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The Inside Story: Revealing the Contents of CAD’s Black Box

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2011 ASEE Annual Conference & Exposition


Vancouver, BC

Publication Date

June 26, 2011

Start Date

June 26, 2011

End Date

June 29, 2011



Conference Session

Design and Graphics Potpourri

Tagged Division

Engineering Design Graphics

Page Count


Page Numbers

22.1472.1 - 22.1472.14



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Paper Authors


Holly K. Ault Worcester Polytechnic Institute

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Holly K. Ault received her B.S., M.S.M.E., and Ph.D. degrees from Worcester Polytechnic Institute in 1974, 1983, and 1988 respectively. She has worked as a Manufacturing Engineer for the Norton Company and Product Development Engineer for the Olin Corporation. She is currently Associate Professor of Mechanical Engineering at Worcester Polytechnic Institute, co-director of the Assistive Technology Resource Center, and director of the Melbourne Global Project Center. In the fall of 2001, she was invited as the Lise Meitner Visiting Professor, Department of Design Sciences, Lund Technical University, Lund, Sweden. Her primary teaching and course development responsibilities include undergraduate and graduate level courses in computer-aided design, mechanical design and rehabilitation engineering. She served as the Director of Liaison for the Engineering Design Graphics Division of ASEE from 1995 - 1998, EDGD Program Chair for the ASEE Annual Conferences in 2002 and 2011, division vice chair in 2003 and division chair in 2004. Her teaching and research interests include computer aided mechanical design, geometric modeling, kinematics, machine design and rehabilitation engineering. She is a member of ASME, ASEE, and ISGG.

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The Inside Story: Revealing the Contents of CAD’s Black BoxTopics covered in introductory solid modeling courses typically include the creation of variousfeatures such as extrusions, revolves and pick-and-place features, modeling strategies, sketchconstraint methods, assemblies, and creating and formatting drawings, amongst other topics fromthe conventional graphics curriculum. Advanced CAD courses may also cover the creation ofmore complex swept and blended surfaces or solids, as well as applications such as simulation,manufacturing and analysis. However, it is uncommon for CAD courses to delve into theunderlying mathematics behind these CAD models. Is it important for students to understand thefoundational mathematics that are used by the CAD systems to create and constrain complexgeometries and parametric models? Does this understanding make them better able to modelparts? This paper will discuss several projects completed in a course on geometric modeling forsenior/graduate level students in mechanical engineering. Students may have diverse CADbackgrounds, and therefore the projects are not dependent upon the use of a particular CADsoftware package. Projects are executed using a combination of CAD software, spreadsheets andequation solvers. Students explore the mathematics used to define cubic and higher order Beziercurves and splines, derive and solve sketch constraint equations, and generate constraintconditions for variational solid models. This exposure to the mathematical foundations within theCAD systems is intended to provide insight that will make the students better able to modelcomplex shapes and build more robust solid models.

Ault, H. K. (2011, June), The Inside Story: Revealing the Contents of CAD’s Black Box Paper presented at 2011 ASEE Annual Conference & Exposition, Vancouver, BC. 10.18260/1-2--18593

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