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CAD/CAM, Parametric Design and Interactivity

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CAD/CAM, Parametric Design and Interactivity Teaching Technology: CAD/CAM, Parametric Design and Interactivity Martin Bechthold Harvard University, Graduate School of Design http://www.gsd.harvard.edu/people/faculty/bechthold/index.html [email protected] The paper discusses a project-based approach to technology teaching, and examines the case of the mobile information unit (MIU) for Harvard University and its art museums. A student competition was held to explore design alternatives for this unit. The winning entry proposed an interactive, pixilated fiber-optics display as well as touch screens. Parametric digital modeling was used in the design and design development of the scheme. Research included the study of structural alternatives, fabrication methods and the modes of interaction between users and the MIU. Keywords: Computer-aided design and manufacturing; fabrication; simulation; prototype; fiber optics. Integrating new technologies – an has taught the subject over the past two years. The introduction teaching objective is to provide an in-depth under- standing of the technology itself, and how it is ap- Computer-aided design and manufacturing (cad/ plied in practice. The teaching methods include lec- cam) techniques have been used by fabricators since tures, workshops, design exercises, case studies and the 1980s, but only fairly recently have architects field trips. In the second part of the course a more become aware of these technologies, and, more im- comprehensive design and prototyping projects portantly, have adjusted their design paradigms and has successfully allowed students to synergize the methods accordingly. Teaching efforts in this area various aspects of cad/cam technology with archi- differ significantly from teaching traditional CAAD tectural design. A project of this type is the mobile or construction classes, since cad/cam depends on information unit. both worlds. With new and emerging technologies the teaching of technology for architecture students Teaching cad/cam technology: has undergone a profound transformation. fundamentals At Harvard’s Graduate School of Design classes in cad/cam have been offered by a number of in- A major question in teaching cad/cam is whether to structors continuously since the mid 1990s. The au- accept the paradigms of current design practice, and thor has been involved in several earlier classes and teach techniques that are immediately useful in that Session 17: Digital Fabrication and Construction - eCAADe 25 767 Figure 1 Design proposal for a mobile information unit. Fiber optics panels on the outside create a pixilated display, while inter- active screens on the interior allow access to more detailed information (design: W. Bao, R. Gould and J. Hernandez). practice context, or teach higher-level concepts that CNC processes (for example cutting flat shapes bases might not be immediately applicable, but ultimately on *.dwg or *.dxf files) the use of these software en- lead to a revision of current practice models under vironments is nevertheless far from ideal, and using incorporation of cad/cam technologies. Learning the same environments in teaching cad/cam only experiences and output of the two teaching philoso- emphasizes the limitations of current practice. Limit- phies can be radically different. These differences will ed accuracy, and the cumbersome process of making be illustrated for the three distinct steps present in modifications by essentially erasing and remodeling any cad/cam based project: computer-aided design are particularly felt in the context of CNC manufac- (CAD), computer-aided manufacturing (CAM), and turing where the digital descriptions of parts have to computer-numerically controlled (CNC) manufactur- be digitally ‘watertight’ and without errors. ing environments. The author’s cad/cam teaching emphasizes use of parametric design development environments Entity-based CAD and surface modeler such as Catia or SolidWorks – environments struc- versus parametric design development tured to support the development and detailing of environments a given design. These powerful environments are Contemporary practices use a variety of non- geared towards producing geometry that is suitable parametric CAD environments for drafting (e.g. Au- for CNC manufacturing efforts. Students first are of- toCAD, MicroStation), conceptual design tools pri- ten irritated by the need to plan and logically struc- marily for surface modeling (e.g. Rhinoceros), as well ture the digital model in order to allow for the types as rendering and other presentation environments. of variations needed in the ongoing design pro- None of these were originally conceived to directly cess, but once the initial hurdles are overcome they support CNC manufacturing efforts. While many of quickly realize the powerful potential of parametric, those environments can be useful in the support of dimensionally-driven modeling and design. The 768 eCAADe 25 - Session 17: Digital Fabrication and Construction introduction to Catia and SolidWorks usually starts files from the design environment to the CAM envi- with simply model assignments, but soon introduces ronment and eventually fabrication can certainly put more advanced techniques that are distinctly differ- this myth into perspective. ent from conventional digital modeling. Techniques Tolerances are a particular issue that cannot be such as patterns, dimensional constraints, equation- overestimated. Students that are used to working driven dimensions, model configurations, design and designing in CAD often tend to assume that the tables, advanced replication tools (e.g. power copies physical world is as accurate and precise as is sug- in Catia) and macros can be introduced fairly early. gestive of the CAD world. Even simple modeling These and other digital modeling strategies facilitate exercises and 2D cutting operations of CNC lasers or a mental re-tooling process that broadens the stu- water jets quickly bring up these issues when parts dent’s design techniques. are supposed to snap into a tight fit but the width of the laser or water jet has not been figured into the Computer-Aided Manufacturing (CAM) and design model. Robust dimensionally-driven mod- Computer-Numerically Controlled (CNC) eling tools allow for tolerances to be incorporated manufacturing into the design model, as well as permitting interfer- Is there value of having students learn to generate ence checks and allowing students to test assembly their own G-code to eventually run CNC machining processes virtually before cutting and assembling operations, or generate files that can be sent directly materials. to a CNC laser cutter? In practice few if any fabricators will accept machine instructions from anyone out- CAD/CAM and design side the company, and few designers will eventually be doing these kinds of operations. Many teaching The temptation is great to have students soon gen- institutions support the ‘service model’ where parts erate designs and produce models and prototypes are not made by students, but by shop operators. using the computer-controlled devices available. In The myth of ‘press the button’ fabrication, often the author’s teaching experience it has been fruitful evoked by terms such as ‘digital fabrication’, still per- to build up understanding and skills incrementally. vades the design community, and teaching institu- Early fabrication exercises are typically extremely tions are no exception here. Having students actually limited, exploring specific devices usually begin- experience first hand the complexities of migrating ning with 2D cutting operations, for example of a Figure 2 Student project of a plywood chair designed parametrically and produced on a CNC rout- er. Scale model tests triggered the design change of eliminat- ing the cantilever still present in the first iteration (Design: S. Panata, C. Talbott). Session 17: Digital Fabrication and Construction - eCAADe 25 769 CNC router, water jet or laser. Typical design assign- unit for Harvard (see next section) demonstrates a ments may be to produce a piece of furniture from more comprehensive design project that begins to a single sheet of plywood, ideally preceded by scale address the real complexities of cad/cam in practice. model studies based on the same parametric digital model. Class design project: interactive mobile The constrained assignments encourage exper- information unit imentation because the restrictions and possibili- ties of the available technology are readily under- The interactive mobile information unit (MIU) was stood. To contextualize these design experiments conceived as a mobile, trailer-based urban kiosk case studies as for example included in [Schodek set up to inform the Harvard community as well 2004] are important. Field trips to fabricators can as the surrounding communities about the many give students real insights in the problems and op- public events at Harvard. A particular focus of the portunities of the technology. Questions such as MIU was to disseminate information about exhibi- how owns the digital model, liability and schedul- tions, events and lectures at the Harvard University ing issues become alive once raised by practitio- Art Museums (http://www.artmuseums.harvard. ners that are actively involved in the application of edu), one of the largest private art collections in the technology. the United States with more than 260,000 artifacts. Intermediate project assignments usually re- From the perspective of the Graduate School of De- main small in scope, but introduce more complex,
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