Computer Numerical Control

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Computer Numerical Control
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CNC Introduction

• C NC CNC
• NC with dedicated computer is known as CNC
• Software controlled
• MCU of CNC is based on a dedicated microcomputer

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CNC Features

• High program storage capacity
• Various forms of program input
• Punched Tape
• Magnetic Tape
• Floppy Disk
• RS-232
• Industrial keypad for manual entry
• Program editing within MCU
• Saves time

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• Fixed cycles programming subroutine
• Reduces the length of program
• Saves execution time
• Saves space
• Easy to use
• Interpolation facility
• Straight line, circular, helical, ..
• Easy Machine set up
• Compensation
• Tool Radius length
• Acceleration deceleration calculations
• Helps to reduce tool marks on the surface due to
  high feed rates

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• Communication interface
• With peripheral devices (Conveyor belt, Robot..)
• Diagnostics
• Start-up diagnostics
• Malfunction
• Tool life monitoring
• Preventive maintenance
• Prog. Check (syntax logic)

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MCU for CNC

• Consists of
• CPU
• Memory
• I/O interface
• Controls for machine axes
• Sequence Control (Miscellaneous controls )

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Central Processing Unit (CPU)
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• Memory
• RAM Operating System
• - ROM Part Program

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• I/O Interface
• Operator Panel
• Tape reader

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• Machine Tool Control
• Position Control
• Spindle Control

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• Sequence Control
• Coolant
• Tool Changer
• Automatic Chucking

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Central Processing Unit (CPU)

• Memory
• RAM Operating System
• - ROM Part Program

• I/O Interface
• Operator Panel
• Tape reader

System bus

• Sequence Control
• Coolant
• Tool Changer
• Automatic Chucking

• Machine Tool Control
• Position Control
• Spindle Control

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CNC Software

• Operating system software
• Control program
• Execute program
• Machine interface software
• Auxiliary functions
• Communication
• Application software
• NC Programs

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DNC

• DNC Direct NC or Distributed NC

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Direct Numerical Control

• Developed in 1960s
• Controlling number of machine tools by a single
  main frame computer through direct connection and
  in real time
• MCUs of Individual Machines were free from
  punched tape reader
• MCUs are connected to Main frame computer by BTR
  Behind tape reader
• Central Computer supplied one block of
  instruction to MT each time on demand.
• 2 way communication between central computer MT

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• Components of Direct NC
• Central Computer
• Bulk Memory
• Number of MTs
• Communication links

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Central Computer
Bulk memory NC Programs
Telecommunication lines
MT1
MT2
MT3
MCU
MCU
MCU
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• Advantages
• High reliability
• Elimination of tape tape reader
• Control no. of MTs with single computer
• Improved computational capabilities
• Improved prog. storage
• Limitations
• No alternative way of prog. Entry in case of
  Central Comp. Failure
• Slow compared to Distributed NC

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Distributed Numerical Control

• Central Computer is connected to MCUs of MTs
• MCUs are computer themselves
• Central Computer uploads complete program in MCU
  on demand
• 2 way communication
• Data information flow
• Can have variety of configuration
• (a) Switching network
• (b) LAN

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Communication

• Flow of Information from Central Computer to MT
• NC Part Prog.
• List of tools
• Machine set up instructions
• Operator Instructions
• Production schedule

• Flow of Information from MT Shop floor to C.
  Comp.
• Piece counts
• Machining time
• Tool life infor.
• Machine uptime/Downtime

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DNC Computer
MCU
MT
MCU
MT
Data Switching Box
MCU
MT
MCU
MT
MCU
MT
DNC Switching Network
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DNC LAN
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• 6.4
• Applications of NC
• Advantages Disadvantages
• Comparison between conventional
  machines/NC/CNC/DNCs

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SAMPLE CNC MACHINES
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CNC TURNING
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CNC MILLING
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CNC Drill
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CNC Grinding
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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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CMM for inspection
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INDUSTRIES MOST AFFECTED by CNC

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

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SAMPLE PRODUCTS OF CNC MANUFACTURING
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AUTOMOTIVE INDUSTRYEngine Block
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AUTOMOTIVE INDUSTRY(Contd)Different Products
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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 PROTOTYPING PRODUCTS
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Axes Designation
Right Hand coordinate system
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• Group I Machines with rotating tool
• Vertical Milling M/c, Drilling M/c, Vertical
  Boring M/c
• Group II Machines with rotating workpieces
• CNC Turning, Horizontal Boring M/c
• Group III Machines without rotating cutter/
  workpiece
• CNC Shaper , Planer
• Assign only Z X
• Y is perpendicular as per right hand rule

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CNC Lathe
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CNC Milling
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Shaper
Z
Y
X
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Z Axis

• Group I
• Along rotating spindle
• Z Takes tool away from workpiece
• Group II
• Along rotating spindle
• Z Takes tool away from workpiece
• Group III
• Perpendicular to the work holding surface
• Z Takes tool away from workpiece

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X Axis

• Group I
• Along the principal motion of tool/WP
• X Towards right when looking spindle from top
• Group II
• Along the principal motion of tool/WP
• X Towards right when looking spindle from
  front
• Group III
• Along the principal motion of tool/WP
• X Along Principal direction of movement

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Y Axis

• Perpendicular to X Z
• Direction As per Right hand rule

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CNC CUTTERS

• Turning center cutters
• Machining center cutters

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TURNING 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 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 wont 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 TOOLS

• 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 TOOLS (contd)

• 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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MACHINING CENTER CUTTING TOOLS (contd)

• 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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MACHINING CENTER CUTTING TOOLS (contd)

• 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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MACHINING CENTER CUTTING TOOLS (contd)

• 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 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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RS-232

• In telecommunications, RS-232 (Recommended
  Standard 232) is a standard for serial binary
  data signals connecting between a DTE (Data
  Terminal Equipment) and a DCE (Data
  Circuit-terminating Equipment). It is commonly
  used in computer serial ports.