Computer Aided Drafting And Design (CADD)

Definition

Computer Aided Drafting And Design (CADD) is the computer process of making engineering drawing and technical documents more closely related to drafting.

• What is CADD ?

Computer Aided Drawing is a technique where engineering drawings are produced with the assistance of computer and, as with manual drawing, is only the graphical means of representing a design.
Computer Aided Design, however, is a technique where the attributes of the computer and those of the designer are blended together into a problem solving term.

• Two Dimensional (2D) CAD

Computer drawing is the representation of an object in the single view format which shows two of the three object dimensions or the multi view format where each view reveals two dimensions.

 

• Three Dimensional (3D) CAD

Computer drawing is the coordinate format. Three dimensional computer aided drawing allows the production of geometric models of a component or product for spatial and visual analysis.

• Advantages Of CADD

• Drafting Stage

1. Increased accuracy
2. Increased drawing speed
3. Easy to revise
4. Availability of drawing libraries
5. Constant drawing quality
6. Multicolor drawing
7. Built in several analysis tools
8. Better presentation (Easy To Visualize)-Pan, Rotate, Animate, Shade, Texture
9. Save on repetition

• CADD Capability

1. Draw
2. Modify
3. Dimension
4. Object snap
5. Layer concept

• Concepts In Working Drawing Creation

2-D CADD

• Draw a group of line that are connected and present

- Orthographic multiview

- Pictorial view

Solid Modeling

• Draw a closed contour and convert to surface.
• Modify this surface to solid object.
• Create an orthographic view from a solid object.

• Limitation Of CADD

Good engineering drawing must have the following characteristics.

• Part or product information is completely given.
• Information is clearly presented.
• Information can be used in manufacturing of part.

Always remind yourself that

"Good drawing cannot be created by using CADD software alone without understanding the drawing concept." 

• Limitation Of CADD (with in scope of drawing creation)

To create a good engineering drawings You must do the following tasks yourself.

1. Apply a proper line weight and style.
2. Select a necessary view.
3. Decide the appropriate places of dimensions.
4. Select an appropriate section techniques.

• Limitation Of CADD (with in scope of drawing interpretation)

No CADD software can create a pictorial view from an orthographic multiview.

Because they are frequently used technical document. Therefore,You must prepare your self for interpreting (or visualizing) them when you become an Engineer.

• Modern System In CADD

Tn modern system the light pen has been replaced by more effective pointing hardware, that is a digitizer tablet, a mouse.

CADD System And Hardware

1. The mainframe computer
2. The minicomputer
3. The Microcomputer

Input Devices

The input devices are used for making selections from a menu, which is a layout of a variety of commands and functions required to operate the system. Sending these command into the computer produces complete engineering drawing.

• Modern System In CADD

1. Impact printer (dot matrix)
2. Non-impact printer include electrostatic, ink-jet and laser
3. Flatbed plotters
4. Drum plotters

• User Interface

CAD systems may be considered as comprising a large number of functions for creating or manipulating the design model. Traditionally, there are two ways in which this is achieved:

Command-based systems

Command-based systems operate by reading a command and its parameters entered by the user, carrying out the required actions, then waiting for the next command.

• User Interface – Menu Driven

The menu-driven approach contrasts markedly with the command

approach. The basic principle is that the user is at any time

presented with a list or menu of the functions that are available

to be selected.

Rules

• The most important of these rules are:
• A clear, well presented screen layout.
• Easy function selection by a well-structured menu system.
• Meaningful function names.
• Meaningful and helpful prompts to the user.
• Easily accessible and clearly written help information.

• CADD Functionality

The main benefits of a computerized drafting and design system over those of manual methods is this ability to represent the design of a component or assembly in a geometrically accurate format so that the same model can be used for other modelling, analysis and manufacturing work.

The functions can be said to fall into three categories:

• Synthesis type functions are concerned mainly with the creation of geometric features and drawing details.
• Modification functions include those which allow for the deletion and editing of existing geometry or detail.
• Management functions are concerned with how the drawing is presented both on the screen and eventually on paper.

• CADD System Selection

There is a large variety of different CADD packages available on the market these days and the design manager is faced with the enormous problem of selecting a package to suit the demands

of the company and its product range. A lot of ease and efficiency has been obtained with the use of CADD systems. Among the more widely used CAD systems are AutoCAD, CATIA, SolidWorks, I-DEAS, and ProEngineer. Most of these packages have both a 2D and 3D component or have an integrated 2D and 3D modeling system. The newer versions of drawing software operate under a menu system which can be accessed through keyboard input or mouse manipulation.

• CADD System Selection

According to these factors, the system must have;

• Functional abilities: the abilities to perform memory circuits.
• Memory capacity : evaluation between main and branch memory circuits.
• Data transfer characteristics : when we consider data transfer between two computers, or a main computer and a station, we have to keep in mind the need to decrease computing time

• CADD System Selection

The size of the company and the amount of investment capital available will be one of the main deciding factors but there are many other questions to be considered:

Mainframe or PC/workstation platform?

Two dimensions or three? Lines, surfaces or solids?

Other analysis tools needed? Will the ability to transfer the

geometry to these modelling and analysis systems be needed?

Compatibility with other systems needed?

How good is the maintenance and support from the suppliers?

How much, how good and how long is the training?

How easy is it to expand the system?

• AutoCAD

AutoCAD is PCbased

CAD software products (late 1982).

System Requirements for AutoCAD

Windows NT or Windows 95/98/2000

Intel 486 or Pentium processor or compatible

32 MB of RAM

50 MB of hard disk space

64MB of disk swap space

2.5 MB of free disk space during installation only

CD-ROM drive

640 x 480 VGA video display (1024 x 768 recommended)

Windows-supported display adapter

Mouse or other pointing device