note on modern machining CAM

1. CAM Systems & CNC Machine
Overview - Lecture 3
Overview to Computer Aided Manufacturing -
ENGR-2963 - Fall 2005
Class Manager - Sam Chiappone

2. History
1955 - John Parsons and US Air Force define a
need to develop a machine tool capable of
machining complex and close tolerance aircraft
parts with the same quality time after time
(repeatability). MIT is the subcontractor and
builds the machine for the project.
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3. History: Continued
1959 - MIT announces Automatic Programmed
Tools (APT) programming language
1960 - Direct Numerical Control (DNC). This
eliminates paper tape punch programs and allows
programmers to send files directly to machine
tools
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4. History: Continued
1968 - Kearney & Trecker machine tool builders
market first machining center
1970’s - CNC machine tools & Distributed
Numerical Control
1980’s - Graphics based CAM systems
introduced. Unix and PC based systems available
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5. History: Continued
1990’s - Price drop in CNC technology
1997 - PC- Windows/NT based “Open Modular
Architecture Control (OMAC)” systems
introduced to replace “firmware” controllers.
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6. Control Systems
Open-Loop Control
– Stepper motor system
– Current pulses sent from control unit to motor
– Each pulse results in a finite amount of revolution of
the motor001” is possible
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7. Control Systems
Open-Loop Limitations
– Control unit “assumes” desired position is achieved
– No positioning compensation
– Typically, a lower torque motor
Open-Loop Advantages
– Less complex, Less costly, and lower maintenance
costs
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8. Control Systems
Closed-Loop Control
– Variable DC motors - Servos
– Positioning sensors -Resolvers
» Feedback to control unit
» Position information compared to target location
» Location errors corrected
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9. Control Systems
Closed-Loop Advantages
– DC motors have the ability to reverse instantly to adjust
for position error
– Error compensation allows for greater positional
accuracy (.0001”)
– DC motors have higher torque ranges vs.. stepper
motors
Closed-loop limitations
– Cost
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10. Three Basic Categories of
Motion Systems
Point to Point - No contouring capability
Straight cut control - one axis motion at a time is
controlled for machining
Contouring - multiple axis’s controlled
simultaneously
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11. Three Basic Categories of
Motion Systems
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12. CNC vs. NC Machine Tools
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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13. CNC
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
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14. NC
Numerical Control (NC) - A control system which
primarily processes numeric input. Limited
programming capability at the machine tool. Limited
logic beyond direct input. These types of systems are
referred to as “hardwire controls” and were popular
from the 1950’s to 1970’s.
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15. Machining Centers
A machining center can be defined as a machine tool
capable of:
– Multiple operation and processes in a single set-up
utilizing multiple axis
– Typically has an automatic mechanism to change tools
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16. Machining Centers
– Machine motion is programmable
– Servo motors drive feed mechanisms for tool axis’s
– Positioning feedback is provided by resolvers to the
control system
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17. Machining Centers
Example - A turning center capable of OD
turning, external treading, cross-hole drilling,
engraving, and milling. All in machining is
accomplished in one “set-up.” Machine may have
multiple spindles.
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18. Machining Centers
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19. Programming Methods
Automatically Programmed Tools (APT)
– A text based system in which a programmer defines a
series of lines, arcs, and points which define the
overall part geometry locations. These features are
then used to generate a cutter location (CL) file.
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20. Programming Methods-APT
– Developed as a joint effort between the aerospace
industry, MIT, and the US Airforce
– Still used today and accounts for about 5 -10% of all
programming in the defense and aerospace industries
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21. Programming Methods-APT
– Requires excellent 3D visualization skills
– Capable of generating machine code for complicated
part programs
» 5 axis machine tools
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22. Programming Methods-APT
Part definition
P1=Point/12,20,0
C1=Circle/Center,P1,Radius,3
LN1=Line/C1. ATANGL,90
Cutter Commands
TLRT,GORT/LN1.TANTO,C1
GOFWD/C1,TANTO,L5
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23. Programming Methods-CAM
Computer Aided Machining (CAM) Systems
– Graphic representation of the part
– PC based
– Integrated CAD/CAM functionality
– “Some” built-in expertise
Speed & feed data based on material and tool specifications
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24. Programming Methods-CAM
– Tool & material libraries
– Tool path simulation
– Tool path editing
– Tool path optimization
– Cut time calculations for cost estimating
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25. Programming Methods-CAM
– Import / export capabilities to other systems
» Examples:
Drawing Exchange Format (DXF)
Initial Graphics Exchange Standard (IGES)
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26. The Process CAD to NC File
Start with graphic representation of part
– Direct input
– Import from external system
» Example DXF / IGES
– 2D or 3D scan
» Model or Blueprint
(At this point you have a graphics file of your geometry)
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27. The Process CAD to NC File
Define cutter path by selecting geometry
– Contours
– Pockets
– Hole patterns
– Surfaces
– Volume to be removed
(At this point the system knows what you want to cut)
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28. The Process CAD to NC File
Define cut parameters
– Tool information
» Type, Rpm, Feed
– Cut method
» Example - Pocket mill zig-zag, spiral, inside-out
» Rough and finish parameters
(At this point the system knows how you want to cut the part)
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29. The Process CAD to NC File
Execute cutter simulation
– Visual representation of cutter motion
Modify / delete cutter sequences
(At this point the system has a “generic” cutter location (CL)
file of the cut paths)
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30. The Process CAD to NC File
Post Processing
– CL file to machine specific NC code
Filters CL information and formats it into NC
code based on machine specific parameters
– Work envelope
– Limits - feed rates, tool changer, rpm’s, etc.
– G & M function capabilities
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31. Output: NC Code
Numerical Control (NC) Language
– A series of commands which “direct” the cutter motion
and support systems of the machine tool.
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32. Output: NC Code
G-Codes (G00, G1, G02, G81)
Coordinate data (X,Y,Z)
Feed Function (F)
Miscellaneous functions (M13)
N - Program sequence number
T - Tool call
S - Spindle command
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33. Output: NC Code
NC Program Example
– N01G90 G80
– N03 GOO T12 M06
– N05 GOO X0 Y0 Z.1 F10 S2500 M13
– N07 G1Z-.5
– N09 G02 X-10. I0J0F20
– N13 X0Y10
– N17 X10Y0
– N19 X0Y-10
– N21 X-10Y0
– N23 M2
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34. Example of CNC
Programming
What What Must Be Done To Drill A Hole On A
CNC Vertical Milling Machine
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35. Tool Home
Top
View
1.) X & Y Rapid To Hole Position
Front
View
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36. Top
View 2.) Z Axis Rapid Move
Just Above Hole
3.) Turn On Coolant
4.) Turn On Spindle
Front .100”
View
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37. Top
View
5.) Z Axis Feed Move to
Drill Hole
Front
View
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38. Top
View 6.) Rapid Z Axis Move
Out Of Hole
Front
View
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39. Top
View 7.) Turn Off Spindle
8.) Turn Off Coolant
9.) X&Y Axis Rapid
Move Home
Front
View
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40. Here’s The CNC Program! Tool At Home
Top O0001
View N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N025 G00 Z.1 M09
Front N030 G91 G28 X0 Y0 Z0
View N035 M30
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41. Tool At Home
Top O0001
View O0001
Number Assigned to this program
Front
View
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42. Tool At Home
Top O0001
View N005 G54 G90 S600 M03
N005 Sequence Number
G54 Fixture Offset
G90 Absolute Programming Mode
S600 Spindle Speed set to 600 RPM
M03 Spindle on in a Clockwise Direction
Front
View
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43. Top O0001
View N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
G00 Rapid Motion
X1.0 X Coordinate 1.0 in. from Zero
Y1.0 Y Coordinate 1.0 in. from Zero
Front
View
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44. Top O0001
View N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
G43 Tool Length Compensation
H01 Specifies Tool length compensation
Z.1 Z Coordinate .1 in. from Zero
Front M08 Flood Coolant On
View
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45. Top O0001
View N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
G01 Straight Line Cutting Motion
Z-.75 Z Coordinate -.75 in. from Zero
Front F3.5 Feed Rate set to 3.5 in./min.
View
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46. Top O0001
View N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N025 G00 Z.1 M09
Front G00 Rapid Motion
Z.1 Z Coordinate .1 in. from Zero
View M09 Coolant Off
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47. O0001
N005 G54 G90 S600 M03
Top
View N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N025 G00 Z.1 M09
N030 G91 G28 X0 Y0 Z0
G91 Incremental Programming Mode
Front G28 Zero Return Command
View X0, Y0, Z0
X,Y,& Z Coordinates at Zero
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48. Top O0001
View N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N025 G00 Z.1 M09
Front N030 G91 G28 X0 Y0 Z0
View N035 M30
M30 End of Program
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49. Output: NC Code - Canned
Cycles
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50. CAD to NC Code
Import DXF Geometry
File IGES Direct input
Tool Path Generation
What you want to cut
How you want to cut
Tool Type
CL Rpm’s – Feeds
Post Process Method
File
Canned cycles
Cut direction
NC Code OEM
N1 G80 G90 Custom
N3 G0 T01 M06 Language
N5 G0 X0 Y0
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51. Advantages of CNC Machine
Tools
Ease of part duplication
Flexibility
Repeatability
Quality control through process control
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52. Advantages of CNC Machine
Tools
Accommodates simple to complex parts geometry
Improved part aesthetics
Increased productivity
Technology costs are decreasing
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53. Advantages of CNC Machine
Tools
Reduced set-up time
Reduced lead times
Reduced inventory
Better machine utilization
Job advancement opportunities
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54. Advantages of CNC Machine
Tools
CNC machine tools are more rigid than
conventional machine tools
– $$$- Climb milling requires about 10 - 15 % less horsepower vs.
conventional cutting, but requires a ridged machine tool with no
backlash
– Increased Rpm’s and feeds
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