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Note for Computer Aided Design and Manufacturing - CADM By ANNA SUPERKINGS

  • Computer Aided Design and Manufacturing - CADM
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  • Mechanical Engineering
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Anna Superkings
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Some large organizations have invested in Rapid Prototyping process. In this process, the part is created by a CAD package and downloaded into the rapid prototyping machine; the machine immediately manufactures the part, using a plastic material. This is a good example of concurrent engineering, sometimes referred as Art to Part concept. CAD Hardware There are basically two types of devices that constitute CAD hardware: a) Input devices, and b) Output devices. A brief description follows. Input Devices These are the devices that we use for communicating with computer, and providing our input in the form of text and graphics. The text input is mainly provided through keyboard. For graphic input, there are several devices available and used according to the work environment. A brief description of these devices is given here. Mouse: This is a potentiometric device, which contains several variable resistors that send signals to the computer. The functions of a mouse include locating a point on the screen, sketching, dragging an object, entering values, accepting a software command, etc. Joystick and trackballs are analogous to a mouse device, and operate on the same principle. Digitizers: Digitizers are used to trace a sketch or other 2-D entities by moving a cursor over a flat surface (which contains the sketch). The position of the cursor provides a feedback to the computer connected with the device. There are electrical wires embedded in orthogonal directions that receive and pass signals between the device and the computer. The device is basically a free moving puck or pen shaped stylus, connected to a tablet. Light Pens: Lockheed’s CADAM software utilized this device to carry out the graphic input. A light pen looks like a pen and contains a photocell, which emits an electronic signal. When the pen is pointed at the monitor screen, it senses light, which is

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converted to a signal. The signal is sent to the computer, for determination of the exact location of the pen on the monitor screen. Touch Sensitive Screens: This device is embedded in the monitor screens, usually, in the form of an overlay. The screen senses the physical contact of the user. The new generation of the Laptop computers is a good example of this device. Other Graphic Input Devices: In addition to the devices described above, some CAD software will accept input via Image Scanners, which can copy a drawing or schematic with a camera and light beam assembly and convert it into a pictorial database. The devices just described are, in general, independent of the CAD package being used. All commercial CAD software packages contain the device drivers for the most commonly used input devices. The device drivers facilitate a smooth interaction between our input, the software, and the computer. An input device is evaluated on the basis of the following factors: • Resolution • Accuracy • Repeatability • Linearity Output Devices After creating a CAD model, we often need a hard copy, using an output device. Plotters and printers are used for this purpose. A plotter is often used to produce large size drawings and assemblies, where as, a laser jet printer is adequate to provide a 3-D view of a model. Most CAD software require a plotter for producing a shaded or a rendered view. CAD Software CAD software is written in FORTRAN and C languages. FORTRAN provides the number crunching, where as, C language provides the visual images. Early CAD packages were turnkey systems, i.e., the CAD packages were sold as an integrated

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software and hardware package, with no flexibility for using second vendor hardware (1970s and 80s). These systems were based on 16-bit word, and were incapable of networking. The modern CAD software utilizes the open architecture system, i.e., software vendors do not design and manufacture their own hardware. Third party software can be used to augment the basic CAD package. Most popular CAD package will facilitate integration of the Finite Element Analysis and other CAD software from more than one vendor. For example, IDEAS preprocessor can work with almost all the FEA packages for pre and post analyses. Networking is an important consideration in applications of CAD software. A model created by one engineer must be readily accessible to others in an organization, which is linked by a LAN or other means. The designer, analyst, management, marketing, vendor, and others generally share a model. This is the concurrent engineering in action, mentioned earlier. CAD Platform In general, we can run CAD software on three different CAD platforms: Mainframe, Workstation, and PC. When the CAD programs first became available, they could only be run on a mainframe computer. However, as the PCs have become faster and cheaper, almost all the CAD vendors have introduced a version of their CAD software that will effectively run on a Pentium or higher computer. Currently, the most popular platforms are PCs and Workstations. Popularity of Workstations stems from their ability to network easily with other computers, and also, due to their large memory storage capability. However, PC platform is still the most preferred medium for most engineers. Increasing popularity of the PC platform can be attributed to several factors, including, total user control, the speed, capability of storing large memory, ease of hardware upgrading and maintenance, and the overall reasonable cost.

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CAD PLATFORMS MAINFRAME WORKSTATIONS PCs Large Data storage Medium size data storage Limited data storage Networked Networked Can be networked Expensive Relatively inexpensive Inexpensive Need interface language Runs on Unix Run on MS-Windows No user control No user control User controlled Good for Large corporations Good for small companies Good for all users

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