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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 9

3D Modeling

3D Modeling Snapshot

•Since Mid 1980’s become common place in industry

Software Types •Wireframe (AutoCAD)

•Surface Modelers (CATIA) Constructive Solid Geometry (CSG)

Boundary Representation Modeler (BMR or B-REP)

•Hybrid Modelers (CATIA/ Solid Works)

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Wireframe Modeler Two types of elements defined

Points (Vertices)

Lines (Edges)

Surfaces (Faces) Theoretically created

Pros & Cons

of

Wireframe Modelers •Simple to adapt from 2D software

•Less Memory required

•Less Processing Power needed

•Cost less

•Ambiguity

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Which of these is the correct representation of a

solid from the wireframe model?

CSG- Constructive Solid Geometry •Allows flexibility in both how primitives are defined and combined

What are these

operations called?

Boolean

3 Types

Union (U)

Difference (-)

Intersection (∩)

What does Solid works

call them?

•Join

•Cut

•Intersection

Does it matter what

order we do them in?

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Primitives using CSG modeling

Boundary Representation (B-REP) •Surfaces or faces define solid

•Contain both linear and curved edges

•Use faceted representation due to size of models

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Surface Modeler Two types of elements used to define surfaces

Points (Vertices)

Lines (Edges)

Actual Surfaces are created

Hybrid Modeler •Use combination of CSG and B-REP features (CATIA/ Solid Works)

Solid Modeling •Include Volume

(weight)

•Apply materials and

analyze

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Most common

techniques:

•Sweeping

•Revolving

•Lofting

With a partner take out a piece of paper and sketch how you

would model a boomerang.

Sweeping •Need Profile (2DSketch or Directrix)

•Direction (Along 3D sketch (path) or Generatrix)

What is our directrix in our boomerang?

Genaratrix?

Directrix-2D

Genaratrix- used to generate 3D

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Generalized Sweeps (Extrude) 2 things needed

Closed profile & Direction

What is needed for the oblique sweep?

Closed profile & path

Revolved Sweeps 2 things needed

Closed profile & Axis

Revolving •Need closed Profile (Sketch)

•Axis

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Lofting •Need 2 or more Profiles (Sketch or Directrix)

•Direction (Along Generatrix or Spine)

What is our directrix in our dryer

housing?

Genaratrix?

Surface Patch •Contains 4 connected Bezier Curves

•Controlled by 12 points

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Quiz!!!!

1. What is needed to create a sketch?

2. What is needed to create a profile?

3. What is needed to create a solid part?

4. What is difference between open & closed loop profiles?

5. What is needed to create a generalized sweep (Extrude)?

6. What is needed to create a revolved sweep?

7. Which of the profiles below are closed loop?

8. Which of the profiles below are open loop?

9. What does CSG stand for?

10. What does B-REP stand for?

1. Work plane

2. Points and lines (Topology)

3. Closed profile/ Direction

4. Closed profile

5. Profile/ Direction

6. Profile/ Axis

7. A and C

8. B

9. Constructive Solid Geometry

10. Boundary Representation

Modeling

Homework

Model Figures 9.109 (C & N)

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Division of parts made up

of more than one surface •Trimmed

•Continuity

•Merging

Continuity

Merged

Divisions of

Continuity A- Discontinuous- has

holes or gaps

B- Positional- Share

boundary

C- Tangent- Smooth

Transition

D- Continuous curvature-

no noticeable transition

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Options to define plane •Through

•Offset/ Parallel

•Angle/ reference

•Point or Edge and Orientation

•Tangent and Orientation

How would you create this?

Constraining Profiles 2 Types of Constraints

•Geometrical (Implicit)

•Dimensional (Explicit)

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Duplicating Part Features Linear and Radial Arrays

What is the main reason for solid modeling software?

Assemblies Hierarchical approach

Network Approach- Toolbox in Solid Works

Instances

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The Goal in Assemblies is to control the degrees

of freedom the product can move

How many degrees of freedom does every object have?

Constraint options:

Surface

Coincident

Offset

Why Solid Modeling? Kinematics

Movement Paths

Clash Detection

Design from Motion

Mass Properties

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Why Solid Modeling?

Ergonomics

Why Solid Modeling?

CAM- Computer Aided Manufacturing

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CAM Rapid Prototyping

Visual Inspection

CNC Path Exported

Virtual Reality

Finite Element Analysis

DATA Exchange

CAD to CAM

Different File Types

DXF- Drafting Exchange Format

IGES- Initial Graphics Exchange Specification

STEP- Standard for the exchange of product

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Homework

Ch 9 figure 19.109 C dimensions

Homework

Ch 9 figure 19.109 N dimensions