Computer Numerical Control
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Computer Numerical Control
Types of AutomationManufacturing
Automation
Hard/ Rigid/ MechanizedAutomation
Soft/ Flexible/ ProgrammableAutomation
Copy milling machines AutomatsSpecial purpose machines
CNC Machines RobotsAutomatically Guided Vehicles (AGVs) Reconfigurable conveyors
Unlimited muscle powerSpeedAccuracyUnmanned operationFlexibilitySimplified generic tooling even for the most complex jobs
Advantages of Soft Automation
Introduction to CNC
Conventionally, an operator decides and adjusts various machines parameters like feed , depth of cut etc depending on type of job , and controls the slide movements by hand.
In a CNC Machine functions and slide movements are controlled by motors using computer programs.
The most basic function of any CNC machine is automatic, precise, and consistent motion control.
The two most common axis types are linear (driven along a straight path) and rotary (driven along a circular path).
Introduction to CNC
Conventionally, an operator decides and adjusts various machines parameters like feed , depth of cut etc depending on type of job , and controls the slide movements by hand.
In a CNC Machine functions and slide movements are controlled by motors using computer programs.
The most basic function of any CNC machine is automatic, precise, and consistent motion control.
The two most common axis types are linear (driven along a straight path) and rotary (driven along a circular path).
Why CNC is Accurate?Light but rigid construction
Hollow design with ribs to have less deflection and low nat. freq., Design improvement using mode shape analysis
Low inertia Keep weight of moving elements low
Low friction and play Guide way elements, Ball lead screws, Pre-loading
Good damping Appropriate material selection
Minimization of thermal effects
Control of ambient temperature (humidity and suspended dust too), Use of thermally stable material, Thermal compensation
Advanced electrical and electronics and computing
Advanced drives, Accurate sensors for position, velocity, force, vibration, temp. etc., Sophisticated feedback control loops, Interpolators
Error compensations Axis calibration & pitch error compensation, Diameter and length compensations, Adaptive control
Accurate manufacture Use of accurate manufacturing processes
Defining AxesPrimary Secondary Tertiary
X U P
Y V Q
Z W R
Spindle is Z axisMoving away is ‚+‘
Imagine table stationaryTake longest as X axis
Defining Axes
Lathe
Vertical Machining Center
Important G CodesG00 Rapid TransverseG01 Linear InterpolationG02 Circular Interpolation, CWG03 Circular Interpolation, CCWG17 XY Plane,G18 XZ Plane,G19 YZ PlaneG20/G70 Inch unitsG21/G71 Metric UnitsG40 Cutter compensation cancelG41 Cutter compensation leftG42 Cutter compensation rightG43 Tool length compensation (plus)G43 Tool length compensation (plus)G44 Tool length compensation (minus)G49 Tool length compensation cancelG80 Cancel canned cyclesG81 Drilling cycleG82 Counter boring cycleG83 Deep hole drilling cycleG90 Absolute positioningG91 Incremental positioning
Important M CodesM00 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
Modal and Non-Modal Commands
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.
Open Loop and Closed Loop System
Tape Preparation
Punch holes in channels 6 and 7 pulse numeric value
Punch holes in channels 7 pulse numeric value
Punch holes in channels 6 pulse numeric value
1= a2= b3=c4=d5=e6=f7=g8=h9=i
1= j2= k3=l
4=m5=n6=o7=p8=q9=r
2= s3=t4=u5=v6=w7=x8=y9=z
Programming : Absolute and Incremental5 – Parity check6 – Zero7- Minus8 – End of info
EIA ASCII
Features of a CNC Systems
The tool or material moves.
Tools can operate in 1-5 axes.
Larger machines have a machine control unit (MCU)
which manages operations.
Movement is controlled by a motors (actuators).
Feedback is provided by sensors (transducers)
Tool magazines are used to change tools
automatically.
Types of InterpolationsPoint to Point - No contouring capability Straight cut control - one axis motion at a time is controlled for machiningContouring - multiple axis’s controlled simultaneously
Sample Programming
Preparatory Information: units, incremental or absolute positioning
Coordinates: X,Y,Z, RX,RY,RZ
Machining Parameters: Feed rate and spindle speed
Coolant Control: On/Off, Flood, Mist
Tool Control: Tool and tool parameters
Cycle Functions: Type of action required
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
Sample Programming
Manual Part Programming: Manual programming of the machinesComputer Aided Programming (CAP): Programming done by a computerManual Data Input (MDI): A manual program is entered into the machine’s controller via its own keyboard
Sample Programming
Tool size = 0.25 inch,Feed rate = 6 inch per minute,Cutting speed = 300 rpm,Tool start position: 2.0, 2.0Programming in inches
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3p4
p5
Motion of tool:p0 p1 p2 p3 p4 p5 p1 p0
Sample Programming
Spindle CCW
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3p4
p5
Set up the programming parameters
N010 G70 G90 G94 G97 M04
Programming in inches
Use absolute coordinates
Spindle speed in rpm
Feed in ipm
Sample Programming
Flood coolant ON
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3p4
p5 Set up the machining
conditions
N020 G17 G75 F6.0 S300 T1001 M08
Machine moves in XY-plane
Feed rate
Tool no.
Spindle speed
Use full-circle interpolation
Sample Programming
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3p4
p5
Move tool from p0 to p1 in straight line
N030 G01 X3.875 Y3.698
Linear interpolation
target coordinates
Sample Programming
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3p4
p5
Cut profile from p1 to p2
N040 G01 X3.875 Y9.125
Linear interpolation
target coordinates
N040 G01 Y9.125
X-coordinate does not change no need to program it
or
Sample Programming
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3p4
p5
Cut profile from p2 to p3
N050 G01 X5.634 Y9.125
Linear interpolation
target coordinates
1”
p3
.125
(x, y)
(6.5, 9)
y = 9 + 0.125 = 9.125(6.5 - x)2 + 0.1252 = (1 - 0.125)2
x = 5.634
Sample Programming
coordinates of center of circle (always in incremental )
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3p4
p5
Cut along circle from p3 to p4
circular interpolation, CCW motion
target coordinates
N060 G03 X7.366 Y9.125 I0.866 J-0.125
Sample Programming
N010 G70 G90 G94 G97 M04 N020 G17 G75 F6.0 S300 T1001 M08 N030 G01 X3.875 Y3.698 N040 G01 X3.875 Y9.125 N050 G01 X5.634 Y9.125 N060 G03 X7.366 Y9.125 I0.866 J-0.125 N070 G01 X9.302 N080 G01 X3.875 Y3.698 N090 G01 X2.0 Y2.0 M30
Complete Programming
Adaptive Control
1. Adaptive control with constraints2. Adaptive control with optimization
Advantage of NC
Increased productivity Reduced tool/fixture storage and cost Faster setup time Reduced parts inventory Flexibility that speeds changes in design Better accuracy of partsReduction in parts handling Better uniformity of parts Better quality control Improvement in manufacturing control
DisadvantagesIncrease in electrical maintenanceHigh initial investmentHigher per-hour operating cost than traditional machine toolsRetraining of existing personnel
NC is a general term used for Numerical Control. CNC refers specifically to COMPUTER NUMERICAL CONTROL. CNC machines are all NC machines but not all NC machines are CNC machine.
Applications
• Traditional machining– Turning, boring, milling, grinding etc.
• Sheet metal manufacture– Turret punch press, pipe bending, flow forming etc.
• Non-traditional machining– Wire-EDM, water-jet cutting, electron beam machining,
laser beam machining, plasma cutting etc.• Coordinate Measuring Machines• Drafting machines• Robots• Rapid Prototyping (RP) machines
NC is a control technique; not a process
END