cad 1st module

7/23/2019 CAD 1st Module

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COMPUTER AIDEDCOMPUTER AIDED

Module : I

ANDAND

MANUFACTURINGMANUFACTURING



COMPUTER AIDED DESIGNCOMPUTER AIDED DESIGN

It is defined as the use of computer

systems to assist in creation,modification and analysis of a design.



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



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.



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.



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.



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



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



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.



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.



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.



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.



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



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.



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.



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.



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.



APPROACHES IN SOLID MODELLINGAPPROACHES IN SOLID MODELLING

There are 2 basic approaches to the problem

of solid modelling

-

Boundary representation [B-rep]



CConstructiveonstructive SSolidolid GGeometryeometry[[CSGCSG oror CC--rep]rep]



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



Boundary representationBoundary representation

[[BB--rep]rep]



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.



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.



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.



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.



EVOLUTION OF CADEVOLUTION OF CAD

PAPER BASED DESIGN

3 D MODELLING & ANALYSIS



PAPER BASED DESIGNPAPER BASED DESIGN



2 D DRAFTING2 D DRAFTING



3 D MODELLING & ANALYSIS3 D MODELLING & ANALYSIS



COMPUTER AIDEDCOMPUTER AIDED


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.



CAM

PROCESS

PLANNINGPPC PROCESSING

ROUTING

GroupTechnology

NC

Programming

Manufacturing of

products

Moving & Handling

of Materials

SCHEDULING

MAINTENANCE

QA/QC



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.



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.



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.



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



DisadvantagesDisadvantages

GT requires long setup time.

It is not suitable for industries where a

large variety of products are manufactured.

.



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.



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.



FINAL

ASSEMBLY

MANUFACTURING

Lead Time

DESIGN

PROCESS

PLANNING



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.



FINAL

ASSEMBLY

MANUFACTURING

Lead Time

DESIGN

PROCESS

PLANNING



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.



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).



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.



CO GCO G



COMPUTER INTEGRATEDCOMPUTER INTEGRATED


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



Elements of CIMElements of CIM



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.



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.



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.



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.



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



DESIGN WORKSTATIONDESIGN WORKSTATION

A design workstation is the system interfacewith the outside world. It includes graphics

terminal, input devices, output devices and

memory.



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



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.



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



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.



TRANSFORMATIONSTRANSFORMATIONS

The editing features available on a cadsystem is executed by using different

transformations.



TRANSLATIONTRANSLATION

ROTATIONROTATION



ROTATIONROTATION



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:



Rotation matrix is an orthogonal matrix

A.AT = AT.A = I

SCALINGSCALING



SCALINGSCALING



CLIPPINGCLIPPING



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



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



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



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



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



f (x , y) = x2 + y2 - r2

Bresenham s Circle DrawingBresenham s Circle Drawing

AlgorithmAlgorithm

1. Start



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

cad 1st module

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