cad cam unit i [pls vis it our blog sres11meches]

CAD CAM

UNIT -I

CAD:

Computer aided design---> It is used to assist in the creation, modification, analysis (or) optimization of a design.

CAM:

In the use of computer systems to plan, manage and control the operations of a mfg plant through direct or indirect computer interface with plant’s resources.

NEED OF CAD/CAM:

To increase productivity of the designer. To improve quality of design. To improve compunction [creative products]. To create mfg databases. To help in production scheduling. To have effective shop floor control.

DESIGN PROCESS:

Computer aided design and automated drafting are utilized in design and documentation of product.

Computers used in process planning and scheduling to perform these functions more efficiently.

Computers used in production to monitoring and controlling the mfg operations. In quality control section, computers are used to perform inspection and perform tests on

products and its computers, and accepted products are delivered to the customer.

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CAD/CAM HARDWARE:

The computers are consists of CAD/CAM hardware are

1. CPU.2. Memory devices3. Input devices4. Display devices5. Hard copy devices6. Storage devices.

BASIC STRUCTURE:

The heart of any computing system is the CPU .In CPU all necessary functions of a computer are carried out. The main functions performed in the CPU are arithmetic and logic operations.

The CPU communicates with the input/output devices. Through input device, the user communicates with the CPU, either to give certain data or

control the operations of CPU. The output device means, through which the CPU gives the results of the computations. Another important unit of computer system is memoryunit.These is the areas where

necessary data (or) program is stored. In present day computer works on the principle called stored-program concept. Where

the sequence of operations to be carried out by the CPU.This stored program is called software in computer terminology.


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PRODUCT CYCLE


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1.Customers and markets: Depending on the particular group,there will be difference in the way the product cycle is activated. In some cases design functions are performed by the costumer and the product is manufactured by the firm .In other cases design &mfg is accomplished bythe same firm.

2.Product concept: The product cycle begine with the concept,an idea for a product .this concept is cultivated,refind,analysed&improved and transferd into the design engg.sections.3.design engineering: With the concept of product and specifications of product drawings can be performed.4.drafting:

After the design,drafting can be performed for the particular product .All types of views are represented in drafting.5.process planning:

Process plan is formulated which specifies the sequence of production operations required to make the product.

7. Order new equipment&tooling:For to develop the particular product if it need any new equipment&tools,they

Can be orded.

8. Production scheduling:


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Scheduling provides a plan that commits the company to manufacture of certain quantities of product by certain dates.

8.production:

In the production section products are developed by the different machines.

9.quality control :

Finished products are entered in to the quality control section ,then check for the quality and quality control accepted products are delivered to the customer

Computers used in manufacturing :

To maintain accuracy of product specifications To maintain quality of products To increase productivity To increase productivity.

Computers used in mfg is brodly classified in to two groups.

1.computer monitory&control.

2.computer for mfg support applications.

1.computer monitory&control.

With the increase in the need for quality mfg.along with the factors of short lead times and short product lives and increasing consumer awareness regulary quality of product it is important for manfactures to initiate steps to achive all these.

2.computer for mfg support applications.

i. Cad-(computer aided design) : the use of computer methods to develop geometric &mfg requirements can be examined.

ii. CADD-(computer aided design & drafting): combining the CAD functions with drafting to generate the production drawing of the product.

iii. CAE-(computer aided engg.) : to use computer methods to support basic error checking , analysis , optimization , manufacturability of a product design

iv. CAM-(computer aided machine): CAD softer used to design the product developed by the CNC machines.

v. CAPP-(computer aided process planning) : the use of computer to generate process plans for the complete manufacturing of products.

vi. CATD-(computer aided tool design.): it is used for developing the tools for manufacturing like jigs & fixtures, dies& moulds.

vii. CAP-(computer aided planning.) : used for many of planning functions such as material required and computer aided scheduling.

viii. CAQ-(computer aided quality assurance) : it is used for assessing the inspection methods & developing quality products.

Cpu (central processing unit):

CPU is the computing system. Based on softer it organises the information processing for any given application


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CPU consist of two operating units1. Control unit 2. Artyhematic logic unit (ALU)

1. Control unit:

The control unit directs the operations of arithmetic logic unit. It seeds the data to the ALU what functions to perform on the data and where to store the results.

The capability of the control unit to accomplish these operations is provided by a set of instructions called executive program, which is stored in memory.

2. ALU:

ALU perform operations such as additions, subtractions, comparisons etc.

These operations are carried out on data in binary from [0.1].

Binary Decimal

0000 0

0001 1

0010 2

0011 3

0100 4

0101 5

0110 6

0111 7

1000 8

1001 9.

Both control unit and ALU perform their functions by utilizing registers.These registers are memory devices which receive, hold and transfer the data.

Sequence of operations performed in the CPU listed below with the diagram.


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PROGRAM COUNTER:

It holds the location of next instruction. The CPU sequences the instructions to be performed by fetching words from according to the contexts of program counter.

After each word is obtained , the program counter is incremented to the merit instruction word.

MEMORY ADDRESS REGISTER:

The location of data contained in the computer’s memory unit must be identified for an instruction. This is the function of memory address register . This unit is used to hold address of data held in memory.

INSTRUCTION REGISTER:

Instruction register is used to hold the instruction for decoding of letters (or) words.

ACUMULATOR:

It is a temporary storage register and it is useful during arithmetic (or) logic unit.

STATUS REGISTER:

These are used to indicate the internal condition of CPU . A status register is a 1-bit register.These are used to identify logical decision outcomes.

ALU:


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It provides the circuits required to perform various calculations such as multiplication and division and addition and subtraction and comparisions.

MEMORY TYPES

Memory is an integral part of computer, it is used to store the data and programs.

Thus CPU must transfer these instructions and data to and from the memory throughout the execution of program.

Memory is divided into 2 categories.

1. Main memory { primary memory }2. Auxiliary memory { secondary memory }

1. Main Memory : The main memory is directly connected to the CPU. The primary storage can be divided into 3 categories.

i) Main data storageii) Control storageiii) Local storage

i) Main data storage: It is the magnetic core or solid state memory. It performs fast access rate , relatively low storage capacity and high cost compared to other memories.

ii) Control storage:

Control storage contains micro programs and it helps in performing it functions.

iii) Local storage:

Local storage is high speed working status used in arithmetic and logical operations.

2. Auxiliary memory:

Programs and data files are not generally kept in primary storage but stored on large capacity auxiliary devices.

Main memory is very expensive and rather limited capacity. Some operations require more data than can be held in main storage at one time. Auxiliary devices are secondary storage and physically external to the computer,

Which means programs and data files are not directly available to the CPU.


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There are 2 types of secondary storages.

i. Sequential access storage.ii. Direct access storage.

i.Sequential access storage: It is used to read one particular recorded in the file all records preceding it must be read.

i. Direct access storage:

With this storage method, individual records can be located and read immediately with out reading other records.

Sequential storage method is lower access rate than direct storage method. Cost per bit of data stored is higher in direct access storage method.

Due to this reason factors tends to define the applications of two storage types. Sequential access storage is suitable for applications where lower level of file activity.

Direct access storage is best suited to files where high level of files activity.

INPUT DEVICES

These are the devices through which the user communicates with the computer to give the instructions .

Input devices are

1. Key board. 2. Mouse. 3. Light pen. 4. Joy stick

5. Digitiser. 6. Scanner

1. Key board:

This is must basic input medium for all computers. Traditional key board consist alphabets, numbers,special keys. For CAD/CAM applications in addition to the keyboard, other analog input devices are used for CAD/CAM applications . these devices may be used for entering graphic data in convenievent form.

2. Mouse:

Mouse is a input device, it consist of 2 buttons and roller. The mouse operates on 3 basic principles—mechanical,optical,opto-mechanical.


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Mechanical mouse contains a free floating ball. The cursor moves on the screen as per the movement of the roller.

Coming to the case of optical mouse, roller replaced with the LED bulb.The cursor moves in X-directions and Y- directions as per the movement is higher , since it has no moving parts.

Opto-mechanical mouse is similar to that of the mechanical mouse, but positions resolved based on optical principle.

3. Joy stick:

It is used to control the screen cursor movement.the joy stick can indicate by the movement of stick which contains a ball seated in spherical cavity.These are most suited for vedio games.

4. Light pen:

Light pen are similar to fountain pens. These are not used for writing purpose. It is used only to detect the in presence of light on the screen with the help of light-

detecting register. The resolution of light pen is poor,where photo sensitive element is conical. It is inconvenient to use over long periods due to its gravity.

5. Digitiser:

A digitiser is most widely used input medium by the CAD designer.it is used for converting the physical locations into coordinate values, so that accurate data can be achieved.

A digitiser consist of rectangular smooth surface as drafting board. A hand held locator is moved in the smooth surface .It contain number of buttons. As per the movement of hand held locator,lines are drafted in the system , in x-axis and y-axis. The digitiser available in large number of sizes from 250*250 mm to 1000*3000 mm .The quality of digitiser can be measured in terms of resolution,accuracy,linearity,repeatability.


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6. Scanner:

A scanner scans images (or) text present on a paper optically and converts in to a digital images as a bit map.

A scanner consist of scan head which moves over the scanned object and sends a bit mapped representation of the object to the scanning system.

The most common type of scanner used is the flat bed scanner.It consist of glass platform,object is placed on glass platform and it is scanned.

Another type is non-contact larger scanner.the scanner sends light in the form of laser and receives a part of the reflected light and measures the coordinates on the surface of the object.

DISPLAY DEVICES

Display devices are most important elements in CAD/CAM .The design work and simulation of mfg can be graphically displayed.

The devices are:

1. Cathode ray tube (CRT)2. Plasma panel display3. Liquid crystal display

1. CathoderayTube:

Elements: In CRT heated cathode omits electrons which are formed in to a stream accelerated and focussed on to display screen. the display screen contains a phosphor-coated surface. The electron beam hit the surface and display the point. The electron beam is controlled by means of deflection plates [horizontal and vertical plates ]

Image –drawing techniques are 2 types.1. stroke –writing.2. raster scan.


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1. stroke-writing:In stroke writing display electron gun directly the vectors on the screen to generate

the image (where in the raster scan , while display surface is divided into matrix of small dots called pixels and the electron beam scans the whole surface area line by line.)

For to maintain a static display , storage tube technology is developed in 1972. This is called direct view storage tube (DVST). Here display is generated by the impingement of electron on the screen. Cathode grid is the part of screen surface , which once exicted by the electron to maintain the image on screen . this is desirable because there being there being no need for refreshing the image .the resolution of 19-inch tube is in the order of 3000*4000 addressable points.

The disadvantage of this system is that once written, partial erasing of image is not possible. If any necessary modifications , could only be made after completely erasing the picture ,and redraw again.

In the raster scan display ,the complete screen is divided in to matrix of pixels from atypical (320*200) to as high as (1280*1024).This distance between the squares is called “dot pitch”.

The display is generated by identifying which pixels need to be bright for a given vector and then full screen display is obtain by scanning the complete screen horizontally line . it represented as 60hz . it means that whole screen is to be completely written in 1/60 th of a second . this is called sequential (or) mon- interlared refreshing. it dependson the resoulution of screen. High resolution require faster refersh rates.

In some law cost – display devies , descreasing the refresh rate to half at 30 hz reduces the rest of monitor. In each of the cycle , only half of the screen image is refreshed , instead of the full one by omitting alternative lines. It is called tnterlaced refreshing.due to this it reduces the cost of monitor . but it is not suitable for dynamic displays , where the display changes fast.Plasma panel display:

CRT display is highly refixed , in some times it is not suitable for partable applications because of the depth , that is necessary for cathode – ray tube .in that situations plasma panel display ia use ful. They are small &flat.they consume a large amount of powder and also resolution is not very good.LCD(LIQUID CRASTAL DISPLAY):

LCD stands for liquid crastal display . liquid crystals exicts in a state between liquid &solid , but are free to move as in aliquid . liquid crystals are actually closer


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to a liquid state , than a solid state, and it sensitive to temperature the LCD’s are wide spread used in partable calculations and laptops . their full screen size , with reasonably low power consumption . it occupy very small desktop space.

The working of LCD is different from CRT .it consist of liquid crystal , which is called numatic phase. The nematic crystal is transparent material.

HARD COPY DEVICESHard copy devices are 3 types

1) Graphical printers 2) Plotters3) Photographic devices . 11 page

1. Graphical printers: This is the fastest way of getting graphical output at low cost . Graphical printers are 3 types.

(a) .impact dot matrix printer.

(b).thermal transfer printer.

( c ).ink-jet printer. (d). larger printer . ( e ). Colour larger printer

(a).Impact dot matrix printer: In this printer, print head consist of vertical bank of needles [9,12 or 24] which moves horizontally over the paper. Print head can make the ink marks by hitting the paper through a ribbon. The resolution available is 60 dots pen inch to 240 dots pen inch. Their cost is comparatively low . But disadvantages is their noise because of impact of pins on paper.(b).Thermal transfer printer: This is similar to dot matrix printer in operations , Where sensitised paper is used for output. It uses special ribbon between paper and print head . The ribbon consist of thin polymer material sports of dye are transformed from the heat sensitive ribbon to the paper. Advantages:

Noise less, low weight of parts. Cost of special ribbon is high and still a developing technologies. It makes 150 to 400 dots pen inch.

(c) .Ink jet printer: It does not use any ribbon , but shoots a set of ink directly on to the paper. In this printer ink nozzles are positioned vertically. This is almost noiseless in operation. Resolution is 300 to 1200 dots/inch. Ink jet printer consist of cat ridge for printing purpose.( d). Larger printer: It is an electrostatic plain copier with the difference that the drum surface is written by a larger beam. A semi conductor larger beam scans the electrostatic ally charged drum. The drum rotates 560 resolutions per minitue.it writes on the drum similar to pixels. Then tower


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powder is released, and the transferred to a sheet of paper. It is relatively expensive compared to dot-matrix printer. The quality of out put is very good, and it works very fast.( e ).Colour larger printer: Colour larger printer operates same principle as larger printer. They are provided with 4 toners:black,cyan,yellow,magenta.The new colour larger printer have the separated drum and tonner assembly for each of the colour. The paper passes through each of the colours like assembly line getting the required colour in the process.

PLOTTERS: Plotters is widely accepted output devices for final output. The accuracy is high in the plotters. All plotters have a range of pens available. Which can be changed under program control. Pens having different width depending on output desired. The types of pens used are fibre tip, roller bal, liquid ink. Various sizes of plotters. DESIGNATION SIZE OF DRAWING

A0 841X1189

A1 594X841

A2 420X594

A3 297X420

A4 210X297

PEN PLOTTERS:

Plotters are two types

( 1 ).flat bed

( 2 ).drum type

(1).Flat bed: In the flat bed plotters , paper is held in a fixed position by vacuum or electrostatic force. The pen cat ridge moves in both x and y axis for making necessary plot. The plot size is limited by the bed size of the plotter. The drum plotter is slightly more complex the y-motion of the plot being obtained by notating drum on which the paper is held with the help of sprocket holes. The x- moment of the pen is arrived by moving in a direction perpendicular to the drum motion. The plotters of present generation are almost drum type. The paper feeding is done by friction feed [ pinch rollers ]. The pen plotters are low initial purchase cost and produce accurate drawings drum plotters are software in process and require high level maintains. Electrostatic plotters:

The plotter head consist of larger number of tiny styluses embedded in to it. these styluses causes electrostatic changes at the required dot positions to make the drawing .The resolution available is 100 to 508 dots/inch. They are fast in process. The factors to be considered while selecting the plotters are plotting area, number of pens, type of pens used,drawing speed,resolution,accuracy is observed.


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Ink jet plotters: With the development of ink jet technology in terms of resolution, speed and cost, a majority of the plotters are now using ink jet for writing.Photographic devices: The photographic recording devices are cameras in front of CRT display. They normally have a smaller built in screen in side the recorder. Which is connected to the CPU.The image from the main computing system is received by these records. The resolutions that are vary from 500 lines to 4000 lines depending on the cost of devices.

STORAGE DEVICES Permanent storage of program and requires a large amount of storage space.The various storage devices are:

1. Floppy disk.2. Winches ten disk ( or ) hard disk.3. magnetic tapes4. compact disk ROMs.5.maganetic tape cartridges.6.DVD.

1.floppy disk: It is the most convenient medium, for handling the data. It consist of a storage disk, which is magnetically located on both sides it is permanently enclosed with square cover. Floppy disk rotates of very high speed. The disk is divided in to concentric rings called tracks. The tracks are further subdivided in to radial sectors. Each sectors can store information about 250 bytes. They are normally available in 3 standard sizes 3.5,5.25,8 inches. The stroge capacity is from 360 kb to 1.5 mb.2. Win chasten disk ( or ) Hard disk:

It is a rigid metal disk, on both sides of magnetic medium is coated. Such hard discs one put to gather sealed permanently. This disc has large storage capacity and it is used to store the data files .This disc is fixed inside the drive. The available storage drives are from 100 gb to 1000gb large amount of data can be stored and used for back up purpose.

3.Magnetic tape: Magnetic tape is used only for data exchange ( or ) backup. A large amount of data storage is possible .A 10.5 inch reel can store about 180 mb of data.

4. Magnetic tape cartridges: Magnetic tape cartridge is in audio cassette is also used in mini computers and micro computers used for mass storage of data. These are used as the backup medium.

5. Compact disc ROMs: It is small aluminium compact disc 120mm size storage capacity is comparatively higher than the floppy drive. The compact disc can storage 700mb of data. It is very easy to handle. The information stored is permanent. The major disadvantages of this technology is, once the disc is written, it cannot be earased.As a result, it becomes like a ROM and hence the name for these devices as CD ROM.presently commercial are available which can store 700 mb on a 5.25 inch removable optical disk using this technology. It is called rewritable compact disc,it can store the data. The data will be erased and rewrite again. This is better useful than normal compact disc.

6. DVD:


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DVD is used for storage purpose .Originally the name is Digital video disc. The available storage DVD’s are 4.7,8.5,9.4,17 gb.some of the early DVD’s are single sided to store the data. Now currently available double sided disc. The data will be stored both sides of disc.


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