1. STUDY ON COMPUTER AIDED DRAFTING AND SOLID MODELING

Drawing has been an integral part of engineering for many years. It is the link between the engineering design and manufacturing. Information regarding the size, shape, dimensions, tolerances and other manufacturing/construction details are quickly communicated to the production construction personnel in the form of drawings prepared according to prescribed drafting standards. These drafting standards are specified for understanding and interpreting the drawings in the same way by various designers and manufacturing personnel. An engineering drawing may be prepared by means of conventional tools such as drafting board, pencil or ink on the tracing paper or alternatively, with the aid of a computer. The method of preparing the drawings by computers is known as Computer Aided Drafting (CAD) or Computer Aided Design and Drafting (CADD).

Concept of computer aided drafting

Computer aided drafting is the creation, storage and manipulation of models of objects and their pictures via computers. Interactive computer graphics is the important case in which a user dynamically controls the picture content, format, size or colours on a video display by means of interaction devices such as key board, mouse etc. Graphics display on a monitor can be converted into hard copy with a plotter or a printer. In computer aided design interactive graphics is used to design components and systems of civil, mechanical, and electronic devices. These systems include structures (buildings. automobile bodies. airplanes and ships, chemical and power plants), optical systems, computer networks etc. The emphasis in computer aided drafting is only on producing precise drawings of components and assemblies.

Advantages and Disadvantages of CAD

A CAD system should be thought of as a tool at your disposal for making drawings. It is a tool used to make the drawings at a higher speed and more accurately. Drawings can be revised and changed much more quickly and accurately than by hand. The storage of drawings is very easy. Employees of an organization  using CAD are likely to follow a set of company standards as they produce drawings. These drawings accumulate in the database which can be utilized for quick accession by all other authorized personnel and can be used for manufacturing.  Hence it is economically sound to let a drawing be prepared by a computer.

There are some negative aspects of computer aided drafting. At certain times you may not be able to use the system due to its overload by simultaneous requests for use. It also may be due to a component being out of service. This may last for several hours or even days until service person can repair the system. This is called as "down-time". The initial investment on a CAD system is high. As the computers are faster in makings the drawings, the manpower requirement automatically comes down and it may lead to social problems.

HARDWARE AND SOFTWARE FOR CAD

The CAD systems may be categorised into two groups

a)  The workstation, and

b)  PC based systems.

The work-station consists of a high resolution monitor, graphics accelerator for quick display of the pictures, facility to work with multiple windows, higher Random Access Memory (RAM) and hard disk storage. The PC is relatively a slow system with lesser memory and display capabilities.

A CAD system consists of a central processing unit, numeric co-processor, 1 to 2 GB RAM. a hard disk drive and a CD drive, a cache memory, a high-resolution monitor , a colour graphics card, a mouse, digitiser and a plotter.

Graphical Input Devices

The main function of graphic input device, sometimes called as graphic interactive device is to specify points and lines usually by controlling the position of a set of cursor cross-hairs on the screen. However, some input devices are touched directly to the screen surface for a more direct interaction. Graphic input devices are also used to select the menu items and to manipulate parts of the constructed images on the screen. Tablet or Digitiser, Mouse, Track Ball and Keyboard.

Output Devices               

The CRT screen, plotter, and printers are the commonly used graphical output devices. The CRT screen can be used only for the display of the drawings. Plotters and printers are used to take the output on a paper (hard copy).

Software

Software is a set of written instructions (programs) that are used to execute a job by a computer system. They are written in a variety of languages. A drafter or a designer will normally use the programs that are already developed and loaded into the system. The software written for a particular class of problems is called as package. The CAD software includes a number of sets of instructions for various purposes such as drawing lines, circles, and dimensioning, sectioning etc. By an appropriate command, a particular segment of the program is invoked and executed to meet a specific requirement. Some of the commercially available softwares for computer aided drafting are Auto CAD, Vision-Designer 2D, Draft Sight.

SOLID MODELING

A solid modeling system is usually an interactive computer graphics system that is intended to create true three-dimensional components and assemblies. Recent advances in CAD software, computers, and graphical displays have made it possible to use solid representations of components being considered in the design process. These solid models can be employed innumerous ways.

Advantages of Solid Modeling

A realistic visual display: By producing a shaded visible surface image of the solid, solid modeling allows a designer to see exactly what has been created.

Easy to deal with different views: Once a part has been created, we have the ability to rotate, shade, section, or produce almost any view required by a designer.

Single associated model database: The solid modeler provides the only database suitable for all CAD operations. Almost all information needed for part generation is contained in the solid model. The algorithm should be able to ensure that it represents physically possible shape that is complete and unambiguous Applications. e.g., automatic generation of a mesh for a finite element analysis