cnc machine tools

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CNC TECHNOLOGYCNC TECHNOLOGYandand

CNC PROGRAMMINGCNC PROGRAMMING

ME 445INTEGRATED MANUFACTURING SYSTEMS

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AUTOMATION IN MANUFACTURING AUTOMATION IN MANUFACTURING SYSTEMSSYSTEMS

TRENDS IN INDUSTRYTRENDS IN INDUSTRY

THE OBJECTIVE: THE OBJECTIVE:

TO BE COMPETITIVTO BE COMPETITIV THROUGH THROUGH INCREASING PRODUCTIVITY AND TOTAL INCREASING PRODUCTIVITY AND TOTAL

QUALITY ASSURANCEQUALITY ASSURANCE

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EFFICIENCY OF EFFICIENCY OF MANUFACTURINMANUFACTURIN

GG

COST = COST OF MANUFACTURING AND COST OF MATERIAL HANDLING

PROFIT = INCOME - COST

PRODUCTIVITY = AVERAGE OUTPUT PER MAN-HOUR

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PROFITPROFIT increases as increases as COSTCOST decreases and as decreases and as PRODUCTIVITYPRODUCTIVITY

increases.increases.

PRODUCTIVITY through PRODUCTIVITY through AUAUTOMATIONTOMATION

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AUTOMATIONAUTOMATION

any means of helping the workers to perform their tasks more efficiently

transfer of the skill of the operator to the machine

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Transferred skill

Results

muscle power engine driven machine tools

First industrial revolution

manipulating skill

mechanization hard automation

vision skill use of position transducers,

cameras

increase of accuracy, part

recognition

brain power cnc machines, industrial robots, soft automation,

computer control of manufacturing

systems

second industrial revolution

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Utilization of computers in Utilization of computers in manufacturing applications has manufacturing applications has proved to be one of the most proved to be one of the most significant developments over significant developments over the last couple of decades in the last couple of decades in

helping to improve the helping to improve the productivity and efficiency of productivity and efficiency of

manufacturing systems.manufacturing systems.

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The metal cutting operations The metal cutting operations (also called machining)(also called machining) is one is one

of the most important of the most important manufacturing processes in manufacturing processes in

industry today industry today (as it was (as it was yesterday)yesterday). .

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MACHINING MACHINING IS THE IS THE REMOVAL OF MATERIALS REMOVAL OF MATERIALS IN FORMS OF CHIPS FROM IN FORMS OF CHIPS FROM

THE WORKPIECE BY THE WORKPIECE BY SHEARING WITH A SHARP SHEARING WITH A SHARP

TOOL.TOOL.

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The main function of a The main function of a machine tool is to control the machine tool is to control the

workpiece-cutting tool workpiece-cutting tool positional relationship in such positional relationship in such a way as to achieve a desired a way as to achieve a desired

geometric shape of the geometric shape of the workpiece with sufficient workpiece with sufficient dimensional accuracy.dimensional accuracy.

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Machine tool provides:

work holdingtool holdingrelative motion between tool and workpiece

primary motion

secondary motion

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Primary motion

Relative motionbetween tool and

workpiece

Secondary motion

Cutting motion

Cutting speed

Feed motion

Feed rate

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machine control unitposition transducers

work holding device

tool holding device

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CLASSIFICATION OF THE CHIP REMOVING METHODS CLASSIFICATION OF THE CHIP REMOVING METHODS ACCORDING TO THE RELATIVE MOTIONACCORDING TO THE RELATIVE MOTION

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CLASSIFICATION OF MACHINE TOOLSCLASSIFICATION OF MACHINE TOOLS

THOSE USING SINGLE POINT TOOLS

THOSE USING MULTIPOINT TOOLS

THOSE USING ABRASIVE TOOLS

lathesshapersplanersboring m/c’setc.

drilling m/c’smilling m/c’sbroaching m/c’shobbing m/c’setc.

grinding m/c’shoning m/c’setc.

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ISO MACHINE TOOL AXIS DEFINITIONISO MACHINE TOOL AXIS DEFINITION

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ISO MACHINE TOOL AXES DEFINITIONS

AXIS MACHINE TOOL WITH SPINDLE MACHINE TOOL WITH NO 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 the workpiece

MACHINE TOOL WITH ROTATING WORKPIECE

MACHINE TOOL WITH ROTATING TOOL

HORIZONTAL AXIS

VERTICAL AXIS

X radial and parallel to cross slide, (+X) when tool goes away from the axis of spindle

horizontal and parallel to work holding surface, (+X) to the right when viewed from spindle towards work piece

horizontal and parallel to the work holding surface, (+X) to the right when viewed 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 RULERIGHT HAND RULEVertical Machine Horizontal Vertical Machine Horizontal

MachineMachine

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STANDARD LATHE STANDARD LATHE COORDINATE SYSTEMCOORDINATE SYSTEM

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STANDARD MILLING MACHINESTANDARD MILLING MACHINECOORDINATE SYSTEMCOORDINATE SYSTEM

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NUMERICALLY CONTROLLED MACHINE NUMERICALLY CONTROLLED MACHINE TOOLS:TOOLS:

An NC machine tool is functionally the An NC machine tool is functionally the same as a conventional machine tool. same as a conventional machine tool.

The technological capabilities NC The technological capabilities NC machine tools in terms of machining machine tools in terms of machining

are no different from those of are no different from those of conventional ones. The difference is in conventional ones. The difference is in the way in which the various machine the way in which the various machine

functions and slide movements are functions and slide movements are controlled.controlled.

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The functions and motions such as;The functions and motions such as;

turning the spindle on and offturning the spindle on and offsetting cutting speedssetting cutting speedssetting feed ratesetting feed rateturning coolant on and offturning coolant on and offmoving tool with respect to workpiecemoving tool with respect to workpiece

are performed by Machine Control Unit are performed by Machine Control Unit (MCU) in NC machine tools.(MCU) in NC machine tools.

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INTRODUCTION TO INTRODUCTION TO CNCCNC

20042004 2424

HISTORYHISTORY

US Air Force commissioned MIT to develop the US Air Force commissioned MIT to develop the first "numerically controlled" machine in 1949. It first "numerically controlled" machine in 1949. It was demonstrated in 1952. was demonstrated in 1952.

At 1970-1972 first Computer Numeric Control At 1970-1972 first Computer Numeric Control machines were developed.machines were developed.

Today, computer numerical control (CNC) Today, computer numerical control (CNC) machines are found almost everywhere, from machines are found almost everywhere, from small job shops in rural communities to small job shops in rural communities to companies in large urban areas. companies in large urban areas.

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DEFINITIONDEFINITION

In In CNC CNC ((Computer Numerical ControlComputer Numerical Control),), the the instructions are stored as a program in a instructions are stored as a program in a micro-computer attached to the machine. micro-computer attached to the machine. The computer will also handle much of the The computer will also handle much of the control logic of the machine, making it control logic of the machine, making it more adaptable than earlier hard-wired more adaptable than earlier hard-wired controllers.controllers.

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CNC APPLICATIONSCNC APPLICATIONS MachiningMachining 2.5D / 3D 2.5D / 3D Turning ~ Lathes, Turning Centre Turning ~ Lathes, Turning Centre Milling ~ Machining Centres Milling ~ Machining Centres FormingForming 2D 2D Plasma and Laser Cutting Plasma and Laser Cutting Blanking, nibbling and punching Blanking, nibbling and punching 3D 3D Rapid Prototyping Rapid Prototyping

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SAMPLESAMPLE CNC MACHINES CNC MACHINES

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CNC TURNINGCNC TURNING

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CNC MILLINGCNC MILLING

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CNC LASER CUTTINGCNC LASER CUTTING

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CNC PLASMA CUTTINGCNC PLASMA CUTTING

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CNC PRESSCNC PRESS

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CNC RAPID PROTOTYPINGCNC RAPID PROTOTYPING

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INDUSTRIES MOST AFFECTED INDUSTRIES MOST AFFECTED by CNCby CNC

Aerospace Aerospace Machinery Machinery Electrical Electrical Fabrication Fabrication Automotive Automotive Instrumentation Instrumentation Mold making Mold making

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SAMPLE PRODUCTSSAMPLE PRODUCTS OF OF

CNC MANUFACTURINGCNC MANUFACTURING

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AUTOMOTIVE INDUSTRYAUTOMOTIVE INDUSTRY

Engine BlockEngine Block

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AUTOMOTIVE AUTOMOTIVE INDUSTRY(Cont’d)INDUSTRY(Cont’d)

Different ProductsDifferent Products

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AEROSPACE INDUSTRYAEROSPACE INDUSTRYAircraft Turbine Machined by Aircraft Turbine Machined by 5-Axis CNC Milling Machine5-Axis CNC Milling Machine

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CNC MOLD MAKINGCNC MOLD MAKING

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ELECTRONIC INDUSTRYELECTRONIC INDUSTRY

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RAPID PROTOTYPING RAPID PROTOTYPING PRODUCTSPRODUCTS

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ADVANTAGES of CNCADVANTAGES of CNC

ProductivityProductivity

Machine utilisation is increased Machine utilisation is increased because more time is spent cutting because more time is spent cutting and less time is taken by positioning. and less time is taken by positioning.

Reduced setup time increases Reduced setup time increases utilisation too. utilisation too.

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QualityQuality

Parts are more accurate. Parts are more accurate.

Parts are more repeatable. Parts are more repeatable.

Less waste due to scrap. Less waste due to scrap.

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Reduced inventoryReduced inventory

Reduced setup time permits smaller Reduced setup time permits smaller economic batch quantities. economic batch quantities.

Lower lead time allows lower stock levels. Lower lead time allows lower stock levels.

Lower stock levels reduce interest Lower stock levels reduce interest charges and working capital charges and working capital requirements. requirements.

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Machining Complex shapesMachining Complex shapes

Slide movements under computer Slide movements under computer control. control.

Computer controller can calculate Computer controller can calculate steps. steps.

First NC machine built 1951 at MIT First NC machine built 1951 at MIT for aircraft skin milling. for aircraft skin milling.

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Management ControlManagement Control

CNC leads to CAD CNC leads to CAD

Process planning Process planning

Production planning Production planning

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DRAWBACKS of CNCDRAWBACKS of CNC High capital cost High capital cost Machine tools cost $30,000 - $1,500,000 Machine tools cost $30,000 - $1,500,000 Retraining and recruitment of staff Retraining and recruitment of staff New support facilities New support facilities High maintenance requirementsHigh maintenance requirements Not cost-effective for low-level production on Not cost-effective for low-level production on

simple partssimple parts As geometric complexity or volume increases As geometric complexity or volume increases

CNC becomes more economicalCNC becomes more economical Maintenance personnel must have both Maintenance personnel must have both

mechanical and electronics expertise mechanical and electronics expertise

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CNC SYSTEM CNC SYSTEM ELEMENTSELEMENTS

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CNC SYSTEM ELEMENTSCNC SYSTEM ELEMENTS

A typical CNC system consists of thA typical CNC system consists of the e following six elements following six elements

Part program Part program Program input device Program input device Machine control unit Machine control unit Drive system Drive system Machine tool Machine tool Feedback system Feedback system

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NC SYSTEM ELEMENTSNC SYSTEM ELEMENTS

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OPERATIONAL FEATURES of OPERATIONAL FEATURES of CNC MACHINESCNC MACHINES

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PART PROGRAMPART PROGRAM A part program is a series of coded instructions A part program is a series of coded instructions

required to produce a part. It controls the required to produce a part. It controls the movement of the machine tool and the on/off movement of the machine tool and the on/off control of auxiliary functions such as spindle control of auxiliary functions such as spindle rotation and coolant. The coded instructions are rotation and coolant. The coded instructions are composed of letters, numbers and symbols and are composed of letters, numbers and symbols and are arranged in a format of functional blocks as in the arranged in a format of functional blocks as in the following examplefollowing example

N10 G01 X5.0 Y2.5 F15.0N10 G01 X5.0 Y2.5 F15.0 | | | | | | | | | | | | | | Feed rate (15 in/min) | | | | Feed rate (15 in/min) | | | Y-coordinate (2.5") | | | Y-coordinate (2.5") | | X-coordinate (5.0") | | X-coordinate (5.0") | Linear interpolation mode | Linear interpolation mode Sequence number Sequence number

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PROGRAM INPUT DEVICEPROGRAM INPUT DEVICE

The program input device is the The program input device is the mechanism for part programs to be mechanism for part programs to be entered into the CNC control. Thentered into the CNC control. The e mostmost commonly used program input commonly used program input devices are devices are keyboardskeyboards,, punched tape punched tape reader, diskette drivers, throgh RS reader, diskette drivers, throgh RS 232 serial ports and networks232 serial ports and networks. .

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MACHINE CONTROL UNITMACHINE CONTROL UNIT The machine control unit (MCU) is the heart of a The machine control unit (MCU) is the heart of a

CNC system. It is used to perform the following CNC system. It is used to perform the following functions: functions:

Read coded instructionsRead coded instructions Decode coded instructions Decode coded instructions Implement interpolations (linear, circular, and Implement interpolations (linear, circular, and

helical) to generate axis motion commands helical) to generate axis motion commands Feed axis motion commands to the amplifier Feed axis motion commands to the amplifier

circuits for driving the axis mechanisms circuits for driving the axis mechanisms Receive the feedback signals of position and speed Receive the feedback signals of position and speed

for each drive axis for each drive axis Implement auxiliary control functions such as Implement auxiliary control functions such as

coolant or spindle on/off, and tool changecoolant or spindle on/off, and tool change

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TYPES of CNC CONTROL TYPES of CNC CONTROL SYSTEMSSYSTEMS

Open-loop controlOpen-loop control Closed-loop controlClosed-loop control

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OPEN-LOOP CONTROL OPEN-LOOP CONTROL SYSTEMSYSTEM

In open-loop control system step motors In open-loop control system step motors are usedare used

Step motors are driven by electric pulsesStep motors are driven by electric pulses Every pulse rotates the motor spindle Every pulse rotates the motor spindle

through a certain amountthrough a certain amount By counting the pulses, the amount of By counting the pulses, the amount of

motion can be controlledmotion can be controlled No feedback signal for error correctionNo feedback signal for error correction Lower positioning accuracy Lower positioning accuracy

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CLOSED-LOOP CONTROL CLOSED-LOOP CONTROL SYSTEMSSYSTEMS

In closed-loop control systems DC or In closed-loop control systems DC or AC motors are usedAC motors are used

Position transducers are used to Position transducers are used to generate position feedback signals generate position feedback signals for error correctionfor error correction

Better accuracy can be achievedBetter accuracy can be achieved More expensiveMore expensive Suitable for large size machine toolsSuitable for large size machine tools

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DRIVE SYSTEMDRIVE SYSTEM

A drive system consists of amplifier A drive system consists of amplifier circuits, circuits, steppingstepping motors motors or or servomotorsservomotors and ball lead-screws. The and ball lead-screws. The MCU feeds control signals (position and MCU feeds control signals (position and speed) of each axis to the amplifier speed) of each axis to the amplifier circuits. The control signals are circuits. The control signals are augmented to actuate augmented to actuate steppingstepping motors motors which in turn rotate the ball lead-which in turn rotate the ball lead-screws to position the machine table. screws to position the machine table.

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STEPPING MOTORSSTEPPING MOTORS A stepping motor provides open-loop,

digital control of the position of a workpiece in a numerical control machine. The drive unit receives a direction input (cw or ccw) and pulse inputs. For each pulse it receives, the drive unit manipulates 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 of the workpiece .

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STEPPING MOTORSSTEPPING MOTORS

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RECIRCULATING BALL RECIRCULATING BALL SCREWSSCREWS

Transform rotational motion of the Transform rotational motion of the motor intomotor into translationaltranslational motion of the nut motion of the nut attached to the machine table.attached to the machine table.

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RECIRCULATING BALL RECIRCULATING BALL SCREWSSCREWS

Accuracy of CNC machines depends on their rigid construction, care in manufacturing, and the use of ball screws to almost eliminate slop in the screws used to move portions of the machine.

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POSITIONINGPOSITIONING

The positioning resolution of a ball screw drive mechanism is directly proportional to the smallest angle that the motor can turn.

The smallest angle is controlled by the motor step size.

Microsteps can be used to decrease the motor step size.

CNC machines typically have resolutions of 0.0025 mm or better.

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MACHINE TOOLMACHINE TOOL

CNC controls are used to control CNC controls are used to control various types of machine tools. various types of machine tools. Regardless of which type of machine Regardless of which type of machine tool is controlled, it always has a slide tool is controlled, it always has a slide table and a spindle to control of table and a spindle to control of position and speed. The machine table position and speed. The machine table is controlled in the X and Y axes, while is controlled in the X and Y axes, while the spindle runs along the Z axis. the spindle runs along the Z axis.

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FEEDBACK SYSTEMFEEDBACK SYSTEM

The feedback system is also referred to The feedback system is also referred to as the measuring system. It uses as the measuring system. It uses position and speed transducers to position and speed transducers to continuously monitor the position at continuously monitor the position at which the cutting tool is located at any which the cutting tool is located at any particular time. The MCU uses the particular time. The MCU uses the difference between reference signals difference between reference signals and feedback signals to generate the and feedback signals to generate the control signals for correcting position control signals for correcting position and speed errors. and speed errors.

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CNC MACHINES FEEDBACK CNC MACHINES FEEDBACK DEVICESDEVICES

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POTENTIOMETERSPOTENTIOMETERS

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POTENTIOMETERSPOTENTIOMETERS

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ENCODERSENCODERS

A device used to convert linear or rotational position information into an electrical output signal.

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ENCODERSENCODERS

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INDUSTRIAL APPLICATIONS of INDUSTRIAL APPLICATIONS of ENCODERSENCODERS

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RESOLVERSRESOLVERS

A resolver is a rotary transformer that produces an output signal that is a function of the rotor position.

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SERVOMOTOR with SERVOMOTOR with RESOLVERRESOLVER

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VELOCITY FEEDBACKVELOCITY FEEDBACK Tachometers: Electrical output is proportional to

rate of angular rotation. Encoders, Resolvers,

Potentiometers: Number of pulses per time is

proportional to rate change of position.

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CNC CUTTERSCNC CUTTERS

Turning center cutters Turning center cutters Machining center cuttersMachining center cutters

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TURNING CENTER CUTTERSTURNING CENTER CUTTERS

Types of cutters used on CNC turning centers

Carbides (and other hard materials) insert turning and boring tools

Ceramics High Speed Steel (HSS) drills and

taps

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STANDART INSERT SHAPESSTANDART INSERT SHAPES V – used for profiling, weakest

insert, 2 edges per side. D – somewhat stronger, used

for profiling when the angle allows it, 2 edges per side.

T – commonly used for turning because it has 3 edges per side.

C – popular insert because the same holder can be used for turning and facing. 2 edges per side.

W – newest shape. Can turn and face like the C, but 3 edges per side.

S – Very strong, but mostly used for chamfering because it won’t cut a square shoulder. 4 edges per side.

R – strongest insert but least commonly used.

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TYPICAL TURNING,THREADING and PARTING

TOOLS

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MACHINING CENTER CUTTING MACHINING CENTER CUTTING TOOLSTOOLS

Most machining centers use some form of HSS or carbide insert endmill as the basic cutting tool.

Insert endmills cut many times faster than HSS, but the

HSS endmills leave a better finish when side cutting.

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MACHINING CENTER CUTTING MACHINING CENTER CUTTING TOOLS (cont’d)TOOLS (cont’d)

Facemills flatten large surfaces quickly and with an excellent finish. Notice the engine block being finished in one pass with a large cutter.

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Ball endmills (both HSS and insert) are used for a variety of profiling operations such as the mold shown in the picture.

Slitting and side cutters are used when deep, narrow slots must be cut.

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Drills, Taps, and Reamers

Common HSS tools such as drills, taps, and reamers are commonly used on CNC machining centers. Note that a spot drill is used instead of a centerdrill. Also, spiral point or gun taps are used for through holes and spiral flute for blind holes. Rarely are hand taps used on a machining center.

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TOOL HOLDERSTOOL HOLDERS

All cutting tools must be held in a holder that fits in the spindle. These include end mill holders (shown), collet holders, face mill adapters, etc. Most machines in the USA use a CAT taper which is a modified NST 30, 40, or 50 taper that uses a pull stud and a groove in the flange. The machine pulls on the pull stud to hold the holder in the spindle, and the groove in the flange gives the automatic tool changer something to hold onto. HSK tool holders were designed a number of years ago as an improvement to CAT tapers, but they are gaining acceptance slowly.

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Offline programmingOffline programming linked to CAD linked to CAD programs. programs.

Conversational programmingConversational programming by the by the operator. operator.

MDIMDI ~ Manual Data Input. ~ Manual Data Input. Manual ControlManual Control using jog buttons or using jog buttons or

`electronic handwheel'. `electronic handwheel'. Word-Address CodingWord-Address Coding using standard G- using standard G-

codes and M-codes. codes and M-codes.

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During secondary motion, either the During secondary motion, either the tool moves relative to the workpiece or tool moves relative to the workpiece or

the workpiece moves relative to the the workpiece moves relative to the tool. In NC programming, it is always tool. In NC programming, it is always assumed that the tool moves relative assumed that the tool moves relative to the workpiece no matter what the to the workpiece no matter what the

real situation is.real situation is.

Basics of NC Part Programming:Basics of NC Part Programming:

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The position of the tool is The position of the tool is described by using a Cartesian described by using a Cartesian coordinate system. If (0,0,0) coordinate system. If (0,0,0) position can be described by position can be described by the operator, then it is called the operator, then it is called

floating zerofloating zero..

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In defining the motion of the In defining the motion of the tool from one point to another, tool from one point to another, either either absoluteabsolute positioningpositioning mode or mode or incrementalincremental positioningpositioning mode mode can be used.can be used.

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1. 1. Absolute positioningAbsolute positioning. In this mode, . In this mode, the desired target position of the tool the desired target position of the tool for a particular move is given relative for a particular move is given relative to the origin point of the program.to the origin point of the program.

2. 2. Incremental positioningIncremental positioning. In this . In this mode, the next target position for the mode, the next target position for the tool is given relative to the current tool tool is given relative to the current tool position.position.

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Structure of an NC Part Structure of an NC Part Program:Program:

Commands are input into the controller in units called blocks or statements.

Block Format:

1. Fixed sequential format2. Tab sequential format3. Word address format

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EXAMPLE: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 z direction at a feed rate of 500 mm/min., with the flood coolant on.3.The is then retracted back 10 mm at the rapid feed rate, and the coolant is turned off.

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1. Fixed sequential format1. Fixed sequential format0050 00 +0025400 +0012500 +0000000 0000 000050 00 +0025400 +0012500 +0000000 0000 000060 01 +0025400 +0012500 -0010000 0500 080060 01 +0025400 +0012500 -0010000 0500 080070 00 +0025400 +0012500 +0000000 0000 090070 00 +0025400 +0012500 +0000000 0000 09

2. Tab sequential format0050 TAB 00 TAB +0025400 TAB +0012500 TAB +0000000 TAB TAB 0060 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

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Modal commandsModal commands: Commands issued : Commands issued in the NC program that will stay in in the NC program that will stay in effect until it is changed by some other effect until it is changed by some other command, like, feed rate selection, command, like, feed rate selection, coolant selection, etc.coolant selection, etc.

Nonmodal commandsNonmodal commands: Commands that : Commands that are effective only when issued and are effective only when issued and whose effects are lost for subsequent whose effects are lost for subsequent commands, like, a dwell command commands, like, a dwell command which instructs the tool to remain in a which instructs the tool to remain in a given configuration for a given amount given configuration for a given amount of time.of time.

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20042004 9696

INFORMATION NEEDED by a INFORMATION NEEDED by a CNCCNC

1. Preparatory Information: units, incremental or absolute positioning

2. Coordinates: X,Y,Z, RX,RY,RZ3. Machining Parameters: Feed rate and spindle speed4. Coolant Control: On/Off, Flood, Mist5. Tool Control: Tool and tool parameters6. Cycle Functions: Type of action required7. Miscellaneous Control: Spindle on/off, direction of

rotation, stops for part movementThis information is conveyed to the machine through a

setof instructions arranged in a desired sequence –

Program.

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BLOCK FORMATBLOCK FORMAT

Sample BlockSample Block N135 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 (on separate lines)

The data within a block should follow the sequence shown in the above sample block

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WORD-ADDRESS CODINGWORD-ADDRESS CODING

N5 G90 G20N5 G90 G20 N10 M06 T3N10 M06 T3 N15 M03 S1250N15 M03 S1250 N20 G00 X1 Y1N20 G00 X1 Y1 N25 Z0.1N25 Z0.1 N30 G01 Z-0.125 F5N30 G01 Z-0.125 F5 N35 X3 Y2 F10N35 X3 Y2 F10 N40 G00 Z1N40 G00 Z1 N45 X0 Y0N45 X0 Y0 N50 M05N50 M05 N55 M30N55 M30

Example CNC ProgramExample CNC Program

Each instruction to the machine consists of a letter followed by a number.

Each letter is associated with a specific type of action or piece of information needed by the machine.

Letters used in Codes

N,G,X,Y,Z,A,B,C,I,J,K,F,S,T,R,M

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G & M CodesG & M Codes

N5 G90 G20N5 G90 G20 N10 M06 T3N10 M06 T3 N15 M03 S1250N15 M03 S1250 N20 G00 X1 Y1N20 G00 X1 Y1 N25 Z0.1N25 Z0.1 N30 G01 Z-0.125 F5N30 G01 Z-0.125 F5 N35 X3 Y2 F10N35 X3 Y2 F10 N40 G00 Z1N40 G00 Z1 N45 X0 Y0N45 X0 Y0 N50 M05N50 M05 N55 M30N55 M30

Example CNC ProgramExample CNC Program

• G-codes: Preparatory Functions involve actual tool moves.

• M-codes: MiscellaneousFunctions – involve actionsnecessary for machining (i.e.spindle on/off, coolant on/off).

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G CodesG Codes

G00G00 Rapid traverseRapid traverse G01 Linear interpolationG01 Linear interpolation G02G02 Circular interpolation, Circular interpolation,

CWCW G03 Circular interpolation, G03 Circular interpolation,

CCWCCW G04 DwellG04 Dwell G08 AccelerationG08 Acceleration G09 DecelerationG09 Deceleration G17 X-Y PlaneG17 X-Y Plane G18 Z-X PlaneG18 Z-X Plane G19 Y-Z PlaneG19 Y-Z Plane G20 Inch Units (G70)G20 Inch Units (G70) G21 Metric Units (G71)G21 Metric Units (G71)

G40 Cutter compensation – G40 Cutter compensation – cancelcancel

G41 Cutter compensation – G41 Cutter compensation – leftleft G42 Cutter compensation- G42 Cutter compensation-

rightright G70 Inch formatG70 Inch format G71 Metric formatG71 Metric format G74 Full-circleG74 Full-circle programming programming

offoff G75 Full-circle programming G75 Full-circle programming

onon G80 Fixed-cycle cancelG80 Fixed-cycle cancel G81-G89 Fixed cyclesG81-G89 Fixed cycles G90 Absolute dimensionsG90 Absolute dimensions G91 Incremental dimensionsG91 Incremental dimensions

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Modal G-CodesModal G-Codes

Most G-codes set theMost G-codes set the machine in a machine in a “mode”“mode” which stays in effectwhich stays in effect until it until it is changed oris changed or cancelled by another cancelled by another GG--code.code. These commandsThese commands are called are called “modal”.“modal”.

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Modal G-Code ListModal G-Code List

G00G00 Rapid TransverseRapid Transverse G01G01 Linear InterpolationLinear Interpolation G02G02 Circular Interpolation, Circular Interpolation,

CWCW G03G03 Circular Interpolation, Circular Interpolation,

CCWCCW G17G17 XY PlaneXY Plane G18G18 XZ PlaneXZ Plane G19G19 YZ PlaneYZ Plane G20/G70 G20/G70 Inch unitsInch units G21/G71 G21/G71 Metric UnitsMetric Units G40 G40 Cutter compensation Cutter compensation

cancelcancel G41 G41 Cutter compensation Cutter compensation

leftleft G42 G42 Cutter compensation Cutter compensation

rightright G43 G43 Tool length Tool length

compensation compensation (plus)(plus)

G43G43 Tool length Tool length compensation compensation (plus)(plus)

G44G44 Tool length Tool length compensation compensation (minus)(minus)

G49G49 Tool length Tool length compensation compensation cancelcancel

G80G80 Cancel canned cyclesCancel canned cycles G81G81 Drilling cycleDrilling cycle G82G82 Counter boring cycleCounter boring cycle G83G83 Deep hole drilling Deep hole drilling

cyclecycle G90G90 Absolute positioningAbsolute positioning G91G91 Incremental Incremental

positioningpositioning

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M CodesM Codes

M00 M00 Program stopProgram stop M01 M01 Optional program stopOptional program stop M02 M02 Program endProgram end M03 M03 Spindle on clockwiseSpindle on clockwise M04 M04 Spindle on counterclockwiseSpindle on counterclockwise M05 M05 Spindle stopSpindle stop M06 M06 Tool changeTool change M08 M08 Coolant onCoolant on M09 M09 Coolant offCoolant off M10 M10 Clamps onClamps on M11 M11 Clamps offClamps off M30 M30 Program stop, reset to startProgram stop, reset to start

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N CodesN Codes

Gives anGives an identifying number for eachidentifying number for each block of information.block of information.

It is generally good practice toIt is generally good practice to increment each block number byincrement each block number by 5 or 5 or 10 to allow additional10 to allow additional blocks to be blocks to be inserted if futureinserted if future changes are changes are required.required.

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X,Y, and Z CodesX,Y, and Z Codes

X, Y, and Z X, Y, and Z codes are used tocodes are used to specify the coordinate axis.specify the coordinate axis.

Number following the codeNumber following the code defines defines the coordinate at the endthe coordinate at the end of the of the move relative to anmove relative to an incremental or incremental or absoluteabsolute reference point.reference point.

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I,J, and K CodesI,J, and K Codes

I, J, and K I, J, and K codes are used tocodes are used to specify specify the coordinate axisthe coordinate axis when defining when defining the center of athe center of a circle.circle.

Number following the codeNumber following the code defines defines the respective coordinatethe respective coordinate for the for the center of the circle.center of the circle.

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FF,,SS, and , and TT Codes Codes

F-codeF-code: used to specify the feed: used to specify the feed raterate

S-codeS-code: used to specify the: used to specify the spindle spindle speedspeed

T-codeT-code: used to specify the tool: used to specify the tool identification number associatedidentification number associated with the with the tool to be used intool to be used in subsequent operations.subsequent operations.

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Application of Some CodesApplication of Some CodesG01 Linear InterpolationG01 Linear Interpolation

Format: N_ G01 X_ Y_ Z_ F_Format: N_ G01 X_ Y_ Z_ F_

Linear Interpolation results in a Linear Interpolation results in a straight line feedstraight line feed move.move.

Unless tool compensation is used, Unless tool compensation is used, thethe coordinates arecoordinates are associated with associated with the centerline of the tool.the centerline of the tool.

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. As an example, for the motion that . As an example, for the motion that occurs in occurs in x-y plane with the same x-y plane with the same maximum speed for the x- and y-axis, maximum speed for the x- and y-axis, initial motion is at an angle of 45o to the initial motion is at an angle of 45o to the axes until motion in one of axes until motion in one of

the axes is completed and then the the axes is completed and then the balance of the motion occurs in the other balance of the motion occurs in the other axis. This is called axis. This is called point-to-point motionpoint-to-point motion..

20042004 110110


5

10

15

20

25

5 10 15 20 25 30

A

B C

Positioning motion from A to CN10 G00 X30000 Y20000 F0

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G01 is another preparatory function to specify that the tool should be moved to a specified location along a straight line path. It is referred to as linear interpolation.

This function is typically used to specify machining of straight features such as turning a cylindrical surface in turning, cutting a slot in milling, etc.

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5

10

15

20

25

5 10 15 20 25 30

A

C

Linear interpolation from A to CN10 G01 X30000 Y20000 F2500

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N10 N10 G00 X1 G00 X1 ZZ11NN115 Z0.15 Z0.1NN2020 G01 Z-0.125 G01 Z-0.125 F5F5NN225 5 X2 Z2 X2 Z2 F10F10

G01 Linear InterpolationG01 Linear Interpolation

X

Z

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G02 Circular InterpolationG02 Circular Interpolation

G02 is also a preparatory function to specify G02 is also a preparatory function to specify that the tool should be moved to a that the tool should be moved to a specified location along a circular path in a specified location along a circular path in a clockwise direction. In order to specify the clockwise direction. In order to specify the path to the MCU, the end point of the arc path to the MCU, the end point of the arc and the location of the center of the arc and the location of the center of the arc should be specified. Within the block in should be specified. Within the block in which the G02 code is programmed, the which the G02 code is programmed, the center of the arc is given by specifying its center of the arc is given by specifying its location relative to the start of the arc. location relative to the start of the arc.

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G02 Circular Interpolation G02 Circular Interpolation (CW)(CW)

The G02 commandThe G02 command requiresrequires an endpoint and a an endpoint and a radiusradius inin order to cut the order to cut the arc.arc.

I,J, and K are relativeI,J, and K are relative to the to the start point.start point.

N_ G02 X2 Y1 I0 J-1 F10N_ G02 X2 Y1 I0 J-1 F10

oror

N_ G02 X2 Y1 R1N_ G02 X2 Y1 R1

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G02 Circular Interpolation G02 Circular Interpolation (CW)(CW)

5

10

15

20

25

5 10 15 20 25 30

C

C

Circular interpolation from A to Babout a circle centered at C N10 G02 X20000 Y10000 I5000 J15000 F2500

A

B

I=5

J=15

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The sequence of some machining operations is may be the same for any part and for any machine. For example, drilling a hole involves the following steps:

Position the tool above the point where the hole will be drilled

Set the correct spindle speed

Feed the tool into the workpiece at a controlled feed rate to a predetermined depth

Retract the tool at a rapid rate to just above the point where the hole started

Canned Cycles

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Some Commonly Used Canned Cycle

Code Function Down feed At bottom Retraction

G81 Drilling Continuous feed

No action Rapid

G82 Spot face, counterbore

Continuous feed

Dwell Rapid

G83 Deep hole drilling Peck No action Rapid

G84 Tapping Continuous feed

Reverse spindle

Feed rate

G85 Through boring(in & out)

Continuous feed

No action Feed rate

G86 Through boring(in only)

Continuous feed

Stop spindle

Rapid

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G81 ILLUSTRATIONG81 ILLUSTRATION

20042004 120120

Three Main parts of a CNC Three Main parts of a CNC programprogram

N5 G90 G2N5 G90 G211 (Absolute units, (Absolute units, metricmetric))

N10 M06 T2 N10 M06 T2 (Stop for tool change, (Stop for tool change, use use tool # 2)tool # 2)

N15 M03 S1200 N15 M03 S1200 (Turn the spindle on (Turn the spindle on CW to CW to 1200 rpm)1200 rpm)

Part 1- Program PetupPart 1- Program Petup

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N20 G00 X1 Y1 N20 G00 X1 Y1 (Rapid to X1,Y1 from (Rapid to X1,Y1 from origin origin point)point)

N25 Z0.125 N25 Z0.125 (Rapid down to Z0.125)(Rapid down to Z0.125) N30 G01 Z-0.125 FN30 G01 Z-0.125 F100100 (Feed down to Z-0.125 at (Feed down to Z-0.125 at

100 mm/100 mm/mminin)) N35 G01 X2 Y2 N35 G01 X2 Y2 (Feed diagonally to X2,Y2)(Feed diagonally to X2,Y2) N40 G00 Z1 N40 G00 Z1 (Rapid up to Z1)(Rapid up to Z1) N45 X0 Y0 N45 X0 Y0 (Rapid to X0,Y0)(Rapid to X0,Y0)

Part 2- Chip RemovalPart 2- Chip Removal

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N50 M05 N50 M05 (Turn the spindle (Turn the spindle off)off)

N55 MN55 M000 0 ((PProgramrogram stop stop))

Part 3- System ShutdownPart 3- System Shutdown

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EXAMPLE OPERATION on CNC EXAMPLE OPERATION on CNC MILLING MACHINEMILLING MACHINE

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G-CODE PROGRAMG-CODE PROGRAM

First pass : conventional mill to a depth of 0.125 around edge profile. Tool 1 is a ½ inch dia. end mill.

% :1002 N5 G90 G20 N10 M06 T1 N15 M03 S1200 N20 G00 X0.125 Y0.125 N30 Z0.125 N35 G01 Z-0.125 F5 N40 X3.875 N45 Y4.125 N50 X0.125 N55 Y0.125

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Second pass: conventional mill to a depth of 0.25 around edge profile.

N35 Z-0.250 N40 X3.875 N45 Y4.125 N50 X0.125 N55 Y0.125 N60 Z0.125

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Third pass: conventional mill to a depth 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 Y1.0 N95 Z0.125

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Fourth pass: climb mill to a depth of 0.125 across remaining material.

N100 Y2.125 N105 X2.625 N110 Z0.125 N115 G00 X-5 Y-5

Z5 N120 M05 N125 M30

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Advanced features:Advanced features:

Execution of the part of the program Execution of the part of the program in a rotated or mirrored position.in a rotated or mirrored position.

Ability to scale the program and Ability to scale the program and produce larger or smaller programs.produce larger or smaller programs.

Three dimensional circular Three dimensional circular interpolation which produces a helical interpolation which produces a helical shape.shape.

Parabolic and cubic interpolation.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

20042004 130130

A system in which a central computer downloads the NC programs block by block to many NC machine tools simultaneously is called Direct Numerical Control (DNC) system.

Direct Numerical Control (DNC):

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This system used to work with the early NC machine tools which can not read more than a block of information at a time. The central computer feed the program information one block at a time. When the machine execute the information, the next block of information would be fed.

Direct Numerical Control (DNC):

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Distributed NC is known by the same Distributed NC is known by the same acronym as Direct Numerical Control (DNC). acronym as Direct Numerical Control (DNC). After the introduction of CNC, the machine After the introduction of CNC, the machine tools have had the capability of storing tools have had the capability of storing large amount of information. Therefore, large amount of information. Therefore, there have been no need to have drip feed there have been no need to have drip feed information system, like, Direct Numerical information system, like, Direct Numerical Control. Instead, Distributed Numerical Control. Instead, Distributed Numerical Control is introduced. In such a system, a Control is introduced. In such a system, a host computer communicate with many host computer communicate with many CNC machine tools via networks and CNC machine tools via networks and download or upload programs.download or upload programs.

Distributed Numerical Control (DNC):

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With Distributed Numerical Control With Distributed Numerical Control systems, it is possible to monitor the systems, it is possible to monitor the activities in individual CNC machine tools activities in individual CNC machine tools on host computer. on host computer.

Therefore, better shop floor control can be Therefore, better shop floor control can be achieved.achieved.

Distributed Numerical Control (DNC):

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NC program preparation may be tedious NC program preparation may be tedious and difficult if the part to be machined and difficult if the part to be machined has a complex geometry. The main has a complex geometry. The main difficulty is to find out the cutter locations difficulty is to find out the cutter locations during the machining. Computers may be during the machining. Computers may be used to assist the programmers in used to assist the programmers in preparing the NC codes.preparing the NC codes.

Computer Aided Part Programming:

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Advantages of applying computer-aided Advantages of applying computer-aided part programming include the following:part programming include the following:

1. It reduces the manual calculations 1. It reduces the manual calculations involves in determining the geometric involves in determining the geometric characteristics of the part.characteristics of the part.

It provides the cutter path simulation.It provides the cutter path simulation. It provides tool collision checking.It provides tool collision checking. It shortens the program preparation time.It shortens the program preparation time. It makes the program preparation easier.It makes the program preparation easier.

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The Aerospace Industries Association sponsored the The Aerospace Industries Association sponsored the work that led to the first part programming language, work that led to the first part programming language, developed in MIT in 1955.developed in MIT in 1955.

This was called:This was called: Automatically Programmed ToolsAutomatically Programmed Tools (APT). (APT). APT is an English like simple programming language APT is an English like simple programming language

which basically produce the which basically produce the Cutter LocationCutter Location (CL) data. (CL) data. Using the cutter location data, the program can generate Using the cutter location data, the program can generate

the actual NC codes by using a postprocessor .the actual NC codes by using a postprocessor .

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The output of any CAD package include the geometric data The output of any CAD package include the geometric data of the part to be machined. Therefore, many CAD/CAM of the part to be machined. Therefore, many CAD/CAM package can produce cutter location (CL) data to be used for package can produce cutter location (CL) data to be used for NC code generation.NC code generation.

There is still to be a process planning module for a workable There is still to be a process planning module for a workable NC code generation. NC code generation.

Some of the CAD/CAM packages that have the NC code Some of the CAD/CAM packages that have the NC code generation capabilities are Computervision, CATIA, CADAM, generation capabilities are Computervision, CATIA, CADAM, ProEngineer, MechanicalDesktop (Auto Desk).ProEngineer, MechanicalDesktop (Auto Desk).

CAD/CAM Based Part Programming:CAD/CAM Based Part Programming:

cnc machine tools

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