineer models of the pattern components were exported in the IGES format, commonly used for importing data into CNC milling software such as SurfCAM or MasterCAM. G-Code, the digital code that directs the automatic "carving" of the designed shape out of blocks of material, was then created in SurfCAM. The CNC milling machine automatically uses a predetermined variety of different shapes and sizes of bits as it follows the "toolpaths" contained in the G-Code.

    The CNC-milled foam patterns were successfully used to cast the freeform column components in stainless steel. The photographs show these prototypes in their "as cast" state and as finished, powder-coated freeform architectural tubes.

    Manufacturing with Solid Freeform Fabrication

    Prototype column components were also manufactured from patterns made using solid freeform fabrication. The STL file format, named after stereolithography, the oldest solid freeform fabrication technology, is typically used for importing data into rapid prototyping machines.

    Manufacturers of commercially available rapid prototyping devices provide and continually update their own proprietary software that automatically generates the tool paths and other required instructions.

    Rapid prototyping software divides a computer model into very thin horizontal layers. The thickness of these layers is specified by the machine operator and determines the relative accuracy of external surfaces. Thicker layers result in faster formation and thinner layers in greater accuracy.

    Additive formation technologies incrementally deposit, cure, or bind very thin layers of material within the "build chamber" of a particular machine. Most build chambers are relatively small, but larger components are routinely subdivided and built in sections. There is also ongoing research into the development larger machines.

    The best additive technologies for making expendable casting patterns are selective laser sintering (SLS) using SinterStation machines by DTM Corporation; multi-jet modeling (MJM) as in the Thermojet, by 3D Systems; three-dimensional printing (3DP) by the Z-Corporation; and fused deposition modeling (FDM) by Stratasys, Inc.

    Specially designed polymers suitable for investment casting are available for SLS, MJM, and FDM. The starch and cellulose powder used in Z Corp's 3D Printers also works very well. The Harvard Design School's 3D Printer, Thermojet machine, and SLS were used to prototype freeform architectural columns. These organically-shaped columns were modeled in ProEngineer and investment-cast in various aluminum alloys.

    Using CAD/CAM in Practice

    For now, additive technologies to directly manufacture architectural components are still too expensive except for making relatively small parts, such as ornamental elements, light fixture housings, or stair rail components.

    The more freeform a component's geometry, and the smaller the quantity required, the more cost-effective the use of solid freeform fabrication. It is likely, however, that as these technologies mature, architects will be able to design large, custom, freeform components that are now impossible or impractical to make.

    The use of subtractive formation to manufacture both large and small freeform architectural components is now more affordable. The only major limitation is the drafting-centric software commonly used by practicing architects.

    To take full advantage of the new CAD/CAM paradigm, architects need to use more advanced solid and surface modeling programs. The cost of programs like SolidWorks and ProEngineer has dropped dramatically in recent years, and is now about the same as conventional architectural software.

    Dr. Kevin Chaite Rotheroe recently founded FreeForm, a design research studio in New York. He is a registered architect and has practiced in London, Chicago, Connecticut, and New York. He and Harvard University have patents pending on a variety of freeform tubes(tm).



    ArchWeek Photo

    ProEngineer CAD models of pattern components.
    Image: Kevin Rotheroe

    ArchWeek Photo

    CNC milling of foam patterns using SurfCAM.
    Photos: Kevin Rotheroe

    ArchWeek Photo

    Finished, powder-coated, stainless steel, freeform column components and castings at the foundry after removing the ceramic molds.
    Photos: Kevin Rotheroe

    ArchWeek Photo

    A ProEngineer model, an assembled 3D printed pattern, and prototype freeform investment cast aluminum columns.
    Image: Kevin Rotheroe

    ArchWeek Photo

    Patterns being 3D printed; the bottom left and right show a 3D printed pattern being invested with ceramic slurry and stucco (respectively); and the top right shows molten metal being poured into a ceramic mold.
    Photos: Kevin Rotheroe


    Click on thumbnail images
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