Please read this disclaimer before proceeding:

�This document is confidential and intended solely for the educational purpose of RMK Group of Educational Institutions. If you have received this document through email in error, please notify the system manager. This document contains proprietary information and is intended only to the respective group / learning community as intended. If you are not the addressee you should not disseminate, distribute or copy through e-mail. Please notify the sender immediately by e-mail if you have received this document by mistake and delete this document from your system. If you are not the intended recipient you are notified that disclosing, copying, distributing or taking any action in reliance on the contents of this information is strictly prohibited.

20ME605�COMPUTER AIDED DESIGN AND�MANUFACTURING

Department: MECHANICAL ENGINEERING�Batch/Year: 2021-2025�Created by:

Dr A.KADIRVEL

�Date: 18.01.2024

Table of Contents

COURSE OBJECTIVES

• Students completing this course are expected to:

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• Explain the advanced aspects of enabling computer aided technologies used in design, manufacturing and rapid product development

• Discuss the use of computers in mechanical component design

• Design the 3D Model of parts, assemblies and explore the features of CNC Machine tools.

• Illustrate the advances in modern techniques of rapid prototyping

• Summarize the various CAD standards in exchange of data, graphics and images

PRE REQUISITE CHART

SYLLABUS

UNIT I INTRODUCTION TO CAD AND CAM 6+6

Product cycle- Design process- sequential and concurrent engineering- Computer aided design – CAD system architecture- Computer graphics – 2D and 3D transformations - homogeneous coordinates - Line drawing -Clipping- Brief introduction to CAD and CAM – Manufacturing Planning, Manufacturing control- CAD/CAM concepts – Lean Production and Just-In-Time Production.

List of Exercise/Experiments

1.Introduction to CAD Software

2.Introduction to Fundamentals of CAM

UNIT II GEOMETRIC MODELING 6+6

Wireframe Modeling - Representation of curves - Hermite curve - Bezier curve - B-spline curves - rational curves -Techniques for surface modeling - Solid modeling techniques - CSG and B-rep- Assembly modeling- Top-down Approach – Bottom -Up Approach.

List of Exercise/Experiments

1. Creation of 3D Assembly model of Machine Elements

2. Detailing of the Assembly model of Machine Elements

UNIT III CAD STANDARDS 6+6

Standards for computer graphics - Graphical Kernel System (GKS) - standards for exchange images - Open Graphics Library (OpenGL) - Data exchange standards - IGES, STEP etc. – communication standards.

List of Exercise/Experiments

1. Export the Assembly model in IGES format.

2. Import the model in STEP & DXF format.

SYLLABUS

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UNIT IV CELLULAR MANUFACTURING AND FLEXIBLE MANUFACTURING SYSTEM 6+6

Group Technology (GT), Part Families – Parts Classification and coding – Computer Aided Process Planning (CAPP) – Production flow Analysis–Cellular Manufacturing – Composite part concept – Types of Flexibility - FMS – FMS Components – FMS Application & Benefits – FMS Planning and Control.

List of Exercise/Experiments

1. Study the Application of CAPP in machining and Turning centre

2. Post Process generation using CAM Package

UNIT V ADDITIVE MANUFACTURING 6+6

Need - Development of RP systems – RP process chain - Impact of Rapid Prototyping on Product Development. - STL file generation. Rapid Prototyping system: Stereolithography (SLA)- Fused Deposition Modeling (FDM)- laminated object manufacturing (LOM)- Selective Laser Sintering (SLS) - Working Principles, details of processes, products, materials, advantages, limitations and applications.

List of Exercise/Experiments

1. Develop a mechanical product using the 3D Printer

2. Obtain the model of the Machine Element using 3D Scanner

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COURSE OUTCOMES �

After successful completion of the course, the students should be able to

CO-PO/PSO Mapping

Lecture Plan �

ACTIVITY BASED LEARNING

UNIT -II

Activity : Drawing on CREO for the following convert the curve to solid .

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Output/ Result:

UNIT 2 : Geometric Modeling

Representation of curves

• Hermite Curve- Bezier curve
• B-spline curves-rational curves
• Techniques for surface modelling
• Surface patch , Coons and bicubic patches
• Bezier and B-spline surfaces
• Solid modelling techniques
• CSG and B-rep

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• Representation of curves
• Types of Curve Equations
• Explicit (non-parametric)
• Y = f(X), Z = g(X)
• Implicit (non-parametric)
• f(X,Y,Z) = 0
• Parametric
• X = X(t), Y = Y(t), Z = Z(t)

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Figure: Différence between synthetic and analytique curves

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Basic Concepts :

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C 0 - Zero-order parametric continuity - the two curves sections must have the same coordinate position at the boundary point.

C 1 - First-order parametric continuity - tangent lines of the

coordinate functions for two successive curve sections are

equal at their joining point.

C 2 - second-order parametric continuity - both the first and

second parametric derivatives of the two curve sections

are the same at the intersection

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Interpolating and approximating curve:

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Convex hull

The convex hull property ensures that a parametric curve will never pass

outside of the convex hull formed by the four control vertices.

Hermite Curve:

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Hermite curves are designed by using two control points and tangent segments at each control point

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Bezier Curve

• A Bezier Curve is obtained by a defining polygon.
• First and last points on the curve are coincident with the first and last
• points of the polygon.
• Degree of polynomial is one less than the number of points
• Tangent vectors at the ends of the curve have the same directions as the
• respective spans
• The curve is contained within the convex hull of the defining polygon.

• Properties Bezier curve
• The Bezier curve starts at P0 and ends at Pn; this is known as ‘endpoint interpolation’ property.
• The Bezier curve is a straight line when all the control points of a curve are collinear.
• The beginning of the Bezier curve is tangent to the first portion of the Bezier polygon.
• • A Bezier curve can be divided at any point into two sub curves, each of which is also a Bezier curve.
• • A few curves that look like simple, such as the circle, cannot be expressed accurately 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.1)

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• Each quadratic Bezier curve is become a cubic Bezier curve, and more commonly, 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 the sequence of
• control points defining the curve can be changes without modify of the curve shape.
• Bezier curve shape can be edited by either modifying one or more vertices of its
• polygon or by keeping the polygon unchanged or simplifying multiple coinciden points at a vertex (Fig .2)

B-spline Curve

• It provide local control of the curve shape.
• It also provide the ability to add control points without increasing the degree of the curve.
• • B-spline curves have the ability to interpolate or approximate a set of given data points.
• The B-spline curve defined by n+1 control points Pi is given by

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• Ni,k(u)'s are B-spline basis functions of degree p.
• The form of a B-spline curve is very similar to that of a Bézier curve. Unlike a Bézier
• curve, a B-spline curve involves more information, namely: a set of n+1 control points, a
• knot vector of m+1 knots, and a degree p.
• • Given n + 1 control points P0, P1, ..., Pn and a knot vector U = { u0, u1, ..., um }, the Bspline
• curve of degree p defined by these control points and knot vector.
• • The knot points divide a B-spline curve into curve segments, each of which is defined on a knot span.
• m = n + p + 1.
• The degree of a Bézier basis function depends on the number of control points.
• • To change the shape of a B-spline curve, one can modify one or more of these
• control parameters: the positions of control points, the positions of knots, and the degree of the curve

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• The degree of a Bezier basis function depends on the number of control points.
• • To change the shape of a B-spline curve, one can modify one or more of these
• control parameters: the positions of control points, the positions of knots, and the degree of the curve.
• • If the knot vector does not have any particular structure, the generated curve will
• not touch the first and last legs of the control polyline as shown in the left figure below.
• • This type of B-spline curves is called open B-spline curves.

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• Properties of B-Spline Curve:

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• The first property ensures that the relationship between the curve and its
• defining control points is invariant under affine transformations.
• The second property guarantees that the curve segment lies completely
• within the convex hull of Pi.
• The third property indicates that each segment of a B-spline
• curve is influenced by only k control points or each control point affects only
• only k curve segments, as shown in Figure 1.
• It is useful to notice that the Bernstein polynomial,
• has the same first two properties mentioned above.

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Surface modelling

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Surface modeling is the next stage of wireframe modeling. In wireframe modeling models are unable to represent complex surfaces of objects like car, ship, aeroplane, wings, castings etc. only a surface profile of these objects.

A surface model represents the skin of an object. These skins have no thickness or material type. Surface models define the surface properties, as well as the edges of objects. These are often capable of clearly representing the solid from the manufacturing.

However, no information regarding the interior of the solid model would be available which could be relevant for generating the NC cutter data. Further the calculation of properties such as mass and inertia etc would be difficult.

Surface modeling facilities would be available as part of the modeling technique and would be used when such surface is present in the product for design.

For example this method is used mode for specific non-analytical surfaces, called sculptures surfaces such as those used for modeling the car bodies and ship-hulls. There are a number of mathematical techniques available for handling these surfaces such as Bezier and B-splines.

Advantage:

1. Eliminates much ambiguity and non-uniqueness present in wireframe models by hiding lines not seen
2. Renders the model for better visualization and presentation, objects appear more realistic
3. Provides the surface geometry for CAM, NC machine
4. Provides the geometry needed by the manufacturing engineer for mold and die design
5. This can be used to design and analysis complex free-formed surfaces of ship hulls, aero plane fuselages and bodies
6. Surface properties such as roughness, color and reflectivity can be assigned and demonstrated

Disadvantages:

1. Provides no information about the inside of an object
2. Curved surfaces need a fine mesh to be accurate
3. Provides wrong results if mesh is too coarse
4. Complicated computation, depending on the number of surfaces

Solid modelling techniques

Constructive Solid Geometry (CSG)

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• Constructive solid geometry (CSG) is a method used in solid modeling for creating
• 3D models in CAD. Constructive solid geometry permits a modeler to make a
• complex surface by applying Boolean operators to join objects. The simplest solid
• objects utilized for the demonstration are called primitives. Classically they are the
• items of simple shape like prisms, pyramids, spheres and cylinders

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• A CSG tree is defined as an inverted ordered binary tree whose leaf nodes are primitives and interior nodes are regularized set operations.

• The creation of a balanced, unbalanced, or a perfect CSG tree depends solely on the user and how he/she decomposes a solid into its primitives
• The general rule to create balanced trees is to start to build

the model from an almost central position and branch out in two opposite directions or vice versa.

• Another useful rule is that symmetric objects can lead to perfect trees if they are decomposed properly.

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• A balanced tress is defines as a tree whose left and right sub trees have almost an equal number of nodes.
• A perfect tree is one whose nL-nR is equal to zero.
• nL = nR = n – 1
• n  number of primitives
• (n-1)  number of Boolean operations
• (2n-1) number of nodes

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Advantages of Solid Modeling:

• • Memory required will be less.
• • Creation of fully valid geometrical solid model.
• • Complex shapes may be developed with the available set of
• primitives.
• • Less skill is enough.
• • Easy to construct out of primitives and Boolean operations.

Limitations of Solid Modeling:

• New computational effort and time are essential wherever
• the model is to be shown in the screen.
• • Getting fillet, chamfer and taper in the model is very
• difficult.

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Boundary Representation ( B- rep)

• Boundary representation is one of the two most popular and widely used schemes to create solid models of physical objects.
• A B-rep model or boundary model is based on the topological notion that a physical object is bounded by a set of faces.
• These faces are regions or subsets of closed and orientable surfaces.
• A closed surface is one that is continuous without breaks.
• • An orientable surface is one in which it is possible to distinguish two sides by using the direction of the surface normal to point to the inside or outside of the solid model under construction.
• Each face is bounded by edges and each edge is bounded by vertices.
• Thus, topologically, a boundary model of an object is comprised of faces, edges, and vertices of the object linked together in such a way as to ensure the topological consistency of the model.

Vertex (V) : It is a unique point (an ordered triplet) in space

Edge (E): It is finite, non-self intersecting, directed space curve bounded by two vertices that are not necessarily distinct

Face (F) : It is defined as a finite connected, non-self-intersecting, region of a closed oriented

surface bounded by one or mor e loops

Loop (L) : It is an ordered alternating sequence of vertices and edges

Genus (G) : It is the topological name for the number of handles or through holes in an object

Body/Shell(B) : It is a set of faces that bound a single connected closed volume. A minimumbody is a point

Advantages of B-rep:

• 1. It is traditionally a popular modeling method related closely to
• traditional drafting.
• 2. It is very suitable tool to build quite extraordinary shapes like
• aircraft and automobiles,
• that are difficult to build using primitives .
• 3. It is comparatively simple to convert a B-rep model into a
• wireframe model because its boundary
• deception is similar to the wireframe definitions.
• 4. In applications B-rep algorithms are reliable and competitive to
• CSG based algorithms .

Limitations of B-Rep:

• 1. It requires large storage memory space as it stores the explicit
• definitions of the model boundaries.
• 2. Sometimes geometrically valid solids are not possible.
• 3. Approximate B-rep is not suitable for manufacturing applications.

UNIT 2: PART- A

UNIT 2: PART- A

UNIT 2: PART- A

UNIT 2: PART- A

UNIT 2: PART- A

UNIT 2: PART- B Questions

UNIT 2: PART- B Questions

UNIT 2: Assignment Questions

SUPPORTIVE ONLINE CERTIFICATION COURSES

REAL TIME APPLICATIONS IN DAY TODAY LIFE AND TO INDUSTRY�Link :�http://home.iitk.ac.in/~jrkumar/download/ME761A/Lecture%204%20Geometric%20Modelling.pdf

The computer compatible mathematical description of the geometry of the object is called as geometric modeling.

• The CAD software allows the mathematical description of the object to be displayed as the image on the monitor of the computer.

• A geometric model contains description of the modelled object’s shape. Since geometric shapes are described by surfaces, curves are used to construct them. • Computer geometric modelling uses curves to control the object’s surfaces as they are easy to manipulate. The curves may be constructed using analytic functions, a set of points, or other curves and surfaces.

Disclaimer:��This document is confidential and intended solely for the educational purpose of RMK Group of Educational Institutions. If you have received this document through email in error, please notify the system manager. This document contains proprietary information and is intended only to the respective group / learning community as intended. If you are not the addressee you should not disseminate, distribute or copy through e-mail. Please notify the sender immediately by e-mail if you have received this document by mistake and delete this document from your system. If you are not the intended recipient you are notified that disclosing, copying, distributing or taking any action in reliance on the contents of this information is strictly prohibited.

Thank you