Computer Aided Manufacturing Lab
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Computer Aided Manufacturing
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Introduction
Raw materials Manufacturing Process Finished part
http://www.leechind.com/images/cylindricalGrinding1b.jpg -
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Manufacturing Processes
Turning Drilling Milling Shaping
EDM Laser machining Ultrasonic machining
http://upload.wikimedia.org/wikipedia/commons/9/92/Ultrasonic_machining_schematic.jpg -
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How does the table move along X- Y- and Z- axes ?
Machine tools
Lathe Milling machine
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Precise components
Controlling tool movements using numerical data
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Numerical control
NC has been defined by the Electronic Industries Association (EIA)
as a system in which actions are controlled by the direct insertion ofnumerical data at some points. The system must automatically
interpret at least some portion of this data
Program of
instruction
Control unit
Machine tool
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Components of a CNC machine
In general there are three basic components of an operational NC
1. Programme of instruction.
2. A machine control unit.
3. Machine tool.
Numerical control (NC) - machine can be controlled electronically
Computer Numerically Controlled (CNC) - machine actually has
its own microprocessor and memory
Direct Numerical Control (DNC) - wired to a central computer
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Need for CNC
To manufacture complex curved geometries in 2D or 3D
using controlled cutter motions
Machining components with repeatable accuracy
Unmanned machining operations
Computer Numerical Control (CNC) - A numerical control system in
which the data handling, control sequences, and response to input is
determined by an on-board computer system at the machine tool.
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Machining center
A machining center can be defined as a machine toolcapable of:
Multiple operation and processes in a single set-uputilizing multiple axis
Typically has an automatic mechanism to changetools
http://img.diytrade.com/cdimg/603157/4330376/0/1190267517/High_Speed_CNC_Milling_Machine.jpg -
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Components Of CNC Machine Tool
control
cabinet
Controller
Servodrive
Machine tablePosition
transducer
Leadscrew
Gear
boxTachometer
Motor
Converting the rotational motion of the motors to a linear motion.
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Lead screws
Leadscrew
Pitch
Nut
Pitch (p): the distance between adjacent screw threads
Number of teeth per inch (n): n = 1 / p
BLU: Basic Length Unit (machine resolution) BLU = p / n
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Position measurement
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Control Loops
Open loop - No position feedback.
Use stepping motor.
motor
table
pulses
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Coordinate systems
Right hand rule
Z axis align with the spindle - +Z moves away from
the workpiece or the spindle. X axis - Lathe: perpendicular to the spindle.
Horizontal machine: parallel to the table.
Vertical machine: +X points to the right.
x
y
z
x
y
z
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Motion control
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Motion control
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Basic Elements of NC Program
a. Preparatory functions: which unit, which interpolator,
absolute or incremental programming, which circular
interpolation plane, cutter compensation, etc.
b. Coordinates: three translational, and three rotational axes.
c. Machining parameters: feed, and speed.
d. Tool control: tool diameter, next tool number, tool change.
e. Cycle functions: drill cycle, ream cycle, bore cycle, mill cycle,clearance plane.
f. Coolant control: coolant on/off, flood, mist.
g. Miscellaneous control: spindle on/off, tape rewind, spindle
rotation direction, pallet change, clamps control, etc.
h. Interpolators: linear, circular interpolation
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Part Program
Part program: A computer program to specify
- Which tool should be loaded on the machine spindle;
- What are the cutting conditions (speed, feed, coolant ON/OFF etc)
- The start point and end point of a motion segment
- how to move the tool with respect to the machine.
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NC WORDS- F and S Codes
F Code. feed speed.
inch/min (ipm), or ipr.
F code must be given before either G01, G02, or G03 can be used.
Example:
N0100 G02 X7.000 Y2.000 I5.000 J2.000 F6.00
S Code. cutting speed code.
Programmed in rpm.
S code does not turn on the spindle, spindle is turned on by a Mcode.
N0010 S1000
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NC WORDS- T and R Codes
T Code. tool number.
Actual tool change does notoccur until a tool change M
code is specified.
R Code. cycle parameter.
The cycle may be programmed in one
block, such as (cycle programming isvendor specific.):
N0010 G81 X1.000 Y2.000 Z0.000 R 1.300
R plane
Z point
Initial height1
2
3
4
5
(1,2,2)
0.3"
1"
0.7"
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NC WORDS M Codes
M Code. miscellaneous word.
m0
m0
m0
m0
m0
Program stop
Optional stop
End of progr
Spindle CW
Spindle CCW
Tool change
Flood coolant
Mist coolant
Coolant off
End of tape
m06
m07
m08
m09
m30
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Offsets
Fixture G10, G54, G54.1
Diameter
Tool Length compensation
Part-Edge compensation
Cutter Compensation Next Slides
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Tool Radius Compensation
Cutter Compensation
Shifting tool path so that the actual finished cut iseither moved to the left or right of the programmed
path.
Normally, shifted exactly by tool radius
Tool Entry and Exit Issues
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Tool Radius Compensation
Start of Compensation.
G41 (or G42) and G01 in the same block ramp takes place at block N0010.
N0010 G01 G42 X0.500 Y1.700
N0020 G01 X1.500
G41 (or G42) and G01 in separate blocks the compensation is effective fromthe start.
N0010 G41N0020 G01 X0.500 Y1.700
N0030 G01 X1.500
(a) G41 (b) G42
G41
G42
G41
G42
(0.5, 1.7)
(1.5, 1.7)
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Tool Radius CompensationInside Corner.
Cutter path is inside a corner, stops at the inside cutting point
N0010 G41
N0020 G01 X1.500 Y2.000
N0030 G01 X0.000 Y1.600
Use of M96 and M97.
Cutting tool that is larger than the height of the step, M97 must be used
N0010 G41
N0020 G01 X1.000 Y1.000
N0030 G01 Y0.800 M97
N0040 G01 X2.000
G42
G41M96
G41M97
(1.5, 2.0)
(0, 1.6)
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Advantages
Increased Program storage capability at
the machine tool
Program editing at the machine tool Control systems upgrades possible
Option -resident CAM system at machine
tool Tool path verification