cnc pp
DESCRIPTION
bengkelTRANSCRIPT
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CNCUpon completion of this topic, student should be to :
Understand the concept and principles of computer numerical control (CNC) system
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INTRODUCTION
Numerical Control (NC) is one in which
the functions and motions of a machine
tool are controlled by means of a
prepared program containing coded
alphanumeric data.
Numerical control (NC) machines are
used in manufacturing tasks, such as
milling, turning, punching,drilling and
welding
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NC OPERATION
CNC stands for Computer Numerical
Control
The functions of a CNC Controller are:
1. To read and store programme information.
2. To interpret the information in a logical
command sequence.
3. To control the motion of the machines
mechanical members.
4. To monitor the status of the machine.
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An open-loop control system for a numerical-control machine
A closed-loop control system for a numerical-control machine
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INDUSTRIAL APPLICATION
Metal Machining Metal Forming Assembly Joining Finishing
Lathes of all types
Milling Machines of all
types
Drilling Machines
Jig borers
Electric Discharge
Machining (including wire
cut machines)
Laser cutting machines
Machining centres
Turning centres
All types of grinding
machines
Gear cutting machines
Punching and
nibbling
Guillotines
Flame cut and
profiling
Folding
Pipe bending
Metal spinning
Pick and place robots,
spot and seam welding
machines and robots,
riveting, looming of
wires and assembly of
components into
printed circuit boards
Plating
Painting
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CNC AXIS
Milling
Turning/latheLinear Axes X Y Z
Rotary Axes A B C
Secondary Linear U V W
Interpolation I J K
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NC MACHINE UNIT
designed to cut away surplus material and leave a component of the required shape and size
The function of machine tools can give the results in consistence and reduced the machining time
machine tool
to read and decode the part programme, and to provide the decoded instructions to the control loops of the machine axes of motion, and to control the machine tool operations
The main grouping of parts of a control could be considered to be the Control Panel, the Tape Reader and The Processors
Machine control unit
(MCU)
two types of control systems :The point-to-point system and the continuous-path system
The point-to-point controls were NC controls, while the continuous path controls could be NC or CNC controls
Machine control system
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NC PROGRAMMING
- Job PlanningJob Planning
Sketch the part Add incremental or absolute dimensions
Ascertain featuring Select fixtures which have minimal projections above
the part
Identify a set-up point Locate the set-up point near:
1. A corner of the part
2. A spot above the fixture
Consider space requirements for:
1. Part loading and unloading
2. Tool change.
Plan operation sequence Mark sequence pattern of sketch.
Test program data for accuracy
Record necessary data for each movement of
the table and tool on the program sheet.
Record instructions for the machine operator Identify, specific:
1. Tools needed.
2. Speed and feed data
3. Tool change points
4. Console switch setting
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PROGRAMMING CODES
A number of standard codes are used to reduce the amount of programming effort needed to command commonly used machining operations, instructions and conditions
G codes call up machining commands
M codes call up machine control activities
T codes call up tool selection
F codes call up feed rates
S codes call up speed
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G codes
Sample G codes
G00 Rapid movement for position
G0I Linear interpolation used for straight-line feed
G02 Circular interpolation, clockwise
G03 Circular interpolartion, counterclockwise
G04 Dwell, a programmed stop to the tool movement
G17 Circular interpolation xy plane
G18 Circular interpolation xz plane
G19 Circular interpolation yz plane
G20 Inch units
G21 Millimetre units
G28 Return to home position
G29 Return from home position
G31 Reverses programmed direction of x axis
G32 Reverses programmed direction of y axis
G41 Tool radius compensation left
G42 Tool radius compensation right
G43 Tool length compensation-positive direction
G44 Tool length compensation-negative direction
G70 Imperial unit
G71 Metric units
G80 Cancel canned cycle
G81 Drilling cycle
G82 Drilling cycle with dwell
G83 Deep hole drilling
G84 Tapping cycle
G85 89-boring cycles
G90 Absolute mode
G91 Incremental mode
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M Codes
M00 Program stop
M02 End of program
M03 Spindle on, clockwise
M04 Spindle on, counter clockwise
M05 Spindle off
M06 Tool change
M07 Oil mist coolant on
M08 Flood coolant on
M09 Coolant off
M30 End of tape
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Coordinate system
Incremental (G91)
movement with respect to the
preceding point in a prescribed sequence
of points
In incremental mode all moves are with respect to the last position reached
Absolute (G90)
the next location always in terms of its relationship to the fixed zero point
All moves are performed with
respect to the axes zero
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Incremental (G91)
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Absolute (G90)
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Linear Interpolation
Under this command the machine tool
will move in a straight line at a defined
feed rate
Ex:
G01 X200 F250Meaning :
G01 Move in a straight line
X200. A distance of 200mm
F250. At a feed rate of 250mm/min
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Circular Interpolation
G02 will cause the path to be transcribed in a clockwise direction
and G03 will cause counter-clockwise motion
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Program Definition
A programmed is a series of instructions to the machine, set out in sequence to -produce a complete machining operation. A programmed is made up of a series of blocks
Programme
A block or programmed line is a set of instructions to the machine that are carried out simultaneously. A block is made up of one or more Words and is terminated by an End of Block which is the Line Feed Character
Block
A word is a specific instruction to the machine that will affect a particular machine function. Every word consists of a Letter Code and a Numerical value
Word
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Type of control system
point-to-point Point-to-point systems are used
mainly in drilling, punching, and
straight milling operations
Contouring used on lathes, milling machines,
grinders, welding machinery, and
machining centres
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WRITING A PROGRAM
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programming
N10 G71 G90 S1500 T1
N20 G00 X0 Y0
N30 G00 X70.0 Y-25.0 Z10.0
N40 G01 Z-5.0 F250
N50 G03 I-25.0 J0
N60 X45.0 Y-50.0
N70 G01 X60.0 Y -50.0
N80 G02 I0 J-15.0
N90 X49.393 Y-75.607
N100 G01 X38.787 Y-65.0
N110 X15.0 Y-65.0
N120 Z10.0
N130 G00 M00
N140 G00 X0 Y0
NXX block number
Block No. 10 set machine to use metric unit, incremental coordinate, spindle speed 1500 rpm, choose tool no. 1.
Block No. 20 rapid movement to centre point (C.P).
Block No. 30 - rapid movement to point 1 (P. 1), cutting tool distance is
5.0 mm from the surface of the work piece.
Block No. 40 cutting tool cuts 10.00 mm deep, feed 250 mm/min
Block No. 50 circular interpolation, counter clockwise, radius 25.0 mm
Block No. 60 tool ends interpolation cutting at P. 4
Block No. 70 linear interpolation until P. 5
Block No. 80 - circular interpolation, clockwise, radius 15.0 mm
Block No. 90 - tool ends interpolation cutting at P. 6
Block No. 100 - linear interpolation until P. 7
Block No. 110 - linear interpolation until P. 8
Block No. 120 tool rises up 10.0 mm
Block No. 130 program stops
Block No. 140 - rapid return to centre point (C.P).
Description
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ADVANTAGES OF COMPUTER
NUMERICAL CONTROL
can be edited when the machine is placed/located.
Editing, correction and optimising; such as machine
tool operations, spindle speeds and speeds; are usually
done in the test run of the tape.
easily changes into metric system if the programme is in
the imperial units.
It is widely used in industry. It is easily adaptable in a
computerised industry system.
Increased flexibility the machine can produce a
specific part, followed by other parts with different
shapes, and at reduces cost.
Greater accuracy computers have a higher sampling rate
and faster operation.
More versatility editing and debugging programmes,
reprogramming, and plotting and printing part shape are
simpler.
Programmes are stored on the machine ready for use.
Programmes and data can be modified on the machine.
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Example 1 (use G90)
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Example 2
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Quiz (use G91)