Post on 19-Feb-2018
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COMPUTER NUMERICALCONTROL
PROGRAMMING BASICS
Milling and Turning
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Cartesian
Coordinate
System
Almosteverythingthatcanbeproducedona
conventionalmachine
tool
can
be
produced
onaCNCMACHINETOOL,withitsmany
advantages.Themachinetoolmovements
usedin
producing
aproduct
are
of
two
basic
types:
point
to
point
(straight
line
movements)
continuouspath(contouringmovements).
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Machines
Using
CNC Early machine tools were designed so that the operator
was standing in front of the machine while operating thecontrols.
This design is no longer necessary, since in CNC theoperator no longer controls the machine tool movements.
On conventional machine tools, only about 20 percent ofthe time was spent removing material. With the addition ofelectronic controls, actual time spent removing metal hasincreased to 80 percent and even higher.
It has also reduced the amount of time required to bringthe cutting tool into each machining position.
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CNCLathe Most lathes are programmed on two axes
The X axis controls the cross motion of the
cutting tool. Negative X (X) moves the tool towards the
spindle centerline;
positive X moves the tool away from thespindle centerline.
The Z axis controls the carriage travel toward oraway from the headstock.
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MillingMachine
Themillingmachinecanbeprogrammedon
threeaxes:
TheXaxis
controls
the
table
movement
left
or
right.
TheYaxis
controls
the
table
movement
toward
or
awayfromthecolumn.
TheZaxiscontrolsthevertical(upordown)
movementofthekneeorspindle.
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Programming
Systems
Two types of programming modes used for CNC,
The incremental system
The absolute system.
Both systems have applications in CNC programming,and no system is either right or wrong all the time.
Most controls on machine tools today are capable ofhandling either incremental or absolute programming.
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Incremental program
Locations are always given as the distance anddirection from the immediately preceding point.
Command codes which tell the machine to move
the table, spindle, and knee are explained hereusing a vertical milling machine as an example:
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Schoolof
Mechanical
and
Manufacturing
EngineeringDecember52012
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Plane
Selection
G17,G18,G19
School
of
Mechanical
and
Manufacturing
EngineeringDecember52012
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SUB
Program
School
of
Mechanical
and
Manufacturing
EngineeringDecember52012
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END