CAD/CAM

O BJECTIVES :

1. Become familiar with common CAD/CAM capabilities.

2. Become familiar with CAD/CAM software Graphical User Interface.

3. Learn terminology specific to CAD/CAM.

4. Learn Geometry Creation techniques common to CAD/CAM.

5. Learn how to use the CAD/CAM software to create tool path and CNC program code.

W HAT IS CAD/CAM?

Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) utilizes computers to design drawings of part feature boundaries in order to develop cutting tool path and CNC machine code (a part program). By using CAM, the cutting tools and all data specific to them are defined and then tool paths are identified by selecting drawing geometry that determine how they are going to be used for cutting. Drawing in CAD is simply constructing a drawing using lines, arcs, circles and points, and positioning them relative to each other on the screen. One of the major benefits of CAD/CAM is the time saved. It is much more efficient than writing CNC code line-by-line.  

CAD/CAM is now the conventional method of creating mechanical drawings and Computer Numerical Control (CNC) programs for machine tools. CAD is the standard throughout the world for generating engineering drawings. The personal computer has become a powerful tool used by manufacturing for these and many other purposes. Engineers seldom use the drafting board to design their projects, they now use computers extensively. Designers can create the drawings needed in other CAD programs and share them electronically with the manufacturing department. Drawings are   onverted to a common file format, such as the Initial Graphics Exchange Specification (IGES) or Drawing Exchange Format (DXF). There have been huge advancements in the design field and Solid Models have become prevalent over two-dimensional drawings. Many CAM systems will import the Solid Model files directly for tool path creation. Then, the manufacturing engineer can create tool path and assign cutting tool information relative to the desired results. CAD is limited, in nature, to the generation of engineering drawings, while CAD/CAM combines both design and manufacturing capabilities. When using CAD/CAM, the drawing may be created from scratch or imported from a CAD program. It is not necessary to have the drawing dimensioned for this operation, but the full scale of the part is required. The CAD/CAM operator assigns the tools and their order of usage while creating the tool path. There are many CAD/CAM programs on the market today. The most popular ones are easy to use, have a solid background and reliability. To make good use of this computing power, it is important to fully understand the machining processes to be carried out. Just as CNC doesn’t change the actual machining, the same is true of CAD/CAM for programming. Remember, the overall objective of CAD/CAM is to generate tool path for a CNC machine in the form of a CNC program. It is imperative to have a full understanding of the rectangular and polar coordinate systems. It is also necessary to have a complete understanding of cutting tool selection, speeds and feeds. Nearly all CAD/CAM programs will automatically develop speed and feeds data based on the tool and work material selection, however, adjustments are frequently necessary. This data base of information can and should be updated to match the requirements for your shop for the best results.

When constructing the part geometry, consider the type of machining operation. For instance, if the desired result is to drill a hole using a standard drill, construction of only the point that represents the center coordinate location of the hole is necessary.

In this book, the most recent versions of Mastercam and EdgeCAM are featured as CAD/CAM software examples and some of the programs created in this text have been verified using the simulation capabilities inherent to these software. This chapter is only intended as an introduction to CAD/CAM. Many other CAD/CAM programs use similar techniques to accomplish the same result.

The following is a short description of the process of using Mastercam to create geometry, tool path and program code for CNC machines: