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1- PROGRAMMING CNC MACHINE

1-1 Coordinate System

During machining, the machine slides perform travel motions in the

motion axes of the machine: longitudinal, lateral and vertical motions. In

order that the motion sequences can be precisely determined, it must be

possible to precisely designate all points in the machine working area. For

this purpose, a coordinate system is entered into the machine: the three-axis

coordinate system, featuring the X, Y and Z axes the three axes intersect at

right angles at the origin or zero point of the coordinate system. The

coordinate system is aligned with the main guide rails, and thus allocated to

the linear motion axes of the machine.

Decisive for allocation of the coordinate system on the universal milling

and drilling units and horizontal machining centers is the horizontal work

spindle show figure(1).

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FIGURE(1):allocation of machine coordinate system to the CNC.

1-2 Relative Tool Motion The travel movements in the three linear motion axes of the machine are

performed by the tool and by the workpiece. The machining direction is the

same in both cases. In order that programming or workpiece machining

remains independent of whether the tool or the workplace is moved during

the machine sequence, the coordinate system is referred to the workpiece.

This means that it is always assumed in programming that the workpiece

remains motionless and that only the tool moves.

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1-3 Machine Planes

The coordinate axis X, Y and Z in the three-axis coordinate system form

the three planes, XY, XZ and ZY.

Each of these three planes may be the machining plane. The XY plane is

the machining plane for workpiace machining using the horizontal work

spindle on universal milling and drilling units and on horizontal machining

centers. The Z-axis is the tool axis. The XZ plane and the ZY plane can also

be the machining plane on universal milling and drilling units equipped with

a vertical milling head. The XY plane is the machining plane for workpiece

machining on vertical machining centers.

1-4 Reference Point

The permanent Reference Point R determined by the machine

manufacturing is located in the boundary sector of the working area of the

machine - in the positive direction of the three coordinate axes X, Y and Z.

The reference point must be traveled to after the machine and the CNC

control system have been switched on. Travel to the reference point takes

place automatica11y show figure (2).

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FIGURE (2):Allocation of reference point.

1-5 Machines Zero Point

The Machine Zero Point M set by the machine manufacturer is located in

the working area of the machine - in the negative direction as referred to

Reference Point R. Machine Zero point M has a precisely defined distance in

the linear motion axis of the machine from Reference Point R; this distance

is stored in the Machine Constant Memory CM in the CNC control system.

2- BASES FOR PROGRAMMING

2-2 Programming Information

This information designates the program for workpiece machining and its

main components - programmed sentences - using the address N and the

numbering system, in order that good comprehensibility is achieved.

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2-3 Geometrical Information (Path Information)

This describes where the machining tool must travel, and under what

conditions it must travel there. Geometrical information is communicated to

the control system using the addresses G, X, Y, and Z. Path Conditions G (or

G functions) and Path Commands X, Y and Z, stipulate the geometrical

content of the program.

2-4 Technological Information

This describes how the workpiece is to be machined. Technological

information is communicated to the control system using the Addresses F, S,

T and M.

Feed Advance Speed F, Spindle Speed S, Tool T and Additional

Functions M (or M functions) stipulate the technological content of the

program. The main types of information for workpiece machining, and their

addresses in the program are show in figure (3)

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FIGURE 3: The main type of information for workpiece machining

and their addressees in the program.

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2-5 Programming Language The information for any workpiece machine operation required must be

communicated to the CNC control system of the machine in a

comprehensible language.

This language is the control system's program language. Just like any

other language, the program language consists of words, with which

sentences are formed. Provided certain formal rules are adhered to,

sentences with meaningful contents are then formed, and produce a logically

structured description, when they are arranged in the correct order: the

program. Programming is nothing other than the description of working

sequences in the programming language, taking into account its formal rules.

Knowledge of the formal rules of the programming language is the most

important precondition for programming.

2-6 Words and Word Structure

Words are the individual information units of a sentence.

Each word (or program word) contains an item of programming, geometrical

or technological information. Program words are commands, which are

communicated to the control system. An address notation is used for writing

the words in the program. In this notation, each word consists of an address

letter and numerical suffix (number or sequence of numbers) with or without

assign.

2-7 Sentence Structure

A sentence (or program sentence) consists of several words and is of

variable length. The type and order of the words in the program sentence are

determined by the programming language of the control system.

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The first word in a program sentence is the word for the sentence

number. This word is followed by words bearing geometrical and

technological information.

The words stand in the program sentence in a stipulated order show

figure (4).

FIGURE(4): Sentence format for programming of CNC control

system.

According to the respective step in the wopkpiece machining required,

the programming sentence will contain a G function (path condition), Path

Commands X, Y, or Z, Technological Data F, S, or T, and an M function

(additional function), all logically linked to one another, to produce the

working instructions to the control system which will generate the required

machine functions.

2-8 Program Structure

A program consists of several program sentences.

The type, number and order of the program sentences in the program are

determined largely by the required workpiece machining operation, but also

depend on the individual solution of the machining problem by the

programmer.

The following applies for the overall structure of a program:

Program start is the program number. The program number is followed by

the first program sentence, which must contain the G function for selection

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of the machining plane. Program end is the final, program sentence, which

must contain the Program End Command M30.

We should point out, in anticipation of subsequent descriptions, that the

first sentences of a program have to create basic preconditions for the

workpiece machining operation required.

These preconditions are:

selection of machining plane;

activation of the workpiece zero point;

selection of the machining tool Spindle Speed 5, Tool Number T, tool

change command);

Travel to the starting point for the required workpiece machining

operation.

3 PROGRAMME WORDS

3-1 Program number

The word (N) for the program number is the name of the program.

A program is clearly identified by its program name.

The word for the program number consists of the address letter N and any

number between 9000 and 9999999. Programs (component programs) are

subdivided into main programs PM and subprograms MM. One and the

same number N may be used simultaneously for one main program PM and

for one subprogram MM, since main and subprograms are stored in separate

memories. The use of one and the same number N simultaneously for

several mains programs PM (or for several subprograms MM will not be

accepted by the CNC control system.

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3-2 Sentence Number

The word for the sentence number is used for unequivocal identification

of the individual program sentence. It is the first word of each sentence in

the program.

The word for the sentence number consists of the address letter N and

any number between 1 and 8999. In manual program input using the

keyboard, the sentence numbers, starting with 1, are prescribed

automatically by the CNC control system in ascending order.

3-3 G - Function

The word for the G function or path condition (G word) stipulates a

condition for compliance with path commands X, Y, or Z. It informs the

CNC control system how the machining tool should travel to the target

points for the required machining of the wopkpiece. The word for the G

function consists of the address letter G and a key number show table (1).

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G FUNCTION and Meaning

G0 Rapid traverse movement

G1 Straight interpolation (travel along a straight line in feed)

G17 Plane selection XY

G40 Remove G41, G42, G43, G44

G41 Tool radius correction, left-hand

G42 Tool radius correction, right-hand

G43 Tool radius correction, up to

G44 Tool radius correction, above

G51 Remove G52

G52 Summon the zero point shift G52 stored at setting of wopkpiece

zero point (RESET AXIS)

G90 Absolute dimension data (reference dimensions)

G91 Incremental dimension data (chain data)

TABLE(1):The main G functions (path conditions)

and their meanings

The programming language of the CNC control system provides a whole

series of encoded G functions, which are described in more detail at another

point. The table illustrates the subdivision of related G functions into groups.

All the G functions (G words) shown in the table remain active in the

program for subsequent program sentences, too, until they are expressly

changed (modal).

3-4 Coordinates

The words for coordinates X, Y and Z are used to describe the tool travel

paths.

They provide the CNC control system with information on the absolute

or incremental target points in the program sentence to which the machining

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tool must travel. The word for the coordinate consists of the address letter of

the coordinate axis X, Y or Z, and a number between 0 and 999999.999.

The maximum coordinate value actually permissible within the possible

numerical range 0 ... 999999.999 depends on the machine and is stored in

the Machine Constant Memory CM of the CNC control system.

3-5 Feed

The word for feed (F word) describes the speed of execution of path

commands X, Y, and Z. It is the precondition for all travel motions which

are not to be performed in rapid traverse G0. The F word consists of the

address letter F and a number between 0 and 4000.000.

The number in the F word may have two meanings:

Feed rate in mm per minute or Rotational feed in mm per revolution .

The meaning of the number in the F word is selected by a G function.

The G function G94 stipulates for the ready condition of the CNC control

system the meaning of the number in the F word with feed rate in mm per

minute. This G function remains active until it is expressly changed.

3-6 Spindle Speed

The word for spindle speed (S word) describes the spindle speed at which

the required wopkpiece machining operation is to be performed.

It is the precondition for running of the spindle.

The S word consists of the address letter S and a numerical value between

20 and 9999. The number in the S word accords directly with the speed

value in revolutions per minute. The maximum speed value actually

permissible within the possible numerical range 50 ... 9999 depends on the

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machine and is stored in the Machine Constant Memory CM of the CNC

control system.

3-7 Tool

The word for the tool (T word) determines the machining tool used.

The T word consists of the address letter T and a numerical value between 0

and 255. The number in the T word accords with the tool number.

Tool data (tool length L and tool radius R) can be stored for a maximum

for 255 tool numbers outside of the program, in the Tool Data Memory TM

of the CNC control system. In combination with one of the tool change

commands M6 and M66, the T word causes automatic inclusion of length L

for the corresponding tool in all travel movements in the tool axis.

3-8 M -Function

The word for the M function or additional function (M word) gives the

CNC control system additional technological information which cannot be

programmed in the F, S or T word. This additional information describes a

machine function (switch function). The word for the M function consists of

the address letter M and a key number. The programming language of the

CNC control system provides a whole series of encoded M functions, which

are described in more detail at another point show table (2).

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M FUNCTION and Meaning

M3 Spindle : right-hand rotation

M4 Spindle : left-hand rotation

M5 Spindle : stop

M6 Manual/automatic tool change with automatic travel to a fixed,

machine-dependent changing position

M8 External cooling lubricant supply ON

M9 Cooling lubricant supply OFF

M13 Spindle : right-hand rotation and external cooling lubricant supply ON

M14 Spindle : Left-hand rotation and external cooling lubricant supply ON

M30 Program end with reset of CNC Control system to Einschaltzustand

M66 Manual tool change in the position last traveled to

TABLE(2): The main M function (additional functions) and their

meaning

4- DIMENSIONING

4-1 Absolute Dimensions (G90)

Absolute dimension data predominate in wopkpiece drawings with

coordinate dimensioning suitable for NC machining.

In dimensioning with absolute dimensions, the coordinates of all

wopkpiece-dimensioning points are referred to the zero point of the

wopkpiece coordinate system.

For this reason, absolute dimensioning is frequently referred to as

reference dimensioning.

Travel to the absolute target point. Its distance from the zero coordinate

point of the wopkpiece is defined by the absolute coordinate value

programmed.

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4-2 Incremental Dimensions (G91)

Wopkpiece drawings are dimensioned not only with absolute

dimension data, but also with incremental dimension data (chain

dimensions).

In dimensioning with incremental dimension data, the coordinates for

each new wopkpiece dimensioning point are referred to the point

previously dimensioned. The previous dimensioning point is in all cases

the zero coordinate point for the following dimension point.

In this form of dimensioning, the individual dimension increments along

the common dimensioning line are combined to form a chain of

dimensions.

5- Tools

5-1 Tool Data

The CNC control system makes it possible to program the drawing

dimensions of the finished component without it being necessary to take

into account tool dimensions.

This makes component programming considerably easier.

Tool dimensions are stored as tool data (length L and radius R) in the tool

data memory TM of the CNC control system.

Here, they can be updated at any time extremely easily and quickly and

without changing the component program.

The required tool data in any case can be retrieved as required from

memory TM by the CNC control system and included automatically in the

program.

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5-2 Measurement of Tool Length L

Tool length L is the distance between the spindle nose and the tool tip.

The spindle nose is the reference edge for tool length L Procedure:

1- Carefully move the ground spindle nose to a plan parallel surface on the

clamped wopkpiece or on the table by actuating the corresponding axis

key.

2-Use a correspondingly long blockage (or a plan parallel ground block) for

this operation.

3- Select the control function RESET AXIS.

4- Set the tool axis to the VALUE 0.

5- Travel back along the tool axis until the tool to be measured can be easily

accommodated in the work spindle.

6- Carefully advance along the tool axis until the tool tip touches the

blockage.

7- Read off and note the coordinate value displayed for the tool axis. The

value noted is tool length L.

5-3 Measurement of Tool Radius

If tool radius R is to be measured in the machine at all, proceed

analogously as for determination of tool length L. However, the work

spindle center must first be set to the value 0 using a plug gauge.

5-4 Input of Tool Data

The tool data determined (length L and radius R) must be entered into the

tool data memory TM of the CNC control system before work is started.

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If it becomes apparent during machining that the component is not

dimensionally accurate, the data for the corresponding tool must be

appropriately corrected in tool data memory TM.

5-5 Plane Selection (G17),(G18),(G19)

In the three-axis coordinate system, the three planes XY, XZ and ZY

are formed by the three axes X, Y and Z. In each of the three planes, the

third axis is in each case perpendicular. Plane selection is the most

important condition for correct performance of all-path commands. It is

made in the first program sentence by a G function.

In wopkpiece machining using a horizontal work spindle on universal

milling and drilling units and on horizontal machining centers, the XY

plane is the machining plane. The Z-axis is the tool axis. In wopkpiece

machining on vertical machining centers, the XY plane is also the

machining plane. The Z-axis is the tool axis.

Plane selection XY is made using G function G17.

G function G17 remains active for subsequent program sentences until it

is rep-laced by G18 or G19.

5-6 Tool Length Correction

The dimension length L of the machining tools is left out of account in

programming. The drawing dimensions of the finished component are

programmed in the tool axis.

Programming assumes that the spindle nose moves along the required

machining path on the wopkpiece.

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5-7 Tool Radius Correction (G40, G41, G42, G43 and G44)

The dimension of radius R of the machining tools is left out of account

in programming. The drawing dimensions of the finished component are

programmed in the machining plane.

Programming assumes, therefore, that the tool center point moves along

the required machining path on the wopkpiece.

5-8 G Functions G43 and G44

In programming of contour machining, the machining tool must be set

to the equidistant path by the programmer using one of the two-G functions

G43 and G44. For this purpose, the following conditions for travel of the

machining tool to the contour must be met after stipulation of the point on

the finished contour at which contour machining is to commence:

A starting point P must be programmed, from which start point PI or

P2 on the finished contour can be reached at a right angle.

Travel at a right angle to the contour prevents the possibility of

contour falsifications at commencement of contour machining.

It must be established whether the cutters of the machining tool are

required to travel up to the contour (G43) or across the contour (G44)

in order that its center point comes to rest offset by radius R referred .

The correct G function G43 or G44 must be contained in the program

sentence containing the instruction to travel to the contour.

5-9 G Functions G41 and G42

Once the machining tool has been adjusted to the equidistant path using

one of G functions G43 or G44, the CNC control system must be informed

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in the next program sentence with a travel movement on which side of the

finished contour the machining tool (viewed in the direction of travel) is

located.

5-10 G Function G40

As soon as the tool center point is required to move again along the

programmed machining path on the wopkpiece, tool radius correction must

be completed by means of programming of G40.

6- WORKPIECE ZERO POINT 6-1 Determination of Workpiece Zero Point

All points on a Workpiece can be clearly designated if the Workpiece

is placed into a coordinate system: the three-axis coordinate system, with the

axes X, Y and Z. That point on the workpiece at which the origin or zero

point of the coordinate. System is located is the workpiece zero point W. It

is designated program zero point.

However, for practical reasons, it is recommendable that the workpiece

zero Pointe stipulated in such a way that the following conditions can be

fulfilled.

• It should be possible to convert the dimensions in the workpiece drawing

coordinate values with the minimum possible effort.

As far as possible, only positive coordinate values should occur in the

Machining plane.

• As few sign changes as possible should be caused.

On milled components, the workpiece zero point is frequently an

external corner point.

It may by recommendable on symmetrical milled components to locate

the workpiece zero point at the workpiece center.

6-2 Stored Zero Point Shift (G51 and G52) The machine zero point M set by the machine manufacturer is the origin

of the Machine’s coordinate system.

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The workpiece zero point W set by the programmer (program zero point)

is the origin of the workpiece's coordinate system.The machine zero point

and workpiece zero point must be related to one another to permit workpiece

machining using the machine.

The reference point is the fixed machine zero point.

The workpiece zero point is located at a distance defined by its coordinate

values from the machine zero point in the coordinate axes X, Y and Z; this

distance is known as the shift.

When workpiece zero point (RESET AXIS) is set, this shift is

automatically transferred to the CNC control system and stored in memory

ZO for zero point shifts under G52.

7- M Functions (Additional Functions)

7-1 Spindle Commands (M3, M4, M5, M13 and M14)

Spindle command M5 is active in the ready condition of the CNC

control system. Each of the spindles commands M3, M4, M5, M13 and M14

will remain active in the program until it is replaced by any other spindle

command. The spindle commands M13 and M14 consist of the basic spindle

command (M3 or M4) and cooling lubricant command M8.

7-2 Cooling Lubricant Commands (M8 and M9)

Cooling lubricant command M9 is active in the ready condition of the

CNC control system. It remains active until M8 or M13 or M14 is

programmed. Cooling lubricant command M8 switches the external cooling

lubricant supply on.

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7-3 Tool Change Commands (M6 and M66)

The tool change commands stipulate the sequence of a tool change and

initiate it. Furthermore, they effect in conjunction with the T word for the

machining tool to be inserted into the work spindle automatic inclusion of

length L of this tool in all subsequent travel motion along the tool axis.

Tool changing commands M6 and M66 are executed immediately, i.e.

before execution of all the other commands in the corresponding program

sentence. For this reason, path commands (words for the coordinates) are

impermissible in a program sentence containing M6 or M66.

7-4 Tool Change Command M6

Command M6 cause the machining tool to travel in rapid traverse to

a fixed changing position. It leaves the workpiece in the positive direction of

its axis. Travel to the changing position takes place only along the tool axis

show figure (5).

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Figure(5) The effect of tool change command M6.

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The coordinate value for the changing position is machine-specific and

is stored in the machine constant memory CM of the CNC control system.

Automatic removal of a tool and return of the tool to the magazine

without insertion of a new tool from the magazine into the spindle can be

programmed. A machining tool inserted into the spindle of the machine

using tool change command M6 must always be removed from the spindle

and returned to the magazine using tool change command M6.

7-5 Tool Change Command M66

Tool change command M66 makes it possible to change the machining

tool manually in the most recent position reached show figure (6).

This change position is a component of the program. It precedes the

sentence containing M66.

On machines without a tool changer, tool change command M66 must

always be used if tool changing is not to be performed in the machine-

specific changing position.

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Figure(6):the effects of tool change command M66.

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7-6 Program End Command M30

The last program sentence of any main program PM must contain the

program end command M30.

The word M30 may be the only word in the last sentence of the program

after the sentence number, but can also be contained in this sentence

together with other words.

8- TYPE OF MOTION CONTROL SYSTEMS 8-1 Point-to-point NC Point-to-point (PTP) is also sometimes called a positioning system. In

PTP, the objective of tte machine tool control system is to move the cutting

tool to a prede fined location. The speed or path by which this movement is

accomplished is not important in point-to-point NC. Once the tool reaches

the desired location, the machining operation is performed at that position.

8-2 Straight-cut NC Straight-cut control systems are capable of moving the cutting tool

parallel to one of the major axes at a controlled rate suitable for machining.

It is therefore appropriate for performing milling operations to fabricate

workpieces of rectangular configurations.

8-3 Contouring NC Contouring is the most complex, the most flexible, and the most

expensive type of machine tool control. It is capable of performing both PTP

and straight-cut operations. In addition, the distinguishing feature of

contouring NC systems is their capacity for simultaneous control of more

than one axis movement of the machine tool. The path of the cutter is

continuously controlled to generate the desired geometry of the workpicce.

For this reason, contouring systems are also called Continuous-path NC

systems.

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FIGURE (7): Contouring (continuous path) NC system for two-dimensional operations.

Straight or plane surfaces at any orientation, circular paths, conical

shapes, or most any other mathematically definable form are possible under

contouring control. Figure 7 illustrates the versatility of continuous path NC.

Milling and turning operations are common examples of the use of

contouring control.

9- TRAVEL INSTRUCTIONS

9-1 Travel in Rapid Traverse (GO)

The word GO in the programming language of the CNC control system

represents an instruction to the machine controlled to move the machining

tool in rapid traverse to the target point in the wopkpiece coordinate system.

After the travel instruction GO, the coordinates of the target point must be

stated in the program. The coordinates can be stated absolute or

incrementally.

The coordinate values for the three axes X, Y and Z can be written in one

sentence. The travel motions in the machining plane take place

simultaneously in travel to a target point in rapid traverse. The travel path of

the tool center point is located along the direct connecting line between the

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starting point and the target point. The positioning logic system of the CNC

control system stipulates when the movement in the tool axis should take

place:

- If the tool is to be moved in rapid traverse GO in the negative direction of

its axis, movement takes place in the tool axis after the travel movements in

the machining plane.

- If the tool is to be moved in rapid traverse GO in the positive direction of

its axis, movement in the tool axis takes place be-fore the travel movements

in the machining plane. Travel instruction GO and target point coordinates

are generally included in one and the same programmed sentence.

9-2 Travel in a Straight Line in Feed Advance (Gl)

The word Gl in the programming language of the CNC control system

is an instruction to the machine controlled to move the machining tool

along a straight line in feed advance to the target point in the wopkpiece

coordinate system.

The straight line may be a straight line parallel to an axis, an inclined

straight line or any spatial straight line. The travel instruction Gl and the F

word necessary for the advance are located in one and the same program

sentence, provided the F word is not already active from a previous

sentence. After the travel instruction Gl, the coordinates for the target point

must be stated in the program.

The coordinates can be stated absolutely or incrementally Only one

target point coordinate need be entered for programming of a straight line

parallel to an axis in the plane. For programming of an oblique straight line

in the plane, the target point coordinates in both axes of the respective

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machining plane XY, XZ or ZY must be stated. The two target point

coordinates must be written in one and the same sentence.

9-3 Travel along a Curved Path at Feed Speed (G2 and G3)

After straight lines, arcs are the most commonly occurring contour

features in wopkpiece machining. In the programming language of the CNC

control system, the word G2 or G5 represents an instruction to the machine

controlled to move the machining tool along a curved path to a target point

in the machining plane at feed speed and to thereby mill an arc.

The travel instruction G2 causes circular motion of the machining tool

between the starting point (arc starting point) and the target point (arc end

point) in a clockwise direction, the travel instruction G3, the same motion in

a counter-clockwise direction. The direction of movement (clockwise or

counter-clockwise) is that as viewed from the machining tool onto the

machining plane in which the arc is to be milled. The travel motions in the

two linear axes of the machining plane occur simultaneously during travel to

the arc end point at feed speed. The travel path of the tool center point

describes a curved path. The term circular interpolation is used, because the

computer of the CNC control system calculates the tool center point path

running along the curved path between the arc starting point and the ace end

point by means of interpolation.

There are two methods of programming an arc:

- An arc of up to 180° can be programmed by stating the arc end point and

the arc radius.

- An arc of greater than 180° must be programmed by stating the arc end

point and the arc mid-point.

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The coordinates for the arc end point in the machining plane and the arc

radius or the coordinates of the arc mid-point must be stated in one and the

same sentence together with the G function G2 or G3 for the direction of

motion of the machining tool for milling of the arc.

9-4 MACHING PROCESS ON CNC MACHINE :

After the engineering drawing to the model by the designer downing

pass technology and limitation the type material to machining.

The model on the CNC machine by the following the steps figure (8,9):

1- Wopkpiece fixed on the bed.

2-Defining zero position for axes (X, Y, Z) to wopkpiece.

3-Limitation the type of material the wopkpiece to limitation the speed,

feed, and type of cutter.

4-Limitation type of cutting direction.

5-Input G-god program.

6-Verify the program.

7-Test program.

8-Start the manufacturing.

9-Obtained the product.

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FIGURE (8): block diagram for operation process on the CNC

machine.

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FIGURE(9): example 2D for machining on CNC milling machine .