10/2/2008Dept of Mechanical Engineering and Mechanics, Drexel University

Fundamentals of Computer Aided Design

• History • Computer Hardware & Software• Basic and Application of CAD

MEM 201

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The Age of Computers

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Definition of Computer Aided Design

• “It is the technology concerned with the use of computer systems to assist in the creation, modification, analysis and optimization of a design”[Groover and Zimmers, 1984]

• Computer Aided Design and Drafting (CADD)– refer to the designing and technical drawing of

various projects on a computer rather than a traditional drawing board.

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What is the ComputerWhat is the Computer--Aided Design?Aided Design?

The use of computer to assist for creation and manipulation- design model represented as a digital data or computer image to assist engineer

in the design process

A general CAD station

A CAD system usually consists of:

· hardware: the computer and associated peripheral equipment;

· software: the computer program(s) running on the hardware;

· data or model created and manipulated by the software;

· human knowledge and activities.

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Hardware

• Input Devices– Keyboard, Mouse– Light pens, Data Tablets, Spaceball

• Output Devices– CRT Monitors, Flat Panel Displays– Plotters, Printers

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The First 2D Software - SKETCHPAD

• Developed at MIT by Ivan Sutherland in 1963.

• Allowed the user to interact with a computer graphically.– CRT monitor, Light Pen, Graphical Interface

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The historical evolution of CAD and system architecture

Business system required large computer connecting to many terminals

• 1st CAD project, MIT in 1959 - 1960, by Ivan Sutherland, developed SKETCHED system, which was an early drawing processing system that used computers, the system included most of the concepts of today's interactive 2D CAD system.

• General Motors DAC-1• Lockheed Corp. CADAM for business application in 1967

Mini-computer to dedicated graphics terminal

• Applicon Corp. introduced AGS in 1968• Computer Vision Corp. introduced CADDS in 1969

Personal Computer (PC) AutoDESK (for low-end user)

• AutoDESK Corp. introduced AutoCAD for 2D CAD system in later 1970's • AutoCAD R 12, and R13 C4 in 1996 • AutoDESK Collection, AutoCAD, AutoVision, Desiger, 3D studio• Mechanical Desktop – parameter based system

Integrated and knowledge-based CAD/CAE/CAM System (for high-end user)

• I-DEAS/Pro-E/UG/CATIA

Mid-range solid modeler

• SolidWorks, Solid Edge

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Design ModelThe descriptions of the design processes are often called models of the design process. The design model describes design as a series of stages and progressing from requirements through conceptual design and preliminary design to detail design and to manufacturing

to record and manipulate ideas, to provide a basis for the evaluation of the design. to communication of the design

At the various stages of the design the design models are developed through a process of analysis and evaluation leading to modifications and refinements. Types of design model can be defined by the following modeled properties

Types of design model:

Design model for function Design model for structureDesign model for form of the component partsDesign model for materialsDesign model for surface conditionDesign model for dimensionsetc.

Role of CAD in Product Development ProcessRole of CAD in Product Development Process

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Role of CAD in Product Development ProcessRole of CAD in Product Development Process

CAD in assisting geometric modelingGraphics or geometric modeling using CAD is used to visualize, analyze, document, and produce a product or process. In fact, geometric modeling itself could be considered both a process and a product.

As a process, geometric modeling produces final design solutions, as well as inputs to the production process, in the form of computer databases.

As a product, geometric modeling is a result of the engineering design process

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Representation of Design ModelRepresentation of Design Model

By drawing

By diagram

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Representation of Design ModelBy digital data - CAD solid modeling

Representation of Design ModelBy digital data - CAD solid modeling

CAD for complex design representation Full-Scale Aircraft Structural Test Fixture

(4206 parts in FASTER system)

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Major functions of a solid modeling based CAD system in design process Major functions of a solid modeling based CAD system in design process

model definition - geometrical or design modeling

model manipulation - to edit and modify in the design model

visualization - image of design model and design results

application - generate interfacing information evaluation/analysis/manufacture

database management - files and data management

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CAD used as a design assistant tool CAD used as a design assistant tool

Basic level - to assist in drafting- Produce 2D engineering drawing and diagram- CAD is only used for Computer-Aided Drafting

Advantages: Productivity - short period of design and lower cost of design workAccuracy - improvements of product qualityConsistency - national standards, in-house standards

Advanced level - to assist in design by 3D modeling

- wireframe model, began to link with CAM and CAE- 3D surface model, shading for image- 3D solid model, completed information and real-photo image

- 3D CAD modeling for visualization - CAD/Design Vision- 3D CAD modeling for analysis - CAD/CAE and FEA- 3D CAD modeling for prototyping - CAD/RP&M- 3D CAD modeling for manufacturing - CAD/CAM/CNC, CAD/CAPP- 3D CAD modeling for simulation - CAD/Real Physical Model- 3D CAD modeling for animation - CAD/Real Physical Model

3D modeling has transformed CAD from Computer-Aided Drafting into Computer-Aided Design

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Example of CAD systems - AutoCADExample of CAD systems - AutoCAD

Icons (Tool Palette) - Composite set of most frequently used commandsPull-Down Menu(Menu Bar) - Listed on the menu bar, contain all the commands. Screen Menu - Containing almost all the commands. Graphics Window - the place used to build up model.Status Line - Give you information about the current status of your modelCommand Window - A place you and AutoCAD can talk to each other

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Features of AutoCAD SystemFeatures of AutoCAD System

Command Entry Styles

Keyboard entryPull-down menusScreen MenusTable Menu and Icons

Geometric Entities and Entry Coordinates

Three parts of AutoCAD Commands

Draw - entities (line, arc, circle, pline etc.)Construct - manipulate of entities (copy, array, chamfer, fillet, mirror, etc.)Modify - edit of entities (erase, trim, move, etc.)

A geometric-based CAD modeler