- What does CAD-CAM really mean?
- CAD-CAM stands for Computer Aided Design - Computer Aided
Manufacture.
These days, CAD is usually performed with 3D or Solid Modelling
software that allows the designer to rotate the design on the screen to
view it from any angle and to see inside the "model" as it exists in
the computer. In the "olden days", CAD was primarily 2D, just like
drawing on paper, except the computer helped automate the drawing
process and modifications were still easier than on paper.
A 3D solid model is built up of simple and complex geometric shapes
such as blocks, cylinders, bevels, curves, holes, etc. and the these
primary shapes are then modified to meet the needs of the design. While
a conceptual design can start without exact dimensions to permit the
designer to explore aesthetics and proportions, eventually it is
necessary to start assigning dimensions (sizes) to the various elements
in the model. This is because the CAM software needs exact dimensions
with which to work.
The CAM software permits the user to take the exact solid model that
has been designed and then define how it will be machined. These steps
are also shown visually in the Case Study under Services/Machining and
Prototyping (Link to other page?) Often a product will consist of many
components and each component has to be manufactured individually,
prior to assembly.
Taking the part's solid model, the CAM software allows the user to
select from the available machine tools such as flat end mills, ball
end mills, drills, thread taps etc. and in order from large to small,
generally a part will be machined from a block of material starting
with roughing operations (to achieve an approximate shape) and moving
to finishing operations as the tools get smaller for the finer details.
If a part requires machining from various sides, then fixtures will
also be required to hold the parts precisely for subsequent operations.
Sometimes a part can be rotated while on the mill (this is called 4th
axis machining) but it all depends on the shape and machining
requirements for the part. The final step of the CAM process is to
generate the tool paths in G-Code which the milling machine's control
then interprets as a sequence of precise moves and feeds in 3 axes.
The CAM software takes each tool's shape attributes into account when
calculating the tool path. Many CAM programs also provide a visual
simulator to assist with the tool path generation and enable the user
to watch virtual machining being performed in the computer, prior to
the actual machining.
- What is G-Code?
- G-Code is an ANSI standard for machine tool control. It can be
written by hand and entered into an editor or it can be computer
generated for more complicated parts. Typically, the final step in the
CAM process it to generate the G-Code file for a specific machine.
Typically the output is tailored to a machine's unique requirements via
a Post Processor. This allows a general purpose CAM program to provide
suitable code for virtually every CNC machine manufactured in the last
30 years!
The code sample below shows what G-Code looks like:
(WinGcnc8 - Post Processor 09/09/04 - First Mill)
N100 G00 X0 Y0 Z0 (Go to the starting point)
N102 (Horizontal Roughing)
N103 M06 T1 (Load next Tool)
N104 M08 (Start Spindle)
N105 M10 (Turn on Mist Coolant)
N106 G00 X-11.438 Y36.167 Z4.862
N107 G01 F500
N108 Z-0.59
N109 F800
N110 X-9.688 Y38.036
N111 X-10.588 Y38.8
N112 X-11.44 Y39.879
N113 X-11.442 Y43.031
N114 X-11.254 Y42.647
The code is quite easy to read and mostly consists of a series "G"
words (or codes) and X, Y, Z coordinates that tell the machine where to
move. Feedrates are preceded with an "F", while tool changes are
preceded by an "M" code and a "T", followed by the next tool (number)
to be used. The "M" codes are usually machine specific. The CAM program
generates this code and the coordinates already take into account, the
changing sizes (diameters, lengths, and shapes) of each tool. Files can
be just several lines or many thousands of lines, according to the
complexity of the part being made. Historically, each line is called a
"block".
- What does Design for Manufacture really mean?
- Design for Manufacture or "DFM" simply means taking into account
"how" something is going to be made during the design process.
Historically, designers conceived great designs with little regard to
how the part or product would eventually be made. The production was
usually left to another group of production engineers. This approach
generally added time delays and added costs in getting a product to
market. DFM was the formal recognition that there was "life after
design". Now a product designer who has adopted DFM will often have
familiarity with production and assembly techniques and will consult
with production staff as well as service or maintenance personnel -
during the design phase. Designing a product using DFM techniques
usually ensures a much shorter overall time to market and a smoother
transition into production. Often product support costs can also be
reduced. It really boils down to more open communication between
departments throughout the design and production .