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CAD/CAM softwares - Short notes series for Mechanical Engineers

Continuing the short notes series for GATE and other engineering exams for Mechanical Engineers, from plant layouts and automation types, we move to CAD/CAM softwares in this article. 

What is a software?

The software is an interactive program written in a standrad programming language such as FORTRAN or C. A CAD/CAM system has different categories of software as follows:

  1. Operating system (OS)
  2. Graphics software
  3. Application software
  4. Programming support software

The DBS (database structure) and DBMS (database management system) of the software determines its quality, speed and ease of information retrieval. 

Let us discuss more on the application software, as the OS and Graphics software is very easy to understand. 

Application software.

The end goal of the user is not just to create a geometric model with the graphics software. The ultimate goal is to use the geometric model for design analysis and manufacturing. The application software helps in mass property calculations, assembly analysis, FEA, mechanicsm analysis, sheet metal design and animation techniques. Let us now look at an examples.

Example: Thermomechanical coupling analysis of disc braking system

In this example we take an example involving full contact disc braking system for heavy duty trucks. The figure below shows the mesh used for solid and thermal analysis. 

Friction between the disc and the stationary components leads to local heat generation which causes non uniform therma expansion, which results in the alteration of the contact and conditions of friction. The figure below shows the variation of temperature variation during braking. 

 

The figure below shows the variation of the contact pressure between the upper friction plate and the piston at different times which shows that with a significant change in contact pressure distribution occurs as the brake system heats up, leading to more severe contact conditions at the inner surface. 

Graphics standards

There are several CAD/CAM softwares in the market. No one signle CAD/CAM package is suitable for all the CAD/CAM users, so in general the geometric modelling is done using the CAD software, then the geometric model is imported to the CAM software provided that the CAD and CAM softwares have the same syntax. 

A good CAD/CAM package includes good softwares and a compatible hardware. The source code of the graphics software is embedded with several subroutine calls. This makes the graphics software hardware dependent. Some graphics requirements are given below:

  1. Software portability: This avoids the hardware dependence of the software.
  2. Image data portability: Information and storage of images should be independent of different graphics devices. 
  3. Text data portability: The text associated with the graphics should be independent of different I/O devices.
  4. Model database portability: Transporting of design and manufacturing data from one application software to another should be simple and economical. 

Based on the needs given above, the graphics systems standards are as follows:

  1. GKS (Graphics Kernel System): It is an ANSI and ISO standard. It interfaces the application program with graphics support package.
  2. IGES (Initial graphics exchange specification): It is an ANSI standard. It enables an exchange of model DB among CAD/CAM software. 
  3. PHIGS (Programmer's hierarchical interactive graphics system): It supports workstattions and their related CAD/CAM applications like 3D modelling of geometry, segmentation and dynamic display.
  4. CGM (Computer graphics metafile): It defines functions needed to describe an image. Such description can be stored or transported from one graphics device to another. 
  5. CGII (Computer graphics interface): It is designed to interface plotters to GKS or PHIGS. It is the lowest deivce independent interface in a graphics system

We hope you have gotr an idea about the main components of CAD/CAM softwares in this article. In the article, we discuss about the Interactive computer graphics like Raster scan graphics, line drawing algorithm etc. 

 

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