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8/12/2019 CAD-CAM Power Point Presentation

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Numerical control(NC)

NC is a form of programmable automation inwhich the mechanical actions of a machine tool orother equipment are controlled by a program

containing coded alphanumeric data.The data represent relative positions between the

tool and a workpart as well as other instructionsneeded to operate the machine.

When the current job is completed, the programof instructions can be changed to process a newjob.

The capability to change the program makes NC

suitable for low and medium production.


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Numerical control(NC) (Cont.)

Numerical control can be applied to awide variety of processes. The applicationscan be divided into two categories:

Machine tool applications, such asdrilling, milling, turning, and other metalworking.

Non-machine tool applications, such asassembly, drafting, and inspection.


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Basic Components of an NC System

An NC system consists of three basic

components:

a program of instructions,

a machine control unit, and

processing equipment.

The general relationship among the three

components is illustrated in Figure 6.1.


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NC Part Program

The program of instructions is the detailed step-by-step commands that direct the actions of the

processing equipment.

In machine tool applications, the program of

instructions is called apart program.

The individual commands refer to positions of a

cutting tool relative to the worktable on which the

workpart is fixtured. Additional instructions are usually included, such

as spindle speed, feed rate, cutting tool selection,

and other functions.


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NC Part Program (Cont.)

The program is coded on a suitable medium forsubmission to the machine control unit.

For many years, the common medium was 1-inchwide punched tape, using a standard format that

could be interpreted by the machine control unit.

Today, punched tape has largely been replaced bynewer storage technologies in modern machine

shops. These technologies include magnetic tape, diskettes,

and electronic transfer of part programs from a

computer.


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Machine control unit (MCU)

MCU consists of a microcomputer andrelated control hardware that stores theprogram of instructions and executes it byconverting each command into mechanical

actions of the processing equipment, onecommand at a time.

The related hardware of the MCU includes

components to interface with the processingequipment and feedback control elements.

The MCU also includes one or more readingdevices for entering part programs into

memory.


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Computer numerical control

(CNC)

Because the MCU is a computer, the termcomputer numerical control (CNC) isused to distinguish this type of NC from its

technological predecessors that were basedentirely on hard-wired electronics.

Today, virtually all new MCUs are based on

computer technology; hence, when we referto NC in this chapter and elsewhere, we

mean CNC.


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Computer numerical control

Figure: Schematic diagram of a CNC machine tool


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Processing Equipment

It accomplishes the processing steps totransform the starting workpiece into a

completed part.

Its operation is directed by the MCU,which in turn is driven by instructions

contained in the part program.

In the most common example of NC,machining, the processing equipmentconsists of the worktable and spindle aswell as the motors and controls to drive

them.


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NC Coordinate Systems

There are two axis systems used in NC, one forflat and prismatic workparts and the other for

rotational parts.

Both axis systems are based on the Cartesian

coordinate system.

The axis system for flat and prismatic partsconsists of the three linear axes (x, y, z) in the

Cartesian coordinate system, plus three rotationalaxes (a, b, c), as shown in Figure 2a.

The x-and y-axes are used to move and positionthe worktable, and the z-axis is used to control

the vertical position of the cutting tool.


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Coordinate systems used in NC

Coordinate systems used in NC: (a) for flat andprismatic work and (b) for rotational work.

a) b)

C di d i NC


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(Cont.)

The a-, b-, and c-rotational axes specifyangular positions about the x-, y-, and z-axes, respectively.

Clock wise rotation looking from the originof the axis indicate a positive direction.

The coordinate axes for a rotational NC

system are illustrated in Figure 2(b).These systems are associated with NC

lathes and turning centers, where the y axis

is not used.


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Coordinate systems used in NC (Cont.)

Figure: Direction of Axes in Vertical Milling


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Coordinate systems used in NC (Cont.)

Figure: Direction of Axes in Lathe Machines


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(Cont.)

Figure: Direction of Axes in Horizontal Milling

Machines


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Origin of the Coordinate axis

The part programmer must decide wherethe origin of the coordinate axis systemshould be located.

This decision is usually based onprogramming convenience.

For example, the origin might be located

at one of the corners of the part. If the workpart is symmetrical, the zero

point might be most conveniently defined

at the center of symmetry.


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Target point

At the beginning of the job, the operator mustmove the cutting tool under manual control tosome target point on the worktable, where the tool

can be easily and accurately positioned.

The target point has been previously referencedto the origin of the coordinate axis system by thepart programmer.

When the tool has been accurately positioned atthe target point, the operator indicates to theMCU where the origin is located for subsequenttool movements.


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Motion Control Systems

The different types of movement required formachining are accomplished by the motion control

system.

Motion control systems for NC can be divided into two

types: point-to-point and

continuous path

Point-to-point systemsmove the worktable to aprogrammed

location without regard for the path taken to get to that

location.


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Point-to-Point System

Figure 3 Point-to-point (positioning)

control in NC. Ateach x-y position,table movementstops to perform the

hole-drillingoperation.


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Continuous Path System

Continuous path systems generally refer tosystems that are capable of continuoussimultaneous control of two or more axes.

The system is able to generate angularsurfaces, two-dimensional curves, or three-dimensional contours in the work part.

This control mode is required in many millingand turning operations.

A simple two-dimensional profile millingoperation is shown in Figure 4 to illustratecontinuous path control.


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Continuous Path System (Cont.)

Figure 4:Continuous path(contouring)control in NC

system. (Note thatcutting tool pathmust be offsetfrom the part out-

line by a distanceequal to itsradius).


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Interpolation Methods

One of the important aspects of contouring is

interpolation.

The paths that a contouring-type NC system is

required to generate often consist of circulararcs and other smooth nonlinear shapes.

Some of these shapes can be defined

mathematically by relatively simple geometric

formulas (e.g., the equation for a circle is x2+y2 = R2).

Others cannot be mathematically defined

except by approximation.


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Interpolation Methods (Contd.)

To cut along a circular path, the circlemust be divided into a series of straightline segments that approximate the curve.

The tool is commanded to machine eachline segment in succession so that themachined surface closely matches thedesired shape.

The maximum error between the nominal(desired) surface and the actual(machined) surface can be controlled bythe lengths of the individual line

segments, as explained in Figure 5.


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Figure 5Approximation of acurved path in NC bya series of straightline segments. In (a)the tolerance isdefined on only theinside of the nominalcurve. In (b) thetolerance is definedon only the outside of

the desired curve. In(c) the tolerance isdefined on both theinside and outside ofthe desired curve.


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A number of interpolation methods areavailable to deal with the various problemsencountered in generating a smoothcontinuous path in contouring. Theyinclude:

Linear interpolation,

Circular interpolation,

Helical interpolation,

Parabolic interpolation

Cubic interpolation.


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Interpolation Methods(Contd.)

Linear interpolation:This is the mostbasic and is used when a straight linepath is to be generated in continuouspath NC. Two-axis and three-axis linear

interpolation routines are sometimesdistinguished in practice, butconceptually they are the same. Theprogrammer specifies the beginningpoint and end points of the straight lineand the feed rate to be used along thestraight line. The interpolator computesthe feed rates for each of the two (orthree) axes to achieve the specified

feed rate.


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Interpolation Methods(Contd.)

Circular interpolation:This methodpermits programming of a circular arcby specifying the followingparameters: (1) the coordinates ofthe starting point, (2) the coordinatesof the endpoint, (3) either the centeror radius of the arc, and (4) the

direction of the cutter along the arc. The generated tool path consists of a

series of small straight line segments(see Figure 5) calculated by the

interpolation module.


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Helical interpolation:This method combines

the circular interpolation scheme for two axesdescribed above with linear movement of athird axis. This permits the definition of ahelical path in three-dimensional space.

Applications include the machining of largeinternal threads, either straight or tapered.

Parabolicand cubic interpolationsThese

routines provide approximations of free form

curves using higher order equations. Theygenerally require considerable computationalpower and are not as common as linear andcircular interpolation.

b l l


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Absolute Versus Incremental

Positioning

Another aspect of motion control is concernedwith whether positions are defined relative to theorigin of the coordinate system or relative to the

previous location of the tool.

The two cases are called absolute positioningand incremental positioning.

In absolute positioning, the workhead locations

are always defined with respect to the origin ofthe axis system.

In incremental positioning, the next workheadposition is defined relative to the present

location. The difference is illustrated in Figure 6.

Ab l t V I t l


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Absolute Versus IncrementalPositioning

Figure 6: Absolute versus

incremental positioning.

The work head is

presently at point (20, 20)

and is to be moved to

point (40, 50). In absolute

positioning, the move is

specified by x = 40, y =

50; but in incrementalpositioning, the move is

specified by x = 20, y=30.

C N i l C l


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Computer Numerical Control

Computer numerical control (CNC) is defined

as an NC system whose MCU is based on adedicated microcomputer rather than on a hard-wired controller.

Computer NC systems include additional

features beyond what is feasible withconventional hard-wired NC.

These features include the following:

Storage of more than one part program

Various forms of program input

Program editing at the machine tool

Fixed cycles and programming subroutines

C t N i l C t l


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Computer Numerical Control

(Cont.)

InterpolationPositioning features for setup

Cutter length and size compensation

Acceleration and deceleration calculations

Communications interface: most modern CNCcontrollers are equipped with a standard RS-232 or othe communications interface. This isuseful for various applications, such as:

down loading part programs from a central data file.

interfacing with peripheral equipment, such asrobots.

collecting operational data such as workpiece

counts, cycle times, and machine utilization.

Th M hi C t l U it f


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The Machine Control Unit for

CNC

The general configuration of the MCU in a CNCsystem is illustrated in Figure 7.

The MCU consists of the following componentsand subsystems:

central processing unit,

memory,

I/O interface,

controls for machine tool axes and spindle

speed, sequence controls for other machine tool

functions.

These subsystems are interconnected by meansof a system bus, as indicated in the figure 7.

Th M hi C t l U it f CNC


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The Machine Control Unit for CNC

(Cont.)

Figure 7: Configuration of CNC Machine

Control Unit

Memory:

ROM - Operating

system

RAM - Part programs

Central Processing

Unit (CPU)

Input/Output

interface

Operator panel

Tape reader

Machine tool controls

Position control

Spindle speed control

Sequence controls

Coolant

Fixture clamping Tool

changer



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(Cont.)

Central Processing Unit: CPU is the brain of the

MCU. It manages the other components in the MCUbased on software contained in main memory.

The CPU can be divided into three sections:

control section,

arithmetic-logic unit,

immediate access memory.

The control section retrieves commands and data from

memory and generates signals to activate other

components in the MCU. The arithmetic-logic unit (ALU) consists of the

circuitry to perform various calculations.

The immediate access memoryprovides a temporary

storage for data being processed by the CPU.

ersona omputers an t e


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Two basic configurations are beingapplied:

the PC is used as a separate front-endinterface for the MCU,

the PC contains the motion control boardand other hardware required to operate themachine tool.

In either configuration, the advantage of

using a PC for CNC is its flexibility toexecute a variety of user software inaddition.

ersona omputers an t eMCU.


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NC Software

There are three types of software programs used in CNCsystems:

machine interface software,

application software.

operating system software,

The principal function of the operating system software isto interpret the NC part programs and generate thecorresponding control signals to drive the machine toolaxes and is stored in ROM in the MCU.

The machine interface software is used to operate thecommunication link between the CPU and the machinetool to accomplish the CNC auxiliary functions.

The application software consists of the NC partprograms.


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Direct Numerical Control (DNC)

The first attempt to use a digital computer todrive the NC machine tool was DNC. This was

in the late 1960s before the advent of CNC.

As initially implemented, DNC involved the

control of a number of machine tools by a

single (mainframe) computer through direct

connection.

Instead of using a punched tape reader to enterthe part program into the MCU, the program

was transmitted to the MCU directly from the

computer, one block of instructions at a time.


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Direct Numerical Control (DNC)

This mode of operation was referred to by thename behind the tape reader (BTR).

The DNC computer provided instruction blocks

to the machine tool on demand.

As each block was executed by the machine, the

next block was transmitted.

The general configuration of a DNC system is

depicted in Figure 8.


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Figure 8: The general configuration of a DNCsystem

Direct Numerical Control (DNC) (Cont.)


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Direct Numerical Control (DNC) (Cont.)

The system consisted of four components: central computer,

bulk memory at the central computer site,

set of controlled machines, and

telecommunications lines to connect the machines tothe central computer.

Advantages claimed for DNC in the early 1970s included:

high reliability

elimination of the tape and tape reader,

control of multiple machines by one computer;

improved computational capability for circularinterpolation;

part programs stored magnetically in bulk memory,

etc.


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Distributed Numerical Control

As the number of CNC machine installations grewduring the 1970s and 1980s, DNC emerged once again,

but in the form of a distributed computer system, or

distributed numerical control (DNC).

The configuration of the new DNC is very similar tothat shown in Figure 8 except that the central computer

is connected to MCUs, which are themselves

computers.

This permits complete part programs to be sent to themachine tools, rather than one block at a time.

It also permits easier and less costly installation of the

overall system.


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There are several ways to configure aDNC system.

F igure 9, 10illustrates two types of

DNC configuration: switching network and

LAN


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F igure 9:Switching network DNC system

Di t ib t d N i l C t l


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F igure 10:LAN type DNC system


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Appl icat ionso f NC

The operating principle of NC has manyapplications.

The applications divide into two categories:

machine tool applications

non-machine tool applications.

Machine Tool Applications

The most common applications of NC are inmachine tool control. Machining was the

first application of NC


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Appl icat ionso f NC (Cont.)

The common NC machine tools are:

NC lathe

NC boring mill, horizontal and

verticalspindle

NC drill press

NC milling machine

NC cylindrical grinder


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Figure 11: Turning Operation


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Figure 12: Drilling Operation


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Figure 13: Milling Operation


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Figure 14: Four-axis CNC horizontalmilling machine


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NC Application Characteristics

In general, NC technology is appropriate for lowto-medium production of medium-to-high variety product.

The following part characteristics have come to be

identified as being most suited to the application of

NC: Batch production

Repeat orders

Complex part geometry

Much metal needs to be removed from the workpar t

Many separate machining operations on the part

The part is expensive

f h l ki


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NC for Other Metalworking

Processes

In addition to the machining process NC

machine tools have also been developed for the

following metal working processes:

Punch pressesPresses for sheet metal bending

Welding machines

Thermal cutting machines, such as oxy-fuelcutting, laser cutting, and plasma arc cutting

Tube bending machines


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Other NC Applications

Some of these machines with NC-type controlsthat position a workhead relative to an object

being processed are the following:

Electrical wire wrap machines

Component insertion machines

Drafting machines

FDM Machines

Coordinate measuring machine

Tape laying machines for polymer composites

Filament winding machines for polymer

composites, etc.


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Advantages of NC

Nonproductive time is reduced

Greater accuracy and repeatability

Lower scrap rates

Inspection requirements are reduced

More-complex part geometries are possible

Engineering changes can be accommodatedmore gracefully

Simpler fixtures are needed

Shorter manufacturing lead times

Reduced parts inventory

Less floor space required

Operator skill-level requirements arereduced


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NC Part programming

NC part programming consists of planning anddocumenting the sequence of processing steps to

be performed on an NC machine.

The traditional input medium dating back to the

first NC machines in the 1950s was 1-inch widepunched tape.

More recently, the use of magnetic tape and

floppy disks have been growing in popularity as

storage technologies for NC.

The advantage of these input media is their much

higher data density.


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NC Cod ing Sys tem

The program of instructions is communicatedto the machine tool using a coding system

based on binary numbers.

This NC coding system is the low-level

machine language that can be understood by

the MCU.

When higher level languages are used, such as

APT, the statements in the program areconverted to this basic code.


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NC Cod ing Sys tem (Con t.)

Part programming can be accomplished

using a variety of methods, which are:

manual part programming

computer-assisted part programming,

part programming using CAD/CAM, and

manual data input.

Binary Numbers and the Binary


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a y u be s a d t e a yCoded Decimal System

In the binary number system, each digit cantake on either of two values, 0 or l.

The meaning of consecutive dig its in thebinary system is based on the number 2 raised

to successive powers. Starting from the right, the first digit is 20

(which equals 1), the second digit is 21(which equals 2), and so forth.

The two numbers, 0 or l, in successive digitpositions, indicate the presence or absence ofthe value. For example, the binary number0101 is equal to the decimal number 5.



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Coded Decimal System (Cont.)

The conversion from binary to decimal operates

as follows:

(0x23)+(1x22)+(0x21)+(1x2)=(0x8)+(1x4)

+(0x2)+ (IxI) = 4+1 = 5 Conversion of the 10 digits in the decimal number

system into binary numbers is shown in Table 1.

Four binary digits are required to represent the tensingle-digit number in decimal.

To encode the decimal value 125 in the binary numbersystem requires a total of 11 digits: 10011100010.

Another problem with the binary number system is thecoding of decimal fractions.


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Coded Decimal System (Cont.)

First 0001 1000

Second 0010 200

Third 0101 50

Fourth 0000 0

Sum 1250

Number

sequence

Binary number Decimal

value

Binary Numbers and the Binary Coded


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Binary Numbers and the Binary Coded

Decimal System (Cont.)

Table 2:Comparison of Binary and Decimal Numbers

0000 0 0101 5

0001 1 0110 6

0010 2 0111 7

0011 3 1000 8

0100 4 1001 9

Binary Decimal Binary Decimal

EIA d ISO C di St d d


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EIA and ISO Coding Standards

In addition to numerical values, the NC codingsystem must also provide for alphabeticalcharacters and other symbols.

Eight binary digits are used to represent all of

the characters required for NC partprogramming.

There are two standard coding systemscurrently used in NC:

the Electronics Industry Associatic (EIA) and

the International Standards Organization (ISO).

The complete listings of EIA and ISO (ASCII)codes for are shown in Table 7.



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g



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Figure: Dimensions of a punched tape


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EIA and ISO Coding Standards (Cont.)

Both EIA and ISO coding schemes weredeveloped when punched tape was the pre-dominant medium for storing NC part

programs.Although punched tape has been largely

superseded by more modern media, it is stillwidely used in industry, if only for backup

storage.To ensure the correctness of the punched tape,

the eight binary digits in the EIA and ISO codesinclude aparity check.

EIA and ISO Coding Standards (Cont )


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In the EIA system, the tape reader is

instructed to count an odd number ofholes across the width of the tape.Whenever the particular number or

symbol being punched requires an evennumber of holes, an extra hole ispunched in column 5, hence making thetotal an odd number.

For example, the decimal number 5 iscoded by means of holes in columns 1and 3. Since this is an even number ofholes, a parity hole would be added.


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The difference between the EIA and ISOsystems is that the parity check in the ISOcode is an even number of holes, called an

even parity. The EIA system uses an oddparity.

Also, whereas the parity hole is in the fifth-digit position in the EIA coding system, it isin the eighth position in the ISO system.

These differences can be seen in Table 4.

EIA d ISO C d f NC


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EIA and ISO Codes for NC

A binary digit is called a bit. In punched tape, the values 0 or 1 are represented

by the absence or presence of a hole in a certainrow and column position.

Out of one row of bits a character is formed.A character is a combination of bits

representing a numerical digit (0-9), an alphabeticalletter (A-Z), or a symbol (Table 4).

Out of a sequence of characters, a word is formed.A word specifies a detail about the operation,

such as xposition, y-position, feed rate, or spindlespeed.

How Instructions Are Formed ?


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How Instructions Are Formed?

Out of a collection of words, a block isformed.

A block is one complete NC instruction.

It specifies the destination for the move,the speed and feed of the cuttingoperation, and other commands thatdetermine explicitly what the machine tool

will do.

For example:

G02 G17 X088.0 Y040.0 F30 EOB

T F t


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Tape Formats

Different formats have been developed over theyears to specify words within an instruction block.

These are often referred to as tape formats,

More generally, they are known asblock

formats.

Block formats are briefly described in Table 5,with two lines of code for the drilling sequence

shown in Figure 16.The word address format with TAB separation

and variable word order has been standardized byEIA as RS-274. It is the block format used on all

modern controllers.

T F t (C t )


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Tape Formats (Cont.)

Word address format uses a letterprefix to identify the type of word.

Repeated words can be omitted. The

words run together, which makes thecode difficult to read (for humans).

Example:

N001 GOOX0700OY0300OM03N002YO6000


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The standard sequence of words in a block is:N_, G_, X_, Y_. Z_, I_, J__, K_, F _. S_. T_, M_

where

N is the identification number. G are the preparatory commands

X are the coordinates along the x axis,

Y are the coordinates along the y axis, Z are the coordinates along the z axis,

I, J, and K specify the arc center of circular tool

motion, usually provided with algebraic signs,

T F t (C t )


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F is the feed rate,

S is the spindle speed,

T is the tool number, and

M are the miscellaneous commands given in

Table 11.3.Thus the following is an example of a word

address NC code:

N040 GOO X0 Y0 Z300 TO 1 M06

Omitted words are assumed to be zero or to bethe same as the value previously defined. The Fand S words were omitted from the example.

T F t (C t )


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Word address format with TABseparation and variable word order isthe same format as the previous,except that words are separated by

TABs, and the words in the block canbe listed in any order.

Example:

N001 GOO X07000 Y03000 M03N002 Y06000


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Figure 15: Example drilling sequence forblock formats described in Table 5.Dimensions are in millimeters.

Word Prefixes Used in Word


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Word Prefixes Used in WordAddress Format

Word

N N01

G G21

X, Y, Z X75.0

U, W U25.0

A, B, C A90.0

R R100.0

Prefix Example

Word

Prefix Example

I, J, K 132 J67

F G94 F40

S S0800

T T14

D D05

P P05 R15.0

M M03

Word Prefixes Used in WordAddress Format


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Address Format

or re xes se n orAddress Format


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Address Format

G Codes and Their Functions


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G Codes Functions

G Codes and Their Functions (Cont.)


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G Codes Functions

M Codes and Their Functions


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M Codes Functions

G Codes and Their Functions (Cont.)


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M Codes Functions

MANUAL PART PROGRAMMING


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Instructions in Word Address Format:

Instructions in word address format consist of a series

of words, each identified by a prefix label.

In preparing the NC part program, the part

programmer must initially define the origin of the

coordinate axes.

This is accomplished in the first statement of the part

program.

origin of the coordinate system can be located at any

desired position.

An example of part program manuscript is shown in

the next Table.




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Part name

Part numberSheetRemarks

MANUSCRIPT

CONTOURINGPROGRAM

Prepared by Date

Checked by DaleMachineTape number

n G X Y Z I J K F S T M Remarks



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The operator is instructed to move the toolto this position at the beginning of the job.

With the tool in position, the G92 code is

used by the programmer to define theorigin as follows:

G92 XO Y-050.0 ZO10.0

where the x, y, and z values specify thecoordinates of the tool location in the

coordinate system.



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a more-complete instruction block wouldbe the following:

G21 G92 XO Y-050.0 ZO10.0

where the G21 code indicates that the

subsequent coordinate values are inmillimeters.

Motions are programmed by the codes

GOO, G01, G02, and G03.GOO is used for a point to-point rapid

traverse movement for example,

GOO X050.0 Y086.5 Z 100.0



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Linear interpolation is accomplished by the G0lcode. This is used when it is desired for the

tool to execute a contour cutting operation

along a straight line path. For example, the

commandG0I G94 X050.0 Y086.5 Z 100.0 F40 S800

Selection of the desired plane is accomplished by

entering one of the codes, G17, G18, or G19,respectively. Thus, the instruction

G02 G17 X088.0 Y040.0 R028.0 F30


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In contouring motions,it is almost alwaysdesirable that the pathfollowed by the center

of the tool beseparated from theactual surface of thepart by a distanceequal to the cutterradius, as shown inFigure 17.



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For a three-dimensional surface, the shape of theend of the cutter would also have to be consideredin the offset computation. This tool path

compensation is called the cutter offset.

Modern CNC machine tool controllers performthese cutter offset calculations automatically when

the programmer uses the G40, G41, and G42 codes.

The G40 code is used to cancel the cutter offsetcompensation. The G41 and G42 codes invoke thecutter offset compensation of the tool path on theleft- or right-hand side of the part, respectively.



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The instruction for profile milling thebottom edge of the part, assuming that thecutter begins along the bottom left corner,would read:

G42 G01 X100.0 Y040.0 D05

where D05 indicates that the radius offsetdistance is stored in the number 5 offset

register in the controller.This data can be entered into the controller in

either of two ways: (1) as manual input or

(2) as an instruction in the part program.



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When the offset data is entered as a partprogram instruction, the statement has theform:

G 10 P05 R10.0where G10 is a preparatory word indicatingthat cutter offset data will be entered; P05

indicates that the data will be entered intooffset register number 05; and R10.0 is the

radius value, here 10.0 mm.

Part Programming Examples


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To demonstrate manual part programming, twoexamples using the sample part shown in Figure18 are taken up.

The first example is a point-to-point program todrill the three holes in the part.

The second example is a two axis contouringprogram to accomplish profile milling around the

periphery of the part.



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Figure 18: Samplepart to illustrate NC partprogramming. Dimensions are in millimeters.



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EXAMPLE 1:Point-to-Point Drilling.N001 G21 G90 G92 X0 Y-050.0 Z010.0; Define origin of axes.

N002 G00 X070.0 Y030.0; Rapid move to first hole location.

N003 G0l G95 Z-15.0 F0.05 S1000 M03; Drill first hole.

N004 G01 Z010.0; Retract drill from hole.N005 G00 Y060.0; Rapid move to second hole location.

N006 G01 G95 Z-15.0 F0.05; Drill second hole.

N007 G0l Z010.0; Retract drill from hole.

N008 G00 X120.0 Y030.0; Rapid move to third hole location.

N009 G01 G95 Z-15.0 F0.05; Drill third hole.

N010 G01 Z010.0; Retract drill from hole.

N01 l G00 X0 Y050.0 M05; Rapid move to target point

N012 M30; End of program, stop machine.



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EXAMPLE 2:Two-Axis MillingThe axis coordinates are shown in Figure

18.

The part is fixtured so that its top

surface is 40 mm above the surface ofthe machine tool table.

Thus, the origin of the axis system willbe 40 mm above the table surface.

A 20-mm diameter end mill with fourteeth will be used.

The cutter has a side tooth engagementlength of 40 mm.



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The bottom tip of the cutter will be

positioned 25 mm below the part topsurface, since the part is 10 mm thick.

The cutter will be operated at a

spindle speed = 1000 rev/min and a

feed rate = 50 mm/min (which

corresponds to 0.20 mm/tooth).

The tool path to be followed by the

cutter is shown in Figure 19.



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Figure 19:Cutter path for profile millingoutside perimeter of sample part.



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NC Part Program Code:

N001 G21 G90 G92 X0 Y-050.0 Z010.0; Define origin of axes.

N002 G00 Z-025.0 S1000 M03; Rapid to cutter depth, turnspindle on.

N003 G01 G94 G42 Y0 D05 F40; Engage part, start cutter offset.N004 G01 X160.0; Mill lower part edge.

N005 G01 Y060.0; Mill right straight edge.

N006 G17 G03 X130.0 Y090.0 R030.0; Circular interpolationaround arc.

N007 G0l X035.0; Mill upper part edge.N008 G01 X0 Y0; Mill left part edge.

N009 G40 G00 X-040.0 M05; Rapid exit from part, cancel offset.

N01 G00 X0 Y050.0; Rapid move to target point.

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