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Transcript of CAD 1st Module
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COMPUTER AIDEDCOMPUTER AIDED
Module : I
ANDAND
MANUFACTURINGMANUFACTURING
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COMPUTER AIDED DESIGNCOMPUTER AIDED DESIGN
It is defined as the use of computer
systems to assist in creation,modification and analysis of a design.
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Before examining the several facets of computer-aided design, let
us first consider the general design process. The process ofdesigning something is characterized by Shigley as an iterativeprocedure, which consists of six identifiable steps or phases:
Recognition of need
Definition of problem
Analysis and optimization
Evaluation
Presentation
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Recognition of needRecognition of need involves the realization by someone that aproblem exists for a system or machine which somecorrective action should be taken. This might be theidentification of some defect in a current machine design by anengineer or the perception of a new product marketingopportun ty y a sa esperson.
Definition of problemDefinition of the problem involves the specification of item to
be designed. This specification includes physical and functionalcharacteristics, cost, quality, and operating performance.
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Synthesis & Analysis and optimization
Synthesis and analysis are closely related and highly iterativein the design process. A certain component or subsystem ofthe overall system is conceptualized by the designer,subjected to analysis, improved through this analysisproce ure, an re es gne . e process s repea e un edesign has been optimized within the constraints imposed onthe designer. The components and subsystems aresynthesized into the final overall system in a similar iterativemanner.
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EvaluationEvaluation is concerned with measuring the design against thespecifications established in the problem definition phase. Thisevaluation often requires the fabrication and testing of aprototype model to assess operating performance, quality,reliability, and other criteria
resen a onThe final phase in the design process is the presentation ofthe design. This includes documentation of the design bymeans of drawings, material specifications, assembly lists, and
so on. Essentially, the documentation requires that a designdata base be created.
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COMPUTER AIDED DESIGN PROCESSCOMPUTER AIDED DESIGN PROCESS
Various tasks which are performed by a modern
computer aided design system can be grouped
into 4 functional areas
GEOMETRIC MODELLING
ENGINEERING ANALYSIS
DESIGN REVIEW & EVALUATIONAUTOMATED DRAFTING
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GEOMETRIC MODELLINGIt is concerned with the computer compatible mathematicaldescription of the geometry of an object. The mathematicaldescription allows the images of the object to be displayedand manipulated on graphics terminal through signals from theCPU of the CAD system
ENGINEERING ANALYSISThe analysis may involve stress strain calculations, heat
transfer computation etc. The computer can be used foranalysis. Specific programs are needed for analyzing differentdesigns
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DESIGN REVIEW & EVALUATION
It is concerned with measuring the design against the
mathematical description of the geometry of an object. It can
be accomplished conveniently using CAD system.
AUTOMATED DRAFTING
It involves the creation of hard copy engineering drawings
directly from the cad data base.
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ADVANTAGES OF CADADVANTAGES OF CAD
Increase productivity of design.
To improve quality of design.
To improve communication.To create a data base of manufacturing.
Reduced engineering personnel
requirements.Standardization in design is possible.
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GEOMETRIC MODELLINGGEOMETRIC MODELLING
It is concerned with the computer compatible mathematicaldescription of the geometry of an object. The mathematical
description allows the images of the object to be displayed
and manipulated on graphics terminal through signals from
the CPU of the CAD system.
To use geometrical modelling the designer construct the
graphical image of the object on graphics terminal by
inputting different commands. During this process thecomputer converts the commands into a mathematical
model, stores it in the database and displays it as an image
on graphics terminal.
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WIRE FRAME MODELLINGWIRE FRAME MODELLING
In the construction of a wire framemodelling the edges of the object are shown
as lines or arcs. They are suited for 2D
representation only.
A limitation of wireframe modelling is that all
lines that define the edges of the model areshown in the image which may result in
ambiguity.
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ADVANTAGESADVANTAGES It is simple to construct
The designer need only little training
It needs less storage space in terms of memory
It takes less manipulation time
DISADVANTAGESDISADVANTAGES
There is a chance of confusion in the surface of a
body as each and every edge is represented aslines or curves
It cannot be used in engineering analysis which
uses mass & volume calculations
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SURFACE MODELLINGSURFACE MODELLING
It is a modelling scheme that adds
information about the surfaces of the
part.
vertices and edges outlining one face at a
time.
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ADVANTAGESADVANTAGES
It gives less confusion when compared to
wireframe modelling.
It adds realism to the displayed geometry.
Complex surfaces are easily identified by this type
of modelling. The shading of surfaces are possible.
DISADVANTAGESDISADVANTAGES
It needs more skilled users.
It needs more processing time and computer
memory.
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SOLID MODELLINGSOLID MODELLING
In solid modelling, the models are
displayed as solid objects to the viewer
with very little risk of misinterpretation.
We may add colours to the part which
makes the picture strikingly realistic.
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ADVANTAGESADVANTAGESIt creates less confusion to the viewer.
It gives more information about the
geometry of the object.
Solid modelling is more suitable for
automated a lications.
It gives a realistic look.
DISADVANTAGESDISADVANTAGES It needs more time for construction of model.
The user skill needs to be higher.
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APPROACHES IN SOLID MODELLINGAPPROACHES IN SOLID MODELLING
There are 2 basic approaches to the problem
of solid modelling
-
Boundary representation [B-rep]
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CConstructiveonstructive SSolidolid GGeometryeometry[[CSGCSG oror CC--rep]rep]
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The CSG systems allow the user to build
the model out of solid graphic primitives,such as rectangular blocks, cubes, spheres,
cylinders, and pyramids.
The most common method of structuringthe solid model in the graphics data base
is to use Boolean operations, described in
the preceding section
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Boundary representationBoundary representation
[[BB--rep]rep]
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The boundary representation approach
requires the user to draw the outline or
boundary of the object on the CRTscreen using an electronic tablet and pen
or analogous procedure.
The user would sketch the various viewsof the object (front, side, and top, more
views if needed), drawing interconnecting
lines among the views to establish theirrelationship.
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COMPARISONCOMPARISON
The two approaches have their relativeadvantages and disadvantages. The C-rep
systems usually have a significant procedural
advantage in the initial formulation of the
It is relatively easy to construct a precise
solid model out of regular solid primitives
by adding, subtracting, and intersecting thecomponents. The building-block approach
also results in a more compact file of the
model in the data base.
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On the other hand, B-rep systems have their
relative advantages. One of them becomesevident when unusual shapes are encountered
that would not be included within the available
repertoire of the CSG systems
Another point of comparison between the twoapproaches is the difference in the way the model
is stored in the data base for the two systems.
The CSG approach stores the model by a
combination of data and logical procedures. Thisgenerally requires less storage but more
computation to reproduce the model and its
image.
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The B-rep system stores an explicit
definition of the model boundaries. Thisrequires more storage space but does not
necessitate nearly the same computation
effort to reconstruct the image.A related benefit of the B-rep systems is
that it is relatively simple to convert back
and forth between a boundaryrepresentation and a corresponding wire-
frame model.
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EVOLUTION OF CADEVOLUTION OF CAD
PAPER BASED DESIGN
3 D MODELLING & ANALYSIS
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PAPER BASED DESIGNPAPER BASED DESIGN
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2 D DRAFTING2 D DRAFTING
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3 D MODELLING & ANALYSIS3 D MODELLING & ANALYSIS
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COMPUTER AIDEDCOMPUTER AIDED
MANUFACTURINGMANUFACTURING
It is the use of computer systems to plan,
manage & control the operations of amanu acturing p ant wit t e p ants
production resources.
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CAM
PROCESS
PLANNINGPPC PROCESSING
ROUTING
GroupTechnology
NC
Programming
Manufacturing of
products
Moving & Handling
of Materials
SCHEDULING
MAINTENANCE
QA/QC
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ROUTING
It is the selection of the most advantageous pathwhich each part of the product will follow while
being transferred from raw materials to finished
work piece.
SCHEDULING
It is the determination of time that is required toperform each operation & also the time required
to perform entire series as routed.
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Group TechnologyGroup Technology
Group Technology is a manufacturing philosophythat exploits similarities in the design, fabrication,
and assembly attributes of products.
roup ec no ogy co e s an a p anumer c
string which represents critical information about
the product in a concise manner.
Comparing the GT codes of two products is a
quick and efficient method for estimating product
similarity in selected attributes.
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GT codes can be used to search a database of
products and retrieve the designs and process plans
of those products which are similar to a givendesign, to generate new process plans automatically
using a knowledge-based system, and to assess
manufacturability of a product design.
GT coding and classification schemes attempt to
capture design and manufacturing attributes such as
the main shape, size, features of the product,production quantity, and material. A large number
of GT coding schemes have been developed for
discrete machined parts including MICLASS, Opitz.
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Advantages of GTAdvantages of GT
It allows similar designs to be easily modified
from existing ones from the data base.
It increases productivity
For each group standard process plans can
be developed
It improves maximum utilization of machines
so that number of machines required is less
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DisadvantagesDisadvantages
GT requires long setup time.
It is not suitable for industries where a
large variety of products are manufactured.
.
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CAD/CAM INTERFACECAD/CAM INTERFACE
CAD/CAM interface allows the data
generated for design and development to
be reused for manufacturing instruction.
CAD/CAM interface allows the
manufacturing function to influence the
design process and also to make thedesigners to know the effects of design
features on manufacturing function.
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SEQUENTIAL ENGINEERINGSEQUENTIAL ENGINEERING
The sequence of operations involved in
manufacturing a new product are
Design
Manufacturing
Assembly
In conventional manufacturing, these
stages proceed sequentially, so the lead
time for a new product is more.
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FINAL
ASSEMBLY
MANUFACTURING
Lead Time
DESIGN
PROCESS
PLANNING
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CONCURRENT ENGINEERINGCONCURRENT ENGINEERING
In order to obtain zero defects, thedesign should be modified to meet
manufacturing requirements at an
earlier stage.
In concurrent engineering, the
operations are done in parallel and areoverlapped. Hence the lead time for a
new product is less.
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FINAL
ASSEMBLY
MANUFACTURING
Lead Time
DESIGN
PROCESS
PLANNING
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RECENT TRENDS IN CAMRECENT TRENDS IN CAMIn order to overcome/eliminate the limitations of
traditional manufacturing approaches, currently thefollowing themes/techniques/methods are being
used in the manufacturing engineering. They are:
1. Group Technology (GT) :
,
together to take advantages of their similarities in
design and manufacturing.
2. Design for Manufacturing and Assembly (DFM/A):It involves the systematic consideration of
manufacturability and assemblability in the
development of a new product design.
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3. Computer Aided Process Planning(CAPP) :
It involves determining the sequence ofprocessing and assembly steps that must be
accomplished to make the product.
.
This approach states that everybody in an
organization should be concerned with
assuring the quality of their work, and withtaking continual steps to try to improve this
quality (i.e., continuous improvement).
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5. Concurrent Engineering (CE) :
It refers to an approach used in product
development in which the functions of designengineering, manufacturing engineering, and other
functions are integrated to reduce the elapsed
time required to bring a new product to market.
6. Rapid Prototyping :
It describes a number of techniques which rapidly
produce solid physical models of components(i.e., prototypes) and products using 3D
computer data by a group of relatively new
manufacturing technologies.
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CO GCO G
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COMPUTER INTEGRATEDCOMPUTER INTEGRATED
MANUFACTURINGMANUFACTURING
CIM is the integration of computer based
monitoring and control of all aspects of the
manufacturing process, drawing on a common
computer network.
CIM = CAD/CAM functions + Business
functions
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Elements of CIMElements of CIM
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CIM MODELCIM MODEL
The Siemens model of CIM comprises themain functions of planning, sales,
purchasing, production planning and
control, computer aided design, computeraided quality control and computer aided
manufacture interconnected by intensive
information flow.
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NOTE: Bill of materials (BOM) is a list of the raw materials, sub-assemblies, intermediate assemblies,
sub-components, components, parts and the quantities of each needed to manufacture the final product.
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In order to be able to process the data in
a comprehensive manufacturing system, a
hierarchical model of an enterprise isused. Each hierarchical level has its own
data processing requirements and there
exists a steady flow of instructions fromthe upper levels to the lower ones.
In order to control and synchronizeparallel activities on each level, an
intensive horizontal data flow takes place.
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Siemens model also incorporates a Computer
Aided Organization (CAO), which comprises
accounting, personnel and finance.
For each module, its sub modules are defined and
their interconnections are explained. A descriptionis given on the required interfaces for the data
exchange and the contents of the data, giving
special considerations to batch & mass production.
Various layouts of production systems and
assembly stations are also considered.
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ADVANTAGES OF CIMADVANTAGES OF CIM
It reduces careless errors in the data.
Sharing of information is possible.
It optimizes data flow in the company.
t promotes t e use o stan ar s.
It allows the checking of data against
standards.
DESIGN WORKSTATIONDESIGN WORKSTATION
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DESIGN WORKSTATIONDESIGN WORKSTATION
A design workstation is the system interfacewith the outside world. It includes graphics
terminal, input devices, output devices and
memory.
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The workstation must accomplish five
functions
It must interface with the central processing unit.
It must generate a steady graphic image for the
user. It must provide digital descriptions of the graphic
image.
It must translate computer commands into
operating functions.
It must facilitate communication between the user
and the system.
INTERACTIVE COMPUTERINTERACTIVE COMPUTER
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INTERACTIVE COMPUTERINTERACTIVE COMPUTER
GRAPHICSGRAPHICS
vgf GraphicsTerminal
User inputdevices
GraphicsPackage
ApplicationProgram
Applicationdatabase
Design workstation
It is an user oriented system which employs
a computer to create, transform and displaydata in the form of pictures and symbols.
ICG consists of both hardware and software.
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The hardware component of ICG is thedesign workstation
The software component of ICG can be
subdivided into 3 modules Application database
Application program
Graphics package
A li ti d t bA li ti d t b
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Application databaseApplication databaseThe database contains mathematical, numerical
and logical definitions of application models.Application program
An application program is driven by the user
through graphics package. It controls, storage as
we as re r eva o a a n o an ou o app ca on
database
Graphics packageA graphics package is the software supportbetween the user and the graphics terminal. It
manages the graphical interaction between the
user and the system.
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TRANSFORMATIONSTRANSFORMATIONS
The editing features available on a cadsystem is executed by using different
transformations.
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TRANSLATIONTRANSLATION
ROTATIONROTATION
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ROTATIONROTATION
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For rotation by an angle θ anticlockwise about the origin, the
functional form is
x ' = x cosθ − y sinθ and y ' = x sinθ + y cosθ. Written in matrixform, this becomes:
Similarly, for a rotation clockwise about the origin, the
functional form is
x ' = x cosθ + y sinθ and y ' = − x sinθ + y cosθ
and the matrix form is:
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Rotation matrix is an orthogonal matrix
A.AT = AT.A = I
SCALINGSCALING
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SCALINGSCALING
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CLIPPINGCLIPPING
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FEM – It is a numerical technique for
finding approximate solutions from partial
differential equations.
CFD – It is a computational technology
particles that flow.
Simulation – It is a technique of
representing the real world by a
computer program.
Analysis softwares
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Analysis softwares ANSYS - It is used for stress strain analysis using finite
element method and also applications including CFD.
NASTRAN – It is a finite element analysis (FEA) program
that was developed for NASA. It is written primarily in
FORTRAN. Manufactured by MSC software corporation.
NISA – Non linear Incremental Structural Analysis.
Manufactured by Cranes software international ltd. used for
heat transfer analysis, composite materials analysis fatigue
and fracture analysis.
FLUENT – manufactured by ANSYS. Inc. used for
applications of CFD.
CAM Software PackagesCAM Software Packages
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CAM Software PackagesCAM Software Packages
Iron CAD – by Novacast -software for foundries.
dieCAS – software for analysis of different die casting
processes.
DEFORM – forging software to analyse metal forming
processes.
Metal Bender – software for sheet metal industry.
Alpha CAM – capable of milling, turning, punching etc.
DDA Line Drawing AlgorithmDDA Line Drawing Algorithm
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DDA Line Drawing AlgorithmDDA Line Drawing Algorithm1. Start
2. Declare variables x0, y0, xn, yn
3. Input values of end points.
4. dx = xn – x0 ; dy = yn – y0
5. For K = 0, Plot pixel at (xk,yk)6. If m < 1 & δx = 1,
yk+1 = y k + m
elseIf m >
1 & δy = 1,
Xk+1 = Xk + 1/m
8. Repeat steps 5-6 until k = n-1
9. Stop
Bresenham’s Line Drawing AlgorithmBresenham’s Line Drawing Algorithm
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Bresenhams Line Drawing AlgorithmBresenhams Line Drawing Algorithm1. Start
2. Declare variables x0, y0, xn, yn
3. Input values of end points.
4. Calculate δy , δx;
5. For K = 0, Plot pixel at (xk ,yk )
6. Calculate initial value of decision arameter as, Pk = 2 δy - δx
7. If Pk < 0 the point along line is (xk+1 , yk ) &
Pk+1 = Pk + 2 δy
else next point along the line is (xk+1 ,yk-1) &
Pk+1 = Pk + 2 δy - 2 δx
8. Repeat steps 5-6 until k = n-1
9. Stop
Bresenham’s Circle DrawingBresenham’s Circle Drawing
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f (x , y) = x2 + y2 - r2
Bresenham s Circle DrawingBresenham s Circle Drawing
AlgorithmAlgorithm
1. Start
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2. Declare variables (xc, yc), r
3. Input values for (xc, yc), r.
4. Obtain 1st point on the circumference of a circle centered onthe origin as (xk ,yk ) = (0,r)
5. For K = 0, Plot pixel at (xk ,yk )
6. Calculate initial value of decision parameter as,
P = 5/4 - r7. If Pk < 0 the point along circle is (xk+1 , yk ) &
Pk+1 = Pk + 2 xk+1 + 1
else next point along the circle is (xk+1 ,yk-1) &
Pk+1 = Pk + 2 xk+1 + 1 - 2 yk+1
8. Repeat steps 5 -7 until xk+1 = yk+1
9. Determine symmetry points in other 7 octants and move
l l t d i l iti l th i f f th i l