CNC MACHINE TOOLS Introduction Module 1.ppt

Professional Elective - 4
CNC Machine Tools
(18ME821)

B. E. MECHANICAL ENGINEERING
SEMESTER - VIII
Professional Elective-4
CNC MACHINE TOOLS
(18ME821)
Module-1
INTRODUCTION TO CNC MACHINE TOOLS:
Evolution of CNC Technology, principles, features,
advantages, applications, CNC and DNC concept,
classification of CNC Machines – turning centre,
machining centre, grinding machine, EDM, types of
control systems, CNC controllers, characteristics,
interpolators– Computer Aided Inspection.

Module-2
STRUCTURE OF CNC MACHINE TOOL: CNC Machine
building, structural details, configuration and
design, guide ways – Friction, Anti friction and other
types of guide ways, elements used to convert the
rotary motion to a linear motion – Screw and nut,
recirculating ball screw, planetary roller screw,
recirculating roller screw, rack and pinion, spindle
assembly, torque transmission elements–gears,
timing belts, flexible couplings, Bearings.

Module-3
DRIVES AND CONTROLS: Spindle drives–DC shunt
motor, 3 phase AC induction motor, feed drives –
stepper motor, servo principle, DC and AC
servomotors, Open loop and closed loop control,
Axis measuring system–synchro, synchro-resolver,
gratings, moiré fringe gratings, encoders,
inductosysn, laser interferometer.

Module-4
CNC PROGRAMMING: Coordinate system, structure
of a part program, G & M Codes, tool length
compensation, cutter radius and tool nose radius
compensation, do loops, subroutines, canned cycles,
mirror image, parametric programming, machining
cycles, manual part programming for machining
centre and turning centre. Computer Aided CNC Part
Programming: Need for computer aided part
programming,Tools for computer aided part
programming, APT, CAD/CAM based part
programming for well-known controllers such as
Fanuc, Heidenhain, Sinumerik etc., and generation
of CNC codes from CAM packages.

Module-5
TOOLING AND WORK HOLDING DEVICES:
Introduction to cutting tool materials – Carbides,
Ceramics, CBN, PCD–inserts classification,
qualified, semi qualified and pre-set tooling,
tooling system for Machining centre and Turning
centre, work holding devices for rotating and fixed
work parts, modular fixtures, economics of CNC,
maintenance of CNC machines.

INTRODUCTION TO
NUMERICAL CONTROL

NC Machine Tool
An NC machine tool is functionally the same as
a conventional machine tool.
The technological capabilities NC machine
tools in terms of machining are no different
from those of conventional ones.
The difference is in the way in which the
various machine functions and slide
movements are controlled.

Definition of Numerical Control (NC)
Numerical control, popularly known as the
NC is very commonly used in the machine
tools.
“Numerical control is defined as the form of
programmable automation, in which the
process is controlled by the numbers, letters,
and symbols.”

In other words, the numerical control
machine is defined as the machine that is
controlled by the set of instructions called as
the program.
In numerical control method the numbers
form the basic program instructions for
different types of jobs.
Hence the name numerical control.

Brief History of the NC
The invention of numerical control has been
due to the pioneering works of John T.
Parsons in the year 1940, when he tried to
generate a curve automatically by milling
cutters by providing coordinate motions.
In the late 1940s Parsons conceived the
method of using punched cards containing
coordinate position system to control a
machine tool. The machine directed to move
in small increments and generate the desired
finish.

In the year, 1948, Parsons demonstrated
this concept to the US Air Force, who
sponsored the series of project at
laboratories of Massachusetts Institute of
Technology (MIT).
After lots of research MIT was able to
demonstrate first NC prototype in the year
1952 and in the next year they were able
to prove the potential applications of the
NC.

Development of the CNC Machines
In the initial years of NC, punched tapes
were for feeding the instructions to the
machine tools via the control unit. The APT
language also marked the arrival of the
computer numerical controlled machines,
popularly known as the CNC machines.

In CNC machines, programs are fed in the
computer was used to control the operations
of the machines. Thus the control unit used
that would read the punched cards in the
NC machines was replaced by the
microcomputer in the CNC machines.
The CNC brought major revolution in the
manufacturing industry.
The next development has been the
combination of computer aided
manufacturing (CAM) and computer aided
designing (CAD) called as CAD/CAM.

Basic components of an NC system
1. Program of instructions
Part program in machining
2. Machine control unit
Controls the process
3. Processing equipment
Performs the process

Components of traditional NC system

CNC MACHINE TOOLS Introduction Module 1.ppt

HISTORY
 US Air Force commissioned MIT to develop
the first "numerically controlled" machine
in 1948. It was demonstrated in 1952.
 At 1970-1972 first Computer Numeric
Control machines were developed.
 Today, computer numerical control (CNC)
machines are found almost everywhere,
from small job shops in rural communities
to companies in large urban areas.

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

Advantages of CNC
 Productivity
Machine utilization is increased because
more time is spent cutting and less time is
taken by positioning.
Reduced setup time increases utilisation
too.

Advantages of CNC
 Quality
Parts are more accurate.
Parts are more repeatable.
Less waste due to scrap.

Advantages of CNC
 Reduced inventory
Reduced setup time permits smaller
economic batch quantities.
Lower lead time allows lower stock levels.
Lower stock levels reduce interest charges
and working capital requirements.

Advantages of CNC
 Machining Complex shapes
Slide movements under computer control.
Computer controller can calculate steps.
First NC machine built 1951 at MIT for
aircraft skin milling.

Advantages of CNC
 Management Control
CNC leads to CAD
Process planning
Production planning

Drawbacks of CNC
 High capital cost
Machine tools cost $30,000 - $1,500,000
 Retraining and recruitment of staff
 New support facilities
 High maintenance requirements
 Not cost-effective for low-level production
on simple parts
 As geometric complexity or volume
increases CNC becomes more economical
 Maintenance personnel must have both
mechanical and electronics expertise

Applications of CNC machines
CNC machines are widely used in the metal cutting
industry and are best used to produce the following types
of products.
 Parts with complicated contours
 Parts requiring close tolerance and/or good repeatability
 Parts requiring expensive jigs and fixyures if produced
on conventional machines
 Parts that may have several engineering changes, such
as during the development stage of a prototype
 In cases where human errors could be extremely costly
 Parts that are needed in a hurry
 Small batch lots or short production runs

Types of CNC machines
The machines controlled by CNC can be classified into
the following categories.
 CNC mills and machining centers
 CNC lathes and turning centers
 CNC drilling machines
 CNC Wirecut EDMs
 CNC grinding machines
 CNC cutting machines (Laser, Plasma, Water Jet,
Electron, or flame)
 CNC fabrication machines (Sheet metal punch press,
bending, or press brake)
 CNC welding machines

Hydraulic plate punching and Marking machine

5-axis CNC travelling column machine

Industries most affected by CNC
 Aerospace
 Machinery
 Electrical
 Fabrication
 Automotive
 Instrumentation
 Mold making

SAMPLE PRODUCTS
OF
CNC MANUFACTURING

AUTOMOTIVE INDUSTRY
Engine Block

AUTOMOTIVE INDUSTRY
Different Products

AEROSPACE INDUSTRY
Aircraft Turbine Machined by 5-Axis CNC Milling
Machine

CNC SYSTEM ELEMENTS
A typical CNC system consists of the
following six elements
1. Part program
2. Program input device
3. Machine control unit
4. Drive system
5. Machine tool
6. Feedback system

OPERATIONAL FEATURES of CNC
MACHINES

1. PART PROGRAM
 A part program is a series of coded instructions
required to produce a part. It controls the
movement of the machine tool and the on/off
control of auxiliary functions such as spindle
rotation and coolant. The coded instructions are
composed of letters, numbers and symbols and are
arranged in a format of functional blocks as in the
following example
N10 G01 X5.0 Y2.5 F15.0
| | | | |
| | | | Feed rate (15 in/min)
| | | Y-coordinate (2.5")
| | X-coordinate (5.0")
| Linear interpolation mode
Sequence number

2. PROGRAM INPUT DEVICE
 The program input device is the
mechanism for part programs to be
entered into the CNC control. The most
commonly used program input devices are
keyboards, punched tape reader, diskette
drivers, throgh RS 232 serial ports and
networks.

3. MACHINE CONTROL UNIT
The machine control unit (MCU) is the heart of a
CNC system. It is used to perform the following
functions:
 Read coded instructions
 Decode coded instructions
 Implement interpolations (linear, circular, and
helical) to generate axis motion commands
 Feed axis motion commands to the amplifier
circuits for driving the axis mechanisms
 Receive the feedback signals of position and speed
for each drive axis
 Implement auxiliary control functions such as
coolant or spindle on/off, and tool change

The functions and motions such as;
turning the spindle on and off
setting cutting speeds
setting feed rate
turning coolant on and off
moving tool with respect to workpiece
are performed by Machine Control Unit
(MCU) in NC machine tools.

TYPES of CNC CONTROL SYSTEMS
 Open-loop control
 Closed-loop control

OPEN-LOOP CONTROL SYSTEM
 In open-loop control system step motors are
used
 Step motors are driven by electric pulses
 Every pulse rotates the motor spindle through a
certain amount
 By counting the pulses, the amount of motion
can be controlled
 No feedback signal for error correction
 Lower positioning accuracy

CLOSED-LOOP CONTROL SYSTEMS
 In closed-loop control systems DC or AC
motors are used
 Position transducers are used to generate
position feedback signals for error
correction
 Better accuracy can be achieved
 More expensive
 Suitable for large size machine tools

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

STEPPING 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 .

RECIRCULATING BALL SCREWS
Transform rotational motion of the motor into
translational motion of the nut attached to the
machine table.

RECIRCULATING BALL SCREWS
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.

POSITIONING
 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.

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

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

Direct Numerical Control (DNC)
Direct numerical control (DNC), also known as distributed
numerical control (also DNC), is a common manufacturing
term for networking CNC machine tools. On some CNC
machine controllers, the available memory is too small to
contain the machining program (for example machining
complex surfaces), so in this case the program is stored in a
separate computer and sent directly to the machine, one block
at a time. If the computer is connected to a number of
machines it can distribute programs to different machines as
required. Usually, the manufacturer of the control provides
suitable DNC software. However, if this provision is not
possible, some software companies provide DNC applications
that fulfill the purpose. DNC networking or DNC
communication is always required when CAM programs are to
run on some CNC machine control

 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.

 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.

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

 With Distributed Numerical Control systems, it
is possible to monitor the activities in individual
CNC machine tools on host computer.
 Therefore, better shop floor control can be
achieved.
Distributed Numerical Control (DNC)

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

INDUSTRIAL APPLICATIONS of
ENCODERS

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

VELOCITY 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.

CNC CUTTERS
 Turning center cutters
 Machining center cutters

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

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 won’t
cut a square shoulder. 4 edges per
side.
 R – strongest insert but least
commonly used.

TYPICAL TURNING,
THREADING and PARTING TOOLS

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.

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.

TOOLS (cont’d)
 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.

TOOLS (cont’d)
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.

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.

CNC PROGRAMMING
 Offline programming linked to CAD programs.
 Conversational programming by the
operator.
 MDI ~ Manual Data Input.
 Manual Control using jog buttons or
`electronic handwheel'.
 Word-Address Coding using standard G-codes
and M-codes.

During secondary motion, either the tool
moves relative to the workpiece or the
workpiece moves relative to the tool. In NC
programming, it is always assumed that the
tool moves relative to the workpiece no
matter what the real situation is.
Basics of NC Part Programming:

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

In defining the motion of the tool
from one point to another,
either
absolute positioning mode or
incremental positioning mode
can be used.

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

Structure of an NC Part Program:
Commands are input into the controller in
units called blocks or statements.
Block Format:
1. Fixed sequential format
2. Tab sequential format
3. Word address format

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.

1. Fixed sequential format
0050 00 +0025400 +0012500 +0000000 0000 00
0060 01 +0025400 +0012500 -0010000 0500 08
0070 00 +0025400 +0012500 +0000000 0000 09
2. Tab sequential format
0050 TAB 00 TAB +0025400 TAB +0012500 TAB +0000000 TAB TAB
0060 TAB 01 TAB TAB TAB -0010000 TAB 0500 TAB 08
0070 TAB 00 TAB TAB TAB -0000000 TAB 0000 TAB 09
3. Word address format
N50 G00 X25400 Y125 Z0 F0
N60 G01 Z-10000 F500 M08
N70 G00 Z0 M09

Modal commands: Commands issued in the
NC program that will stay in effect until it is
changed by some other command, like, feed
rate selection, coolant selection, etc.
Nonmodal commands: Commands that are
effective only when issued and whose
effects are lost for subsequent commands,
like, a dwell command which instructs the
tool to remain in a given configuration for a
given amount of time.

INFORMATION NEEDED by a CNC
1. Preparatory Information: units, incremental or absolute
positioning
2. Coordinates: X,Y,Z, RX,RY,RZ
3. Machining Parameters: Feed rate and spindle speed
4. Coolant Control: On/Off, Flood, Mist
5. Tool Control: Tool and tool parameters
6. Cycle Functions: Type of action required
7. Miscellaneous Control: Spindle on/off, direction of
rotation, stops for part movement
This information is conveyed to the machine through a set
of instructions arranged in a desired sequence – Program.

BLOCK FORMAT
Sample 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

WORD-ADDRESS CODING
 N5 G90 G20
 N10 M06 T3
 N15 M03 S1250
 N20 G00 X1 Y1
 N25 Z0.1
 N30 G01 Z-0.125 F5
 N35 X3 Y2 F10
 N40 G00 Z1
 N45 X0 Y0
 N50 M05
 N55 M30
Example CNC Program
Each instruction to the 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

G & M Codes
 N5 G90 G20
 N10 M06 T3
 N15 M03 S1250
 N20 G00 X1 Y1
 N25 Z0.1
 N30 G01 Z-0.125 F5
 N35 X3 Y2 F10
 N40 G00 Z1
 N45 X0 Y0
 N50 M05
 N55 M30
Example CNC Program
• G-codes: Preparatory Functions
involve actual tool moves.
• M-codes: Miscellaneous
Functions – involve actions
necessary for machining (i.e.
spindle on/off, coolant on/off).

G Codes
 G00 Rapid traverse
 G01 Linear interpolation
 G02 Circular interpolation,
CW
 G03 Circular interpolation,
CCW
 G04 Dwell
 G08 Acceleration
 G09 Deceleration
 G17 X-Y Plane
 G18 Z-X Plane
 G19 Y-Z Plane
 G20 Inch Units (G70)
 G21 Metric Units (G71)
 G40 Cutter compensation –
cancel
 G41 Cutter compensation –
left
 G42 Cutter compensation-
right
 G70 Inch format
 G71 Metric format
 G74 Full-circle programming
off
 G75 Full-circle programming
on
 G80 Fixed-cycle cancel
 G81-G89 Fixed cycles
 G90 Absolute dimensions
 G91 Incremental dimensions

Modal G-Codes
 Most G-codes set the machine in a “mode”
which stays in effect until it is changed or
cancelled by another G-code. These
commands are called “modal”.

Modal G-Code List
 G00 Rapid Transverse
 G01 Linear Interpolation
 G02 Circular Interpolation, CW
 G03 Circular Interpolation,
CCW
 G17 XY Plane
 G18 XZ Plane
 G19 YZ Plane
 G20/G70 Inch units
 G21/G71 Metric Units
 G40 Cutter compensation
cancel
 G41 Cutter compensation left
 G42 Cutter compensation right
 G43 Tool length compensation
(plus)
(plus)
(minus)
cancel
 G80 Cancel canned cycles
 G81 Drilling cycle
 G82 Counter boring cycle
 G83 Deep hole drilling cycle
 G90 Absolute positioning
 G91 Incremental positioning

M Codes
 M00 Program stop
 M01 Optional program stop
 M02 Program end
 M03 Spindle on clockwise
 M04 Spindle on counterclockwise
 M05 Spindle stop
 M06 Tool change
 M08 Coolant on
 M09 Coolant off
 M10 Clamps on
 M11 Clamps off
 M30 Program stop, reset to start

N Codes
 Gives an identifying number for each block
of information.
 It is generally good practice to increment
each block number by 5 or 10 to allow
additional blocks to be inserted if future
changes are required.

X,Y, and Z Codes
 X, Y, and Z codes are used to specify the
coordinate axis.
 Number following the code defines the
coordinate at the end of the move relative
to an incremental or absolute reference
point.

I,J, and K Codes
 I, J, and K codes are used to specify the
coordinate axis when defining the center
of a circle.
 Number following the code defines the
respective coordinate for the center of the
circle.

F,S, and T Codes
 F-code: used to specify the feed rate
 S-code: used to specify the spindle speed
 T-code: used to specify the tool
identification number associated with the
tool to be used in subsequent operations.

Application of Some Codes
G01 Linear Interpolation
Format: N_ G01 X_ Y_ Z_ F_
 Linear Interpolation results in a straight
line feed move.
 Unless tool compensation is used, the
coordinates are associated with the
centerline of the tool.

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

5
1 0
1 5
2 0
2 5
5 1 0 1 5 2 0 2 5 3 0
A
B C
P o s i t i o n i n g m o t i o n f r o m A t o C
N 1 0 G 0 0 X 3 0 0 0 0 Y 2 0 0 0 0 F 0

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.

5
1 0
1 5
2 0
2 5
5 1 0 1 5 2 0 2 5 3 0
A
C
L i n e a r i n t e r p o l a t i o n f r o m A t o C
N 1 0 G 0 1 X 3 0 0 0 0 Y 2 0 0 0 0 F 2 5 0 0

N10 G00 X1 Z1
N15 Z0.1
N20 G01 Z-0.125 F5
N25 X2 Z2 F10
X
Z

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

G02 Circular Interpolation (CW)
 The G02 command requires an
endpoint and a radius in order
to cut the arc.
 I,J, and K are relative to the
start point.
N_ G02 X2 Y1 I0 J-1 F10
or
N_ G02 X2 Y1 R1

G02 Circular Interpolation (CW)
5
1 0
1 5
2 0
2 5
5 1 0 1 5 2 0 2 5 3 0
C
C
C i r c u l a r i n t e r p o l a t i o n f r o m A t o B
a b o u t a c i r c l e c e n t e r e d a t C
N 1 0 G 0 2 X 2 0 0 0 0 Y 1 0 0 0 0
I 5 0 0 0 J 1 5 0 0 0 F 2 5 0 0
A
B
I = 5
J = 1 5

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

Some Commonly Used Canned Cycle
Code Function Down feed At bottom Retracti
on
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

Three Main parts of a CNC program
 N5 G90 G21 (Absolute units, metric)
 N10 M06 T2 (Stop for tool change, use
tool # 2)
 N15 M03 S1200 (Turn the spindle on CW to
1200 rpm)
Part 1- Program Petup

 N20 G00 X1 Y1 (Rapid to X1,Y1 from origin
point)
 N25 Z0.125 (Rapid down to Z0.125)
 N30 G01 Z-0.125 F100 (Feed down to Z-0.125 at
100 mm/min)
 N35 G01 X2 Y2 (Feed diagonally to X2,Y2)
 N40 G00 Z1 (Rapid up to Z1)
 N45 X0 Y0 (Rapid to X0,Y0)
Part 2- Chip Removal

 N50 M05 (Turn the spindle off)
 N55 M00 (Program stop)
Part 3- System Shutdown

EXAMPLE OPERATION on CNC
MILLING MACHINE

G-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

 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

 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

 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

Advanced features:
 Execution of the part of the program in a
rotated or mirrored position.
 Ability to scale the program and produce
larger or smaller programs.
 Three dimensional circular interpolation
which produces a helical shape.
 Parabolic and cubic interpolation.

Program Loading:
 Through keyboard
 Through punched tape reader
 Through diskette drive
 Through RS 232 serial port
 Through network interface card

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

Advantages of applying computer-aided part
programming include the following:
 1. It reduces the manual calculations
involves in determining the geometric
characteristics of the part.
 It provides the cutter path simulation.
 It provides tool collision checking.
 It shortens the program preparation time.
 It makes the program preparation easier.

 The Aerospace Industries Association
sponsored the work that led to the first part
programming language, developed in MIT in
1955.
 This was called: Automatically Programmed
Tools (APT).
 APT is an English like simple programming
language which basically produce the Cutter
Location (CL) data.
 Using the cutter location data, the program can
generate the actual NC codes by using a
postprocessor .

 The output of any CAD package include the
geometric data of the part to be machined.
Therefore, many CAD/CAM package can
produce cutter location (CL) data to be used
for NC code generation.
 There is still to be a process planning module
for a workable NC code generation.
 Some of the CAD/CAM packages that have the
NC code generation capabilities are
Computervision, CATIA, CADAM, ProEngineer,
MechanicalDesktop (Auto Desk).
CAD/CAM Based Part Programming:

CNC MACHINE TOOLS Introduction Module 1.ppt

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CNC MACHINE TOOLS Introduction Module 1.ppt