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CNC stands for Computer Numerical Control and has been
around since the early 1970's. Prior to this, it was called NC, for
Numerical Control. (In the early 1970's computers were introduced to these
A CNC machine is a Stand-alone machines controlled by a computer. Today,
computer numerical control (CNC) machines are found almost everywhere, from
small job shops in rural communities to big companies in large urban areas.
There is hardly a facet of manufacturing that is not in some way touched by
these innovative machine tools. Everyone involved in the manufacturing
environment should be well aware of what is possible with these
sophisticated machine tools. The design engineer must possess enough
knowledge of CNC to perfect dimensioning and tolerancing techniques for
workpieces to be machined on CNC machines. The tool engineer must understand
CNC in order to design fixtures and cutting tools for use with CNC machines.
Quality control people should understand the CNC machine tools used within
their company in order to plan quality control and statistical process
control accordingly. Production control personnel should be abreast of their
company's CNC technology in order to make realistic production schedules.
CNC programmers, setup people, operators, and others working directly with
the CNC equipment must have an extremely good understanding of CNC.
CNC Machine Tools
The specific application for CNC machines vary from
one machine type to another, all forms of CNC have common benefits, such as:
All forms of CNC machine tools is improved automation. The operator
intervention related to producing workpieces can be reduced or eliminated.
Many CNC machines can run unattended during their entire machining cycle,
freeing the operator to do other tasks. This gives the CNC user several side
benefits including reduced operator fatigue, fewer mistakes caused by human
error, and consistent and predictable machining time for each workpiece.
Since the machine will be running under program control, the skill level
required of the CNC operator is also reduced as compared to a machinist
producing workpieces with conventional machine tools.
CNC technology is consistent and accurate workpieces. CNC machines
boast almost unbelievable accuracy and repeatability specifications. This
means that once a program is verified, two, ten, or one thousand identical
workpieces can be easily produced with precision and consistency.
CNC machine tools offer flexibility. Since these machines are run
from programs, running a different workpiece is almost as easy as loading a
different program. Once a program has been verified and executed for one
production run, it can be easily recalled the next time the workpiece is to
be run. This leads to yet another benefit, fast change-overs. Since these
machines are very easy to setup and run, and since programs can be easily
loaded, they allow very short setup time.
Motion Control Systems
The most basic function of CNC machine is automatic,
precise, and consistent Motion Control Systems. CNC machines allow Motion Control Systems in
a revolutionary manner. All forms of CNC equipment have two or more
directions of motion, called axes. These axes can be precisely and
automatically positioned along their lengths of travel. The two most common
axis types are linear (driven along a straight path) and rotary (driven
along a circular path).
Almost all current CNC controls use a word address format
for programming. By word address format, we understand that the CNC program
is made up of sentence-like commands. Each command is made up of CNC words.
Each CNC word has a letter address and a numerical value. The letter address
(X, Y, Z, etc.) tells the control the kind of word and the numerical value
tells the control the value of the word. Words in a CNC command tell the CNC
machine what it is we wish to do at the present time.