CAD (Computer Aided Draughting and Design) is much more than drawing lines by electronic means. There are many reasons for using CAD;
The most potent driving force is competition. In order to win business, companies used CAD to produce better designs more quickly and more cheaply than their competitors.
Productivity is much improved by a CAD program enabling you to easily draw polygons, ellipses, multiple parallel lines and multiple parallel curves.
The speed is increased by the use of automatic fillets and chamfers;
The computer ability to "snap" automatically to particular geometric points and features will spread the accurate positioning of linework.
Copy, rotate and mirror facilities are also very handy when drawing symmetrical parts.
Many hatch patterns are supplied with CAD programs. Filling areas in various colours is a requirement in artwork and presentations.
Different style fonts for text are always supplied with any CAD programs.
The possibility of importing different graphic file formats and scanning of material (photographs) into a CAD program is also an asset especially as the image can be manipulated, retouched and animated.
The ability to zoom in and out is an asset when drawing to scale. CAD information is stored in digital form and hence, irrespective of the size of the final printed drawings, it is possible to accurately dimension components automatically.
Another advantage of a CAD system is its ability to store entities, which are frequently used on drawings. Libraries of regularly used parts can be purchased separately or can be created by the draughtsman. For repetitive use on a drawing, a typical item may be retrieved and positioned in seconds, also oriented at any angle to suit particular circumstances.
Using CAD products, assembly drawings can be constructed by inserting existing component drawings onto the assembly drawing and positioning them as required.
Clearance between different components can be measured directly from the drawing and, if required, additional components designed using the assembly as reference.
CAD is very suitable for repetitive and fast documentation where a product is one in a range of sizes. Assume that you manufacture a range of motor driven pumps operating at different pressures. Many parts will be used in different combinations in the range and the computer database documentation is programmed accordingly.
A computerized tender can be sent with the appropriate specification and technical details. On receipt of an order, all of the documentation relating to manufacture, testing, dispatching and invoicing will be available.
Previously, engineers and drafters wasted almost 30% of their time looking for drawings and other documents. Editing drawings to effect revisions and produce updated parts lists is quick and easy using a CAD product.
When you're working on paper and a customer wants to change a drawing, you have to draw it all over again;
In CAD, you make the change immediately and print out a new drawing in minutes, or you can transmit it via E-mail or Internet all over the world instantly.
On paper creating complex geometry often involves a lot of measuring and location of reference points; In CAD it is a breeze and revisions are even simpler.
Many CAD programs include a macro or an add-on programming language that allow customizing it.
Customizing your CAD program to suit your specific needs and implementing your ideas can make your CAD system different from your rivals.
CAD can enable companies to produce better designs that are almost impossible to produce manually and to eliminate dubious options during the conceptual design phase;
For example in area of complex surfaces and Finite-element analysis.
Many CAD systems permit the rapid generation of models of proposed designs as wire-frames. The computer memory stores details of all the geometric data to define each part of the frame. From the dimensions of the components, the computer will calculate surface areas, volumes, weights for different materials, center of gravity, moments of inertia and radii of gyration; it can also use the applicable value for stress and other calculations, which are necessary part of design.
The solid modeling created in CAD can be transferred to a Finite Element Analysis (FEA) program, which will then verify whether the suggested design will be capable of supporting the expected loads.
The biggest contribution of computers to the design process is soft prototyping - the process of creating a 3D-computer model of a design that can be subjected to computer-based testing. Soft prototypes are almost faster and cheaper to built than real prototypes and are often better at their main activity than a real ones; That because model shop prototypes usually use processes and materials very different from those ultimately used for the production version of the product.
The soft prototypes can resemble the final product much more closely than any real material prototypes. Realistic images of the soft prototypes can be used by marketing people to produce sales collateral, manuals and the whole gamut of marketing materials. They can even be used for testing marketing to determine whether the product is worth producing at all. Sale departments use 3D illustrations in brochures and literature for promotional applications.
Presentation programs with rendering models and animation in 3D form a large part of selling and advertising in today competitive market.
CAD will be linked to CAM (Computer Aided Manufacture) whenever possible.
CAD/CAM systems could produce computerized instructions for computerized machine controllers: lathes, mills, machining centers, turret punches, welding equipment, automated assemblies, etc.
A typical design involves producing part drawings in a CAD program right up to completion of design and making layers of the geometry required for the CAM processing software.
The description of part created in a CAD program is translated into an appropriate format, such as DXF or IGES, and then loaded into the CAM program which are used then to create tool paths that trace this description.
This path can be edited and combined with other tool path files where necessary and the combined forms a complete program for the machine tool to manufacture the part.
The resulting NC program can be exported back into the CAD system to produce a simulated backplot of the toolpath or imported into a solid modeling NC program to produce a computer model for checking before manufacture.

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