12 cnc & part programming

Brief history
1942 Bendix Corporation, a USA helicopter blade manufacturing company,
needs three-dimensional cam parts.
 Coordination of movements is necessary.
1947 John Parson (a Bendix corporation worker) using punched tapes
is able to control simultaneously axes movements of a machine
 MIT collaborates
1953 Numerical Control (NC) term appears at M.I.T.
1970 Computer Numerical Control (CNC) is created
 Microprocessors origin.
1980 Direct Numerical Control (DNC) is possible.
A large number of machines are controlled by a computer.
Definition
 CNC (Computer Numerical Control (CNC) refers to the method of controlling a machine
tool or the machining process by means of a computer.
 Coded numerical instructions are inserted into the CNC
NC Punched Tape
INTRODUCTION

INTRODUCTION-Numerical Control (NC)
Numerical Control (NC)
 NC (numerical control) machine tools are the machine tool, of which the various functions are
controlled by : letters , numbers and symbols.
 The NC machine tool runs on a program fed to it; without human operator. The NC program consist of
a set of instruction or statement for controlling the motion of the drives of the machine tools as well
as the motion of the cutting tool.

CNC Machine Tools
 In CNC (Computer Numerical Control) machines, a dedicated computer is used to perform the most of
basic NC machine functions.
 CNC (Computer Numerical Control) machine is a NC machine which uses a dedicated computer as the
machine control unit.
 The entire program is entered and stored in computer memory. The machining cycle for each
component is controlled by the program contained in the computer memory.
Input / Output
Devices
Machine Tool
Memory (ROM) Control
program for : Z Slide
X Slide
Memory (RAM)
Part Program
Feed Back Unit
INTRODUCTION-CNC Machine Tools

CNC Machine Tools
INTRODUCTION-CNC Machine Tools
 Input / Output Console : It is the unit through which part program is fed to the CNC machine tool
system and required output is taken out. It basically consists of monitor and Keyboard.
 Microprocessor : This controller takes input from Input / Output device, Feedback from feedback unit
and actuates the drives as well as the tool of the machine tool.
 Memory : It consists of RAM & ROM. The RAM stores part program, while ROM stores the programs
for machine control.
 Feedback unit : The feedback unit takes input from machine tool and transfers it to control unit for
necessary corrections.
 Machine tool : Machine tool is operated by the control unit.
 Interfaces : They are the connections between the different components of the CNC machine tool
system.

 DNC is a manufacturing system in which a number of machines are controlled by a computer
through direct- connection and in real time.
The configuration of the DNC system can be divided into:
Satellite computers are minicomputers and they serve to take some of the burden off central computer. Each
satellites controls several machine tools.
 DNC system without satellite computer.
 DNC system with satellite computer.
DNC Machine Tools
INTRODUCTION-DNC Machine Tools

INTRODUCTION-DNC Machine Tools
DNC system without satellite computer
DNC system with satellite computer

Loop control types
OPEN LOOP
INTRODUCTION
 It does not have any feedback mechanism.
 It only has motion control but do not have any provision for feedback, which is needed to be compared
with input for better control & correction of drive system.

Machine control feedback: position & velocity
VIDEO
Loop control types
CLOSED LOOP
INTRODUCTION
 It has a feedback mechanism.
 It has the motion control with a provision of feedback of feedback.
 Which can be used for accurately controlling the drive system by comparing it with the input
information until the required or desired position is achieved.

The disk has many circular tracks, the higher the
number of tracks the higher the resolution.
These devices do not lose position when power
is removed (homing sequence not needed on
startup).
They do not accumulate errors (not affected by
noise signal).
They are more complex and expensive.
CNC machine tool description
Feedback devices
ABSOLUTE ROTARY ENCODER
An encoder is a sensor for converting rotary motion or position to
analog/digital signal.
VIDEO
VIDEO
INTRODUCTION

CNC machine tool description
Feedback devices
INCREMENTAL ROTARY ENCODER
The feedback signal is always referenced to a start
or home position. They need an external processing
of signals.
In the event of a power failure, it must be
reinitialized.
They are susceptible to noise, thus, errors.
They are simpler and cheaper.
An encoder is a sensor for converting rotary motion or position to
analog/digital signal.
VIDEO
INTRODUCTION

1. The part program is fed to the
machine through the tapes or
other such media.
2.In order to modify the program,
the tapes have to be changed.
3. In NC machine tool system, tape
reader is a part of machine
control unit.
4. System has no memory storage
and each time it is run using the tape.
5. It can not import CAD files.
6.It can not use feedback system.
1. In CNC machine tool system, the
program is fed to the machine
through the computer.
2.The programs can be easily modified
with the help of computer.
3. The microprocessor or minicomputer
forms the machine control unit.
The CNC machine does not
need tape reader.
4.It has memory storage ability, in which
part program can be stored.
5. System can import CAD files and
convert it to part program.
6.The system can use feedback system.
1. The part program is fed to
the machine through the
Main computer
2. In order to modify the
program, single
computer is used
3. Large memory of DNC
allows it to store a large
amount of part program.
4. Same part program can be
run on different machines
at the same time.
5. The data can be processed
using the MIS software so
as to effectively carry out
the Production planning
and scheduling.
CNC Machine Tool System DNC Machine Tool SystemNC Machine Tool System
Comparison between NC, CNC and DNC machine tools

CNC manufacturers
Programming languages
First systems developed and use a programming language similar to
FORTRAN or BASIC
Automatically Programmed Tools (APT) and its many variants
COMPACT II
Dedicated CAM systems
In these systems a dedicated CAM system
helps in developing the CNC part programs
May be linked to a major CAD system such
as AutoCAD, Solidworks, CADKEY,….
Examples
Mastercam
Virtual Gibbs
Smartcam
Edgecam
Alphacam
CAD/CAM systems
Major CAD systems have integrated
manufacturing systems for better interfacing and
translation
Examples are:
Pro engineer – Pro Manufacture
Unigraphics
I-DEAS – Solids machining
CATIA
Intergraph
INTRODUCTION

The axes are named
according to DIN 66217.
VIDEO
Three-axes milling machine
Six-axis milling machine
Turning machine
VIDO
A+
C+
B+
AXIS NOMENCLATURE

M - Machine Zero or home: This is set by the manufacturer as the origin of the coordinate
system of the machine.
W -Part zero or point of origin of the part: This is the origin point that is set for
programming the measurements of the part. It can be freely selected by the programmer.
R-Machine Reference point. This is a point on the machine established by the
manufacturer around which the synchronization of the system is done. The control positions
the axis on this point.
Reference systems
AXIS NOMENCLATURE

Reference systems
AXIS NOMENCLATURE

Fill the tool carousel.
Define Tool Length & Radius Offsets
Once he workholding device is properly
installed and aligned, set part X,Y&Z zero
datum.
Check coolant and air supply levels,
ensure work area is clean, …
CNC MACHINE SETUPAND OPERATION

Machine Reference (R) setting
TOOL LENGTH
COMPENSATION OFF
G44
TOOL LENGTH
COMPENSATION ON
G43
RRRR
T1
L1 L2 L3 L4
RRRR
T2 T3 T4
OFFSET TABLE
TOOL TOOL
OFFSE
T
RADIUS LENGTH
T1 D1 55.234
T2 D1 72.345
T3 D1 61.098
T4 D1 66.683
… … ... …
CNC-REFERENCE SYSTEMS

Tool on the workpiece
Low accuracy.
Time consuming method.
Only tool length (L) values are measured.
W
T1 T2 T3 T4
L4 = 0L3 < 0
L2 > 0
L1 < 0
W
Tool is rotating and thus, part or referencing block gets marked.
RRRR

Using a tool length setter gauge
Good accuracy.
Time consuming method.
Only tool length (L) values are measured.
W
L2<0L1=0
RR
L1
M
50
z1
z2
L2
50
L1= z1-50 L2= z2-50
R
R
BASEDONAREF.TOOLBASEDONMACHINEDATUM
VIDEO
Part or referencing block does not get marked. TOOL LENGTH MEASUREMENT

Part zero (W) setting
Prior to defining part zero, procedure should be:
1. Study how the drawing is dimensioned.
2. Decide on the workholding device type and part zero (W) definition.
Machine operator defines part zero (W) position anywhere.
Most common positions:
o Left lower side of the part (all data position values are positive).
o Part symmetry axis.
o
o
CLAMP CASE Centering pins side.
VISE CASE Stationary chuck & vise stop side.
Movable chuck
Stationary chuck
Vise stop
Centering pinsClamps
Clamps (with or without centering pins) Vise (with or without vise stop)

X
Z
Y
Symmetry
X
Y
Z
Y
X
Z
Y
X
Y
Z
Y
VISE VISE
Stationary chuck & Y axis part symmetryX-Y axis part symmetry

X
Y
Z
X
Z
VISE CLAMP
X
Y
Z
X
Stationary chuck & left lower part Stationary chuck & Y axis part symmetry

VIDEO
Using the tool
Low accuracy.
Tool is rotating and thus, part gets
marked.
Using a mechanical edge finder1 2
Low accuracy.
Optical edge finder similar
X
DATUM SETTING
X
Y DATUM SETTING
VIDEO
YZ

3
Using a touch probe
High accuracy.
X
Y DATUM SETTING
VIDEO VIDEO Z

2 types:
1. Touch-trigger probes
2. Scanning probes (continuous measuring)
PRO & CON:
A ost any machined geometry may be measured in-situ.
uced machine downtime.
P t unclamping for measuring is avoided.
I nnot consider possible machine axes errors.
lm
Red
ar
t ca
Touch probe stylus tips
3
Using a touch probe

BASIC ISO PART PROGRAMMING
CNC manufacturers

BASIC ISO PROGRAMMING
Preparatory
functions
or G-codes
Speed function
Block identification
Identifies the block of information.
Block structure
N**** G** X****.*** Y****.*** Z****.*** A****.*** B****.*** C****.*** F****.** S****.**
Linear and angular
positioning data Feed function
T** D** M** N** ; *****
Miscellaneous or auxiliary functions
Tool offset number
Tool number
Number of block repetitions
Block comment
Not ISO,
corresponds to
FAGOR 8055M
=

Feed function (F) Speed function (S)
The speed function S is the speed at which the
tool (in milling) or part (in turning) rotates.
The maximum S value is limited by the machine
parameters.
The feed function F is the speed at which the tool
center point moves.
The programmed F is effective working in linear
(G01) or circular (G02, G03).
The maximum F value is limited by the machine
parameters.

Tool number (T)
The "T" code identifies the tool position in the tool magazine.
Tool offset number (D)
The tool offset contains the tool dimensions.
Each tool may have several offsets associated with it.
… … … … … … … …
…
TOOL TOOL
OFFSE
T
RADIUS LENGTH …
T1 D1 8.002 55.234 …
D2 7.502 55.234 …
D3 8.002 55.026 …
TOOL TOOL
OFFSE
T
RADIUS LENGTH …
T2 D1 4.000 72.345 …
D2 11.990 60.036 …
D3 7.500 33.110 …

M functions DESCRIPTION
M00 Program STOP / Spindle STOP / Coolant OFF
M03 Spindle ON clockwise
M04 Spindle ON counterclockwise
M05 Spindle STOP
M06 Tool change
M08 Coolant ON
M09 Coolant OFF
M30 End of program
Auxiliary or Miscellaneous (M) functions

Preparatory functions or G-codes
M functions MODAL DESCRIPTION
G00 * Rapid traverse
G01 * Linear interpolation
G02 * Clockwise circular interpolation
G03 * Counterclockwise circular interpolation
G05 * Controlled corner rounding
G07 * Square corner
G36 * Automatic radius blend
G39 * Chamfer
G40 * Cancellation of tool radius compensation
G41 * Left-hand tool radius compensation
G42 * Right-hand tool radius compensation
G43 * Tool length compensation
G44 * Cancellation of tool length compensation
G90 * Absolute programming
G91 * Incremental programming
… … …
MODAL = Once programmed, it remains active until
another incompatible G function is
programmed or until M30 / EMERGENCY
or RESET.

It is a positioning linear movement at maximum
F value defined in the machine parameters.
Not valid for cutting.
It can be programmed as G00, G0 or G.
Rapid traverse (G00) Linear interpolation (G01)
It is a working linear movement at the
programmed F value.
It can be programmed as G01 or G1.
…
N80 G00 X500 Y300
…
…
N120 G01 X500 Y300 F400
…
(TP)
(SP)
(TP)
(SP)
G00 X Y
TP
G01 X Y
TP

Rapid traverse (G00)
EXERCISE 1
Linear interpolation (G01)
= SP
w

I
J
SP
TP
CC
I
J
SP
TP
CC
It is a working circular movement at the programmed F value.
It can be programmed as G02 or G2 / G03 or G3.
Clockwise circular interpolation (G02)
Counterclockwise circular interpolation (G03)
…
N60 G02 X300 Y300 I200 J0
…
CARTESIANCOORDINATES
WITHARCCENTER
G02 X Y I J
TP Distance from the SP to
the Circle Center (CC).
…
N60 G03 X300 Y300 I0 J200
…
G03 X Y I J
TP Distance from the SP to
the Circle Center (CC).

SP
TP
SP
TP
…
N40 G02 X400 Y150 R150
…
…
N40
…
CARTESIANCOORDINATES
WITHARCRADIUS
G02 X Y R
R + : Arc < 180ºTP
A complete circle cannot be programmed.
G02 X400 Y150 R-150
R+
…
N40 G03 X400 Y300 R150
…
…
N40 G03 X400 Y300 R-150
…
R+
G03 X Y R
R + : Arc < 180ºTP

EXERCISE 2 EXERCISE 3
EXERCISE 4 EXERCISE 5
SP
w
SP
w
w
SP
w
SP

EXERCISE 6
SP
w

Absolute programming (G90)
Incremental programming (G91)
G90: The positioning data refers to the part zero (default).
G91: The positioning data corresponds to the distance to be travelled from the point where the
tool is situated.
N100 G01 X-25 Y0 ; P5
N110 G01 X0 Y-30 ; P6
…
= SP
w
…
N70 G01 G90 X70 Y15 F350 ; P2
N80 G01 X70 Y30 ; P3
N90 G01 X45 Y45 ; P4
N100 G01 X20 Y45 ; P5
N110 G01 X20 Y15 ; P6
…
…
N70 G01 G91 X50 Y0 F350; P2
N80 G01 X0 Y15 ; P3
N90 G01 X-25 Y15 ; P4

EXERCISE 7
w
EXERCISE 8
SP
SP

Square corner (G07) Round corner (G05)
The CNC starts executing the following block as
soon as the position programmed in the current
block has reached the dead band (default)
Sharp edges, Machining time ↑, Shocks ↑.
To be used with G00: face milling, canned
cycles, …
The CNC starts executing the following block as
soon as deceleration of the currently executing
axes start (“?” distance depends on the feedrate
F value) Rounded edges, Machining time ↓
NOT to be used with G00: slot milling,
engraving, contouring,…
Fx
…
N60 G01 G07 X50 Y100 F400
N70 G01 X140 Y100 F300
…
…
N60 G01 G05 X50 Y100 F400
N70 G01 X140 Y100 F300
…
w
t
Fy
t
w
DEAD BAND: The range
through which an input can be
varied without initiating response
t
Fy
t
Fx
Acceleration
Constant feed
Deceleration

Cancellation of tool radius compensation (G40)
Left-hand tool radius compensation (G41)
Right-hand tool radius compensation (G42)
The CNC automatically calculates the path the tool should follow based on the contour of the part
and the tool radius value stored in the tool offset table.

Automatic radius blend (G36) Chamfer (G39)
It rounds a corner with a determined radius,
without having to calculate the center nor the
start and end points of the arc.
Function G36 is not modal.
…
N60 G01 G36 R5 X250 Y450 F400
N70 G01 X400 Y0
…
…
N60 G01 G39 R15 X350 Y600 F400
N70 G01 X500 Y0
…
G36 R
It chamfers corners between two straight lines,
without having to calculate intersection points.
Function G39 is not modal.
G39 R

Face milling
N00 T1 D1 ; Ø28mm end-mill, assign tool 1 value D1
N10 M06 ; Tool change action
N20 G00 G43 X14 Y40 Z100 F400 S1500 M03
N30 G00 Z58
N40
N50
N60
N70
N80
N90
G01 X116 Y40
G00 X116 Y54
G01 X14 Y54
G00 X14 Y68
G01 X116 Y68
G00 X116 Y82
N100 G01 X14 Y82
N110 G00 X14 Y96
N120 G01 X116 Y96
N130 G00 Z100
N130 M30 ; End of program
SP
60
70
20 40 60 80 100
100
80
60
40
20
Security
~ 2 mmdistance
For exercises consider:
ae = 50% of tool Ø

Cancellation of tool radius compensation (G40)
Left-hand tool radius compensation (G41)
Right-hand tool radius compensation (G42)
…
N50 G01 G41 X77.5 Y70 F400 N60
N60 G01 X100 Y70
N70 G01 X100 Y60
N80 G03 X85 Y45 I0 J-15
N90 G02 X70 Y30 I-15 J0
N100 G01 X50 Y30
N110 G01 X20 Y20
N120 G01 X25 Y70
N130 G03 X55 Y70 I15 J0
N140 G01 X77.5 Y70
N150 G01 G40 X77.5 Y100
…
G41
Tool entry & exit should always be perpendicular to the workpiece contour.
Tool entry & exit should be avoided to be from a workpiece edge may produce burr.
20 25 50 55 70 85 100
30
20
45
70
60
SP
•
22.5
30

Face milling
EXERCISE 9
Tool: Ø50mm HSS end-mill, z=4
Material: Aluminium
•CASE A apTOTAL=5mm;
•CASE B apTOTAL=5mm;
•CASE C apTOTAL=5mm;
ap=5mm
ap=2.5mm RPT
ap=1mm RPT & G91

+Z
60
40
20
5
100
85 • •
65 • •
40
•
SP
35 55 65 85
Slot milling
EXERCISE 10
Tool: Ø16mm H.M. end-mill, z=3
Material: Steel
ap TOTAL = 5mm ; ap = 2.5mm

Cycles are referred to repetitive program sequences commonly used In machining operations
that makes easier programming.
• Canned cycles or Fixed cycles: They are an inbuilt feature of the CNC usually
permanently stored as a pre-program and cannot be altered by the user (G80-G89)
• User-defined cycles or Sub-routines: They are created when the necessary fixed
cycle is not available.
FIXED CYCLES OR CANNED CYCLES
CANNED
CYCLE
NUMBER
DESCRIPTION
G80 Canned cycle cancellation
G81 Drilling cycle
G84 Tapping cycle
G85 Reaming cycle
G87 Rectangular pocket cycle
G88 Circular pocket cycle

G81 G98/G99 X Y Z I K
G81: Drilling cycle
Only one drill machining
N0 T1 D1 ; Ø8mm drill N10 M06
N20 G00 G43 X30 Y20 Z100 F300 S1400 M03
N30 G81 G98 X30 Y20 Z2 I-15 K100 ; P1
N40 G80 N50 M30
Four drills machining
N0 T1 D1 ; Ø8mm drill N10 M06
N20 G00 X30 Y20 Z100 F300 S1400 M03
N30 G81 G99 X30 Y20 Z2 I-15 K100 ; P1
N40 G00 X80 Y20 ; P2
N50 G00 X80 Y50 ; P3
N60 G00 G98 X30 Y50 ; P4
N70 G80
N80 M30
Valid for drilling depth
≤ 3*Ø
Valid for pecking cycle
Dwell time
(1/100s)
I.P. R.P.
Distance from
w to the
drilling depth
Distance from
w to the R.P.
Machining
coordinates
Withdrawal
planes
Z
I
15
Initial Plane (I.P.) - G98
Reference Plane (R.P.) - G99
W
8
4 3
1 2

G81 G98/G99 X Y Z I K
G81: Drilling cycle
Valid for drilling depth
≤ 3*Ø
Valid for pecking cycle
Four drills machining
N0 T1 D1 ; Ø8mm drill
N10 M06
N20 G00 G43 X30 Y20 Z100 F300 S1400 M03 ; Z100
N30 G81 G99 X30 Y20 Z2 I-15 K100 ; Z2
N40 G00 G98 X30 Y50 ; Z100
N50 G81 G99 X80 Y50 Z27 I10 K100 ; Z27
N60 G00 G98 X80 Y20 ; Z100
N70 G80
N80 M30
Dwell time
(1/100s)
I.P. R.P.
Distance from
w to the
drilling depth
Distance from
w to the R.P.
Machining
coordinates
Withdrawal
planes
Z
Z’R.P. - G99
Ref. Plane’ (R.P.) - G99’
W
15
I’
I
25
10
8
2 3
1 4

G84: Tapping cycle
N0 T7 D7 ; M-10 tap
N10 M06
N20 G00 G43 X50 Y20 Z100 F600 S600 M03
N30 G84 G98 X50 Y20 Z2 I-60 R0
N40 G80
N50 M30
Z
I
Ref. Plane (R.P.) - G99
W
60
G84 G98/G99 X Y Z I K R
Dwell time
(1/100s)
I.P. R.P.
Distance from
w to the thread
depth
Distance from
w to the R.P.
Machining
coordinates
Withdrawal
planes
Type of tapping
R=0 Normal tapping
R=1 Rigid tapping

N0 T4 D4 ; Ø12H6 reamer
N10 M06
N20 G00 G43 X30 Y20 Z100 F500 S2500 M03
N30 G85 G99 X30 Y20 Z2 I-35 K100
N40 G00 G98 X30 Y50
N50 G85 G99 X80 Y50 Z22 I-15 K100
N60 G00 X80 Y20
N70 G80
N80 M30
G85 G98/G99 X Y Z I K
Dwell time
(1/100s)
I.P. R.P.
Distance from
w to the
reaming depth
Distance from
w to the R.P.
Machining
coordinates
Withdrawal
planes
G85: Reaming cycle
12
2 3
1 4
Z
Z’R.P. - G99
Ref. Plane’ (R.P.) - G99’
W
35
I’
I
20
15

Lathe-Turning operation
N010 T01
N020 G01 X25 G95 F0.3 S500 M03
N030 G01 Z-7.5
N040 G01 X40 Z-15
N050 G01 Z-25
N060 G01 X60 Z-35
N070 G40 G00 X200 Z100

EXERCISES
Facemilling/Profilemilling
EXERCISE 11
Material: Steel

EXERCISES
Facemilling/Profilemilling
EXERCISE 12
Material: Aluminium

12 cnc & part programming

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