evolution of cad/cam

CAD/CAM Module I AM/JA
DepartmentofMechanicalEngineering-AJCE
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Module 1
Evolution of CAD/CAM and CIM segments of generic CIM, computers and workstation, elements of
interactive graphics, input/ output display, storage devices in CAD - an overview of CIM software
2D Graphics: Line drawing algorithms, DDA line algorithm – circle drawing, Bressnham`s circle drawing
algorithm– 2D translation, rotation, scaling – clipping -3D Graphics (basic only).
Design process – CAD process: wireframe, surface, solid modeling; Engineering analysis; design review
& evaluation, automated drafting – CAD hard ware, software, data presentation, CAD software packages
DISCLAIMER
These notes are not the ultimate ‘look-up’ for Model and University exams. Students are advised to read the
references mentioned at the end thoroughly for the exams
INTRODUCTION
CAD- Computer-Aided Design
CAM-Computer-Aided Manufacturing
CIM-Computer Integrated Manufacturing
The use of computers in design and manufacturing applications makes it possible to remove much of the
tedium and manual labor involved.
For example, the many design specifications, blueprints, material lists, and other documents needed to
build complex machines can require thousands of highly technical and accurate drawings and charts. If
the engineers decide structural components need to be changed, all of these plans and drawings must be
changed. Prior to CAD/CAM, human designers and draftspersons had to change them manually, a time
consuming and error-prone process. When a CAD system is used, the computer can automatically
evaluate and change all corresponding documents instantly. In addition, by using interactive graphics
workstations, designers, engineers, and architects can create models or drawings, increase or decrease
sizes, rotate or change them at will, and see results instantly on screen.
CAD is particularly valuable in space programs, where many unknown design variables are involved.
Previously, engineers depended upon trial-and-error testing and modification, a time consuming and
possibly life-threatening process. However, when aided by computer simulation and testing, a great deal
of time, money, and possibly lives can be saved. Besides its use in the military, CAD is also used in civil
aeronautics, automotive, and data processing industries.
CAM, commonly utilized in conjunction with CAD, uses computers to communicate instructions to
automated machinery. CAM techniques are especially suited for manufacturing plants, where tasks are
repetitive, tedious, or dangerous for human workers.

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Computer integrated manufacturing (CIM), a term popularized by Joseph Harrington in 1975, is also
known as autofacturing. CIM is a programmable manufacturing method designed to link CAD, CAM,
industrial robotics, and machine manufacturing using unattended processing workstations. CIM offers
uninterrupted operation from raw materials to finished product, with the added benefits of quality
assurance and automated assembly.
EVOLUTION OF CAD/CAM AND CIM
The story of CAD/CAM was accelerated in early 1950s. Upto year 2011 it has become one of the
supreme technology available on Planet earth. It is being used in almost all the fileds of engineeirng but
primarily in mechanical engineering branches. the development in the field is still gaining speed.
 19th
century Industrial revolution.
 20th
century Computer revolution.
 CAD/CAM has gone through four major phases.
First phase was at 1950’s.
 Era of conceiving interactive graphics.
 Demonstration of Numerical Control concept on three - axis milling machine.
 Conception of light pen.
 Development of Automatically Programmed Tools (APT).
Second Phase 1960s
 Sketch pad system was introduced.(tool for create drawings and make alterations)
 The term “Computer Aided Design” was appeared.
 This leads to extending it beyond basic drafting concepts.
 Development of some design modules by General Motors & Lockheed Aircrafts etc.
 Development of direct view storage tubes(DVST), it is a display unit.
Third 1970’s
 Conference arranged in this era was leads to the development in this area.
 3-D concept for drafting and modeling.
 Development of mass property calculations, finite element modeling, NC tape generation and
verification.
4th
Post 1980
 Integrate or automate the various elements of design and manufacturing.
 Concentrated on accurate representation of elements.
 Analysis and simulation tools.
 Development of solid modeling theory.
 Development of various 3D CAD softwares.

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SEGMENTS OF GENERIC CIM
Nine major elements of a CIM system are in Fig 1.2. They are:
Marketing
Product Design
Planning
Purchase
Manufacturing Engineering Factory
Automation Hardware Warehousing
Logistics and Supply Chain Management
Finance
Information Management
Fig.1.2 Major Elements of a CIM System
i. Marketing: The need for a product is identified by the marketing division. The specifications
of the product, the projection of manufacturing quantities and the strategy for marketing the
product are also decided by the marketing department. Marketing also works out the
manufacturing costs to assess the economic viability of the product.
ii. Product Design: The design department of the company establishes the initial database
for production of a proposed product. In a CIM system this is accomplished through

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activities such as geometric modeling and computer aided design while considering the
product requirements and concepts generated by the creativity of the design engineer.
Configuration management is an important activity in many designs. Complex designs are
usually carried out by several teams working simultaneously, located often in different parts
of the world. The design process is constrained by the costs that will be incurred in actual
production and by the capabilities of the available production equipment and processes. The
design process creates the database required to manufacture the part.
iii. Planning: The planning department takes the database established by the design
department and enriches it with production data and information to produce a plan for
the production of the product. Planning involves several subsystems dealing with
materials, facility, process, tools, manpower, capacity, scheduling, outsourcing, assembly,
inspection, logistics etc. In a CIM system, this planning process should be constrained by
the production costs and by the production equipment and process capability, in order
to generate an optimized plan.
iv. Purchase: The purchase departments is responsible for placing the purchase orders and
follow up, ensure quality in the production process of the vendor, receive the items,
arrange for inspection and supply the items to the stores or arrange timely delivery
depending on the production schedule for eventual supply to manufacture and assembly.
v. Manufacturing Engineering: Manufacturing Engineering is the activity of carrying out the
production of the product, involving further enrichment of the database with performance
data and information about the production equipment and processes. In CIM, this requires
activities like CNC programming, simulation and computer aided scheduling of the
production activity. This should include on- line dynamic scheduling and control based on
the real time performance of the equipment and processes to assure continuous production
activity. Often, the need to meet fluctuating market demand requires the manufacturing
system flexible and agile.
vi. Factory Automation Hardware: Factory automation equipment further enriches the
database with equipment and process data, resident either in the operator or the equipment to
carry out the production process. In CIM system this consists of computer controlled
process machinery such as CNC machine tools, flexible
vii. Warehousing: Warehousing is the function involving storage and retrieval of raw
materials, components, finished goods as well as shipment of items. In today’s complex
outsourcing scenario and the need for just-in-time supply of components and subsystems, logistics
and supply chain management assume great importance.
viii. Finance: Finance deals with the resources pertaining to money. Planning of investment,
working capital, and cash flow control, realization of receipts, accounting and allocation
of funds are the major tasks of the finance departments.
ix. Information Management: Information Management is perhaps one of the crucial tasks in CIM.
This involves master production scheduling, database management, communication, manufacturing
systems integration and management information systems.

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It can be seen from Fig that CIM technology ties together all the manufacturing and related functions
in a company. Implementation of CIM technology thus involves basically integration of all the activities
of the enterprise.
Activities of cim
Engineering design.
 Mechanical product design.
 Drafting
 CAE
Manufacturing engineering.
 CAM
 CAPP
 GT
 Simulation
 Robotics
Factory production.

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 Data collection.
 Robots & machine tools.
 Quality assurance.
Information management.
 Systems integration (customer systems)
 Communication
 Data base management.
 PPC
ELEMENTS OF INTERACTIVE GRAPHICS
Interactive Computer Graphics: Interactive Computer Graphics involves a two way communication
between computer and user. Here the observer is given some control over the image by
providing him with an input device for example the video game controller of the ping pong
game. This helps him to signal his request to the computer. The computer on receiving signals
from the input device can modify the displayed picture appropriately. To the user it appears
that the picture is changing instantaneously in response to his commands. He can give a series
of commands, each one generating a graphical response from the computer. In this way he
maintains a conversation, or dialogue, with the computer.
Block Diagram for elements of Interactive graphics is given below in Figure 1.4
INPUT DEVICES
 Keyboard
 Mouse
 CAD keyboard  Plotter
 Templates
 Space Ball
MAIN SYSTEM
 Computer
 CAD Software
 Database
 CAD Software Database
OUTPUT DEVICES
 Hard Disk Network
 Printer
 Network
 Plotter
HUMANU DESIGNER

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Figure 1.4 Elements of Interactive Graphics
What is Computer Graphics
 Anything to do with visual representations on a computer, including
 Text (e.g. Japanese characters 大学)
 Computer Images
 3D Graphics: CG special effects, games, animations
 Scientific Visualization
What is Interactive Computer Graphics?
 Creation, storage and manipulation of images and drawing with the control of the user over
digital computer.
 Interactive graphics system consist of
 input (e.g., mouse, tablet and stylus, scanner, live video streams…)
 processing (and storage)
 display/output (e.g., screen, paper-based printer, video recorder, etc..)
 human being
 In passive computer graphics the user dose not have any control over image. Like TV
images.
 Image can be created using stroke writing approach & raster graphics approach.
 User can do the following functions using ICG.
 Modelling. Creation of image by the use of point, line, circle etc.
 Storage. Save the image.
 Manipulation.
 Viewing. Seeing the images (zoom in, zoom out, orthographic view, isometric view
etc….)

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Computer
Figure 1.5 Basic Computer Architecture
Note: Go through the detailed description of Basic Computer Architecture you have studies earlier
CLASSIFICATION OF CAD COMPUTERS
Computers can be generally classified by size and power as follows
 Personal computer: A small, single-user computer based on a microprocessor.
 Workstation: A powerful, single-user computer. A workstation is like a personal computer,
but it has a more powerful microprocessor and, in general, a higher-quality monitor.
 Minicomputer: A multi-user computer capable of supporting up to hundreds of users
simultaneously.
 Mainframe: A powerful multi-user computer capable of supporting many hundreds or
thousands of users simultaneously.
 Supercomputer: An extremely fast computer that can perform hundreds of millions of
instructions per second.
 Supercomputer
Supercomputer is a broad term for one of the fastest computers currently available. Supercomputers
are very expensive and are employed for specialized applications that require immense amounts of
mathematical calculations (number crunching). For example, weather forecasting requires a
supercomputer. Other uses of supercomputers scientific simulations, (animated) graphics, fluid
dynamic calculations, nuclear energy research, electronic design, and analysis of geological data
(e.g. in petrochemical prospecting). Perhaps the best known supercomputer manufacturer is Cray
Research.

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Mainframe
Mainframe is a very large and expensive computer capable of supporting hundreds, or even
thousands, of users simultaneously. The chief difference between a supercomputer and a mainframe
is that a supercomputer channels all its power into executing a few programs as fast as possible,
whereas a mainframe uses its power to execute many programs concurrently. In some ways,
mainframes are more powerful than supercomputers because they support more simultaneous
programs. But supercomputers can execute a single program faster than a mainframe.
Minicomputer
It is a midsize computer. A mini computer is the computer which is referred to as the mid sized
computers and they serve as the same functions as the normal desktop computers. Mini computers
are the one which are found between the main frame computers and the work station computers.
These types of computers are quite easy to be handled and are serving the similar functions as other
computers. This size computer can support a larger range of people. The total numbers of people
who can use the mini computers are from 4-400 users at the same time. At times the mini computers
are often referred to as the multi processing computers which show that the computer can be used to
perform certain tasks at the same time.
The other distinction that exists among the mini computers is that the computer had its own different
types of hardware and software’s. Even at time the operating system unit in the mini computers is
also different this in fact is the major difference among all the other computers and the mini
computers.
Workstation
It is a type of computer used for engineering applications (CAD/CAM), desktop publishing, software
development, and other types of applications that require a moderate amount of computing power
and relatively high quality graphics capabilities. Workstations generally come with a large, high-
resolution graphics screen, at large amount of RAM, built-in network support, and a graphical user
interface. Most workstations also have a mass storage device such as a disk drive, but a special type
of workstation, called a diskless workstation, comes without a disk drive. The most common
operating systems for workstations are UNIX and Windows. Like personal computers, most
workstations are single-user computers. However, workstations are typically linked together to form
a local-area network, although they can also be used as stand-alone systems.
N.B.: In networking, workstation refers to any computer connected to a local-area network. It
could be a workstation or a personal computer.

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Microcomputer
A microcomputer is a computer with a microprocessor as its central processing unit. They are
physically small compared to mainframe and minicomputers. Many microcomputers (when equipped
with a keyboard and screen for input and output) are also personal computers. Monitors, keyboards
and other devices for input and output may be integrated or separate. Computer memory in the form
of RAM, and at least one other less volatile, memory storage device are usually combined with the
CPU on a system bus in one unit. Other devices that make up a complete microcomputer system
include batteries, a power supply unit, a keyboard and various input/output devices used to convey
information to and from a human operator (printers, monitors, human interface devices).
Microcomputers are designed to serve only one user at a time, although they can often be modified
with software or hardware to concurrently serve more than one user. Microcomputers fit well on or
under desks or tables, so that they are within easy access of users.
Hardware Requirements of CAD
Input Devices in CAD
Various devices are available for data input on graphics workstations. Most systems have a keyboard and one
or more additional devices specially designed for interactive input. These include a mouse, trackball, joystick,
tablet light pen etc.
Input Devices
Output Devices
Storage Devices
Analog
Key Board,Mouse
Track ball
Joy Stick
Digital
Light Pen
Tablet
Input Devices

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Analog IO
Analog input devices sense continuous parameters. The information that they provide is given as a continuous
range of values, not just an on or off indicator. Position will be a continuous outcome.
Digital IO
Digital input devices may be either on or off; they may not hold any other values.
Keyboards
An alphanumeric keyboard on a graphics system is used primarily as device for entering text strings. The
keyboard is an efficient device for inputting such nongraphic data as picture labels associated with a graphics
display. Keyboards can also be provided with features to facilitate entry of screen coordinates, menu
selections, or graphics functions.
Mouse
A mouse is small hand-held box used to position the screen cursor. The main goal of any mouse is to translate
the motion of your hand into signals that the computer can use. Wheels or rollers on the bottom of the mouse
can be used to record the amount and direction of movement. Another method for detecting mouse motion is
with an optical sensor,. For these systems, the mouse is moved over a special mouse pad that has a grid of
horizontal and vertical lines. The optical sensor detects movement across the lines in the grid.
Since a mouse can be picked up and put down at another position without change in cursor movement, it is
used for making relative changes in the position of the screen cursor. One, two, or three buttons are usually
included on the top of the mouse for signaling the execution of some operation, such as recording cursor
position or invoking a function.
Ball Mouse(mechanical)

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The mechanical mouse contains a free-floating ball with rubber coating on the underside which,
when moved on a firm plane surface, is able to follow the movement of the hand. The mot ion of
the ball is resolved into X- and Y-motions by means of the two rollers pressed against the ball.
They, in turn, control the cursor on the screen, which can then be utilized for any desired
applications by means of the clicking of the buttons on the mouse. This can only suffice to point on
the screen but not for giving positional data. Further the mouse is a relative device and not an
absolute pointing device.
Optical Mouse
The main components of the optical mouse are:
 Inbuilt optical sensor
 High speed camera which can take 1000 pictures at a time
 LED
These optical mouses do have an inbulit optical sensor. The optical sensor reads the movements of the optical
mouse (moved by the user) with the help of the light rays which comes out from the bottom. ( The area in
which a light glows). When the user moves the optical mouse, the LED (Light Emitting Diode) present inside
the mouse emits the light according the minute movements. These movements are send to the camera as light
rays. The camera captures the difference in light rays as images. When the camera captures the images, each
and every pictures and compared to one another with the digital technology. With the comparison, the speed
of the mouse and the direction of the movement of the mouse are rapidly calculated. According to the
calculation, the pointer moves on the screen.
Track Ball
Track ball has a ball and socket construction but the ball must be rolled with fingers or the palm of the hand.
The cursor moves in the direction of the roll at a rate corresponding to rotational speed. The user must rely
heavily on the tactile sense when using a trackball since there is no correspondence between the position of
the cursor and the ball. The ball momentum provides a tactile feed back. Trackballs are effective for tracking,
following or pointing at moving elements. Track discs also perform a similar function.
Basically the trackball rolls against a trackball roller which then turns a slotted chopper wheel which is
scanned by an optical sensor which converts your movement into digital information which is then sent to
your computer via a USB connection.

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Joysticks
Joystick is a potentiometric device that contains sets of variable resistors which feed signals that indicates the
device position to the computer. These devices rely on the operator’s sense of touch and hand-eye co-
ordination to control the position of the cursor on the screen. Joystick devices are normally set so that side-to-
side movement produces change in X Co-ordinates and front to back movements produce change in Y Co-
ordinates. Thus they are best suited for pointing in tasks such as menu selection or creating simple schematics.
Many users prefer joysticks because they allow rapid cursor movement for relatively small device movements,
enabling graphic operations to be performed quickly. Three dimensional capability is possible by moving the
handle up and down or by twisting it to provide data entry in the Z axis.
Lightpen
A lightpen resembles a fountain pen in the method of holding, but it works on the principle of light
rather than ink. from which it derives its name. The lightpen is a pointing or picking device that
enables the user to select a displayed graphics item on a screen by directly touching its surface in
the vicinity of the item. The application program processes the information generated from the
touching to identify the selectable item to operate on. The lightpen itself does not emit light but
rather detects it from the graphics items displayed on the screen. Using the emitted light as an
input, it sends an interrupt signal to the computer to determine which was seen by the pen. The
lightpen normally operates as a logical pick in conjunction with a vector refresh display.

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Digitizers
A digitizer is the most widely used input medium by the CAD designer. It is used for converting the physical
locations into coordinate values so that accurate transfer of data can be achieved. A digitizing tablet is
considered as a pointing and locating device. It is a small, low-resolution digitising board often used in
conjunction with a graphics display. The tablet is a flat surface over which a stylus or a puck can be moved by
the user. The close resemblance of the tablet and stylus to paper and pencil contributes to its popularity as an
input device. The puck contains a rectile and at least one pushbutton. The engraved cross-hairs of rectile help
locate a point for digitising. Pressing the pushbutton sends the coordinates at the cross-hairs to the computer.
The sizes of digitising tablets range from 11 x 11 to 36 x 36 inches. The resolution of a tablet is 0.005 inch or
200 dots per inch.
The tablet operation is based on sensitising its surface area to be able to track the pointing element (stylus or
puck) motion on the surface. The surface of the tablet is magnetised and is embedded with wires in the x and v
directions. The physical motion of the stylus is converted by the wires into a digital location signal, which is
then routed to the computer and displayed on the graphics terminal.

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Output Devices
Output Devices
Also audio outputs(but not used in CAD)
Printers
(i).Impact printers: They use small hammers or print heads containing small pins to strike a ribbon to form
dot matrix images. Colors are introduced through the use of multiple ribbons or single ribbons with different
color bands. Color intensity is fixed and creating shades is almost impossible. Because of the low resolution,
copy quality is poor. Impact printers are suitable for high speed, low cost, highvolume hard copies.
(ii) Inkjet printer: Inkjet printers produce images by propelling fine droplets of ink on to the medium to be
printed. Droplets can be generated in continuous streams or pulses. Some of the droplets get charged and are
returned to the reservoir, while uncharged droplets attach to the printing surface to form graphics. The laser jet
printers are capable of giving good quality color prints with shading at reasonable cost.
(iii) Laser printer: Laser printer is one of the most widely used output devices. This type combines high
speed with high resolution and the quality of output is very fine.
Plotters-
 2 types- Drum plotter, Flat Bed plotter
Display Devices
 Storage Tube
 Calligraphic
refresh graphic
displays
 Raster Refresh
displays
Hard Copy Devices
 Printers
o Impact
o Inject
o Laser
 Plotters
o Flat
o Drum
o

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Plotters are special output devices used to produce hard copies of large graphs and designs on paper. Plotters
are often used for the production of cad/cam drawings, engineering drawings, architectural plans and business
charts.
Drum Plotter
 A drum plotter is pen plotter that wraps the paper around a drum with a pin feed attachment.
The drum then rotates the paper as pens move across it and draw the image. It was the first
output device used to print graphics and large engineering drawings. There are two types of
drum plotters, external and internal. With an external drum plotter, the paper is wrapped
around its external surface, while the internal drum plotter uses a sheet of paper wrapped
around its internal surface.

Flat-Bed Plotter
 A flat-bed plotter is a mechanical drafting device used with many CAD programs for
designers. The paper remains stationary on a flat surface while a pen moves across it
horizontally and vertically. This plotter may use several different colors of pens to create the
graphics. The size of the graphic is limited to the size of the flat-bed plotter's surface.
Pen Movement
in X direction
Pen Movement in
Y Direction

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DISPLAY DEVICES
Typically, the primary output device in a graphics system is a video monitor. The operation of most video
monitor is based on the standard cathode-ray tube(CRT) design.
Cathode Ray Tube
 A heated cathode emits a high speed electron beam into phosphor coated glass screen.
 Electrons energize the phosphor coating , causing it to glow.
 Can make an image by focusing the electron beam, changing its intensity, and controlling its point of
contact against the phosphor coating
 used in TVs and computer monitors
Factors affecting quality of image
 Type of phosphor coating.
 Color is required.
 The pixel density.
 Amount of computer memory available to generate the picture.

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TYPE OF GRAPHICS TERMINALS.
 Storage tube display
 Calligraphic refresh graphic displays
 Raster Refresh displays
Storage Tube Display device
 Storage tube refers the ability of the screen to retain the image.(image will be retained for
approximately 2 hours)
 Thus avoiding the need to rewrite the image.
 For erasing the image the screen is flooded by a particular voltage by flood gun.
 The individual lines cannot be selectively removed.
 Lowest cost
 Capable showing large amount of data.
 Lack of animation capability.
 Unable to use light pen.
 Not used in modern display systems
Calligraphic Refresh Graphic Display

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 Image will be regenerated many times per second to avoid noticeable flickering.(approx 50/s), thus
name refresh displays
 Screen elements are capable of maintain there brightness for only a short time(in micro sec)
 Image is refreshed by Directed beam to retrace repeatedly.
 On densely filled screen, it is difficult to avoid the flickering .
 Selective erasure and alteration is possible (continually refreshed)
 Possible to provide animations.
 It is the oldest of modern graphics technologies.
 Other names are vector refresh or stroke writing refresh
 Display process is as follows- Each time controller checks buffers and give stimulations to vector
generator to produce display in CRT
Display
Refresh rate on a random-scan system depends on the number of lines to be displayed . Picture definition is
now stored as a set of line-drawing commands in an area of memory referred to as the refresh display file.
Sometimes the refresh display file is called the display list, display program, or simply the refresh buffer.
To display a specified picture, the system cycles through the set of commands in the display file, drawing each
component line in turn. After all line- drawing commands have been processed, the system cycles back to the
first line command in the list. Random-scan displays are designed to draw al the component lines of a picture
30 to 60times each second
RASTER REFRESH DISPLAY
 Electron beam is trace in zig zag pattern.
 It is same as TV screen except the type of input signal
(TV --------------- analog signal,
computer -------- digital signal).
 Number of storage space required is depends on number of intensity level.
 Quality of the image can be increased by adding color or by increasing the pixel density.
Refresh
Buffer
Controller CRTVector
Generator
Line information
is stored
Checks buffer
before each
refresh display
Commands
electron gun to
move to display
buffer commands

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 Two bits required for four intensity level.
 Animations are possible.
 Color capability.
 The screen is divided into small phosphor elements called pixels.
 Ranges from 256*256 to 1024*1024.
 Each pixel can glow with different brightness.
 Color screens provide for pixels to have different colors.
 Electron beam sweep along horizontal line on the screen from left to right, it will energize the pixel
during the sweep.
 When the sweep of one line is completed it moves to the next line
 After sweeping the entire screen the process is repeated at a rate of 30 to 60 scans/sec
 Each pixel is either on or off, ie lit or not lit

In a raster- scan system, the electron beam is swept across the screen, one row at a time from top to bottom.
As the electron beam moves across each row, the beam intensity is turned on and off to create a pattern of
illuminated spots. Picture definition is stored in memory area called the refresh buffer or frame buffer. This
memory area holds the set of intensity values for all the screen points. Stored intensity values are then
retrieved from the refresh buffer and “ painted” on the screen one row (scan line) at a time (fig.below). Each
screen point is referred to as a pixel or pel (shortened forms of picture element).
BufferElectron
Gun
Controller

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Refreshing on raster-scan displays is carried out at the rate of 60 to 80 frames per second, although some
systems are designed for higher refresh rates. Sometimes, refresh rates are described in units of cycles per
second, or Hertz (Hz), where a cycle corresponds to one frame. At the end of each scan line, the electron beam
returns to the left side of the screen to begin displaying the next scan line. The return to the left of the screen,
after refreshing each scan line, is called the horizontal retrace of the electron beam. And at the end of each
frame (displayed in 1/80th to 1/60th of a second), the electron beam returns (vertical retrace)to the top left
corner of the screen to begin the next frame.
CIM Hardware comprises the following:
 Manufacturing equipment such as CNC machines or computerized work centers, robotic
work cells, DNC/FMS systems, work handling and tool handling devices, storage devices,
sensors, shop floor data collection devices, inspection machines etc.
 Computers, controllers, CAD/CAM systems, workstations / terminals, data entry terminals,
bar code readers, RFID tags, printers, plotters and other peripheral devices, modems, cables,
connectors etc.,
Line Drawing Algorithms

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Primary design criteria for line drawing displays are as follows
 Line should appear straight
 Line should start and end accurately
 Line should have continuous brightness along their length
 Display lines should be independent of line length and orientation
 Lines should be drawn rapidly
4.3.1 DDA Algorithm
The digital differential analyser generates lines from their differential equations. The DDA worlo
on the principle that x and y are simultaneously incremented by small steps proportional to the
first derivatives of x and y.
Fig. 4.2 The DDA algorithm.
The governing differential equation for a straight line (Figure 4.2) is
where (x1, y1) and (x2, y2) are the end points of the required straight line, and y, is the initial value
for any given step along the line. Equation 4.2 represents a recursion relation for successive
values of y along the required line. For simple DDA algorithm, either Ax or Ay, which ever is
larger, is chosen as one raster unit.
The digital differential analyzer generates lines from their differential equations. The DDA works on
the principle that X and Y are simultaneously incremented by small steps proportional to the first
derivatives of X and Y. In the case of a straight line the first derivatives are constant and are
proportional to DX and DY, where D is a small quantity.

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In the real world of limited precision displays, addressable pixels only must be generated. This can
be done by rounding to the next integer after each incremental step. After rounding, a pixel is
displayed at the resultant X and Y locations. An alternative to rounding is the use of arithmetic
overflow. X and Y are kept in registers that have integer and fractional parts. The incrementing
values which are less than unity are repeatedly added to the fractional part and whenever the result
overflows the corresponding integer part is incremented. The integer parts of X and Y are used to
plot the line. This would normally have the effect of truncating. The DDA is therefore initialized by
adding 0.5 in each of the fractional parts to achieve true rounding.
The symmetrical DDA generates reasonably accurate lines since a displayed pixel is never away
from a true line by half the pixel unit. A Pascal procedure for a simple DDA is given below :
Procedure DDA (X1, Y1, Y2 : X2, integer) ;
length : var ;
i : integer;
X, Y, X-incr, Y-incr : real ;
begin
length : = abs (X2– X1) ;
if abs (Y2–Y1) < length then length: = abs (Y2–Y1);
X - incr : = (X2 – X1) /length ;
Y - incr : = (Y2 – Y1) /length ;
X : = X1 + 0.5 ; Y = Y1 + 0.5 ;
for i : = 1 to length do
begin
plot (trunc (X) ; trunc(Y) ;
X : = X + X - incr ;
Y : = Y + Y - incr ;
end;
end.
It can be noted that lines drawn on a raster display may have a jagged or staircase appearance unless
the lines are vertical or horizontal. This is because the points that are plotted must be pixel grid
points and many of these may not lie on the actual line.
EXAMPLE
To draw a straight line from connecting two points (2, 7) and (15, 10)
X1 = 2, X2 = 15 abs(X2 – X1) = 13

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Y1 = 7, Y2 = 10 abs(Y2 – Y1) = 3
Bresenham’s Line Algorithm(out of syllabus,included as seen in a QP)

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 An accurate, efficient raster line drawing algorithm developed by Bresenham, scan converts
lines using only incremental integer calculations that can be adapted to display circles and
other curves.
 Keeping in mind the symmetry property of lines, lets derive a more efficient way of drawing
a line.
 Choices are(xk +1, yk) and (xk+1, yK+1)
d1 = y – yk = m(xk + 1) + b – yk
d2 = (yk + 1) – y = yk + 1- m(xk + 1) – b
 Steps
 Input the two end points and store the left end point in (x0,y0)
 Load (x0,y0) into the frame buffer (plot the first point)

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 Calculate the constants Δx, Δy, 2Δy and 2Δy-2Δx and obtain the starting value for the
decision parameter as
p0 = 2Δy- Δx
o At each xk along the line, starting at k=0, perform the following test:
If pk < 0 , the next point is (xk+1, yk) and
pk+1 = pk + 2Δy
Otherwise
Point to plot is (xk+1, yk+1)
pk+1 = pk + 2Δy - 2Δx
Repeat above step Δx times

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Bresenham Circle ( Xc, Yc, R):
Description: Here Xc and Yc denote the x – coordinate and y – coordinate of the center of the
circle. R is the radius.
1. Set X = 0 and Y = R
2. Set D = 3 – 2R
3. Repeat While (X < Y)

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4. Call Draw Circle(Xc, Yc, X, Y)
5. Set X = X + 1
6. If (D < 0) Then
7. D = D + 4X + 6
8. Else
9. Set Y = Y – 1
10. D = D + 4(X – Y) + 10
[End of If]
11. Call Draw Circle(Xc, Yc, X, Y)
[End of While]
12. Exit
Draw Circle (Xc, Yc, X, Y):
1. Call PutPixel(Xc + X, Yc, + Y)
2. Call PutPixel(Xc - X, Yc, + Y)
3. Call PutPixel(Xc + X, Yc, - Y)
4. Call PutPixel(Xc - X, Yc, - Y)
5. Call PutPixel(Xc + Y, Yc, + X)
6. Call PutPixel(Xc - Y, Yc, + X)
7. Call PutPixel(Xc + Y, Yc, - X)
8. Call PutPixel(Xc - Y, Yc, - X)
9. Exit

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Transformation
A transformation is the process of mapping points to other locations. Changes in orientation, size and
shape are accomplished with geometric transformations that alter the coordinate descriptions of the
objects.
Transformations are used to
 position objects
 to shape objects
 to change viewing positions,
 even to change how something is viewed (e.g. the type of perspective that is used).
Use of transformations in CAD
In mathematics, "Transformation" is the elementary term used for a variety of operation such as
rotation, translation, scaling, reflection, clipping etc. CAD is used throughout the engineering
process from conceptual design and layout, through detailed engineering and analysis of components
to definition of manufacturing methods. Every aspect of modeling in CAD is dependent on the
transformation to view model from different directions we need to perform rotation operation. To
move an object to a different location translation operation is done. Similarly Scaling operation is
done to resize the object.
Coordinate Systems
In CAD three types of coordinate systems are needed in order to input, store and display model
geometry and graphics. These are the Model Coordinate System (MCS), the World Coordinate
System (WCS) and the Screen Coordinate System (SCS).
Model Coordinate System
The MCS is defined as the reference space of the model with respect to which all the model
geometrical data is stored. The origin of MCS can be arbitrary chosen by the user.
World Coordinate System
As discussed above every object have its own MCS relative to which its geometrical data is stored.
In case of multiple objects in the same working space then there is need of a World Coordinate
System which relates each MCS to each other with respect to the orientation of the WCS. It can be
seen by the picture shown below.

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Screen Coordinate System
In contrast to the MCS and WCS the Screen Coordinate System is defined as a two dimensional
device-dependent coordinate system whose origin is usually located at the lower left corner of the
graphics display as shown in the picture below. A transformation operation from MCS coordinates
to SCS coordinates is performed by the software before displaying the model views and graphics.
Viewing Transformations
As discussed that the objects are modeled in WCS, before these object descriptions can be projected
to the view plane, they must be transferred to viewing coordinate system. The view plane or the
projection plane, is set up perpendicular to the viewing zv axis. The World coordinate positions in
the scene are transformed to viewing coordinates, then viewing coordinates are projected onto
the view plane.
The transformation sequence to align WCS with Viewing Coordinate System is.
1. Translate the view reference point to the origin of the world coordinate system.
2. Apply rotations to align xv, yv, and zv with the world xw, yw and zw axes, respectively.

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Transformations
Translation Rotation Reflection Scaling Clipping
TRANSLATION
A translation is applied to an object by repositioning it along a straight line path from one coordinate
location to another. We translate a two-dimensional point by adding translation distances, tx and ty,
to the original coordinate position (x,y) to move the point to a new position (x',y')
The translation distance pair (tx, ty) is called translation vector or shift vector
Matrix representation of translation
This allows us to write the two-dimensional translation equations in the matrix form:
Example: If line A(3,5) , B(4,8) is translated into three units along the positive x-axis and four units
along the positive y axis, find new coordinates of line
Solution
Given A(3,5), B(4,8).
dx=3, dy= 4
The new points are given by A’(x,y)=(3+3, 5+4)=(6,9)
B’(x,y)=(4+3,8+4)=(7,12)

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ROTATION
A two-dimensional rotation is applied to an object by repositioning it along a circular path in the x-y plane. When we
generate a rotation we get a rotation angle (θ) and the position about which the object is rotated (xr , yr) this is known
as rotation point or pivot point. The transformation can also be described as a rotation about rotation axis that is
perpendicular to x-y plane and passes through the pivot point. Positive values for the rotation angle define counter-
clockwise rotations about the pivot point and the negative values rotate objects in the clockwise direction.
Here, r - constant distance of the point from the origin.
Φ - original angular position of the point from the horizontal
θ - rotation angle
we can express the transformation by the following equations
we know the coordinate of x and y in polar form
on expanding and equating we get
The same equations we can write in matrix form as

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Where the rotation matrix R is
Hence it is
the anti-clockwise direction to position P2. The co-ordinates of P2 can be obtained
by multiplying the co-ordinates of P1 by the matrix:
The new coordinates are
SCALING
Scaling is a kind of transformation in which the size of an object is changed. Remember the change is size
does no mean any change in shape. This kind of transformation can be carried out for polygons by multiplying
each coordinate of the polygon by the scaling factor. Sx and Sy which in turn produces new coordinate of (x,y)
as (x',y'). The equation would look like

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or
here S represents the scaling matrix.
NOTE: If the values of scaling factor are greater than 1 then the object is enlarged and if it is less that 1 it
reduces the size of the object. Keeping value as 1 does not changes the object.
Uniform Scaling: To achieve uniform scaling the values of scaling factor must be kept equal.
Differential Scaling: Unequal or Differential scaling is produce incases when values for scaling factor are
not equal.
As per usual phenomenon of scaling an object moves closer to origin when the values of scaling
factor are less than 1. To prevent object from moving or changing its position while is scaling we
can use a point that is would be fixed to its position while scaling which is commonly referred as
fixed point (xf yf).

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REFLECTION
Reflection is nothing more than a rotation of the object by 180o
. In case of reflection the image formed is on the opposite
side of the reflective medium with the same size. Therefore we use the identity matrix with positive and negative signs
according to the situation respectively.
The reflection about the x-axis can be shown as:
The reflection about the y-axis can be shown as:
REFLECTION ABOUT A ORIGIN
When both the x and y coordinates are flipped then the reflection produced is relative to an axis that is perpendicular to
x-y plane and that passes through the coordinate origin. This transformation is referred as a reflection relative to
coordinate origin and can be represented using the matrix below.

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REFLECTION ABOUT AN ARBITRARY LINE
Reflection about any line y= mx + c can be accomplished with a combination of translate-rotate-reflect
transformations.
Steps are as follows
1. Translate the working coordinate system (WCS) so that the line passes through the origin.
2. Rotate the WCS such that one of the coordinate axis lies onto the line.
3. Reflect about the aligned axis
4. Restore the WCS back by using the inverse rotation and translation transformation.
REFLECTION ABOUT AN ARBITRARY POINT
As seen in the example above, to reflect any point about an arbitrary point P (x,y) can be accomplished by translate-
reflect transformation i.e. the origin is first translated to the the arbitrary point and then the reflection is taken about the
origin. And finally the origin is translated back to its original position.
CLIPPING

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3D TRANSFORMATIONS
HOMOGENEOUS COORDINATES
We have seen that basic transformations can be expressed in matrix form. But many graphic
application involve sequences of geometric transformations. Hence we need a general form of matrix
to represent such transformations. This can be expressed as:
Where P and P' - represent the row vectors.
T1 - is a 2 by 2 array containing multiplicative factors.
T2 - is a 2 element row matrix containing translation terms.
We can combine multiplicative and translational terms for 2D geometric transformations into a
single matrix representation by expanding the 2 by 2 matrix representations to 3 by 3 matrices. This
allows us to express all transformation equations as matrix multiplications, providing that we also
expand the matrix representations for coordinate positions. To express any 2D transformations as a
matrix multiplication, we represent each Cartesian coordinate position (x,y) with the homogeneous
coordinate triple (xh,yh,h),such that
Thus, a general homogeneous coordinate representation can also be written as (h.x, h.y, h). For 2D
geometric transformations, we can choose the homogeneous parameter h to any non-zero value.
Thus, there is an infinite number of equivalent homogeneous representations for each coordinate
point (x,y). A convenient choice is simply to h=1. Each 2D position is then represented with
homogeneous coordinates (x,y,1). Other values for parameter h are needed, for eg, in matrix
formulations of 3D viewing transformations.
Expressing positions in homogeneous coordinates allows us to represent all geometric transformation
equations as matrix multiplications. Coordinates are represented with three element row vectors and
transformation operations are written as 3 by 3 matrices.

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Rotation
Projections
Homogenous factor
Translation
Scaling/ Reflection
3D TRANSFORMATION SAMPLE MATRIX
a b c d
e f g h
i j k l
m n o p
.
TRANSLATION
In three-dimensional homogeneous coordinate representation, when a point P is translated to P' with coordinated
(x,y,z) and (x',y',z') can be represented in matrix form as:
Where,
ROTATION
Unlike 2D, rotation in 3D is carried out around any line. The simplest rotations could be around coordinate axis. As in
2D, positive rotations produce counter-clockwise rotations.
Rotation in term of general equation is expressed as

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Where,
R = Rotation Matrix
Rotation matrix when an object is rotated about X axis can be expressed as:
Rotation matrix when an object is rotated about Y axis can be expressed as:
Rotation matrix when an object is rotated about Z axis can be expressed as:
SCALING
Scaling an object in three-dimensional is similar to scaling an object in two-dimensional. Similar to 2D scaling an object
tends to change its size and repositions the object relative to the coordinate origin. If the transformation parameter are
unequal it leads to deformation of the object by changing its dimensions. The perform uniform scaling the scaling factors
should be kept equal
i.e.
Where,

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NOTE: A special case of scaling can be represented as reflection.
if the value of Sx, Sy or Sz be replaced by -1 it will return the reflection of the object against the standard plane whose
normal would be either x axis, y axis or z axis respectively.
REFLECTION
In 3D-reflection the reflection takes place about a plane whereas 2D reflection it used take place about an axis. The
matrix in case of pure reflections, along basic planes, viz. X-Y plane, Y-Z plane and Z-X plane are given
below:
Transformation matrix for a reflection through X-Y plane is:
Transformation matrix for a reflection through Y-Z plane is:
Transformation matrix for a reflection through Z-X plane is:

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OVERVIEW OF CAD/CAM
What is CAD?
CAD if often defined in a variety of ways and includes a large range of activities. Very broadly it can be
said to be the integration of computer science (or software) techniques in engineering design. At one end
when we talk of modeling, iIt encompasses the following:
 Use of computers (hardware & software) for designing products
 Numerical method, optimizations etc.
 2D/3D drafting
 3D modeling for visualization
 Modeling curves, surfaces, solids, mechanism, assemblies, etc.
The models thus developed are first visualized on display monitors using avariety of techniques including
wire frame displa, shaded image display, hidden surface removed display and so on. Once the designer is
satisfied, these models are then used for various types of analysis / applications. thus, at the other end it
includes a number of analysis activities. These could be:
 Stress (or deflection) analysis, i.e. numerical methods meant for estimating the behaviour of an
artifact with respect to these parameters. It includes tools like the Finite Element Method (FEM).
 Simulation of actual use
 Optimization
 Other applications like
o CAD/CAM integration
o Process planning
These are activities which normally use models developed using one or more of the techniques mentioned
above. These activities are often included in other umbrellas like CAM or CAE. A term often used is CAx
to include this broad set of activities. They all use CAD models and often the kind of application they
have to be used ina determines the kind of amodel to be developed. Hence, in this course I cover them
under the umbrella of CAD. In this course we will strive to give an overview of modelling techniques
followed by some applications, specifically CAM.
Thus there are three aspects to CAD.
 Modeling
 Display/ Visualization
 Applications

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MODELING
Modeling typically includes a set of activities like
 Defining objects
 Defining relation between objects
 Defining properties of objects
 Defining the orientations of the objects in suitable co-ordinate systems
 Modification of existing definition (editing)
DISPLAY / VISUALIZATION
Displaying the model requires the following:
 Mapping objects onto screen coordinates: Models are typically made in a model coordinate
system. this could be the world coordinate system, or a coordinate system local to the object.
these coordinate systems are typically three dimensional in nature. To display the object on a 2D
screen, the object coordinates need to be mapped on to the 2D coordinate system of the screen.
This requires two steps:
o Viewing transformations: The coordinates of the object are transformed in a manner as if
one is looking at the object through the screen. This coordinate system is referred to as
the viewing coordinate system.
o Projections: The object in the viewing coordinate system is then projected onto the two
dimensional plane of the screen.
 Surface display or shading / rendering: In displaying the objects on the screen one often likes to
get a shaded display of the object and get a good feel of the three dimensional shape of the object.
This requires special techniques to render the surface based on its shape, lighting conditions and
its texture.
 Hidden line removal when multiple surfaces are displayed: In order to get a proper feel of the
three dimensional shape of an object, one often desires that the lines / surfaces which are not
visible should not be displayed. this is referred to as hidden line / surface removal.
APPLICATIONS
Once a model is visualized on the screen and approved by the conceptual designer, it has to go through a
number of analysis. Some of the kinds of usage this model might have to go through are the following:
 Estimating stresses / strains / deflections in the objects under various static loading conditions
 Estimating the same under dynamic loading conditions
 Visualizing how a set of objects connected together would move when subject to external
loading. This leads to a whole set of activities under simulation. These activities would vary
depend upon the application the object is to be subject to.
 Optimizing the objects for
o Developing 2D engineering drawings of the object

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o Developing a process plan of the object
 Manufacturing the object using NC / CNC machines and generating the programs for these
machines so as to manufacture these objects.
USES OF CAD
 To create conceptual product models.
 Editing the model for improvement.
 Display the model into several colours
 Rotate & view the objects.
 Create & display all inner details.
 Check the clearance between the mating parts.
 Prepare the detailed component drawing.
 Store the database for modification
BENEFFITS OF CAD
 Productivity improvement in design
 Shorter lead time.
 Flexibility in design.
 Improved design analysis.
 Fewer of design errors.
 Easier visualization of drawings.
 Standardization of design, drafting, and documentation.
ENGINEERING DESIGN PROCESS
The engineering design process is a formulation of a plan or scheme to assist an engineer in
creating a product. The engineering design is defined as component, or process to meet desired
needs. It is a decision making process (often iterative) in which the basic sciences, mathematics,
and engineering sciences are applied to convert resources optimally to meet a stated objective.
Among the fundamental elements of the design process are the establishment of objectives and
criteria, synthesis, analysis, construction, testing and evaluation.

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Design process Proposed by Shigley
1. Recognition of need: Recognition of need involves the
realization by someone that a problem exists for which some feasible solution is to be found. This
might be the identification of some defects in the present machine design activity by an engineer
or the perception of a new product marketing opportunity by the salesman.
2. Definition of problem: This involves a thorough specification of the item to be designed. This
specification will generally include functional and physical characteristics, cost, quality, performance,
etc. This also involves problems like the cost and the performance like the cooling system,
environmental hazards.
3. Synthesis: During the synthesis phase of the design process various preliminary ideas are
developed through research of similar products or designs in use.
4. Analysis and Optimization: The resulting preliminary designs are then subjected to appropriate
analysis to determine their suitability for the specified design constraints. If the design fails to satisfy
the constraints, they are then redesigned or modified on the basis of feedback from the analysis. This
iterative process is repeated until the proposed design meets the specifications or until the designer is
convinced that the design is not feasible. The components, sub-assemblies or sub-systems are then
synthesized into the final overall system in a similar iterative manner.
5. Evaluation: The assessment or evaluation of the design against the specification established during
the problem definition phase is then carried out. This often requires the fabrication and testing of a
prototype model to evaluate operating performance quality, reliability, etc. Evaluation is the
comparison of actual impacts against strategic plans.
Synthesis
Problem Definition
Recognition of Need
Evaluation
Analysis and Optimization
Presentation

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6. Presentation: The final phase in the design process is the presentation of the design .This includes
documentation of the design through drawings, material specifications, assembly lists and so on.
This involves the re-modeling of the prototype if necessary, the 2D and 3D drawing representation of
the product, the bills of materials, and the complete materials specification
CAD PROCESS
Computer aided Design
GEOMETRIC MODELING
 Computer representation of geometry of a component using a software is called geometric
modeling.
 Stored in computer as mathematical description.
 Three types of commands in modeling
 To generate basic models like lines, points, circles etc.
 Used for transformations
 Used to join various elements to form the shape.
 Types.
 Wire frame modeling.
 Surface modeling.
Synthesis
Problem Definition
Recognition of Need
Evaluation
Analysis and Optimization
Presentation
Geometric Modeling
Automatic Drafting
Engineering Analysis
Design Review and Evaluation

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 Solid modeling.
Wire Frame model
 Wire-frame model consists only of lines, circles, and curves
 Model is represented by its edges.
 Wire-frame models represent 3D part shapes with interconnected line elements
 Wire-frames contain no information about the surfaces,
 No differentiate between the inside and outside of objects
 Hidden line elimination is available.
In wire frame modeling the object is represented by its edges. In the initial stages of CAD, wire frame
models were in 2-D. Subsequently 3-D wire frame modeling software was introduced. The wire frame
model of a box is shown in Fig. 6.2 (a). The object appears as if it is made out of thin wires. Fig. 6.2(b),
6.2(c) and 6.2(d) show three objects which can have the same wire frame model of the box. Thus in the
case of complex parts wire frame models can be confusing. Some clarity can be obtained through hidden
line elimination. Though this type of modeling may not provide unambiguous understanding of the
object, this has been the method traditionally used in the 2-D representation of the object, where
orthographic views like plan, elevation, end view etc are used to describe the object graphically.

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The difference between 2D and 3D wire frame model is given below:
Surface modeling
 The component is represented by its surface
 Can calculate surface area, surface intersections
 Automatic hidden line removal
 It created by connecting various surface elements.
 It can be built from wire frame model.
 Represented by
 set of plane corss-sectional curves. Eg. Manifolds.
 Array of points in space through intersecting curves.

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 Irregular mesh of curves.
 Required more computational time.
 More skill in their construction.
 Difficult to interpret without hidden line removal.
 Applications
 Ship building, automobile body building, cutting out of shoe leather etc.
In this approach, a component is represented by its surfaces which in turn are represented by their
vertices and edges. For example, eight surfaces are put together to create a box, as shown in Fig. 6.3.
Surface modeling has been very popular in aerospace product design and automotive design. Surface
modeling has been particularly useful in the development of manufacturing codes for automobile
panels and the complex doubly curved shapes of aerospace structures and dies and moulds.
Apart from standard surface types available for surface modeling (box, pyramid, wedge, dome, sphere,
cone, torus, dish and mesh) techniques are available for interactive modeling and editing of curved
surface geometry. Surfaces can be created through an assembly of polygonal meshes or using advanced
curve and surface modeling techniques like B-splines or NURBS (Non-Uniform Rational B-splines).
Standard primitives used in a typical surface modeling software are shown in Fig. 6.4. Tabulated surfaces,
ruled surfaces and edge surfaces and revolved are simple ways in which curved geometry could be
created and edited.

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Solid Modeling
 Most powerful of 3-D modeling
 It will give complete information about the model.
 Mass properties such as area, volume, weight, CG, MI can be determined quickly.
 It allows the designer to develop & evaluate alternative models.
 Cross section can be cut through
 Helps to interference checking of moving parts.
 Used for technical illustrations.
 Approaches to solid model.
 Constructive solid geometry (CSG).
 Boundary representation.
 In CSG models are created by basic elementary shapes known as primitives like blocks,
cylinders, cones, and pyramids.
 The boolean operations like union, difference and intersections are used to make the shape.
 Easy to construct.
 Boundary representation-It is accurate and give internal and external geometric descriptions.
 User to draw the out line of various view of (t.v, s.v, f.v etc) the object by the use of input
devices on the CRT.
 Then interconnected them
The representation of solid models uses the fundamental idea that a physical object divides the 3-D
Euclidean space into two regions, one exterior and one interior, separated by the boundary of the solid.
Solid models are:
• Bounded
• Homogeneously three dimensional
• Finite
In most of the modeling packages, the approach used for modeling uses any one of the following three
techniques:
i. Constructive solid geometry (CSG or C-Rep)
ii. Boundary representation (B-Rep)
iii. Hybrid method which is a combination of B-Rep and CSG.

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Constructive Solid Geometry (CSG)
In a CSG model, physical objects are created by combining basic elementary shapes known as primitives
–)
primitives, a block and a cylinder which are located in space as shown in Fig.
A “union” operation (A ∪
difference operation (A – B) will create a block with a hole (Fig. 6.5. (D)). An intersection operation (A
Boundary Representation
Boundary representation is built on the concept that a physical object is enclosed by a set of faces which
themselves are closed and orientable surfaces. Fig. 6.6 shows a B-rep model of an object. In this model,
face is bounded by edges and each edge is bounded by vertices.
The entities which constitute a B-rep model are:

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Advantages of Solid Modeling
 A solid model is a 3-D representation of an object. It is an accurate geometric description which
includes not only the external surfaces of part, but also the part’s internal structure. A solid model
allows the designer to determine information like the object’s mass properties, interferences, and
internal cross sections.
 Solid models differ from wire frame and surface models in the kind of geometric information
they provide. Wire frame models only show the edge geometry of an object. They say nothing
about what is inside an object. Surface models provide surface information, but they too lack
information about an object’s internal structure. Solid models provide complete geometric
descriptions of objects.
 Engineers use solid models in different ways at different stages of the design process. They can
modify a design as they develop it. Since computer-based solid models are a lot easier to change
and manipulate than the physical mock-ups or prototypes, more design iterations and
modifications can be easily carried out as a part of the design process.
 Using solid modeling techniques a design engineer can modify a design several times while
optimizing geometry. This means that designers can produce more finished designs in less time
than by using traditional design methods or 2-D CAD drafting tools.

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 Solid models can be used for quick and reliable design analysis. Solid models apart from
geometric information provide important data such as volume, mass, mass properties and centre
of gravity. The designer can also export models created to other applications for finite element
analysis (FEA), rapid prototyping and other special engineering applications.
 Finally designers can generate detailed production drawings directly from the solid model. This
capability increases design productivity considerably. Another important feature of solid
modeling is associatively. Detailed drawings are linked to solid model through the associatively
feature. This is a powerful function - as an engineer modifies a design, the drawings get updated
automatically. In bidirectional associatively, any modifications made to geometry in the drawing
are reflected in the model. In more advanced design and manufacturing environments, solid
models are used for rapid prototyping and automated manufacturing applications.
(ii) ENGINEERING ANALYSIS
. In the formulation of nearly any engint:ering design project some type of analysis is required. The
analysis may involve stress-strain calculations, heat transfer computations or the use of differential
equations to describe the dynamic behaviour of the system designed. CAD systems include engineering
analysis software, which can be called to operate on the current design model.
Two important examples of this type are :
(a) Analysis of mass properties (b) Finite Element Analysis
(a) The analysis of mass properties provides properties of a solid object being analysed such as
the surface area, weight, volume, centre of gravity and moment of inertia. For a plane surface (or a
cross section of a solid object) the corresponding computations include the perimeter, area, and
inertial properties.
(b) The finite element analysis is a powerful feature of the CAD system. With this method, the object
is divided into a large number of finite elements which form an interconnecting net-work of concentrated
nodes. By using a computer with significant computational capabilities, the entire object can be analyzed
for stress-strain, heat transfer and other characteristics by calculating the behavior at each node. By
determining the inter-connecting behaviors at all the nodes in the system, the behavior of the entire object
can be assessed. The output of the finite element analysis is often best presented by the system in
graphical format on the CRT screen for easy visualization by the user. For example, in stress-strain
analysis of an object the output may be shown in the form of deflected shape, superimposed over the
unstressed object. Colour graphics can also be used to accentuate the comparison before and after
deflection of the object. If the finite element analysis indicate behavior of the design which is undesirable,
the designer can modify the shape and recomputed the finite element analysis for the revised design.

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(III) DESIGN REVIEW AND EVALUATION
. Checking the accuracy of the design can be accomplished conveniently on the graphic terminal.
Semiautomatic dimensioning and tolerancing routines which assign size specification to surface indicated
by user help to reduce the possibility of dimensioning error. The designer can zoom the part design details
and magnify the image on the graphic screen for close scrutiny. A procedure called layering is often
helpful in design review.
For Example : A good application of layering involves overlaying the geometric image of the final shape
of the machined part on top of the image of the rough casting. This ensures that to accomplish the final
machined dimensions. This procedure can be performed in stage processing of the part.
(IV) AUTOMATED DRAFTING. Automated drafting involves the creation of hard-copy engineering
drawing directly from the CAD Data base. In some early computer-aided design departments, auto-
mation of the drafting process represent the principal justification for investing in the CAD system.
Indeed, CAD system can increase productivity in the drafting function by roughly five time over manual
drafting.
Representations of CIM

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TQM
Marketing
CIM

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Elements of CIM
Product design.
 Establishes the initial database for production of proposed product.
 It is accomplished through geometric modeling.
Production planning.
 It take the database established by the product design, enriches it with production data.
 Produce a plan for the product production.
 The cost incurred and production equipment’s capacity will be consider.
Production control.

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 Further enriches the output of production planning dept with performance data and information
about production equipment and processes.
 In CIM this activity includes
 Modeling, simulation, and computer aided scheduling of the production activity.
 Continuous optimization of production activity is must.
Production equipment
 It enriches the database with equipment and process data and information.
 The equipment consist of
 computer controlled machines like CNC.
 FMS
 Robots
 Material handling systems
 Inspection equipments
Production process.
 It create the finished product with the help of the production equipments.
 This is done with the help of data information and knowledge resident in the operator or CIM
system.
 This process consist of
 Material removal.
 Material forming.
 Automated quality assurance.
Advantages of CIM
 Responsiveness to Rapid Changes in Market Demand and Product Modification.
 Better Use of Materials, Machinery, Personnel, Reduction in Inventory.
 Better Control of Production and Management of the Total Manufacturing Operation.
 The Manufacture of High-Quality Products at Low Cost.
 Improved competitiveness

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 Lower total cost.
 High productivity.
 Less work in process inventory.
 Long time profitability.
PREPARE NOTES FOR SOFTWARES BY YOUR OWN
Suggested extra reading;
 http://en.wikipedia.org/wiki/Comparison_of_3D_computer_graphics_software
 Principles of Automation and Advanced Manufacturing Systems- Dr K.C. Jain, Sanjay Jain
 CAD/CAM-Concepts and Applications- Chennakesava R. Alavala
 CAD/CAM- M Groover, E. Zinners

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