Computer-aided Design
Computer-aided design (CAD) is the use of a computer to help in the drawing of designs from which objects are going to be constructed or manufactured.
CAD/CAM is short for computer-aided design and computer-aided manufacture. In CAD/
CAD /CAM the computer is involved in all the stages from design to manufacture.
FACILITIES PROVIDED BY A CAD SYSTEM
1 A method of inputting and storing the data needed for drawing an object. Often this is done by using a graphical display. Such a terminal needs a means of digitizing existing drawings such as a graphics tablet. Alternatively a means of indicating positions on a screen is needed, such as a light pen or a mouse.
The user of a graphical display unit would normally be able to:
(a) Select standard shapes, such as circles, squares, etc.
(b) Select line thicknesses, dotted lines, etc.
(c) Shade areas of diagrams.
(d) Add text information.
Fig.8 The hardware used in a typical computer-aided design system
2 A means of editing designs once they have been produced. It would usually be possible to improve freehand lines, delete areas, change scales, etc.
3 The ability to display objects clearly. This can be done:
(a) By showing a ‘three-dimensional’ view, possibly with the object able to rotate on the screen.
(b) By showing different ‘elevations’ of the object- i.e. a set of views of it from certain different directions.
4 A means of drawing designs accurately on paper. Usually the hardware would include a large flat-bed plotter for this purpose.
Often the software would include further facilities associated with the object being designed, e.g.:
1 Costing of materials used.
2 Simulated tests of the object being designed .
Examples of the use of CAD
in civil engineering
In highway construction, programs have been developed to aid design. One of these, MOSS, is based on superimposing the planned road on a computer ‘map’ of the area. The program helps spot potential difficulties and can calculate various costs. It has been found that use of CAD has meant that designs for new roads have been produced three times more quickly.
It is hoped that in the future CAD programs will, in conjunction with others, be able to produce specifications and estimates of quantities of materials required.
in kitchen design
Kitchen designers can use a program to help a customer to decide on their kitchen layout. The dimensions of the kitchen are entered into the computer. The computer has on file the shapes of various standard units, such as cupboards, cooker, sink, etc. These can be manipulated on the screen until the customer is satisfied with the result. The computer can then be used to work out the cost of the units chosen.
Design of machine parts
Packages are available which allow parts which have been designed separately to be connected together on the screen.
Advantages of CAD over manual design
1 Some types of drawing can be produced more quickly.
2 Top quality drawings can be produced with clear lettering by someone who is not a skilled draughtsman.
3 If a series of similar drawings has to be made this can be done very quickly.
4 The computer can check for obvious errors in drawings.
5 Once a design is stored in the computer, calculations can be done on the data-such as costing, etc.