unit 1 &2.pdf

ME8691
COMPUTER AIDED DESIGN AND
MANUFACTURING
DEPARTMENT OF MECHANICAL ENGINEERING
NAMAKKAL-637207
PGP COLLEGE OF ENGINEERING
AND TECHNOLOGY

INDEX
UNITS PAGE NO.
I. INTRODUCTION 4
II. GEOMETRIC MODELING 22
III. CAD STANDARDS 33
IV. FUNDAMENTAL OF CNC AND PART PROGRAMING 47
V. CELLULAR MANUFACTURING AND FLEXIBLE
MANUFACTURING SYSTEM (FMS) 58

SYLLABUS(REGULATION–2017)
OBJECTIVES:
 To provide an overview of how computers are being used in mechanical component design
 To understand the application of computers in various aspects of Manufacturing viz.,
Design, Proper planning, Manufacturing cost, Layout & Material Handling system.
UNIT I INTRODUCTION 9
Product cycle- Design process- sequential and concurrent engineering- Computer aided
design – CAD system architecture- Computer graphics – co-ordinate systems- 2D and 3D
transformations- homogeneous coordinates - Line drawing -Clipping- viewing
transformation-Brief introduction to CAD and CAM – Manufacturing Planning,
Manufacturing control- Introduction to CAD/CAM –CAD/CAM concepts ––Types of
production - Manufacturing models and Metrics – Mathematical models of Production
Performance
UNIT II GEOMETRIC MODELING 9
Representation of curves- Hermite curve- Bezier curve- B-spline curves-rational curves-
Techniques for surface modeling – surface patch- Coons and bicubic patches- Bezier and
B-spline surfaces. Solid modeling techniques- CSG andB-rep
UNIT III CAD STANDARDS 9
Standards for computer graphics- Graphical Kernel System (GKS) - standards for
exchange images- Open Graphics Library (OpenGL) - Data exchange standards - IGES,
STEP, CALS etc. - communication standards.
UNIT IV FUNDAMENTAL OF CNC AND PART PROGRAMING
9
Introduction to NC systems and CNC - Machine axis and Co-ordinate system- CNC
machine tools- Principle of operation CNC- Construction features including structure-
Drives and CNC controllers- 2D and 3D machining on CNC- Introduction of Part
Programming, types - Detailed Manual part programming on Lathe & Milling machines
using G codes and M codes- Cutting Cycles, Loops, Sub program and Macros-
Introduction of CAM package.
UNIT V CELLULAR MANUFACTURING AND FLEXIBLE MANUFACTURING
SYSTEM (FMS)9
Group Technology(GT),Part Families–Parts Classification and coding–Simple Problems in
Opitz Part Coding system–Production flow Analysis–Cellular Manufacturing–Composite
part concept–Types of Flexibility - FMS – FMS Components – FMS Application &
Benefits – FMS Planning and Control– Quantitative analysis in FMS
TOTAL : 45 PERIODS
ME8691 COMPUTER AIDED DESIGN AND MANUFACTURING L T P C
3 0 0 3

OUTCOMES: Upon the completion of this course the students will be able to
CO1 Explain the 2D and 3D transformations, clipping algorithm, Manufacturing models and
Metrics
CO2 Explain the fundamentals of parametric curves, surfaces and Solids
CO3 Summarize the different types of Standard systems used in CAD
CO4 Apply NC & CNC programming concepts to develop part programme for Lathe &
Milling Machines
CO5 Summarize the different types of techniques used in Cellular Manufacturing and
FMS
TEXT BOOKS:
1. Ibrahim Zeid “Mastering CAD CAM” Tata McGraw-Hill PublishingCo.2007
2. Mikell.P.Groover “Automation, Production Systems and Computer Integrated
Manufacturing”, Prentice Hall of India, 2008.
3. Radhakrishnan P, SubramanyanS.andRaju V., “CAD/CAM/CIM”, 2nd Edition, New
Age International (P) Ltd, New Delhi,2000.
REFERENCES:
1. Chris McMahon and Jimmie Browne “CAD/CAM Principles", "Practice and
Manufacturing management “ Second Edition, Pearson Education, 1999.
2. Donald Hearn and M. Pauline Baker “Computer Graphics”. Prentice Hall, Inc,1992.
3. Foley, Wan Dam, Feiner and Hughes - "Computer graphics principles & practice"
Pearson Education -2003
4. William M Neumann and Robert F.Sproul “Principles of Computer Graphics”, McGraw
Hill Book Co. Singapore, 1989.
ME8691 COMPUTER AIDED DESIGN AND MANUFACTURING L T PC 3 0 0 3
UNIT I INTRODUCTION
PART –A
1. Why should we go for CAD? (Nov/Dec2015)
There are four fundamental reasons for implementing CAD system which are asfollows
 To increase the Productivity of the designer
 To improve the qualities of the design
 To improve Communications
 To create a database for engineering
2. Mention any four applications of computer aided design in
mechanicalengineering?(Nov/Dec 2015)
The applications of computer aided design in mechanical engineering cover alltypes of
manufacturing operations such as milling, turning wire cut EDM, punching, etc.

3. List the types of 2D geometric transformation? (Nov/Dec 2015)
 Windowing and viewing transformation, Zooming transformation
 Clipping transformation, Reflection transformation
4. What is the design process? Mention the steps involved in shigley’s model for the
design process? (May/June 2016)
The engineering design process is a methodical series of steps that engineers usein creating
functional products and processes. The process is highly iterative - parts ofthe process
often need to be repeated many times before another can be entered – thoughthe part(s) that
get iterated and the number of such cycles in any given project can be
highly variable.
5. What is Translation?
Translation is one of the important types of transformer. This is used to move theentity
after moving all points of new entity are parallel to all points of old entity.
6. Define Concurrent Engineering?
Concurrent Engineering is also known as Simultaneous Engineering. Here whilethe
product is designed the design and manufacturing process are carried outsimultaneously
this technique facilitates the design engineer to improve the efficiency ofproduct design
and process.
7. List out the factor consider for CAD ?
 Reliability, Cost Factor
 Comparability with other system
 Memory Requirements and Storage requirements
8. What is the main drawback of wire frame modeling ?
The main drawback in terms of representation of objects in wireframe model is
 Lack of clarity
 The part geometry model is complex in the case of 3D wireframe system
 Hidden line causes the image to be confused
9. Draw the flow diagram of Sequential Engineering

10. What are the disadvantages of Beizer Curve ?
 The Curve does not pass through the control points which may be inconvinient tothe
designer
 The Bezier curve lacks control it only has the global control nature
 If one control point is changed the whole curve changes thus the designer cannotselectively
change part of the curve
11. What is meant by morphology design?
Morphology design refers the study of the chronological structure of designprojects.
12. List the various stages in the life cycle of a product? (May/June 2016)
 Introduction Stage, Maturity Stage
 Growth Stage, Decline Stage
1) Define computergraphics.
Computer graphics may be defined as the process of creation, storage and
manipulation of drawings and pictures with the aid of a number.
2) What are the functions ofIGC?
a. Solid modeling
b. Storage
c. Manipulation
d. Viewing
3) What are the various display control facilities ingraphics?
i.VectorGeneration
ii. Windowing and viewingtransformation.
iii. Clippingtransformation
iv. Zooming
v. Panning
vi. Transmitting information on a network and
vii. Graphicslibraries.

4) What is meant by viewpoint?
The viewpoint is the area on the screen in which the contents of the window are to
be displayed as an image.
5) What is viewing transformation and windowing transformation?
The processes of mapping from the model co-ordinate system to the screen co-
ordinate system is known as viewing transformation
The viewing transformation in which no rotation is applied is called the windowing
transformation.
6) What is meant by Clipping?
Clipping is the process of determining the visible portion of a drawing lying within
a window and discarding the rest.
7) State the use of reflection transformation.
It allows a copy of the object to be displayed while the object is reflected about a line or
aplane.
8) What is the use shading Technique?
This technique is used to display the images in natural way. It is based on the
recognition of distance and shape as a function of illumination.
9) How information is transmitted on a network?
The data must be encoded using a protocol. Protocol is a set of rules that control
the exchange of data between the communicatingdevices.
10) What are the main types of 2Dtransformations?
i.Translation
ii. Scaling
iii. Reflection
iv. Rotation
v. Shearing
11) What is meant by concurrent engineering?
The concept and practice of various functions or departments working together,
from the beginning, to engineer a product.

12) What are the advantages of Concurrent engineering?
1. The design decisions are taken by a team of multi disciplinaryexperts.
2. Changes and modification on the product design will befaster.
3. Higherquality.
13) What are the characteristics of concurrent engineering?
1. Product responsibilities lies on team of multi disciplinary group.
2. Integration of design, process planning and production will be achieved.
3. Frequent review of design and development process.
4. Rapid prototyping.
14) Define CAD. Mention areas of application of CAD.
The computers help in design and draft is commonly expressed by the term
“Computer Aided Design” (CAD). A CAD system helps designer in various ways
1. Invites and promotes interaction through various input/output devices.
2. Allows manipulation of image (such as scalling, translation, rotation) in the
computer screen.
3. Enable the designer to carry out the engineering analyses for stress, vibration,
noise thermal distortions and more using FEA.
4. Design optimization through simulation and animation.
5. Automated drafting.
15) What is mean by Co-Ordinate Systems?
When a design package is initiated, the display will have a set of co-ordinate
values. These are called default co-ordinates. A user co-ordinate system is one in which
the designer can specify his own co-ordinates for a specific design application.
PART B
1. Discuss about Sequential Engineering and Concurrent Engineering (May/June
2016)(Nov/Dec2015)
Sequential Engineering Concurrent Engineering
Sequential engineering is the term used to
explain the method of production in a linear
system. The various steps are done one after
another, with all attention and resources
focused on that single task
In concurrent engineering, various tasks are
handled at the same time, and notes sentially in
the standard order. This means that info found
out later in the course can be added to earlier
parts, improving them, and also saving time.
Sequential engineering is a system by which a
group within an organization works
sequentially to create new products and
services.
Concurrent engineering is a method by which
work several groups within an organization
simultaneously to create new products and
services.

The sequential engineering is a linear product
design process during which all stages of
manufacturing operate in serial.
The concurrent engineering is a non linear
Product design process during which all stages
of manufacturing operate at the same time.
Both process and product design run in serial
and take place in the different time.
Both process and product design run in serial
and take place in the different time
Process and Product are not matched to attain
optimal matching
Process and Product are co ordinatedto Attain
optimal matching of requirements for effective
quality and delivery.
Decision making done by only group of
experts.
Decision making involves full team
Involvement.
2. Explain in detailed about product cycle?
Product cycle integrate processes, people, data, and business and gives a product
information for industries and their extended activity. Product cycle is the process of
managing the entire lifecycle of a product from starting, through design and manufacture,
to repair and removal of manufactured products.
There are several Product cycle models in industry to be considered, one of the
possible product cycle is given below

Step 1: Conceive
Imagine, Specify, Plan, Innovate
The first step is the definition of the product requirements based on company,
market and customer. From this requirement, the product's technical data can be defined. In
parallel, the early concept design work is performed defining the product with its main
functional features. Various media are utilized for these processes, from paper and pencil
to clay mock-up to 3D Computer Aided Industrial Design.
Step 2: Design
Describe, Define, Develop, Test, Analyze and Validate
This is where the completed design and development of the product begins,
succeeding to prototype testing, through pilot release to final product. It can also involve
improvement to existing products as well as planned obsolescence. The main tool usedfor
design and development is CAD. This can be simple 2D drawing / drafting or
3Dparametric feature based solid/surface modeling.
This step covers many engineering disciplines including: electronic, electrical,
mechanical, and civil. Besides the actual making of geometry there is the analysis of the
components and assemblies.
Optimization, Validation and Simulation activities are carried out using Computer
Aided Engineering (CAE) software. These are used to perform various tasks such as:
Computational Fluid Dynamics (CFD); Finite Element Analysis (FEA); and Mechanical
Event Simulation (MES). Computer Aided Quality (CAQ) is used for activities such as
Dimensional tolerance analysis. One more task carried out at this step is the sourcing of
bought out components with the aid of procurement process.
Step 3: Realize
Manufacture, Make, Build, Procure, Produce, Sell and Deliver
Once the design of the components is complete the method of manufacturing is finalized.
This includes CAD operations such as generation of CNC Machining instructions for the
product„s component as well as tools to manufacture those components, using integrated
Computer Aided Manufacturing (CAM) software. It includes Production Planning tools for
carrying out plant and factory layout and production simulation. Once details components
are manufactured their geometrical form and dimensions can be verified against the
original data with the use of Computer Aided Inspection Equipment (CAIE). Parallel to the

engineering tasks, sales and marketing work take place. This could consist of transferring
engineering data to a web based sales configuration.
Step 4: Service
Use, Operate, Maintain, Support, Sustain, Phase-out, Retire, Recycle and Disposal
The final step of the lifecycle includes managing of information related to service
for repair and maintenance, as well as recycling and waste management information. This
involves using tools like Maintenance, Repair and Operations Management software.
3. Discuss about 2D and 3D transformation?

4. EXPLAIN IN DETAILED ABOUT DESIGN PROCESS? (May/June 2016)
It is a process in which we initiate the design and come up with a number of design
concepts and then narrow down to the single best concept.
This involved the following steps.
 Identification of customer needs
 Problem definition, Gathering Information
 Conceptualization, Concept selection
Feasibility Study
Designs can be futile unless satisfying the original need is feasible
 At this stage, the product appears in abstract forms, but is they feasible?
 Alternative solutions must be subjected to physical and economic analyses and be
realizable from both
The Feasibility Study using analysis of several alternatives establishes the design concept
as something which can be realized and accepted Some examples
(i) A building must be comfortable to live in:
Heating, ventilation and air conditioning are required. Specify limits of temperature,
humidity, velocity and fresh air constituency.
(ii) National fossil fuel supplies are low:
Alternative forms of energy supply are required. Specify amount and where they are
needed, and any restrictions of space, time or pollution levels.
Preliminary Design
 Main purpose is selection of the best possible solution from a choice of alternatives Make
comparisons against given criteria & constraints
 Must maintain an open mind; use your judgment
Detailed design
 Aim is to produce a complete set of working drawings which are then transmitted to the
manufacturer
 This stage of design is far less flexible than those previous
 Design should now reflect all of the planning both for manufacture andconsumption stages
Construction/testing of various components may berequired
Production
 Here, the device or system is actually constructed, and planning for this shouldhave been
incorporated into the design
 Knowledge of the capability of the machines is required, since it must bepossible to build
and assemble the components as specified
 Special jigs, fixtures and even machines may be required

 Planning is vital; including quality control hold points, methods of inspection,standards for
comparison etc...
 Timing of construction may be important e.g. Climates
Distribution
 Transportation of the manufactured article, complete or in subassembly formmust be
anticipated in the design
 Packaging, availability of vehicles, regulations for use of thoroughfares ,shelf/component
life, warehouse storage facilities, special handling,environmental control of temperature
and humidity may need to be addressed
Consumption
 The product is now used by the consumer
 If the design is effect, it will have met the need
 The design may yet not be complete; redesigns and modifications may berequired
depending on field trials or consumer feedback
 May need to consider maintenance of components and supply of spare parts
orsubassemblies
Retirement
 The product will be discarded as its life cycle terminates
 It may have become obsolete whilst still serviceable and therefore the designmay not have
been fully economical
 Disposal and recovery of useful materials should have been included in the design Threats
to safety should be guarded against

5. Rotate the rectangle shown in fig 300 counter clockwise about the line EF and find
new coordinates of the rectangle (Nov/Dec2015)

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6. Rotate the rectangle (0,0), (2,0), (2,2), (0,2) as shown,300counter clockwise aboutthe centroid and the
new co ordinates of the rectangle(Nov/Dec 2015)

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UNIT II GEOMETRIC MODELING
PART A
1. What are the limitation of Hermite curves?(May/June 2016)
 It is difficult to select the magnitude as well as angle of the tangent vector at thetwo end points of the curve
segment
 Curves are difficult to control because of global shape control characteristics.
 The cubic curve never reduces exactly to a conical section and poorlyapproximate asymptotic curve
2. What are the advantage and disadvantage of wire frame model?(May/June2016)
Advantage
 Wire frame models are more clear than 2D representation
 It is widely used method
Disadvantage
 Representation of model in wire frame models is lack in clarity
 During surface definition there might be confusion by eliminating hidden lines

3. Difference between analytical curves interpolated curves and approximatedcurves. (Nov/Dec 2015)
S.NO ANALYTICAL
CURVE
INTERPOLATED
CURVE
APPROXIMATED
CURVE
1.
These curves are represented
by a simple mathematical
equation
It is drawn by the
interpolating thegiven data
points
It provides the most flexibility
in drawingcurves for
complexshapes
2.
They have a fixed form cannot
be modified to achieve the
shapes that violates the
mathematical equations
These curves havelimited
flexibility inshape creation
The model of automobile
fender can be easily created
with
the help of approximated
curves
4. What are the types of surfaces that CAD/CAM systems use?
 Open and closed surfaces
 Flattening a surface
 Surface patches
 Faces
 Skins and volumes
 Transition to solids
5. What is meant by coon surface?
In mathematics, a Coons patch, is a type of manifold parameterization used incomputer graphics to smoothly
join other surfaces together, and in computationalmechanics applications, particularly in finite element
method and boundary elementmethod, to mesh problem domains into elements.

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6. What do you understand by the form element method of geometricconstruction?
Geometric constructions of figures and lengths were restricted to the use of onlya straightedge and compass
(or in Plato's case, a compass only; a technique now calleda Mascheroni construction). Although the term
"ruler" is sometimes used instead of"straightedge," the Greek prescription prohibited markings that could be
used to make
measurements. Furthermore, the "compass" could not even be used to mark offdistances by setting it and then
"walking" it along, so the compass had to be consideredto automatically collapse when not in the process of
drawing a circle.
7. Specify the applications of this method of modeling in comparison to that of thevariant type?
The finite element method is used to describe the detailed properties of theatmospheric boundary layer by use
of a high-resolution model and its bulk properties byuse of a simple vertically integrated model. Features of
the finite element method thatcan be exploited for applications to the atmospheric boundary layer include
thecapability to use different basis functions in different parts of the domain, ability to gridover irregular
terrain, ease of using time-dependent basis functions and the natural waythat surface boundary conditions and
vertically integrated properties enter the model.
8. What are the limitations in utilizing the sweep method for geometric?
 In computational geometry, a sweep line algorithm or plane sweep algorithm is atype of algorithm that uses a
conceptual sweep line or sweep surface to solve variousproblems in Euclidean space.
 The idea behind algorithms of this type is to imagine that a line (often a verticalline) is swept or moved across
the plane, stopping at some points. Geometricoperations are restricted to geometric objects that either intersect
or are in theimmediate vicinity of the sweep line whenever it stops, and the complete solution isavailable once
the line has passed over all objects
9. Generate the conical surface obtained by rotation of the line segment AB aroundthe z-axis with A=
(1,0,1) and B= (7,0,7)(Nov/Dec 2015)
Solution
From the given coordinates, the coordinate‟s matrix can be written by

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10. For a cubic Bezier curve, carry a similar matrix formulation to a cubic spline?
A Bézier curve is a parametric curve frequently used in computer graphics andrelated fields. Generalizations
of Bézier curves to higher dimensions are called Béziersurfaces, of which the Bézier triangle is a special
PART – B
1. Discuss in detail about approximate synthetic curve representation? (Nov/Dec2015)
Hermite curve:

25
A Hermite curve is a spline where every piece is a third degree polynomialdefined in Hermite form: that is, by
its values and initial derivatives at the end points ofthe equivalent domain interval. Cubic Hermite spines are

26
normally used forinterpolation of numeric values defined at certain dispute values x1x2x3, ….., xn toachieve a
smoothcontinuous function. The data should have the preferred functionvalue and derivative at each Xk. The
Hermite formula is used to every interval (Xk,Xk+1)individually. The resulting spline become continuous and
will have first derivative.Cubic polynomial splines are specially used in computer geometric modeling toattain
curves that pass via defined points of the plane in 3D space. In these purposes,each coordinate of the plane is
individually interpolated by a cubic spline function of adivided parameter‗t„.Cubic splines can be completed
to functions of different parameters, in severalways. Bicubic splines are frequently used to interpolate data on
a common rectangulargrid, such as pixel values in a digital picture. Bicubic surface patches, described bythree
bicubic splines, are a necessary tool in computer graphics. Hermite curves aresimple to calculate but also
more powerful. They are used to well interpolate betweenkey points.
The following vectors needs to compute a Hermite curve:
P1: the start point of the Hermite curve
T1: the tangent to the start point
P2: the endpoint of the Hermite curve
T2: the tangent to the endpoint
Figure shows the functions of Hermite Curve of the 4 functions (from left to right:h1, h2, h3, h4).
Functions of Hermite Curve
A closer view at functions ‗h1„ and ‗h2„, the result shows that function ‗h1„ startsat one and goes slowly to
zero and function ‗h2„ starts at zero and goes slowly to one.At the moment, multiply the start point with
function ‗h1„ and the endpoint withfunction ‗h2„. Let s varies from zero to one to interpolate between start
and endpoint of
Hermite Curve. Function ‗h3„ and function ‗h4„ are used to the tangents in the similarway. They make
confident that the Hermite curve bends in the desired direction at thestart and endpoint.
2. Write short notes on Bezier and B-spline curve? (May/June 2016)
Bezier curve
Bezier curves are extensively applied in CAD to model smooth curves. As thecurve is totally limited in the
convex hull of its control points P0, P1,P2 & P3, the pointscan be graphically represented and applied to
manipulate the curve logically. Thecontrol points P0 and P3 of the polygon lie on the curve .The other two
verticesdescribed the order, derivatives and curve shape. The Bezier curve is commonly tangentto first and
last vertices.Cubic Bezier curves and Quadratic Bezier curves are very common. Higherdegree Bezier curves
are highly computational to evaluate. When more complex shapesare required, Bezier curves in low order are
patched together to produce a compositeBezier curve. A composite Bezier curve is usually described to as a
‗path„ in vectorgraphics standards and programs. For smoothness assurance, the control point at whichtwo
curves meet should be on the line between the two control points on both sides.

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A general adaptive method is recursive subdivision, in which a curve's controlpoints are verified to view if the
curve approximates a line segment to within a lowtolerance. If not, the curve is further divided parametrically
into two segments, 0 ≤ t ≤0.5 and 0.5 ≤ t ≤ 1, and the same process is used recursively to each half. There
arefuture promote differencing techniques, but more care must be taken to analyze
errortransmission.Analytical methods where a Bezier is intersected with every scan line engagefinding roots
of cubic polynomials and having with multiple roots, so they are not oftenapplied in practice. A Bezier curve
is described by a set of control points P0 through Pn,where ‗n„ is order of curve. The initial and end control
points are commonly the endpoints of the curve; but, the intermediate control points normally do not lie on the
curve.
(i) Linear Bezier curves
Linear Bezier Curve
As shown in the figure the given points P0 and P1, a linear Bezier curve is merelya straight line between those
two points. The Bezier curve is represented by
(ii) Quadratic Bezier curves
Quadratic Bezier Curve
As shown in the figure, a quadratic Bezier curve is the path defined by thefunction B(t), given points P0, P1,
and P2
This can be interpreted as the linear interpolate of respective points on the linear Beziercurves from P0 to P1
and from P1 to P2 respectively. Reshuffle the preceding equationgives:
The derivative of the Bezier curve with respect to the value‗t„ is
From which it can be finished that the tangents to the curve at P0 and P2intersect at P1. While‗t„ increases
from zero to one, the curve departs from P0 in the direction of P1, thenturns to land at P2 from the direction of
P1.
The following equation is a second derivative of the Bezier curve with respect to ‗t„:
A quadratic Bezier curve is represent a parabolic segment. Since a parabolacurve is a conic section, a few
sources refer to quadratic Beziers as ‗conic arcs„.

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(iii) Cubic Bezier curves
The function B Pi, Pj, Pk (t) for the quadratic Bezier curve written by points Pi, Pj, and Pk,the cubic Bezier
curve can be described as a linear blending of two quadratic Beziercurves:
The open form of the curve is:
For several choices of P1 and P2 the Bezier curve may meet itself.Any sequence of any four dissimilar points
can be changed to a cubic Beziercurve that goes via all four points in order. Given the beginning and ending
point of a
few cubic Bezier curve, and the points beside the curve equivalent to t = 1/3 and t =2/3, the control points for
the original Bezier curve can be improved.
The following equation represent first derivative of the cubic Bezier curve with respectto t:
Properties Bezier curve
 The Bezier curve starts at P0 and ends at Pn; this is known as ‗endpointinterpolation„ property.
 The Bezier curve is a straight line when all the control points of a cure arecollinear.
 The beginning of the Bezier curve is tangent to the first portion of the Bezierpolygon.
 A Bezier curve can be divided at any point into two sub curves, each of whichis also a Bezier curve.
 A few curves that look like simple, such as the circle, cannot be expressedaccurately by a Bezier; via four
piece cubic Bezier curve can similar a circle,with a maximum radial error of less than one part in a thousand
(Fig.2.8).
Circular Bezier Curve
Each quadratic Bezier curve is become a cubic Bezier curve, and morecommonly, each degree „n‟ Bezier
curve is also a degree „m‟ curve for any m >n.
 Bezier curves have the different diminishing property. A Bezier curves does not‗ripple„ more than the
polygon of its control points, and may actually ‗ripple„less than that.
 Bezier curve is similar with respect to t and (1-t). This represents that thesequence of control points defining
the curve can be changes without modify ofthe curve shape.
 Bezier curve shape can be edited by either modifying one or more vertices ofits polygon or by keeping the
polygon unchanged or simplifying multiplecoincident points at a vertex.
B-Spline Surfaces
 The B-spline surface approximates a characteristics polygon as shown andpasses through the corner points of
the polygon, where its edges are tangentialto the edges of the polygon

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 This may not happen when the control polygon is closed
 A control point of the surface influences the surface only over a limited portionof the parametric space of
variables u and v.
The expression for the B-spline surfaces is given by
3. Briefly explain the different scheme used to generate a solid model? (Nov/Dec2015)
TECHNIQUES IN SURFACE MODELLING
 Constructive solid geometry (CSG and C-rep)
 Boundary representation method (B-rep)
CONSTRUCTIVE SOLID GEOMETRY (CSG and C-rep)
 Constructive solid geometry (CSG) (formerly called computational binary solidgeometry) is a technique used
in solid modeling.
 Constructive solid geometry allows a modeler to create a complex surface orobject by using Boolean
operators to combine objects.
 Often CSG presents a model or surface that appears visually complex, but isactually little more than cleverly
combined or de-combined objects
 The simplest solid objects used for the representation are called primitives.
Typically they are the objects of simple shape.
The set of allowable primitives is limited by each software package. Some softwarepackages allow CSG on
curved objects while other packages do not.
 It is said that an object is constructed from primitives by means of allowableoperations, which are typically
Boolean operations on sets :Union, intersectionand difference as well as geometric transformations of those
sets
Boolean Operations
The CSG is constructed by the following Boolean operation

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4. What do you understand by boundary representation technique in solidmodeling, explain briefly the
structure of B-rep technique (May/June 2016)
Boundary representation method (B-rep)
 In solid modeling and computer-aided design, boundary representation oftenabbreviated as B-rep or BREP is
a method for representing shapes using thelimits.
 Consisting of two parts: topological description of connectivity and orientation ofvertices, edges and faces,
and geometric description for embedding theseelements in space
 The topological description specifies vertices, edges and faces abstractly, andindicates their incidences and
adjacencies.
 The geometric representation specifiessurface equations, edge equations, andvertices coordinates.
 A vertex is a unique point in space
 An edge is a finite, non-self-intersecting, directed space curve bounded by twovertices that are not necessarily
distinct.
 A face is a finite connected, nonself-intersectingregion of a closed orientedsurface bounded by one or more
loops.
 A loop is an ordered alternating sequence ofedges and vertices.
The Euler-Poincar´e Formula - necessary conditions for consistency
(1).For solids that have a closed, orientable surface and no holes or no interiorvoids:
V - E + F = 2
(2).For solids bounded by a single connected surface and with holes, but eachface ishomeomorphic to a disk:
V - E + F = 2(1 - G)
where G is the number of handles, called genus
Advantages of b-rep
 Appropriate to construct solid models of unusual shapes
 Relatively simple to convert a b-rep model to wireframe model
Disadvantages of b-rep
 Requires more storage
 Not suitable for applications like tool path generation
 Slow manipulation
5. Discus the various methods in surface modeling?
i. Surface Patch
ii. Coons Patch
iii. Bicubic Patch
iv. Be„zier Surface
v. B-Spline Surface
i. Surface Patch

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The patch is the fundamental building block for surfaces. The twovariables u and v vary across the patch; the
patch may be termed biparametric.The parametric variables often lie in the range 0 to 1. Fixing the value of
one ofthe parametric variables results in a curve on the patch in terms of the othervariable (Isoperimetric
curve). Figure shows a surface with curves at intervalsof u and v of 0 : 1.
ii. Coons Patch
The sculptured surface often involve interpolation across an intersecting mesh ofcurves that in effect comprise
a rectangular grid of patches, each bounded by fourboundary curves. The linearly blended coons patch is the
simplest for interpolatingbetween such boundary curves. This patch definition technique blends for
fourboundary curves Ci(u) and Dj(v) and the corner points pij of the patch with the linearblending functions,
Using the expression
iii. Bicubic Patch
The bi-cubic patch is used for surface descriptions defined in terms ofpoint and tangent vector information.
The general form of the expressions for abi-cubic patch is given by:
This is a vector equation with 16 unknown parameters kij which can be foundby Lagrange interpolation
through 4 x 4 grid.

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iv. Bezier Surface
A Bézier surface patch is defined by its 4 x 4 Bézier geometry matrix GB, whichspecifies the control points of
the surface. As in the case of Bézier curves, the cornerpoints of GB specify actual points on the edge of the
interpolated surface, while the―inner‖ points are intermediate points which indirectly specify the tangent
vectors to thesurface. The x, y, and z directions of the surface are calculated independently; thus, for a3D
surface patch. there will actually be separate geometry matrices GBx, GBy and GBzone for each direction.
The geometry matrix GBk is given by
Advantages of Surface Modeling
 It is less ambiguous.
 Complex surfaces can be easily identified.
 It removes hidden line and adds realism.
Disadvantages of Surface Modeling:
 Difficult to construct.
 Difficult to calculate mass property.
 More time is required for creation.
 Requires high storage space.
 Also requires more time for manipulation.
Representation of curves- Hermite curve- Bezier curve- B-spline curves-rational curves-Techniques for
surface modeling – surface patch- Coons and bicubic patches- Bezier and B-spline surfaces. Solid modeling
techniques- CSG and B-rep

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