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CNC
TECHNOLOGY
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INTRODUCTION TO
CNC AND METALCUTTING
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HISTORY
US Air Force commissioned MIT to develop thefirst "numerically controlled" machine in 1949. Itwas demonstrated in 1952.
At 1970-1972 first Computer Numeric Controlmachines were developed.
Today, computer numerical control (CNC)machines are found almost everywhere, fromsmall job shops in rural communities tocompanies in large urban areas.
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DEFINITION
In CNC (Computer Numerical Control), theinstructions are stored as a program in amicro-computer attached to the machine.
The computer will also handle much of thecontrol logic of the machine, making itmore adaptable than earlier hard-wired
controllers.
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CNC APPLICATIONS
Machining
2.5D / 3D
Turning ~ Lathes, Turning Centre
Milling ~ Machining Centres Forming
2D
Plasma and Laser CuttingBlanking, nibbling and punching
3D
Rapid Prototyping
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SAMPLECNC MACHINES
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CNC TURNING
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CNC MILLING
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CNC LASER CUTTING
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CNC PLASMA CUTTING
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CNC PRESS
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CNC RAPID PROTOTYPING
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INDUSTRIES MOST AFFECTEDby CNC
Aerospace
Machinery
Electrical Fabrication
Automotive
InstrumentationMold making
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SAMPLE PRODUCTS
OFCNC MANUFACTURING
AUTOMOTIVE INDUSTRY
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AUTOMOTIVE INDUSTRY
Engine Block
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AEROSPACE INDUSTRY
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AEROSPACE INDUSTRYAircraft Turbine Machined by
5-Axis CNC Milling Machine
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CNC MOLD MAKING
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ELECTRONIC INDUSTRY
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RAPID PROTOTYPINGPRODUCTS
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ADVANTAGES OF CNC
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Utilization of computers in
manufacturing applications hasproved to be one of the most
significant advantages &developments over the last coupleof decades in helping to improve
the productivity and efficiency ofmanufacturing systems.
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ADVANTAGES of CNC
Productivity
Machine utilisation is increased becausemore time is spent cutting and less time istaken by positioning.
Reduced setup time increases utilisationtoo.
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PROFITincreases as COST decreasesand as PRODUCTIVITYincreases.
PRODUCTIVITY through AUTOMATION
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AUTOMATION
any means of helpingthe workers to performtheir tasks more
efficiently
transfer of the skill ofthe operator to themachine
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Transferred
skillResults
muscle power engine drivenmachine tools
First industrial
revolution
manipulating
skill
mechanization hard automation
vision skill use of positiontransducers,
cameras
increase of
accuracy, part
recognition
brain power cnc machines, industrialrobots, soft
automation,
computer control of
manufacturing
systems
second industrial
revolution
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EFFICIENCY OF
MANUFACTURING
COST = COST OFMANUFACTURING ANDCOST OF MATERIAL
HANDLING
PROFIT = INCOME - COST
PRODUCTIVITY =
AVERAGE OUTPUT PERMAN-HOUR
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ADVANTAGES of CNC
Quality
Parts are more accurate.
Parts are more repeatable.Less waste due to scrap.
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ADVANTAGES of CNC
Reduced inventory
Reduced setup time permits smallereconomic batch quantities.
Lower lead time allows lower stock levels.
Lower stock levels reduce interest chargesand working capital requirements.
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ADVANTAGES of CNC
Machining Complex shapes
Slide movements under computer control.
Computer controller can calculate steps.First NC machine built 1951 at MIT foraircraft skin milling.
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ADVANTAGES of CNC
Management Control
CNC leads to CAD
Process planningProduction planning
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FUNDAMENTAL OFMETAL CUTTING
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The metal cutting operations (alsocalled machining)is one of the
most important manufacturingprocesses in industry today (as it
was yesterday).
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MACHINING IS THE REMOVAL
OF MATERIALS IN FORMS OF
CHIPS FROM THE WORKPIECE
BY SHEARING WITH A SHARP
TOOL.
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The main function of a machinetool is to control the workpiece-
cutting tool positional relationship in
such a way as to achieve a desiredgeometric shape of the workpiece
with sufficient dimensionalaccuracy.
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Machine tool provides:
work holdingtool holding
relative motion between tooland workpiece
primary motionsecondary motion
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Primary motion
Relative motionbetween tool and
workpieceSecondary motion
Cutting motion
Cuttingspeed
Feed motion
Feed rate
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CLASSIFICATION OF THE CHIP REMOVINGMETHODS ACCORDING TO THE RELATIVE MOTION
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CLASSIFICATION OF MACHINE TOOLS
THOSE USING
SINGLE
POINTTOOLS
THOSE USING
MULTIPOIN
T TOOLS
THOSE USING
ABRASIVE
TOOLS
lathes
shapers
planersboring m/cs
etc.
drilling m/cs
milling m/cs
broaching m/cshobbing m/cs
etc.
grinding m/cs
honing m/cs
etc.
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BASIC COMPONENTSOF CNC SYSTEMS
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m a c h i n e c o n t r o l u n i t
p o s i t i o n t r a n s d u c e r s
w o r k h o l d i n g d e v i c e
t o o l h o l d i n g d e v i c e
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ISO MACHINE TOOL AXIS DEFINITION
ISO MACHINE TOOL AXES DEFINITIONS
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AXIS MACHINE TOOL WITH SPINDLE MACHINE TOOL WITHNO SPINDLE
Z axis of spindle,(+Z) as tool goes away from the work piece
perpendicular to work
holding surface, (+Z) as
tool goes away from theworkpiece
MACHINE
TOOL WITH
ROTATING
WORKPIECE
MACHINE TOOL WITH
ROTATING TOOL
HORIZONT
AL AXIS
VERTICAL
AXIS
X radial andparallel to
cross slide,
(+X) when
tool goes away
from the axis
of spindle
horizontal
and parallel
to work
holding
surface,
(+X) to the
right whenviewed
from
spindle
towards
work piece
horizontal
and parallel
to the work
holding
surface,
(+X) to the
right whenviewed
from
spindle
towards
column
parallel to and positive in
the principal direction of
cutting (primary motion)
Y apply right hand rules
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RIGHT HAND RULEVertical Machine Horizontal Machine
STANDARD LATHE
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STANDARD LATHECOORDINATE SYSTEM
STANDARD MILLING MACHINE
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STANDARD MILLING MACHINECOORDINATE SYSTEM
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NUMERICALLY CONTROLLED MACHINE
TOOLS:An NC machine tool is functionally the sameas a conventional machine tool. The
technological capabilities NC machine toolsin terms of machining are no different fromthose of conventional ones. The differenceis in the way in which the various machine
functions and slide movements arecontrolled.
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The functions and motions such as;
turning the spindle on and off
setting cutting speeds
setting feed rate
turning coolant on and offmoving tool with respect to workpiece
are performed by Machine Control Unit(MCU) in NC machine tools.
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MACHINE TOOLAUTOMATION
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CNC SYSTEM ELEMENTS
A typical CNC system consists of thefollowing six elements
Part program
Program input deviceMachine control unit
Drive system
Machine tool Feedback system
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NC SYSTEM ELEMENTS
OPERATIONAL FEATURES f
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OPERATIONAL FEATURES ofCNC MACHINES
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PART PROGRAM A part program is a series of coded instructions required
to produce a part. It controls the movement of themachine tool and the on/off control of auxiliary functionssuch as spindle rotation and coolant. The codedinstructions are composed of letters, numbers andsymbols and are arranged in a format of functional
blocks as in the following exampleN10 G01 X5.0 Y2.5 F15.0| | | | || | | | Feed rate (15 in/min)
| | | Y-coordinate (2.5")| | X-coordinate (5.0")| Linear interpolation mode
Sequence number
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PROGRAM INPUT DEVICE
The program input device is themechanism for part programs to beentered into the CNC control. The most
commonly used program input devices arekeyboards, punched tape reader, diskettedrivers, throgh RS 232 serial ports and
networks.
MACHINE CONTROL UNIT
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MACHINE CONTROL UNITThe machine control unit (MCU) is the heart of a CNC
system. It is used to perform the following functions:
Read coded instructions
Decode coded instructions
Implement interpolations (linear, circular, and helical) togenerate axis motion commands
Feed axis motion commands to the amplifier circuits fordriving the axis mechanisms
Receive the feedback signals of position and speed foreach drive axis
Implement auxiliary control functions such as coolant orspindle on/off, and tool change
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TYPES of CNC CONTROLSYSTEMS
Open-loop controlClosed-loop control
OPEN LOOP CONTROL
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OPEN-LOOP CONTROLSYSTEM
In open-loop control system step motors areused
Step motors are driven by electric pulses
Every pulse rotates the motor spindle through acertain amount
By counting the pulses, the amount of motioncan be controlled
No feedback signal for error correction Lower positioning accuracy
CLOSED LOOP CONTROL
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CLOSED-LOOP CONTROLSYSTEMS
In closed-loop control systems DC or ACmotors are used
Position transducers are used to generate
position feedback signals for errorcorrection
Better accuracy can be achieved
More expensive Suitable for large size machine tools
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CONTROL
Desired path (p, v, a)
3-axis position control (encoder feedback)
Velocity control (tachometer feedback) Torque control (current feedback)
Path generator
Linear interpolation Circular interpolation
Complex path interpolation (contouring)
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DRIVE SYSTEM
A drive system consists of amplifiercircuits, stepping motors or servomotorsand ball lead-screws. The MCU feeds
control signals (position and speed) ofeach axis to the amplifier circuits. Thecontrol signals are augmented to actuatestepping motors which in turn rotate the
ball lead-screws to position the machinetable.
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STEPPING MOTORS
A stepping motor provides open-loop, digitalcontrol of the position of a workpiece in anumerical control machine. The drive unitreceives a direction input (cw or ccw) and pulse
inputs. For each pulse it receives, the drive unitmanipulates the motor voltage and current,causing the motor shaft to rotate bya fixed angle(one step). The lead screw converts the rotary
motion of the motor shaft into linear motion ofthe workpiece .
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STEPPING MOTORS
RECIRCULATING BALL
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RECIRCULATING BALLSCREWS
Transform rotational motion of the motorinto translational motion of the nut attached to themachine table.
RECIRCULATING BALL
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RECIRCULATING BALLSCREWS
Accuracy of CNCmachines depends ontheir rigid
construction, care inmanufacturing, andthe use of ball screwsto almost eliminate
slop in the screwsused to move portionsof the machine.
COMPONENTS OF
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COMPONENTS OFRECIRCULATING BALL SCREWS
Ball screw
Ball nut (anti-backlash)
Ways Linear bearings
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POSITIONING
The positioning resolution of a ball screw drivemechanism is directly proportional to thesmallest angle that the motor can turn.
The smallest angle is controlled by the motorstep size.
Microsteps can be used to decrease the motorstep size.
CNC machines typically have resolutions of0.0025 mm or better.
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MACHINE TOOL
CNC controls are used to control varioustypes of machine tools. Regardless ofwhich type of machine tool is controlled, it
always has a slide table and a spindle tocontrol of position and speed. Themachine table is controlled in the X and Y
axes, while the spindle runs along the Zaxis.
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FEEDBACK SYSTEM
The feedback system is also referred to asthe measuring system. It uses position andspeed transducers to continuously monitor
the position at which the cutting tool islocated at any particular time. The MCUuses the difference between referencesignals and feedback signals to generate
the control signals for correcting positionand speed errors.
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CNC MACHINES FEEDBACK
DEVICES
ENCODERS
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ENCODERS
A device used to convert linear orrotational position information intoan electrical output signal.
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ENCODERS
INDUSTRIAL APPLICATIONS of
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INDUSTRIAL APPLICATIONS ofENCODERS
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RESOLVERS
A resolver is a rotarytransformer that producesan output signal that is a
function of the rotorposition.
SERVOMOTOR with
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RESOLVER
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DRIVE MOTORS
DC servo motors
AC servo motors
Stepper motors
Hydraulic motors
OS O C
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POSITION FEEDBACK
Incremental encoder
Quadrature
Absolute encoder
Resolver Tachometer
No feedback (open
loop)
POTENTIOMETERS
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POTENTIOMETERS
POTENTIOMETERS
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POTENTIOMETERS
CNC P i
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CNC Programming
Manual Write code directly
Computer-assisted
Draw cutter path
CAD/CAM
Draw the part
Cutter path is generated
VELOCITY FEEDBACK
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VELOCITY FEEDBACK
Tachometers:Electrical output is proportional to rate ofangular rotation.
Encoders, Resolvers, Potentiometers:Number of pulses per time is proportionalto rate change of position.
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CNC MACHINES
CUTTING TOOLS (CUTTERS)
CNC CUTTERS
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CNC CUTTERS
Turning center cutters
Machining center cutters
TURNING CENTER CUTTERS
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TURNING CENTER CUTTERS
Types of cutters used on CNC turningcenters
Carbides (and other hard materials) insert
turning and boring toolsCeramics
High Speed Steel (HSS) drills and taps
STANDART INSERT SHAPES
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STANDART INSERT SHAPES
Vused for profiling, weakestinsert, 2 edges per side.
Dsomewhat stronger, used forprofiling when the angle allows it,2 edges per side.
Tcommonly used for turning
because it has 3 edges per side. Cpopular insert because the
same holder can be used forturning and facing. 2 edges perside.
Wnewest shape. Can turn andface like the C, but 3 edges per
side. SVery strong, but mostly used
for chamfering because it wontcut a square shoulder. 4 edgesper side.
Rstrongest insert but leastcommonly used.
,THREADING and PARTING
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THREADING and PARTINGTOOLS
MACHINING CENTER CUTTING
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TOOLS Most machining centers
use some form of HSS orcarbide insert endmill asthe basic cutting tool.
Insert endmills cut manytimes faster than HSS,but the
HSS endmills leave a
better finish when sidecutting.
MACHINING CENTER CUTTING
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TOOLS (contd)
Facemills flatten largesurfaces quickly andwith an excellentfinish. Notice theengine block beingfinished in one passwith a large cutter.
MACHINING CENTER CUTTING
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TOOLS (contd)
Ball endmills (bothHSS and insert) areused for a variety ofprofiling operations
such as the moldshown in the picture.
Slitting and sidecutters are used when
deep, narrow slotsmust be cut.
MACHINING CENTER CUTTING
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TOOLS (contd)Drills, Taps, and Reamers
Common HSS tools such asdrills, taps, and reamers arecommonly used on CNCmachining centers. Note that aspot drill is used instead of acenterdrill. Also, spiral point orgun taps are used for throughholes and spiral flute for blindholes. Rarely are hand tapsused on a machining center.
TOOL HOLDERS
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TOOL HOLDERS
All cutting tools must be held in a holderthat fits in the spindle. These include endmill holders (shown), collet holders, facemill adapters, etc. Most machines in theUSA use a CAT taper which is a modifiedNST 30, 40, or 50 taper that uses a pull
stud and a groove in the flange. Themachine pulls on the pull stud to hold theholder in the spindle, and the groove inthe flange gives the automatic toolchanger something to hold onto. HSK toolholders were designed a number of years
ago as an improvement to CAT tapers,but they are gaining acceptance slowly.
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CNC PROGRAMMING
CNC PROGRAMMING
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CNC PROGRAMMING
Offline programminglinked to CAD programs. Conversational programmingby the operator.
MDI~ Manual Data Input.
Manual Controlusing jog buttons or `electronichandwheel'.
Word-Address Codingusing standard G-codesand M-codes.
Basics of NC Part Programming
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During secondary motion, either the toolmoves relative to the workpiece or the
workpiece moves relative to the tool. InNC programming, it is always assumed
that the tool moves relative to the
workpiece no matter what the realsituation is.
Basics of NC Part Programming:
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The position of the tool is describedby using a Cartesian coordinatesystem. If (0,0,0) position can be
described by the operator, then it iscalled floating zero.
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In defining the motion of the toolfrom one point to another,either
absolutepositioningmode orincrementalpositioningmode
can be used.
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Structure of an NC Part Program:
Commands are input into the controller inunits called blocksor statements.
Block Format:
1. Fixed sequential format
2. Tab sequential format3. Word address format
EXAMPLE:
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EXAMPLE:Assume that a drilling operation is to be
programmed as:
1. The tool is positioned at (25.4,12.5,0) by a
rapid movement.2. The tool is then advanced -10 mm in the zdirection at a feed rate of 500 mm/min., with theflood coolant on.
3.The is then retracted back 10 mm at the rapidfeed rate, and the coolant is turned off.
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1. Fixed sequential format0050 00 +0025400 +0012500 +0000000 0000 000060 01 +0025400 +0012500 -0010000 0500 08
0070 00 +0025400 +0012500 +0000000 0000 09
2. Tab sequential format0050 TAB 00 TAB +0025400 TAB +0012500 TAB +0000000 TAB TAB0060 TAB 01 TAB TAB TAB -0010000 TAB 0500 TAB 080070 TAB 00 TAB TAB TAB -0000000 TAB 0000 TAB 09
3. Word address formatN50 G00 X25400 Y125 Z0 F0N60 G01 Z-10000 F500 M08N70 G00 Z0 M09
Modal commands: Commands issued in the
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Modal commands: Commands issued in theNC program that will stay in effect until it is
changed by some other command, like, feedrate selection, coolant selection, etc.
Nonmodal commands: Commands that areeffective only when issued and whoseeffects are lost for subsequent commands,like, a dwell command which instructs thetool to remain in a given configuration for agiven amount of time.
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CNC PROGRAMMING
INFORMATION NEEDED by a
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CNC
1. Preparatory Information: units, incremental or absolutepositioning2. Coordinates: X,Y,Z, RX,RY,RZ3. Machining Parameters: Feed rate and spindle speed4. Coolant Control: On/Off, Flood, Mist
5. Tool Control: Tool and tool parameters6. Cycle Functions: Type of action required7. Miscellaneous Control: Spindle on/off, direction of
rotation, stops for part movement
This information is conveyed to the machine through a setof instructions arranged in a desired sequenceProgram.
BLOCK FORMAT
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Sample BlockN135 G01 X1.0 Y1.0 Z0.125 F5
Restrictions on CNC blocks Each may contain only one tool move Each may contain any number of non-tool move G-
codes Each may contain only one feedrate Each may contain only one specified tool or spindle
speed The block numbers should be sequential Both the program start flag and the program number
must be independent of all other commands (onseparate lines)
The data within a block should follow the sequence
WORD-ADDRESS CODING
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WORD-ADDRESS CODING
N5 G90 G20 N10 M06 T3 N15 M03 S1250
N20 G00 X1 Y1 N25 Z0.1 N30 G01 Z-0.125 F5 N35 X3 Y2 F10 N40 G00 Z1
N45 X0 Y0 N50 M05 N55 M30
Example CNC Program
Each instruction to the machineconsists of a letter followed by anumber.
Each letter is associated with aspecific type of action or piece ofinformation needed by the machine.
Letters used in Codes
N,G,X,Y,Z,A,B,C,I,J,K,F,S,T,R,M
G & M Codes
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G & M Codes
N5 G90 G20 N10 M06 T3 N15 M03 S1250
N20 G00 X1 Y1 N25 Z0.1 N30 G01 Z-0.125 F5 N35 X3 Y2 F10 N40 G00 Z1
N45 X0 Y0 N50 M05 N55 M30
Example CNC Program
G-codes: Preparatory Functionsinvolve actual tool moves.
M-codes: MiscellaneousFunctionsinvolve actionsnecessary for machining (i.e.spindle on/off, coolant on/off).
G Codes
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G Codes
G00 Rapid traverse G01 Linear interpolation
G02 Circular interpolation,CW
G03 Circular interpolation,CCW
G04 Dwell
G08 Acceleration
G09 Deceleration
G17 X-Y Plane
G18 Z-X Plane
G19 Y-Z Plane
G20 Inch Units (G70) G21 Metric Units (G71)
G40 Cutter compensationcancel
G41 Cutter compensationleft
G42 Cutter compensation-right
G70 Inch format G71 Metric format G74 Full-circle programming
off G75 Full-circle programming
on G80 Fixed-cycle cancel G81-G89 Fixed cycles G90 Absolute dimensions G91 Incremental dimensions
Modal G-Codes
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Modal G-Codes
Most G-codes set the machine in a mode
which stays in effect until it is changed orcancelled by another G-code. Thesecommands are called modal.
Modal G-Code List
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Modal G-Code List
G00 Rapid Transverse G01 Linear Interpolation
G02 Circular Interpolation, CW
G03 Circular Interpolation,CCW
G17 XY Plane
G18 XZ Plane
G19 YZ Plane G20/G70 Inch units
G21/G71 Metric Units
G40 Cutter compensationcancel
G41 Cutter compensation left
G42 Cutter compensation right
G43 Tool length compensation(plus)
G43 Tool lengthcompensation (plus)
G44 Tool lengthcompensation (minus)
G49 Tool lengthcompensation cancel
G80 Cancel canned cycles
G81 Drilling cycle
G82 Counter boring cycle
G83 Deep hole drilling cycle
G90 Absolute positioning
G91 Incremental positioning
M Codes
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M Codes
M00 Program stop M01 Optional program stop M02 Program end M03 Spindle on clockwise M04 Spindle on counterclockwise M05 Spindle stop M06 Tool change M08 Coolant on M09 Coolant off M10 Clamps on M11 Clamps off M30 Program stop, reset to start
N Codes
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N Codes
Gives an identifying number for each blockof information.
It is generally good practice to incrementeach block number by 5 or 10 to allowadditional blocks to be inserted if future
changes are required.
X Y and Z Codes
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X,Y, and Z Codes
X, Y, and Z codes are used to specify thecoordinate axis.
Number following the code defines the
coordinate at the end of the move relativeto an incremental or absolute referencepoint.
I J and K Codes
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I,J, and K Codes
I, J, and K codes are used to specify thecoordinate axis when defining the centerof a circle.
Number following the code defines therespective coordinate for the center of the
circle.
F S and T Codes
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F,S, and T Codes
F-code: used to specify the feed rate
S-code: used to specify the spindle speed
T-code: used to specify the toolidentification number associated with thetool to be used in subsequent operations.
Application of Some CodesG01 Li I t l ti
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G01 Linear Interpolation
Format: N_ G01 X_ Y_ Z_ F_
Linear Interpolation results in a straight
line feed move.
Unless tool compensation is used, the
coordinates are associated with thecenterline of the tool.
Application of Some CodesG01 Li I t l ti
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G01 Linear Interpolation
. As an example, for the motion that occurs in x-y plane with the same maximum speed for the x-and y-axis, initial motion is at an angle of 45o tothe axes until motion in one of
the axes is completed and then the balance ofthe motion occurs in the other axis. This is called
point-to-point motion.
Application of Some CodesG01 Li I t l ti
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G01 Linear Interpolation
5
1 0
1 5
2 0
2 5
5 1 0 1 5 2 0 2 5 3 0
A
B C
P o s i t i o n i n g m o t i o n f r o m A t o C
N 1 0 G 0 0 X 3 0 0 0 0 Y 2 0 0 0 0 F 0
Application of Some CodesG01 Li I t l ti
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G01 Linear Interpolation
G01 is another preparatory function to specifythat the tool should be moved to a specifiedlocation along a straight line path. It is referred
to as linear interpolation.
This function is typically used to specifymachining of straight features such as turninga cylindrical surface in turning, cutting a slot inmilling, etc.
Application of Some CodesG01 Li I t l ti
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G01 Linear Interpolation
5
1 0
1 5
2 0
2 5
5 1 0 1 5 2 0 2 5 3 0
A
C
L i n e a r i n t e r p o l a t i o n f r o m A t o C
N 1 0 G 0 1 X 3 0 0 0 0 Y 2 0 0 0 0 F 2 5 0 0
G01 Linear Interpolation
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N10 G00 X1 Z1N15 Z0.1N20 G01 Z-0.125 F5
N25 X2 Z2 F10
G01 Linear Interpolation
X
Z
G02 Circular Interpolation
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G02 Circular Interpolation
G02 is also a preparatory function to specify thatthe tool should be moved to a specified locationalong a circular path in a clockwise direction. Inorder to specify the path to the MCU, the end
point of the arc and the location of the center ofthe arc should be specified. Within the block inwhich the G02 code is programmed, the centerof the arc is given by specifying its locationrelative to the start of the arc.
G02 Circular Interpolation (CW)
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G02 Circular Interpolation (CW)
The G02 command requiresan endpoint and a radius inorder to cut the arc.
I,J, and K are relative to the
start point.
N_ G02 X2 Y1 I0 J-1 F10
or
N_ G02 X2 Y1 R1
G02 Circular Interpolation (CW)
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G02 Circular Interpolation (CW)
5
1 0
1 5
2 0
2 5
5 1 0 1 5 2 0 2 5 3 0
C
C
C i r c u l a r i n t e r p o l a t i o n f r o m A t o B
a b o u t a c i r c l e c e n t e r e d a t C
N 1 0 G 0 2 X 2 0 0 0 0 Y 1 0 0 0 0
I 5 0 0 0 J 1 5 0 0 0 F 2 5 0 0
A
B
I = 5
J = 1 5
Canned Cycles
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The sequence of some machining operations is maybe the same for any part and for any machine. Forexample drilling a hole involves the following steps:Position the tool above the point where the hole will bedrilledSet the correct spindle speedFeed the tool into the workpiece at a controlled feedrate to a predetermined depthRetract the tool at a rapid rate to just above the pointwhere the hole started
Some Commonly Used Canned Cycle
C d F ti D f d At b tt R t ti
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Code Function Down feed At bottom Retraction
G81 Drilling Continuousfeed
No action Rapid
G82 Spot face,counterbore
Continuous
feedDwell Rapid
G83 Deep hole drilling Peck No action Rapid
G84 Tapping Continuousfeed
Reverse
spindleFeed
rate
G85 Through boring(in& out) Continuousfeed No action Feedrate
G86 Through boring(inonly)
Continuous
feedStop
spindleRapid
G81 ILLUSTRATION
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Three Main parts of a CNCprogram
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program
N5 G90 G21 (Absolute units, metric)
N10 M06 T2 (Stop for tool change, usetool # 2)
N15 M03 S1200 (Turn the spindle on CW to1200 rpm)
Part 1- Program Petup
Three Main parts of a CNCprogram
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program
N20 G00 X1 Y1 (Rapid to X1,Y1 from origin
point) N25 Z0.125 (Rapid down to Z0.125) N30 G01 Z-0.125 F100 (Feed down to Z-0.125 at
100 mm/min) N35 G01 X2 Y2 (Feed diagonally to X2,Y2) N40 G00 Z1 (Rapid up to Z1) N45 X0 Y0 (Rapid to X0,Y0)
Part 2- Chip Removal
Three Main parts of a CNCprogram
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program
N50 M05 (Turn the spindle off)
N55 M00 (Program stop)
Part 3- System Shutdown
EXAMPLE OPERATION on CNCMILLING MACHINE
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MILLING MACHINE
G-CODE PROGRAM
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First pass : conventional mill toa depth of 0.125 around edgeprofile. Tool 1 is a inch dia.end mill.
%
:1002N5 G90 G20N10 M06 T1N15 M03 S1200N20 G00 X0.125 Y0.125N30 Z0.125N35 G01 Z-0.125 F5
N40 X3.875N45 Y4.125N50 X0.125N55 Y0.125
Second pass:
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conventional mill to a
depth of 0.25 aroundedge profile.
N35 Z-0.250
N40 X3.875
N45 Y4.125
N50 X0.125
N55 Y0.125
N60 Z0.125
Third pass:conventional mill to a
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co e t o a to adepth of 0.125 around
pocket profile.
N65 G00 X1.25 Y1.0
N70 G01 Z-0.125 F5
N75 X1.75
N80 Y2.5
N85 X1.25
N90 Y1.0N95 Z0.125
Fourth pass: climbmill to a depth of
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mill to a depth of0.125 acrossremaining material.
N100 Y2.125
N105 X2.625N110 Z0.125
N115 G00 X-5 Y-5 Z5
N120 M05N125 M30
Advanced features:
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Execution of the part of the program in arotated or mirrored position.
Ability to scale the program and producelarger or smaller programs.
Three dimensional circular interpolationwhich produces a helical shape.
Parabolic and cubic interpolation.
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Program Loading:
Through keyboard
Through punched tape reader Through diskette drive
Through RS 232 serial port
Through network interface card
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Direct Numerical Control (DNC):
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This system used to work with the early NCmachine tools which can not read more than ablock of information at a time. The centralcomputer feed the program information oneblock at a time. When the machine execute theinformation, the next block of information wouldbe fed.
Distributed Numerical Control (DNC):
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Distributed NC is known by the same acronymas Direct Numerical Control (DNC). After theintroduction of CNC, the machine tools havehad the capability of storing large amount of
information. Therefore, there have been noneed to have drip feed information system, like,Direct Numerical Control. Instead, DistributedNumerical Control is introduced. In such a
system, a host computer communicate withmany CNC machine tools via networks anddownload or upload programs.
Distributed Numerical Control (DNC):
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With Distributed Numerical Control systems, itis possible to monitor the activities in individualCNC machine tools on host computer.
Therefore, better shop floor control can beachieved.
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NC program preparation may be tedious anddifficult if the part to be machined has acomplex geometry. The main difficulty is to findout the cutter locations during the machining.Computers may be used to assist theprogrammers in preparing the NC codes.
Computer Aided Part Programming:
Advantages of applying computer aided part
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Advantages of applying computer-aided partprogramming include the following:
1. It reduces the manual calculationsinvolves in determining the geometriccharacteristics of the part.
It provides the cutter path simulation.
It provides tool collision checking.
It shortens the program preparation time.
It makes the program preparation easier.
The Aerospace Industries Association
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The Aerospace Industries Associationsponsored the work that led to the first part
programming language, developed in MIT in1955.
This was called:Automatically ProgrammedTools(APT).
APT is an English like simple programminglanguage which basically produce the CutterLocation(CL) data.
Using the cutter location data, the program cangenerate the actual NC codes by using apostprocessor .
CAD/CAM Based Part Programming:
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The output of any CAD package include thegeometric data of the part to be machined.Therefore, many CAD/CAM package canproduce cutter location (CL) data to be used for
NC code generation. There is still to be a process planning module
for a workable NC code generation.
Some of the CAD/CAM packages that have the
NC code generation capabilities areComputervision CATIA CADAM