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CNC Defined CNC technology was developed
in the United States in the 1950's for the US Air Force by metalworking
machine tool builders. It was a major advance in the ability
of machines to faithfully reproduce complex part machining steps
more accurately without human intervention or variability.
CNC stands for Computer Numerically
Controlled. CNC always refers to how a machine operates,
that is, its basic method of controlling movement. Put another
way, a CNC machine uses a stream of digital information (code)
from a computer to move motors and other positioning systems
in order to guide a spindle over raw material.
A CNC machine uses mathematics
and coordinate systems to understand and process information
about what to move, to where, and how fast. Most CNC machines are able
to move in three controlled directions at once. These directions
are called axes (pronounced ax-ees). The axes are given simple
names such as X, Y and Z (based on the Cartesian Coordinate System). The X axis
is always the longest distance a machine or a part of a machine
must travel. X may be the movement from front to
back, Y the movement from left to right, and the
Z is almost always vertical movement (normally the spindle's positioning movement up
and down).
A CNC machine must be able to
communicate with itself to operate. A computer numeric control unit sends
position commands to motors. The motors must talk back to the
control that, indeed, they have acted correctly to move
the machine a given distance. The ability of CNC machines to move in three
(or more) directions at once allows them to create almost any desired pattern
or shape. All of this processing happens very fast.
Advantages of CNC Production
Lower Labor Requirements
A CNC machine can eliminate several
processing steps. Where once a sheet of material would move from
one production machine step to another, the CNC machine can
do more operations in one set-up. Full sheets of material may
be used, rather than "pre-blanking" on a saw or other
machine. One operator can do the jobs of several people.
CNC machines require good operators
to make good parts. But once the company's part programming information
(knowledge) is contained in electronic files, the craftsmanship
of the company resides in the machine, not in human operators.
Training for new employees relates to how the machine operates
and what the company expects for finished part quality, not in
teaching the operator information about basic trade skills.
Better Production Parts
No human could hope to control
the movements of a machine as precisely as a CNC. These machines
work with very small units of measure. A CNC is able to drill
a hole at one end of the worktable, move to the far corner and
return to make the same hole again with only a few ten-thousandths
of an inch error. The accuracy of a CNC can be explained this
way: take a hair off your head and slice it the long way six
times. The sliver you have left is about the margin of error
with the machine.
Increased Productivity
A CNC may also be programmed
to allow for wood grain, material type and special cutter requirements.
Humans are not able to balance all of these factors in a repeated
way over extended periods of time. Machines may work two or three
shifts per day without shut-down. The only limiting factors in
CNC production relate to material availability and cutter wear.
CNC machines used to be associated with
high-volume production due to the time involved in machine programming.
New computer technologies, along with software advances, now
allow easy programming of CNC machines for custom or one-of parts. In
fact, the ability of a CNC to accept precise mathematic information
to create custom parts reduces production costs by reducing potential
errors.
Better, Safer Production
A CNC machine does not require
any positioning of the spindle to be made by hand during production.
The operator's main job is to monitor the machining process and
make any needed corrections. Most machines feature at least one
emergency stop button to instantly halt production should a part
processing error occur.
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