1. ME 2402 COMPUTER INTEGRATED
MANUFACTURING (CIM)
YEAR/SEMESTER : IV/VII
UNIT I – COMPUTER AIDED DESIGN
Prepared By
MANIMARAN.M
ASSISTANT PROFESSOR
K.RAMAKRISHNAN COLLEGE OF ENGINEERING
TRICHY
2. UNIT I – COMPUTER AIDED DESIGN
Concept of CAD as drafting and designing facility, desirable features
of CAD package, drawing features in CAD – scaling, rotation,
translation, editing, dimensioning, labeling, zoom, pan, redraw and
regenerate, typical CAD command structure, wire frame modeling,
surface modelling and solid modelling (concepts only) in relation to
popular packages.
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3. What is CAD/CAM?
CAD – design activity that involves the effective use
of the computer to
Create,
Modify and
Document in engineering design.
CAM – an effective use of computers and computers
technology in the
Manufacturing planning
Manufacturing control 6/25/2015M.MANIMARAN KRCE TRICHY
4. The scope of CAD/CAM and CIM
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6. CAD DESIGN PROCESS
Presentation
Evaluation
Analysis & Optimization
Synthesis
Problem Definition
Recognition of Need
Automated Drafting
Design Review &
Evaluation
Engineering Analysis
Geometric Modelling
CAD
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7. CAD as Drafting and Designing Facility
Draft – the process of preparing drawings with help of
computers.
Advantages of Computer – Aided Drafting
It is a fast and convenient method
Drawings can be stored in Database
Modify the drawings can be done easily and quickly
Good accuracy
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8. Software Packages for Modelling
There are number of CAD packages available for modelling as followed as
AutoCAD
Pro-E
Unigraphics
CATIA
Solid works
Hyper mesh
Star ccm +
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9. Characteristics of a CAD packages
According to Newman and Sproull, Any graphic package
should have the below characteristics,
1) Simplicity
2) Consistency
3) Completeness
4) Robustness
5) Performance
6) Economy
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10. DESIRABLE FEATURES OF A CAD PACKAGE
1. Geometric modelling features
2. Editing or Manipulation features
3. Display control features
4. Drafting features
5. Programming facilities
6. Analysis features
7.Connecting features
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11. 1. Geometric Modelling Features
A) Features to aid geometric construction methods
Cartesian and polar coordinates
Absolute and incremental dimensions
Units
Grid and
Snap
B) 2D analytical features
Points, Lines, Arcs, Circles, and Splines
C) 3D wireframe modelling features
3D lines, 3D faces, Ruled surfaces, Rotational sweep and Tapered
sweep
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12. (contd..)
D) Surface modelling features
should be able to generate various types of sculptured surfaces
such as Bezier, Coons, B – splines
E) Solid modelling features
examples of block, cylinder, sphere, cone, prism etc.,
F) Skinning and profiling features
G) Assembly features
surface filtering and trimming
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13. 2. Editing (or) Manipulation features
- Editing or manipulating the existing models at any
stage of the product design
a) Transformation features
Translate, Rotate, Scale, Mirror, copy, et.,
b) To alter the existing drawings
Stretching, Trimming, Undo, Delete, Erase, etc.,
c) Symbols features
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14. 3. Display control features
To provide a user friendly interface with effective visuals
characteristics such as
a) Window to identify a set of entities for editing functions
b) Zoom to change the scale of display of the object
c) Pan to move the object on screen without changing the
scale
d) Hidden to remove the hidden lines or surfaces for viewing the
geometry
e) Animation to display the number of images in sequence to imitate
the actual motion
f) Shading to show the 3D view of the image on screen complete
and shade as it appears on the image 6/25/2015M.MANIMARAN KRCE TRICHY
15. 4. Drafting features
The developed model can be utilized for the purpose
of sharing and communicating the information for
other applications.
It have used different dimension types such as linear,
angular, radius, circular, baseline and limit dimensions
etc.,
In the features, sectioning to get a better visualization
of the model or object. 6/25/2015M.MANIMARAN KRCE TRICHY
16. 5. Programming Features
Integration with small programs developed in programming
language to avoid repetitive tasks.
Programming facility allows the user to program specifically for an
application
Programming facility in a packages,
(i) GRIP in Unigraphics
(ii) vb.net and lisp for Auto CAD
Programs help the user to input the least amount of information for
any required design
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17. 6. Analysis Features
In modelling features, the package should have many analysis features and facilities
such as include,
Calculation of area
Calculation of volume
Calculation of mass
Calculation of moment of inertia
Calculation of Centre of gravity
In FEA, the developed model is converted into finite element mesh and the all the
required data are calculated for analysis.
Animation facility is also used to see the assembly of the model 6/25/2015M.MANIMARAN KRCE TRICHY
18. 7. Connectivity Features
The model or object so generated in any of the package
must be capable enough to be used as a input to any
other analysis package with or without converter.
The data (graphics) losses is minimum while transferring the
data from one package to another.
It should have very good data interfacing (connectivity)
with other associated modules.
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19. DRAWING FEATURES IN A CAD PACKAGE
Scaling
Rotation
Translation
Editing
Dimensioning
Labeling
Zoom
Pan
Redraw and
Regenerate 6/25/2015M.MANIMARAN KRCE TRICHY
20. Drawing features in CAD
Scaling transformation used to change, increase or decrease the
size of an object without alter the shape.
Rotation the movement of an object in such a way that the distance
between a certain fixed point and any given point of that
body.
Translation moving an object across the screen from one position to
another position.
Editing changes the properties of a specific object by the editing
commands of package.
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21. (contd..)
Dimensioning provides the dimension of the selected entity.
1. Linear dimension
2. Aligned dimension
3. Radius dimension
4. Angular dimension
Labelling it should be labelled for better documentation and
reference.
Pan moves the drawing display along the direction of the
mouse swipe.
Redraw refreshes the display in the current viewport.
Regenerate regenerates the entire drawing from the current view port.
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22. (Contd..)
Zoom Magnifying a portion of current drawing on the screen.
It helps to improve the accuracy of Drawing by enlarging the
details
1. All zooms
2. Centre zooms
3. Dynamic zooms
4. Extends zooms
5. Previous zooms
6. Scale zooms
7.Window zooms
8. Object zooms
9. Real time zooms
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24. GEOMETRIC MODELLING
Geometry modelling is the use of a CAD system to develop a
mathematical description of the geometry of an object.
The geometric modelling can be classified into
1. Wire frame modelling
2. Surface modelling
3. Solid modelling
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25. WIRE FRAME MODELLING
Wire frame models can be consider as networks of
interconnected lines to represent the edges of the physical
objects
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26. Merits and Demerits of wire frame modelling
It is simple and easy to create
This is basis for surface model
Accurate information about the location of surface
Automatic generations of cutter paths to drive NC machine tool
CPU time required to edit or update a wire frame model is small
compare with surface and solid modelling.
Calculation of section properties and mass properties are
impossible
It has limited use in manufacturing and analysis
Presentation of circular holes and curved surfaces are poor
Interference checking will be difficult
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27. SURFACE MODELLING
A surface model can be built by defining the surface on the
wire frame
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28. Surface Entities
1.Plane surface
This is a simplest surface.
A planer surface is generated
through number of coplanar points.
2. Rules surface
This is a linear surface
A surface is interpolated b/w two
guiding curves “rails”
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29. (contd..)
3. Surface of revolution
It is generated Axi-symmetric surfaces
It is generated by rotating a plane curve
in a space about the for certain angle of
rotation
4. Translated surface
Generated by extruding a 2D entity along the specified direction.
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30. (contd..)
5. Bezier surface
This is a synthetic surface that
approximate data points.
The Bezier surface is generated from
the basis of Bezier curve.
This type of surfaces can permit twist in
the surface
6. B-Spline surface
Generated from the basis B-spline curve
Another synthetic surface and local
control surface 6/25/2015M.MANIMARAN KRCE TRICHY
31. (contd..)
7. Coons patch surface
It is used to create a surface using
curves that form closed boundaries.
The patches may be triangular or
rectangular type
8. Fillet surface
It is obtained by blending two
surfaces with a fillet radius
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32. Application of surface modelling
It can used sheet metal works and thin moulded plastic parts
Body panels of passenger cars
Structural components of aircraft and marine structure
Plastic container, telephones, impellers of pumps and turbine,
glass marking
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33. Merits and Demerits of surface modelling
Merits
To check the aesthetic look of the product
Complex surface can be created very easily (shoes, car panels, doors )
It can be used to perform Interference checking
Demerits
It require more computational time compared with wire frame
Mass properties (weight, volume and Moment Inertia) cannot be
derived from surface models
More skill is required for surface modelling
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34. SOLID MODELLING
Solid modeling is based on complete, valid and unambiguous
geometric representation of physical object.
Complete points in space can be classified.(inside/ outside)
Valid vertices, edges, faces are connected properly.
Unambiguous there can only be one interpretation of object
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35. Constructive solid geometry (CSG)
Objects are represented as a combination of simpler solid objects
(primitives) such as cube, cylinder, cone, torus, sphere etc.
The physical operations are modelled by combining these primitives
by a set of Boolean operations.
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36. Tree structure of model
Binary tree scheme is used to store
the model in the data structure
Any node may have one parent
and two child node.
The root node (R) has no parent
and leaf node (L) has no children.
Object = (A∩B)-(CU(DUE)
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37. Advantages of CSG
CSG is powerful with high level command.
Easy to construct a solid model – minimum step.
CSG modeling techniques lead to a concise database
less storage.
Can be converted to the corresponding boundary
representation.
Less skill is enough
Disadvantages of CSG
More computational effort and time are required whenever
the model is to be displayed on the screen
Getting fillet chamfer and taperness in the model is very
difficult 6/25/2015M.MANIMARAN KRCE TRICHY
38. Boundary Representation (B-rep)
The solid model created by using B-rep technique may be stored in the
graph based on data structure system
Vertices are connected to form edges and these edges are connected
together to form the face which makes the complete solid
B-rep Vs CSG
In the CSG the number of basic primitives available are limited
The performance of B-rep scheme is very much superior to that of CSG for
complex engineering models.
Conversion of CSG to B-rep is possible, but B-rep to CSG is not possible
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39. Euler’s Equation
For bodies without holes should satisfy EULER’S RULE
V – E + F = 2
V- No. of Vertices
E – No.of Edges
F – No. of Faces
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40. (contd..)
For bodies with holes and re-entrant face, should satisfy Euler
Poincare formula
V – E + F – H + 2P = 2B
H – No. of holes
P – No. of passages
B – No. of separate bodies
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41. Advantages of B-rep
Computational effort and time required to display the
models are less
Combining wire frame and surface models are possible
Complex engineering objects can be modelled very easily
Disadvantages of B-rep
The data to be stored is more and it requires more memory
complex curve and surfaces only approximated
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42. Advantages of solid modelling
Mass properties of physical model can be calculated
quickly
Cross section views of model can be obtained easily
It can be used for interference/clearance checking of
moving parts
Aesthetic look of finished object can be visualized in the
computer
Solid model is very much useful for finite element analysis
They can help to produce NC machining instructions
automatically.
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