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Nov 7, 2013 (3 years and 9 months ago)

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MEEM4403 Computer-Aided Design Methods
Numerical Control
Automated Manufacturing!
MEEM4403 Computer-Aided Design Methods
Schematic of an NC machine tool
MCU – machine control unit
Controls the motion of the NC machine tool.
DPU – data processing unit
Reads and interprets the part program; sends
immediate commands to CLU.
CLU – control loop unit
Reads positions sensors and sends control signals to
motors.
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
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MEEM4403 Computer-Aided Design Methods
History of NC machining
1947 – U.S. Air Force has great need for
automated machining of freeform surfaces.
late 1940’s – John Parson devises method
involving drilling holes at locations specified
on punch cards.
1951 – Servo-mechanisms Lab at MIT sub-
contracted to refine system.
1952 – Lab demonstrates modified milling machine
(First NC machine).
MEEM4403 Computer-Aided Design Methods
History of NC machining
NC Punched Tape (Figure 11.2 from Text):
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
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MEEM4403 Computer-Aided Design Methods
History of NC machining
1970 – Computer controller developed (called
Computer Numerical Control - CNC).
1970’s – Direct Numerical Control developed.
One mainframe
computer controls
many machines.
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
MEEM4403 Computer-Aided Design Methods
History of NC machining
1980’s – Distributed Numerical Control
(DNC) developed.
Mainframe computer sends
program to PC controlling each
NC machine.
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
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MEEM4403 Computer-Aided Design Methods
Creating an NC Program
1.Establish coordinate systems – tool path
coordinate system must match machine tool
coordinate system.
z – direction: same as tool spindle rotation or
workpiece rotation axis.
+ve tool moves away from workpiece.
x – direction: first feed direction (tool
movement with respect to workpiece).
+ve tool moves away from workpiece.
y – direction: chosen to give right-hand
coordinate system.
MEEM4403 Computer-Aided Design Methods
Establishing Coordinate
Systems
• Lathe Coordi-
nate System:
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
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MEEM4403 Computer-Aided Design Methods
Establishing Coordinate
Systems
• Vertical Drill
Coordinate System:
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
MEEM4403 Computer-Aided Design Methods
Establishing Coordinate
Systems
• Horizontal
Milling Machine
coordinate
system:
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
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MEEM4403 Computer-Aided Design Methods
Establishing Coordinate Systems
• Some machine tools have secondary slide
motions labeled u, v, and w.
• Some machine tools have rotational motions
about x, y and z axes labeled a, b and c
respectively.
• a 2-axis machine allows controlling two motions
simultaneously, a 3-axis machine allows
controlling three motions simultaneously, etc.
• 2-axis, 3-axis, 4-axis and 5-axis machines are
most popular; 9-axis is also available.
MEEM4403 Computer-Aided Design Methods
The Hexapod Machine
How many axes is this one?
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MEEM4403 Computer-Aided Design Methods
Creating an NC program
2.Specifying Commands
A common format is the “Word address format”:
N_ G_ X_ Y_ Z_ I_ J_ K_ F_ S_ T_ M_
where:
the letter denotes a type of instruction or instruction
parameter,
‘_’ is a number that gives the instruction number or
parameter value
letter and number pairs (words) can be omitted if
they have not changed from the last command.
MEEM4403 Computer-Aided Design Methods
Creating an NC program
E.g. N040 G00 X0 Y0 Z300
- means “move the tool to the coordinates
(0,0,300)”
N – is the sequence number
G – is the preparatory command (move
instruction)
X, Y, and Z – are relative or absolute
coordinates of the cutter
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MEEM4403 Computer-Aided Design Methods
Creating an NC program
I, J and K – are the center coordinates for
tracing arcs
F – is the feed rate
S – is the spindle speed
T – is the tool number
M – is miscellaneous commands
MEEM4403 Computer-Aided Design Methods
Preparatory Commands
From: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
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MEEM4403 Computer-Aided Design Methods
Miscellaneous Commands
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
MEEM4403 Computer-Aided Design Methods
Example
Part to be programmed:
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
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MEEM4403 Computer-Aided Design Methods
Example
NC code:
N001 G91// put in incremental mode
N002 G71// use metric units
N003 G00 X0.0 Y0.0 Z40.0 T01 M06
// move to (0,0,40), change to tool 01
N004 G01 X65.0 Y0.0 Z-40.0 F950 S717 M03
// relative, 2-axis move to (65,0,-40), start
// spindle rotation
MEEM4403 Computer-Aided Design Methods
Example
N005 G01 X10.0 F350 M08
// relative move to (10,0,0); start coolant
N006 G01 X110.0// straight moves
N007 G01 Y70.0
N008 G01 X-40.86
Figure from: K. Lee, “Principles of CAD/CAM/CAE Systems,” Addison-Wesley, 1999
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MEEM4403 Computer-Aided Design Methods
Example
N009 G02 X-28.28 Y0.0 I14.14 J5.0
// move clockwise to (-28.28,0,0) along arc
// centered at (14.14, 5.0, 0)
N010 G01 X-40.86
N011 G01 Y-70.0// last cut
N012 G01 X-75.0 Y0.0 Z40.0 F950 M30
// return to start, turn off spindle and coolant
MEEM4403 Computer-Aided Design Methods
Studying for Final Exam
• Do Practice Exam
• Textbook questions:
– Ch. 6: 1, 3, 4 (optional: 2)
– Ch. 7: 4
– Ch. 9: questions from optimization lecture
– Ch. 11: read
– Ch. 14: 1