page 117
DI:15. COMPUTER AIDED DESIGN (CAD)
DI:15.1 DESIGN
• Recall the basic process of design (or at least one of the many)
Defined |
|
Need |
|
Problem |
|
Definition |
|
Conceptual |
|
Design |
Correction & |
|
|
|
Optimization |
Detailed |
|
Design |
Correction & |
|
|
|
Optimization |
Analysis & |
|
Evaluation |
|
Final Design
•The important phases of this diagram are,
-The ongoing refinement of the overall design
-The ongoing refinement of the detailed design
-The analysis of the design
•This diagram (or at least the main concepts) form the basis for CAD systems. A complete CAD system will provide as much of the structure above as possible.
•Some of the tools provided in a CAD environment are,
-Innovative and conceptual design
-Qualitative design analysis
-Structuring of part (eg. assemblies)
-Knowledge based/intelligent design tools
-Engineering design information (standards lookup, or electronic catalogues)
page 118
-Optimization
-Design interfaces, and tools
•Some applications are well suited to 2D CAD systems,
-PCBs (Printed Circuit Board Design)
-ICs (Integrated Circuit Design)
-Mapping (road maps, topographical maps)
•Consider the example of a sheet metal layout
•3D CAD systems are becoming widely used for Mechanical design in a number of businesses these days including,
-Aircraft Design
-Automotive
-Consumer electronics
-etc.
•CAD systems provide advantages such as,
-Visualization
-Minimizes design errors
-Graphical display of hard to visualize information (eg. 3D warping of plastic part)
-Standardized drawings, and documents
-Faster lead time
-Customer perception is improved
-Productivity improvement over time
-Developing alternate concepts
-Evaluation of alternate concepts
page 119
-Analytical investigation of parts
-Experimental investigation
-Detailed drawings and specifications
-Preliminary ‘construction’ of design prototype
-Easy bridge to prototype construction
-Easy to change designs
-Optimization
DI:15.2 CAD HISTORY
• A very brief history of CAD development is listed 1940s - First digital computer developed
1950s - Commercial computers become available
1955 - CRTs begin being used in military projects
1957 - APT II (Automatic Programmed Tool) developed for generating NC control. Automated NC used in industry.
1959 - Stromberk Carlson develops a system to interpret graphics on tape, then output them to a screen, or print on special paper
1963 - Ivan Sutherland presents a paper on “Sketchpad” which allows interactive graphics 1965 - Lockheed introduces a CAD/CAM system, and a FEM system. McDonnell intro-
duces CADD
1966 - Business world sees Wall Street Journal title “Electronic Sketching; Engineers Focus on Screen to Design Visually via Computer; Keyboard Enlarges, Rotates ‘Drawings’; Lockheed, GM Enthusiastic About Uses”
1971 - David Prince writes first book on computer graphics
1975 - ICAM (Integrated Computer Aided Manufacturing) project is begun by US Airforce
1976 - Color raster graphics technology begins to develop.
1979 - Development of IGES begins
1980 - Introduction of PCs revolutionizes all markets
1980s - Solid Modeling on UNIX
1990s - Solid Modeling on low end systems
DI:15.3 BASIC REQUIREMENTS OF CAD SYSTEMS
•A CAD System must,
-Allow a user to input geometry, and other information
-Provide methods for manipulating the geometry
-Provide for display output for the user
-Allow storage of the design in formats which can be used in other CAD and CAM packages