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While working with computer aided design, the first thing which strikes our mind that how we implement our pencil and scale design in computer technology. It's quite obvious that we don't use pencil, scale, and rubber in a computer to draw designs. Well, losing any of these tools results to an incomplete design, but not so in CAD.
CAD is an electronic tool that enables us to make a quick an accurate design with the use of software in the computer. With the help of this software we can easily make drawings just by clicking the buttons of a keyboard. It has number of advantages over simple handmade designs, such as CAD drawings are neat, clean and highly presentable. Electronic drawings can be modified quite easily can be presented in a variety of formats.
To own a CAD program was not as easy as it is now. A decade ago CAD's price was too high to be purchased by common engineer designers. Only a few professionals could afford it. In recent years, however, computer prices have decreased significantly and more professionals are taking advantage of CAD.
There are several types of CAD programs available in industries nowadays. Some are specially mend for general drawing work while others are dedicated on specific engineering applications. There are programs that enable us to perform 2D drawings, 3D drawings, rendering, shading, engineering calculations, space planning, structural design, project management, etc.
COMPUETR AIDED MANUFACTURING (CAM)
CAD has now extended its division to yet another engineering branch called computer aided manufacturing. CAM is a common method for manufacturing used by large corporations. CAD and manufacturing program are often integrated into one system called CAD-CAM. These systems import CAD drawings into CAM programs to automate the manufacturing process.
It's like suppose an engineer draws a car design using CAD. The CAD drawing is brought into a computer aided engineering program for engineering analysis. When the design is finalized, the drawing is brought into a CAD-CAM system that uses numerical data from the CAD drawing for actual manufacturing.
CAD HARDWARE AND SOFTWARE
There are two parts of a computer system, hardware and software and here CAD system is no exception. Computer hardware is the physical components of the computer such as central processing unit, monitor and plotter. Computer software is the program that determines the application of a system. Here we will be more concern with the software thing rather than going into detail study of the hardware system which is beyond the need of the topic.
A CAD program contains thousands of programs that enable us to perform specific drawing tasks. A task may involve drawing an object, editing an existing drawing, display a view of the drawing, printing or saving it, or controlling any other operations of the computer. The functions contain a number of commands that enable us to specify exactly what we want to do and how we want to do it.
The functions as mentioned above are organized into modules that provide an easy access to all commands. The program is further divided into modules such as draw, edit, data, output, function control, data storage and management. A program may also have a number of specialized functions such as layers, database and 3D. let's go in detail through the CAD modules:
Data storage and management
The drawing function module enables us to access to all drawing function of CAD. Whenever we need to draw something, this module is used. The draw module enable us to draw circles, ellipses, text, lines, arcs, borders, symbols, dimensions and many other drawing components.
Draw is CAD most frequently used module because all drawing work is accomplished using it.
The edit module lets us to change existing drawing elements and manipulate them in a number of ways. We can move, copy or erase drawing components. We can also change the dimensions of the drawing by simply enlarging or reducing the size. We can change the color and line type of drawing components. We can also change the size and style of text and dimensions, as well as edit a dimension to show different units of measurement.
The data output module enables us to display drawings on the screen and then print them on paper. There are two separate sets of functions that help accomplish these:
View display function
The view-display functions allow us to display different views of a drawing on the screen. These functions are used quite often, whenever we need to edit or draw something, we need to focus on that portion of the drawing. With the help of view display functions, we can zoom in or out in a specific portion of the drawing.
The print and plot functions allows us to print drawings using the printer or a plotter. We can control many aspects of printing and plotting. We can print the same drawing in different sizes by applying the appropriate scale factor. We can plot the drawings with specific color, pen thickness, and line types.
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BEGINNING TO DRAW
THE COORDINATE SYSTEM (2D system)
The coordinate system is another method to locate the exact address of the point in space (drawing) and it also enables to locate points by specifying distances from a fixed reference point. You can locate a point by giving its distances in the x-axis and y-axis direction, measuring along an angle.
The coordinate system is available when a function requires data input in the form of point locations. We may use it while drawing, editing or any time we need to locate a point. The most common coordinate systems are as follows:
Cartesian coordinates, also known as rectangular system of measurement which simply means that whenever we locate a point in the system it form a rectangle while tracing it, with vertical and horizontal component taking into account. The horizontal values, X- coordinates, are measured along X-axis. The vertical values, called Y-coordinates. The meeting point of x-axis and y-axis is called the origin (0, 0). The positive X values are measured to the right and the positive Y values are measured above the origin point. The negative X and Y values are measured to the left and below respectively.
Polar coordinates allows us to define a point by specifying the distance and the direction from given point. This mode of measurement is quite helpful; in working with the angles. To draw a line at an angle, we need to specify how long a line we want to draw and specify the angle.
Multiple parallel lines
Arcs and circles
Ellipses and elliptical arcs
THE EDIT FUNCTIONS
The edit module gives a great flexibility in changing CAD drawings. If we were to draw using only drawing functions of CAD, it would probably take same amount of time as it would on a drawing board. But CAD's editing functions made CAD dynamic tool that results in significant time savings.
The following are the basic capabilities of the edit module:
Erasing drawing objects
Moving drawing objects
Copying drawing objects
Changing the appearance of the drawing objects
SELECTING OBJECTS TO EDIT
In order to apply any of the edit functions, we need to first select the drawing objects that need to be edited. Following are the basic methods for selecting drawing objects for editing.
Selecting objects one by one
Selecting objects by enclosing them in a window
Selecting objects using selection filters
Making groups of selected objects
ERASING DRAWING OBJECTS
CAD provides a fast, accurate and convenient means of erasing drawings. Once we have entered the erase command, you are in the erase mode; any objects we select now will be instantly erased. We can use any method described above to select the object.
MOVING DRAWING OBJECTS
CAD allows us to move drawing objects within a drawing in a convenient manner. We can simply rearrange the existing drawing objects, as we like.
The first step is to select the drawing which we have to move by just highlighting it. The second step is to indicate a base point. Then we indicate the destination point where we want to place the drawing.
COPYING DRAWING OBJECTS
The software also allows us to make quick copies of an existing copying. First we just select the object to be copied then we use the copy function and place the object as indicated earlier.
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The 3D capabilities allow us to draw pictorial views such as isometrics, oblique views and perspectives. The views drawn with CAD provide absolute correctness and are lot flexible in terms of editing and display. We can rotate a model on screen just like an actual model, and display views from different angles. Engineers often use this method which is more flexible to view the design in an easier way to decide whether it will work or not.
PICTORIAL VIEW CONCEPT
It is quite difficult to represent a 3D drawing in a 2D mode such as computer screen of a drawing paper. This is only possible through optical illusion.
The views that we draw on 2D media are 2D representation of 3D images. We use same the concept of drawing 3D as we draw in paper using coordinate system in 2D.
Oblique views are the simplest form of the pictorial views that can be drawn by using parallel projection lines from an elevation. There are standards established to draw oblique views at specific angles. A common standard used is to draw an oblique view by projecting lines at 45. To measure depth along a 45 angle, we need to scale it down by ¾ or ½ of the actual distance. For example, if the actual depth of the object is 10", we measure 9" or 6". The ¾ scale factor creates an effect as if the object is viewed from a slightly higher angle than the ½ scale factor.
Isometric views are more realistic than oblique views. The object appears to be tilted at a 30°€ angle on both sides. An isometric is defined by three planes called isoplanes: top isoplane, right isoplane and left isoplane.
On a drawing board, we use 30° triangle to draw the three planes of an isometric. The same principle is applied in CAD with the help of various functions. The right isoplane is drawn with the 30°€ and 90° angles, the left isoplane with 150°€ and 90° and the top plane with 30°€ and 150° angles. All distances are measured using 1:1 scale i.e. actual size, to show depth, width and height. Polar coordinates are particularly helpful to measure distances along an angle.
THE 3D COORDINATES SYSTEM
3D coordinates system contains three dimensions, which is shown with the help of three axes: X, Y and Z. The axes meet at the point in the shape of a tripod. This point is called the origin point, which is the (0, 0, 0) location of all coordinates.
The three axes also form imaginary planes: XY plane, XZ plane and YZ plane. All these planes are perpendicular to each other. This generates a perfect space where we can see a drawing 3D space by moving it up and down and sidewise in any angle which we like to.
The 3D coordinates can be entered using the following formats:
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We can rotate a 3D model on the screen and display different views by specifying an exact viewpoint. The viewpoint simply means the position of the camera from which the view is to be taken.
There are two main protocols used to display views:
View coordinate geometry
Object coordinate geometry
We are now going into more detail about the point's mentioned above.
VIEW COORDINATE GEOMETRY
In this case it is assumed that the camera (viewpoint) remains stationary and the 3D model is rotated to display a desired view. The model can be rotated around the X, Y or Z axis. We need to specify around which axis the rotation will take place and by how much degree.
OBJECT COORDINATE GEOMETRY
This viewpoint is just the opposite of "view coordinate geometry" i.e. the model remains stationary and the camera (viewpoint) is moved to a display a desired view. We can use any of the coordinate methods to specify an exact viewpoint.
DISPLAYING ISOMETRIC VIEWS
To display an isometric view we need to specify the direction from which the view is to be taken. The most convenient way is to indicate the direction with the help of spherical coordinates. We need to specify two angles: an angle in XY plane (longitude) and an angle from the XY plane (latitude). The longitude determines the orientation in the XY plane and the latitude determines the height of the viewpoint.
3D DRAWING AID FUNCTIONS
The common 3D drawing -aid functions are as follows:
3D ready-made shapes
Shading and rendering
3D READY-MADE SHAPES
CAD allows us to draw various types of ready-made shapes in a few simple steps. For example, to draw a cube, we don't really need to draw the cube by drawing all the lines or 3D faces of each of the sides. We can just instantly draw a cube by specifying its dimensions.
Similarly we can draw number of commonly used geometrical shapes just by specifying their shape and size.
EXTRUDING OBJECTS IN THE LINEAR DIRECTION
Cad allows carving or taking out the desire 2D geometrical figure from 3D shapes. For example, we can extrude a rectangle from a cuboids or a triangle from a prism. When we use the linear extrusion function, we are prompted to select the objects to be extruded and specify the direction of the extrusion (axis of the extrusion).
SHADING AND RENDERING
There is a number of shading and rendering programs available that can be used to make 3D drawings very realistic. These programs allow us to create colors, shades and shadows exactly as they would appear in a picture. These programs are quite large and complex and require powerful computer hardware. With the help of rendering programs, you can specify a number of shading and rendering parameters and create a 3D scene. we can assign colors and textures to different surfaces of a model.
COMPUTER AIDED MANUFACTURING (CAM)
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DEFINATION: Computer-Aided Manufacturing (CAM) is the use of computer software and hardware in the translation of computer-aided design models into manufacturing instructions for numerical controlled machine tools.
APPLICATIONS OF COMPUTER-AIDED MANUFACTURING
The field of computer aided design has steadily advanced over the past four decades to the stage at which conceptual designs for new products can be made entirely within the framework of CAD software. From the development of the basic design to the Bill of Materials necessary to manufacture the product there is no requirement at any stage of the process to build physical prototypes.
Computer-Aided Manufacturing takes this one step further by bridging the gap between the conceptual design and the manufacturing of the finished product. Whereas in the past it would be necessary for design developed using CAD software to be manually converted into a drafted paper drawing detailing instructions for its manufacture, Computer-Aided Manufacturing software allows data from CAD software to be converted directly into a set of manufacturing instructions.
CAM software converts 3D models generated in CAD into a set of basic operating instructions written in G-Code. G-code is a programming language that can be understood by numerical controlled machine tools - essentially industrial robots - and the G-code can instruct the machine tool to manufacture a large number of items with perfect precision and faith to the CAD design.
Modern numerical controlled machine tools can be linked into a 'cell', a collection of tools that each performs a specified task in the manufacture of a product. The product is passed along the cell in the manner of a production line, with each machine tool (i.e. welding and milling machines, drills, lathes etc.) performing a single step of the process.
For the sake of convenience, a single computer 'controller' can drive all of the tools in a single cell. G-code instructions can be fed to this controller and then left to run the cell with minimal input from human supervisors.
BENEFITS OF COMPUTER-AIDED MANUFACTURING
While undesirable for factory workers, the ideal state of affairs for manufacturers is an entirely automated manufacturing process. In conjunction with computer-aided design, computer-aided manufacturing enables manufacturers to reduce the costs of producing goods by minimizing the involvement of human operators.
In addition to lower running costs there are several additional benefits to using CAM software. By removing the need to translate CAD models into manufacturing instructions through paper drafts it enables manufactures to make quick alterations to the product design, feeding updated instructions to the machine tools and seeing instant results.
In addition, many CAM software packages have the ability to manage simple tasks such as the re-ordering of parts, further minimizing human involvement. Though all numerical controlled machine tools have the ability to sense errors and automatically shut down, many can actually send a message to their human operators via mobile phones or e-mail, informing them of the problem and awaiting further instructions.
All in all, CAM software represents a continuation of the trend to make manufacturing entirely automated. While CAD removed the need to retain a team of drafters to design new products, CAM removes the need for skilled and unskilled factory workers. All of these developments result in lower operational costs, lower end product prices and increased profits for manufacturers.
PROBLEMS WITH COMPUTER AIDED MANUFACTURING
Unfortunately, there are several limitations of computer-aided manufacturing. Obviously, setting up the infrastructure to begin with can be extremely expensive. Computer-aided manufacturing requires not only the numerical controlled machine tools themselves but also an extensive suite of CAD/CAM software and hardware to develop the design models and convert them into manufacturing instructions - as well as trained operatives to run them.
Additionally, the field of computer-aided management is fraught with inconsistency. While all numerical controlled machine tools operate using G-code, there is no universally used standard for the code itself. Since there is such a wide variety of machine tools that use the code it tends to be the case that manufacturers create their own bespoke codes to operate their machinery.
While this lack of standardization may not be a problem in itself, it can become a problem when the time comes to convert 3D CAD designs into G-code. CAD systems tend to store data in their own proprietary format (in the same way that word processor applications do), so it can often be a challenge to transfer data from CAD to CAM software and then into whatever form of G-code the manufacturer employs.