Teaching CAD in Mechanical and Manufacturing Engineering Programs – An Experience at University of Calgary – D. Xue Department of Mechanical and Manufacturing Engineering, University of Calgary Calgary, Alberta, Canada T2N 1N4 E-mail: [email protected] Abstract theory, primarily computer graphics, for satisfying requirements in engineering design and manufacturing. This paper introduces our experience of teaching a Since many advanced functions, such as finite element CAD course in mechanical and manufacturing analysis (FEA), motion analysis, CNC simulation and engineering programs at University of Calgary. Three machining, and computational fluid dynamics (CFD), aspects of the CAD knowledge, including computer have been added to the CAD systems in the past graphics theory, practice of CAD systems, and decade, focus of teaching CAD courses has also been applications of CAD in engineering design and shifted from computer graphics to applications of CAD manufacturing, are discussed based on the in engineering design and manufacturing. requirements for the mechanical and manufacturing Presently CAD is considered as a fundamental engineering programs. The various components of a component in mechanical and manufacturing CAD course at University of Calgary, including engineering programs. CAD is usually introduced lectures, laboratories, textbooks, assignments, and through the following three types of courses. course projects, are provided at the end of this paper. • Junior undergraduate course in engineering 1. Introduction graphics: to use a CAD system as an electronic drafting tool to practice engineering graphics Development of CAD tools was started by the knowledge. pioneer work of the SKETCHPAD project at the MIT • for designing an electronic drafting board to replace Senior undergraduate course and junior graduate the conventional mechanical drafting board [1]. In course in CAD/CAM/CAE: to use a CAD system as 1970s, considerable theoretical results have been a tool for engineering design, manufacturing, and achieved in computer graphics, such as solid modeling, analysis. free form curve and surface modeling, and • Senior graduate course for special purposes: to use visualization of 3-D geometric objects. In 1980s, and to develop specialized CAD systems for commercial CAD systems, such as AutoCAD by complex shape modeling, customized finite element Autodesk for 2-D drafting and Pro/Engineer by generation, computer animation, and so on. Parametric Technology Corporation (PTC) for 3-D modeling, were introduced. Today CAD systems are In recent years, the following questions are often widely used in engineering design and manufacturing, raised due to the improvement of CAD functions. including geometric modeling, structure analysis, (1) Should a CAD course be offered in mechanical and motion analysis, CNC machining, rapid prototyping, manufacturing engineering programs? and so on. Two issues are usually considered to decide The CAD courses were introduced to mechanical whether a course should be offered. First the topics and manufacturing engineering programs in 1980s with in the course have to be essential for the program. the advances of computer hardware and software Second the materials of the course take systematic technologies. Due to the limited functions of CAD approach to learn. For a good CAD system, it takes systems in late 1980s and early 1990s, most of the only days, if not hours, to learn the fundamental efforts in these CAD courses were devoted to the CAD functions of 3-D modeling and 2-D drafting. Therefore questions are raised on whether a CAD • Hardware and Software course should be offered. In other words, are we − Input devices: keyboards, mice, digitizers satisfied if the students have some fundamental − Output devices: monitors, raster printers, vector knowledge on 3-D and 2-D geometric modeling? plotters − (2) What should be offered in a CAD course? Computer systems: operating systems, Suppose we agree that a CAD course should be programming languages, computer networks offered in the mechanical and manufacturing − Computer graphics tools: OpenGL, VRML [5,6] engineering programs as what has been well • 2-D Drafting accepted by most present mechanical and − Primitives: lines, circles, arcs, ellipses, etc. manufacturing engineering programs, the questions − Area filling: solid filling, pattern filling on what should be offered are often raised. Should − Clipping of 2-D primitives in views we focus on the CAD theory – the computer graphics? Should we introduce sophisticated • 3-D Solid Modeling functions of a CAD system? Or should we focus on − Data structures: CSG, B-reps, half-space the engineering applications of CAD systems? − Boolean operations: union, intersection, This paper aims at answering the above two difference questions by studying the three aspects of CAD − Euler’s law knowledge required for the mechanical and • Geometric Transformation and Mapping manufacturing engineering programs. − 2-D transformations: translation, rotation, etc. • CAD Theory – Computer Graphics − 3-D transformations: translation, rotation, etc. • Practice of CAD Systems − Mapping between two coordinate systems • Applications of CAD in Engineering Design and • 3-D Geometric Viewing Manufacturing − Projections: perspective projection, parallel These three aspects of CAD knowledge are projection discussed with details in Sections 2.1, 2.2, and 2.3, − Windows, view ports, and their mapping respectively. • Modeling of Curves and Surfaces − 2. Three Aspects of CAD Knowledge Analytic curves: lines, circles, conics, etc. − Synthetic curves: Hermite cubic curves, Bezier For each aspect of CAD knowledge, we focus on curves, B-spline curves, NURBS curves the following two issues: − Analytic surfaces: planar surfaces, ruled surfaces, surfaces of revolution, tabulated • CAD Knowledge cylinders • Use of CAD Knowledge in Design and − Synthetic surfaces: bicubic surfaces, Bezier Manufacturing surfaces, B-spline surfaces, NURBS surfaces In addition, case study examples are also given to • Detection of Visible Curves and Surfaces support our discussions. − Detection of visible curves 2.1. CAD Theory in a CAD Course − Detection of visible surfaces CAD theory, primarily computer graphics, serves • as the foundation to develop CAD systems and to Illumination and Shading understand CAD concepts. Since the objective of a − Color models: RGB, CMY CAD course in mechanical and manufacturing − Light properties: diffuse reflection, specular engineering programs is not to implement new CAD reflection, ambient reflection systems, questions on whether computer graphics − Shading models for polygons: constant shading, should be introduced or what topics in computer Gouraud shading graphics should be introduced are often raised. − Transparency properties of materials − Shadows 2.1.1. CAD Theory – Computer Graphics − By studying the popular computer graphics and Surface texture mapping CAD textbooks [2-8], the major topics of computer • Computer Animation graphics are grouped into the following categories. − Motion simulation − Virtual reality with sensor devices 2.1.2. Applications of CAD Theory in Design and Table 1. Selection of computer graphics topics Manufacturing Although a good understanding of computer Computer Graphics Topics N C I graphics theory helps students to use CAD systems Hardware and Software – Input devices X more effectively, considerable efforts are required to – Output devices X learn the topics in computer graphics. Since the – Computer systems X objective of the CAD course in mechanical and – Computer graphics tools X manufacturing engineering programs is not to develop 2-D Drafting new CAD systems, some of the computer graphics – Primitives X topics may never have chances to be employed by – Area filling X engineering students in their future careers. – Clipping of 2-D primitives in views X In this section, the required computer graphics 3-D Solid Modeling – Data structures X topics for a CAD course are identified by studying the – Boolean operations X relations between computer graphics topics and their – Euler’s law X applications in mechanical and manufacturing Geometric Transformation and Mapping engineering. We classified these topics into three major – 2-D transformations X categories, – 3-D transformations X – Mapping between two coordinate systems X • Not Required 3-D Geometric Viewing • Concepts Only – Projections X • In-depth Formulation – Windows, view ports X Modeling of Curves and Surfaces as shown in Table 1. – Analytic curves X The major potential applications of the computer – Synthetic curves X graphics knowledge in mechanical and manufacturing – Analytic surfaces X engineering are listed as follows. – Synthetic surfaces X Detection of Visible Curves and Surfaces • Hardware and Software – Detection of visible curves X − Selection of computer systems (e.g., PC or – Detection of visible surfaces X Silicon Graphics workstations, MS Windows or Illumination and Shading UNIX) – Color models X − – Light properties X Selection of input and output devices (e.g., – Shading models for polygons X mouse or digitizer, raster printer or vector – Transparency properties of materials X plotter) – Shadows X − Selection of computer graphics tools for – Surface texture mapping X developing customized CAD systems when the Computer Animation required functions are not provided in existing – Motion simulation X CAD systems – Virtual reality with sensor devices X N: Not Required • 3-D Solid Modeling C: Concepts Only − More effective