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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
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.
6/25/2015M.MANIMARAN KRCE TRICHY
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
The scope of CAD/CAM and CIM
6/25/2015M.MANIMARAN KRCE TRICHY
SHIGLEY’S DESIGN PROCESS
PRESENTATION
EVALUATION
ANALYSIS & OPTIMIZATION
SYNTHESIS
PROBLEM DEFINITION
RECOGNITION OF NEED
6/25/2015M.MANIMARAN KRCE TRICHY
CAD DESIGN PROCESS
Presentation
Evaluation
Analysis & Optimization
Synthesis
Problem Definition
Recognition of Need
Automated Drafting
Design Review &
Evaluation
Engineering Analysis
Geometric Modelling
CAD
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
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 +
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
(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
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
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
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
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
6/25/2015M.MANIMARAN KRCE TRICHY
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
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.
6/25/2015M.MANIMARAN KRCE TRICHY
DRAWING FEATURES IN A CAD PACKAGE
Scaling
Rotation
Translation
Editing
Dimensioning
Labeling
Zoom
Pan
Redraw and
Regenerate 6/25/2015M.MANIMARAN KRCE TRICHY
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.
6/25/2015M.MANIMARAN KRCE TRICHY
(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.
6/25/2015M.MANIMARAN KRCE TRICHY
(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
6/25/2015M.MANIMARAN KRCE TRICHY
Typical CAD Command Structure
Drawing commands
Editing commands
Text commands
Display commands
Dimensioning commands
Setting commands
Hatching commands
3D Surface commands
3D Solid commands
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
WIRE FRAME MODELLING
Wire frame models can be consider as networks of
interconnected lines to represent the edges of the physical
objects
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
SURFACE MODELLING
A surface model can be built by defining the surface on the
wire frame
6/25/2015M.MANIMARAN KRCE TRICHY
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”
6/25/2015M.MANIMARAN KRCE TRICHY
(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.
6/25/2015M.MANIMARAN KRCE TRICHY
(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
(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
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
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.
6/25/2015M.MANIMARAN KRCE TRICHY
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)
6/25/2015M.MANIMARAN KRCE TRICHY
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
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
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
(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
6/25/2015M.MANIMARAN KRCE TRICHY
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
6/25/2015M.MANIMARAN KRCE TRICHY
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.
6/25/2015M.MANIMARAN KRCE TRICHY
THANK YOU…
6/25/2015
M.MANIMARAN KRCE TRICHY

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Unit i computer aided design

  • 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. 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 5. SHIGLEY’S DESIGN PROCESS PRESENTATION EVALUATION ANALYSIS & OPTIMIZATION SYNTHESIS PROBLEM DEFINITION RECOGNITION OF NEED 6/25/2015M.MANIMARAN KRCE TRICHY
  • 6. CAD DESIGN PROCESS Presentation Evaluation Analysis & Optimization Synthesis Problem Definition Recognition of Need Automated Drafting Design Review & Evaluation Engineering Analysis Geometric Modelling CAD 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 + 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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. 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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. 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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. 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 23. Typical CAD Command Structure Drawing commands Editing commands Text commands Display commands Dimensioning commands Setting commands Hatching commands 3D Surface commands 3D Solid commands 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 25. WIRE FRAME MODELLING Wire frame models can be consider as networks of interconnected lines to represent the edges of the physical objects 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 27. SURFACE MODELLING A surface model can be built by defining the surface on the wire frame 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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” 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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. 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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. 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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) 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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 6/25/2015M.MANIMARAN KRCE TRICHY
  • 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. 6/25/2015M.MANIMARAN KRCE TRICHY