Computer Modeling
Fundamentals
2-D Graphics
Use computer to draft
Not a modeling process
Requires slow speed and
small memory for computer
3-D idea existed, but was not
realizable.
Began in early 60s
3-D Computer Graphics
Use computer to model 3-D objects
(parts)
Use computer to assemble all parts
Computer makes all drawings as
desired
Requires high speed and large
memory for computer
Popular commercial packages:
SolidWorks, Pro/E, AutoCAD
3-D Modeling
Wireframe modeling
Solid modeling (B-rep)
(Boundary representation)
Solid modeling (CSG)
(Constructive solid geometry)
Wireframe Modeling
An object is defined by its edges
and vertices.
Advantages: simple, fast, easy
extension from 2-D to 3-D,
requirement of less computer
memory
Disadvantage: ambiguity
Ambiguity
Solid Modeling
(B-rep)
An object is defined by its edges and
boundary surfaces.
Extension of wireframe modeling.
Advantages: no ambiguity, easy to
calculate physical properties, such as
area, volume, moment of inertia, etc.
Disadvantage: not appealing to
engineers.
Solid Modeling
(CSG)
An is object defined by basic geometric
shapes (geometric primitives).
Geometric primitives: cube, block, prisms,
cylinder, sphere, cone, torus, etc.
Use Boolean operations to manipulate
primitives.
Advantages: more natural to engineers
Disadvantage: not capable to calculate
physical properties.
Geometric Primitives
Boolean Operations
Union (addition):
Intersection: A
B
Difference (subtraction):
A-B, B-A
Part Modeling in Terms of Features
Extruded Feature
Uniform cross
section.
Extruding in the
direction
perpendicular to the
cross section.
Extruded cut can
also be made.
Revolved Feature
construction by
revolving a uniform
cross-section along
a circular path.
The revolved angle
can be selected.
Revolved cut can
also be made.
Summary
3-D solid modeling is a process to construct a
machine (structure) virtually.
CSG 3-D modeling uses the same process as
real manufacturing process.
Construction of parts is the key step of 3-D
modeling.
Pro/E use CSG 3-D modeling to construct
parts, and uses B-rep method to calculate
physical properties.