CAD and CAM software packages are
closely related to one another. In fact, they share the first two
thirds of their respective acronyms: CAD / CAM stand for Computer-
Aided Design and Computer-Aided Manufacturing. CAD programs
typically are used to draw the part being developed. CAM programs are
used for generating the toolpath for the CNC machine that will cut
the part. The boundary between the two programs is often blurred as
CAM programs often have drawing capabilities and CAD programs often
have “plug in” programs, or added optional features, that allow them
to generate toolpaths.
CAD/CAM programs get installed on a
computer and, contrary to popular belief, learning to navigate the
various functions is not rocket science. At first, the different
file formats and industry terms can be overwhelming. The good news
is that with each successive completion of the cycle, from drawing,
to toolpath, to cutting a part, the method becomes more familiar
and, subsequently, easier to reproduce.
CAD Software Creates Drawings in 2D
or 3D Formats.
Traditionally, CAD programs were
primarily for engineering drawings and drafting. Its usefulness has
evolved beyond the tasks of precise dimensioning. Expanded
capabilities now include realistic renderings, dynamic analysis of
moving elements and various finite element engineering analyses.
A few standard 2D formats include: .DWG,
.DXF, and .EPS. 2D CAD files typically share the same graphical
element in that they are vector-based. Vector graphics consist of
lines, arcs and other elements, in contrast to the pixels that make
up a raster file, like a digital photo. Vector graphics define these
lines, arcs and polylines with simple mathematical equations. 3D CAD
files are similar, but much more complex. Hundreds and even
thousands of facets are calculated when creating 3D CAD files such
as, .STL, .3DS, and .RAW. This is just a sampling of some of the
more standard formats specific to different CAD programs. Other
formats, such as .IGS, define 3D surfaces and lines using complex
parametric equations. CAM software helps convert and manipulate a
CAD drawing into a toolpath. CAM software imports a CAD drawing and
saves it in its own native file format. There are some programs that
have both CAD and CAM capabilities in one software package, which is
a convenient feature, but the transfer of files between two separate
and standard CAD / CAM programs is not complicated. In fact, most
CAD and CAM programs have built-in capabilities to both import and
export several file formats.
The toolpath generated by most CAM
programs is in a standard manufacturing programming language called
G- Code. Consisting of “G” and “M” codes or commands, a G- Code file
guides the path of the cutter through the material by outputting
code for linear or circular motions. CAM software also embeds
parameters into the G-Code, such as tool width, toolpath position,
cut depth, feeds and speeds, and others. These CAM parameters become
increasingly important as the files being cut become more complex.
For instance, a 2D part only requires that the depth of the cut be
specified along with the path once the tool reaches the desired
depth. When a 3D part is being carved, the full program description
can consist of hundreds of thousands of G-Code commands specifying
the toolpath. The program for 3D parts usually consists of very
small line segments that form the desired shape.
Another necessary step that CAM packages
complete before outputting a toolpath is referred to as
post-processing. This post-processing (or posting) customizes the
G-Code commands and parameters to communicate with a specific CNC
machine. The G-Codes and functions often remain the same, but
posting serves to format the syntax of the file to meet with the
protocol of a given CNC machine’s controller. Because of the great
deal of freedom found in the international standards for G-Code,
individual controllers may require different formats. The
post-processing customizes the format to the specific controller
being used.
The scope of CNC machining applications
is so vast, that a good CNC Software Suite (CAD / CAM) needs to
accommodate a wide range of machining methods covering several
different markets.
Geometrics
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