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									CAD/CAM Principles and Applications          13 CNC Programming 13-1/13-24
by P.N.Rao


13. CNC Programming




13.1 Part Programming Fundamentals


       Process planning
       Axes selection
       Tool selection
       Cutting process parameters planning
       Job and tool setup planning
       Machining path planning
       Part program writing
       Part program proving

13.1.1 Process planning

       Machine tool used
       Fixture(s) required
       Sequence of operations
       For each of operation
             Cutting tools required
             Process parameters
CAD/CAM Principles and Applications        13 CNC Programming 13-2/13-24
by P.N.Rao




Fig. 13.1    The steps involved in the development of a proven part
            program in NC machining
CAD/CAM Principles and Applications           13 CNC Programming 13-3/13-24
by P.N.Rao




Fig. 13.2 A typical component for NC machining

      Table 13.1 Process plan for the component shown in Fig. 13.2

  Op.            Description                           Tools
  No.
  10      End mill the top face, 100 100 mm     Shell end mill,    60 mm
  20      End mill the steps, 20 100 5 mm       Shell end mill,    60 mm
  30      Mill pocket, 40 40 8 mm               HSS End mill,      10 mm
  40      Drill the six holes, 6 15 mm          HSS twist drill,   6 mm


13.1.2 Axes selection
CAD/CAM Principles and Applications            13 CNC Programming 13-4/13-24
by P.N.Rao




Fig. 13.3 Part for NC machining shown with axes system at the centre




Fig. 13.4     Same part as in Fig. 13.3 but with axes system at the bottom
            left corner
CAD/CAM Principles and Applications             13 CNC Programming 13-5/13-24
by P.N.Rao




13.1.3 Tool selection


13.1.4 Cutting process parameters planning


13.1.5 Job and tool setup planning


13.1.6 Machining path planning


13.1.7 Part program writing


13.1.8 Part program proving




Fig. 13.5     Tool path of the part for proving the NC part program
CAD/CAM Principles and Applications             13 CNC Programming 13-6/13-24
by P.N.Rao




Fig. 13.6    Shaded 3D image of the tool cutting the part for providing
            more realistic proving of the NC part program (Courtesy Virtual
            Gibbs Inc.)


13.1.9 Documentation for NC



13.2 Manual Part Programming Methods


       N115 G81 X120.5 Y55.0 Z-12.0 R2.0 F150 M3

13.2.1 ISO standards for coding


Character             Address For

A             Angular dimension around X axis
B             Angular dimension around Y axis
CAD/CAM Principles and Applications            13 CNC Programming 13-7/13-24
by P.N.Rao

C             Angular dimension around Z axis
D             Angular dimension around special axis or third feed function*
E             Angular dimension around special axis or second feed
              function*
F             Feed function
G             Preparatory function
H             Unassigned
I             Distance to arc centre or thread lead parallel to X
J             Distance to arc centre or thread lead parallel to Y
K             Distance to arc centre or thread lead parallel to Z
L             Do not use
M             Miscellaneous function
N             Sequence number
O             Reference rewind stop
P             Third rapid traverse dimension or tertiary motion dimension
              parallel to X*
Q             Second rapid traverse dimension or tertiary motion dimension
              parallel to Y*
R             First rapid traverse dimension or tertiary motion dimension
              parallel to Z*
S             Spindle speed function
T             Tool function
U             Secondary motion dimension parallel to X*
V             Secondary motion dimension parallel to Y*
W             Secondary motion dimension parallel to Z*
X             Primary X motion dimension
Y             Primary Y motion dimension
Z             Primary Z motion dimension

       * Where D, E, P, Q, R, U, V, and W are not used as indicated, they
       may be used elsewhere.


       N5 G2 X 53 Y 53 Z 53 U..V..W..I..J..K..F5 S4 T4 M2 *

13.2.2 Co-ordinate function


       13.2.3 Feed function


       13.2.4 Speed function
CAD/CAM Principles and Applications              13 CNC Programming 13-8/13-24
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       13.2.5 Tool function



13.3 Preparatory functions


CODE                  FUNCTION

G00           Point-to-point positioning, rapid traverse
G01           Line interpolation
G02           Circular interpolation, clockwise (WC)
G03           Circular interpolation, anti-clockwise (CCW)
G04           Dwell
G05           Hold/Delay
G06           Parabolic interpolation
G07           Unassigned
G08           Acceleration of feed rate
G09           Deceleration of feed rate
G10           Linear interpolation for “long dimensions” (10 inches-100
inches)
G11           Linear interpolation for “short dimensions” (up to 10 inches)
G12           Unassigned
G13-G16       Axis designation
G17           XY plane designation
G18           ZX plane designation
G19           YZ plane designation
G20           Circular interpolation, CW for “long dimensions”
G21           Circular interpolation, CW for “short dimensions”
G22-G29       Unassigned
G30           Circular interpolation, CCW for “long dimensions”
G31           Circular interpolation, CCW for “short dimensions”
G32           Unassigned
G33           Thread cutting, constant lead
G34           Thread cutting, linearly increasing lead
G35           Thread cutting, linearly decreasing lead
G36-G39       Unassigned
G40           Cutter compensation-cancels to zero
G41           Cutter radius compensation-offset left
G42           Cutter radius compensation-offset right
G43           Cutter compensation-positive
G44           Cutter compensation-negative
CAD/CAM Principles and Applications                13 CNC Programming 13-9/13-24
by P.N.Rao

G45-G52       Unassigned
G53           Deletion of zero offset
G54-G59       Datum point/zero shift
G60           Target value, positioning tolerance 1
G61           Target value, positioning tolerance 2, or loop cycle
G62           Rapid traverse positioning
G63           Tapping cycle
G64           Change in feed rate or speed
G65-G69       Unassigned
G70           Dimensioning in inch units
G71           Dimensioning in metric units
G72-G79       Unassigned
G80           Canned cycle cancelled
G81-G89       Canned drilling and boring cycles
G90           Specifies absolute input dimensions
G91           Specifies incremental input dimensions
G92           Programmed reference point shift
G93           Unassigned
G94           Feed rate/min (inch units when combined with G70)
G95           Feed rate/rev (metric units when combined with G71)
G96           Spindle feed rate for constant surface feed
G97           Spindle speed in revolutions per minute
G98-G99       Unassigned


Motion group
     *G00             Rapid Positioning
     G01              Linear Interpolation
     G02              Circular interpolation Clockwise
     G03              Circular interpolation Counter clockwise

Dwell
        G04           Dwell

Active plane selection group
      *G17        XY Plane selection
      G18         XZ Plane selection
      G19         YZ Plane selection

Cutter compensation group
      *G40      Cutter compensation, Cancel
      G41       Cutter radius Compensation left
      G42       Cutter radius Compensation right
CAD/CAM Principles and Applications             13 CNC Programming 13-10/13-24
by P.N.Rao



Units group
      *G70            Inch units
      G71             Metric units

Hole making canned cycle group
     *G80       Canned Cycle Cancel
     G81-G89 Canned Cycles definition and ON

Co-ordinate system group
     *G90        Absolute co-ordinate system
     G91         Incremental co-ordinate system

Preset
     G92              Absolute pre-set, Change the datum position


       13.3.1 Co-ordinate system group, G90 and G91




Fig. 13.7 Absolute (G90) and incremental (G91) systems


       13.3.2 Units group, G70, G71


       13.3.3 Active plane selection group, G17, G18, G19
CAD/CAM Principles and Applications             13 CNC Programming 13-11/13-24
by P.N.Rao




Fig. 13.8     XY plane selection for vertical axis milling machines

G17 XY Plane selection




Fig. 13.9     XY plane selection for horizontal axis milling machines

G18 XZ Plane selection




Fig. 13.10 XZ plane selection for horizontal axis milling machines
CAD/CAM Principles and Applications          13 CNC Programming 13-12/13-24
by P.N.Rao



G19 YZ Plane selection




Fig. 13-11 YZ plane selection for horizontal axis milling machines

       13.3.4 Preset, G92




Fig. 13-12 Setting the workpiece on the machine table

       N015 G92 X200.0 Y170.0 Z50.0
CAD/CAM Principles and Applications         13 CNC Programming 13-13/13-24
by P.N.Rao




       13.3.5 Motion group, G00, G01, G02, G03


Rapid Positioning, G00




Fig. 13-13 Positioning, preparatory function G00


       N105 G90 G00 X150.0 Y30.0


Absolute programming A to B

       N110 G90 G00 X50.0 Y45.0 Z 40.0
       N120 X90.0 Y90.0 Z70.0
CAD/CAM Principles and Applications          13 CNC Programming 13-14/13-24
by P.N.Rao




Fig. 13-14 Positioning, preparatory function G00 in 3 dimensions

Incremental programming A to B

       N110 G90 G00 X50.0 Y45.0 Z 40.0
       N120 G91 X40.0 Y45.0 Z30.0

Incremental programming B to A

       N110 G90 G00 X90.0 Y90.0 Z 70.0
       N120 G91 X-40.0 Y-45.0 Z-30.0

Linear or Straight line Interpolation, G01


       N115 G01 X110.0 Y30.0 F250
CAD/CAM Principles and Applications          13 CNC Programming 13-15/13-24
by P.N.Rao




Fig. 13-15 Linear interpolation, preparatory function G01

Incremental programming A to B

       N110 G90 G00 X50.0 Y45.0 Z 40.0
       N120 G91 G01 X40.0 Y45.0 Z30.0 F350

Incremental programming B to A

       N110 G90 G00 X90.0 Y90.0 Z 70.0
       N120 G91 G01 X-40.0 Y-45.0 Z-30.0 F350


Circular Interpolation, G02 / G03




Fig. 13.16 Circular interpolation, preparatory function G02/G03


       N125 G02 X65.0 Y60.0 I35.0 J-10.0 F250
CAD/CAM Principles and Applications          13 CNC Programming 13-16/13-24
by P.N.Rao




Fig. 13.17 Circular interpolation in XY plane using G17 plane selection




Fig. 13.18 Circular interpolation in XZ plane using G18 plane selection


Dwell, G04



13.4 Miscellaneous Functions, M


CODE                         FUNCTION
CAD/CAM Principles and Applications             13 CNC Programming 13-17/13-24
by P.N.Rao



M00                   Program stop, spindle and coolant off
M01                   Optional programmable stop
M02                   End of program-often interchangeable with M30
M03                   Spindle on, CW
M04                   Spindle on, CCW
M05                   Spindle stop
M06                   Tool change
M07                   Coolant supply No. 1 on
M08                   Coolant supply No. 2 on
M09                   Coolant off
M10                   Clamp
M11                   Unclamp
M12                   Unassigned
M13                   Spindle on, CW + coolant on
M14                   Spindle on, CCW + coolant on
M15                   Rapid traverse in + direction
M16                   Rapid traverse in - direction
M17-M18               Unassigned
M19                   Spindle stop at specified angular position
M20-M29               Unassigned
M30                   Program stop at end tape + tape rewind
M31                   Interlock by-pass
M32-M35               Constant cutting velocity
M36-M39               Unassigned
M40-M45               Gear changes; otherwise unassigned
M46-M49               Unassigned
M50                   Coolant supply No. 3 on
M51                   Coolant supply No. 4 on
M52-M54               Unassigned
M55                   Linear cutter offset No. 1 shift
M56                   Linear cutter offset No. 2 shift
M57-M59               Unassigned
M60                   Piece part change
M61                   Linear piece part shift, location 1
M62                   Linear piece part shift, location 2
M63-M67               Unassigned
M68                   Clamp piece part
M69                   Unclamp piece part
M70                   Unassigned
M71                   Angular piece part shift, location 1
M72                   Angular piece part shift, location 2
M73-M77               Unassigned
CAD/CAM Principles and Applications           13 CNC Programming 13-18/13-24
by P.N.Rao

M78                   Clamp non-activated machine bed-ways
M79                   Unclamp non-activated machine bed-ways
M80-M99               Unassigned




13.5 Program Number




Fig. 13-19 Example

       N001 G92 X0 Y0 Z0          absolute presetting at A.
       N002 G90             absolute programming.
       N003 G00 X25.0 Y25.0 Z2.0 T01 S3000 M03 tool brought rapidly
       at B,
                                              2 mm above XY plane.
       N004 G01 Z-12.0 F120       tool goes down to full depth.
       N005 Y75.0                       proceeds to C.
       N006 X65.0                       proceeds towards right to D.
       N007 G02 Y25.0 I0 J-35.0         cuts curved profile till E.
       N008 X25.0                 proceeds to B.
       N009 Z2.0            tool moves 2 mm above the XY plane
       N010 G00 Z50.0 M05         spindle stops and rapidly moves up
       N011 X0 Y0                 rapid move to start position 0,0
       N012 M30             end of program and tape rewind
CAD/CAM Principles and Applications        13 CNC Programming 13-19/13-24
by P.N.Rao




Fig. 13-20 Component for example 13.2




Fig. 13-21 Tool path for machining the component for example 13.2
CAD/CAM Principles and Applications           13 CNC Programming 13-20/13-24
by P.N.Rao




Fig. 13-22 Offset Tool path for machining contours that are not parallel to
          the principal axes



13.6 Tool Length Compensation




Fig. 13-23 Tool length compensation




13.7 Canned Cycles
CAD/CAM Principles and Applications      13 CNC Programming 13-21/13-24
by P.N.Rao




Fig. 13.24 Typical motions embedded in G81 canned cycle




Fig. 13.25 Example for canned cycles.
CAD/CAM Principles and Applications                13 CNC Programming 13-22/13-24
by P.N.Rao

                   Table 13-2 Standard canned cycle motions

 Cann      Feed from         At programmed depth       Used for
 ed        surface           (end of feed point)
 cycle
 numb                        Dw          Spindle
                                      Spindle
 er                          ell         return
                                      speed
                                         motion
 G80       Off               --  Stop    --            Cancel canned cycle
 G81       Constant          --  --      Rapid         Drilling, centre drilling
 G82       Constant          Yes --      Rapid         Counter sinking,
 G83       Intermittent      --  --      Rapid         Counter boring
 G84       Constant          --  Reverse Feed          Deep hole drilling
 G85       Constant          --  --      Feed          Tapping
 G86       Constant          --  Stop    Rapid         Reaming
 G87       Constant          --  Stop    Manual        Boring
 G88       Constant          Yes Stop    Manual        Multiple Boring
 G89       Constant          Yes --      Feed          Boring
                                                       Boring




Fig. 13.26 Component for NC program in example 13.3
CAD/CAM Principles and Applications         13 CNC Programming 13-23/13-24
by P.N.Rao

13.8 Cutter Radius Compensation




Fig. 13-27 Cutter radius compensation

       G40 Compensation `off'.
       G41 used when the cutter is on the left of the programmed path
           when looking in the direction of the tool movement, i.e. the
           radius compensation is considered to the left of the progra-
           mmed profile.




Fig. 13.28 Example showing the cutter radius compensation using the G
          codes G42
CAD/CAM Principles and Applications       13 CNC Programming 13-24/13-24
by P.N.Rao




Fig. 13.29 Example showing the cutter radius compensation using the G
          codes G41 and G42




Fig. 13.30 Example for contour programming using the cutter radius
         compensation

								
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