Download - Chapter 9 3 d Modelling
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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