CHAPTER 3

Computer-Aided Design and Drafting (CADD)

Learning Objectives

• Define CADD and CAD• Describe the CADD workstation and

peripheral equipment• Identify common CADD software

manufactures and products• Describe and compare CADD formats• Identify disciplines and industry

concepts related to CADD

Learning Objectives

• Explain the use of animation and virtual reality in the design process

• Demonstrate an understanding of basic CADD techniques including drawing and editing, line standards and layers, reusing content, plotting, file templates, and storing and managing files

• Explain basic surface and solid modeling techniques

Learning Objectives

• Demonstrate an understanding of parametric solid modeling

• Identify, describe, and use national CADD standards

• Discuss issues related to productivity with CADD

• Describe sustainable design and CAD practices

Computer-Aided Design and Drafting (CADD)

• Entire range of design and drafting with the aid of a computer

• Computer-aided design (CAD)• Computer-aided drafting (CAD)• Used by several industries and

most engineering and architectural related disciplines

CADD Workstation

• Hardware• Computer provides:• Data processing

• Calculations

• Communication with peripheral equipment

CADD Software Products

• Numerous and constantly changing• Many CADD software

manufactures• Rapidly evolving CADD market

CADD Software Products

• General-purpose• Mechanical computer aided design

(MCAD)• Other disciplines such as

architectural, civil, structural• Software packages• Product lifecycle management

(PLM)

Common CADD Software Manufactures

Common CADD Formats

• 2-D drawings• 3-D wireframe models• 3-D surface models• 3-D solid models

Choosing a CADD Format

• Design and drafting practices• Project requirements• Collaboration and communication• Software and training costs• Known industry standard product• Stability and usability• Support and training• Personal preference

Two-Dimensional (2-D) Drawings

• Established and often required design and drafting format

• Common in all engineering and architectural industries and related disciplines

• Describes design intent and product requirements

• Can provide computer numerical control (CNC) machine code

2-D Drawings

Three-Dimensional (3-D) Wireframe Models

• Basic 3-D CAD model• Include object edges and vertices• Can provide geometry for:• 2-D drawings

• 3-D computer numerical control (CNC) machine code

• Replaced by 3-D surface and solid modeling

3-D Wireframe Models

3-D Surface Models

• Include object edges, vertices, and surfaces

• Complex curves and forms• Can provide geometry for:• 2-D drawings

• 3-D solid models

• 3-D computer numerical control (CNC) machine code

3-D Surface Models

3-D Solid Models

• Most complex CAD format• Include object edges, vertices,

surfaces, and mass• Exact digital representation of a

product• May require some surface modeling• Offer engineering analysis and testing• Can provide geometry for:• 2-D drawings• 3-D computer numerical control (CNC)

machine code

3-D Solid Models

Industry and CADD

• CADD can store many forms of data

• CADD supports:• Manufacturing

• Marketing

• Sales

• Service

• Maintenance

Product Lifecycle Management (PLM)

• Supported by CADD• PLM software helps coordinate:• Design and manufacturing

• Visualization and presentation

• Maintenance and disassembly

Web-Based Collaboration

• Common to modern design and drafting

• Supports the design and documentation process

• Uses product data management (PDM) systems

• Allows for increased outsourcing

Prototyping

Prototyping

Computer-Aided Engineering (CAE)

Animation

• Engineering animations• Basic element of product design and

analysis

• eLearning animations• Additional classroom learning tool or an

online or distance learning presentation

• Entertainment animations• Movies, television, and video games

Computer-Aided Manufacturing (CAM)

• Major innovation• Common process• Helps produce consistent and

quality products• Computer-aided design/computer-

aided manufacturing (CAD/CAM)• Computer numerical control (CNC)

Computer-Integrated Manufacturing (CIM)

• Computer and software controls most, if not all, portions of manufacturing

• Incorporates CAD, CAM, robotics, electronics, hydraulics, pneumatics, computer programming, and process control

Additional CADD Applications

Virtual Reality (VR)

• Allows one or more people to move and react in a computer-simulated environment

• Provides interaction with a model during the design process

• Requires special interface devices• Walk-through• Fly-through

VR Applications and Devices

• Through-the-window VR (passive VR)• Head Mounted Display (HMD)• Binocular Omni-Orientation Monitor

(BOOM)• Cave Automatic Virtual Environment

(CAVE)• Haptic Interface• Web-Enabled Virtual Reality Modeling

Language (VRML)

Basic CADD Techniques

• Drawing and Editing• Line Standards and Layers• Reusing Content• Plotting• File Templates• Storing and Managing Files

Drawing and Editing

• Commands for creating and modifying all elements of a drawing

• Techniques vary depending on:• CADD software

• Preferred design techniques

Drawing and Editing

Line Standards and Layers

• Help organize and assign properties to objects

• Separate objects into logical groups for formatting and display purposes

Line Standards and Layers

Example Mechanical Drafting Layers

Layer Name Line Type Line Weight Color

ObjectSolid

(Continuous).02 in. (0.6 mm) Black

Hidden Hidden (Dashed) .01 in. (0.3 mm) Blue

Center Center .01 in. (0.3 mm) Green

DimensionSolid

(Continuous).01 in. (0.3 mm) Red

ConstructionSolid

(Continuous).01 in. (0.3 mm) Yellow

BorderSolid

(Continuous).02 in. (0.6 mm) Black

Phantom Phantom .01 in. (0.3 mm) Magenta

SectionSolid

(Continuous).01 in. (0.3 mm) Brown

Reusing Content

• CADD offers the ability to reuse:• Objects and object properties

• Text and dimension settings

• Drafting symbols

• Sheets

• Typical drawing details

Plotting a Hard Copy

• Often required• Creates a plot that can be viewed

and marked without having a computer

• Each CADD system uses a specific method to plot• Plotting theory is similar

• Electronic plotting (exporting)

Drawing Scale and Scale Factor

• Important consideration when plotting• Automated by most CADD software,• Remains an important concept

• Example application:• A 1:4 scale drawing has a scale factor of 4

(4 1 = 4)• Multiply the scale factor of 4 by values

such as text height of .12 in. (3 mm) to find the .48 in. (12 mm) scaled text height

File Templates

• Preset settings for specific applications

• Standard items required for multiple projects

• Save time• Improve consistency

Common Elements of a File Template

• Units settings• Drawing and design settings and aids• Layers• Color, material, and lighting standards• Annotation standards• Common symbols• Display settings• Sheets and sheet items• Plot settings

Storing and Managing Files

• Save files immediately after you begin work

• Save at least every 10 to 15 minutes• Develop an organized structure of

file folders• Use a specific file naming system• Follow established file management

techniques

Surface Modeling Techniques

• Polygonal modeling• Surfaces are quick and easy to modify

• Common for character design for games

• NURBS• Non-uniform rational basis spline

• Non-uniform rational B-spline Accurate curves and surfaces Used by most CAD systems

NURB Geometry

• Complex mathematical spline representation with control points

• Change control points to alter the curve

NURB Geometry

Direct Surface Modeling

Procedural Surface Modeling

Solid Primitives

• Boolean operations• Also apply to more complex solid

models

Feature-Based Solid Modeling

• Construct solid models using intuitive feature tools• Often begins with a 2-D sketch

• Sketch used to develop a sketched feature

• Additional features add or subtract solid material

Parametric Solid Models

• Most common feature-based solid models

• Often store model history• History-based solid modeling

• Captures design intent using parameters

• Maintains design constraints

History-Free Solid Modeling

• Often associated with basic solids (dumb solids)

• Makes design changes easy• Helps support collaboration• Explicit modeling

Parametric Solid Model Work Environments

• Part• Assembly (subassemblies and

assembly)

Part Model Elements

• Sketch• Sketched feature• Placed (built-in, added, automated)

features• Feature pattern• Reference (work, reference

geometry) features• Catalog (library) feature

Assembly Modeling

• Add and constrain existing components• Bottom-up design

• Create components within an assembly file (in-place)• Top-down design

• Assembly constraints (mates)

Assembly Modeling

Extracting Drawing Content from Models

• Editing the model adjusts the corresponding drawing

• Some edits to the drawing modify the linked model

CADD Standards

• Design and drafting requirements• Appearance• Technique• Operating procedures• Record keeping method

CADD Standards

• File storage, naming, and backup• File templates• Units of measurement• Layout characteristics• Borders and title blocks• Symbols• Layers, and text, table, and

dimension styles• Plot styles and plotting

CADD Standards

• American Society of Mechanical Engineers (ASME) standards

• CADD Skill Standards• United States National CAD

Standard

Design Planning

• Important and productive time• Determines how you approach a

project• Without proper planning you may

become frustrated and waste time

Design Planning

• Helps establish:• Drawing layout

• Drafting settings

• How and when to perform specific tasks

• What objects and symbols to create

• The best use of CADD and equipment

• An even workload

Ergonomic Workstation

• Helps prevent most computer-related injuries

Positive Work Habits

• Concentrate on good posture• Keep your stress level low• Take periodic breaks• Apply stretching and other exercises• Locate noisy plotters in a separate

room and keep other noise to a minimum

• Ensure adequate air-conditioning and ventilation

Stretches to Help Avoid Repetitive Injury