CNC Milling (1)

7/23/2019 CNC Milling (1)

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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



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SUB

Program

School

of

Mechanical

and

Manufacturing



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END

CNC Milling (1)

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