cams ys overview
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CAM Systems & CNC Machine
Overview - Lecture 3
Overview to Computer Aided Manufacturing -
ENGR-2963 - Fall 2005
Class Manager - Sam Chiappone
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Intro to CAM
ChiapponeRensselaer Polytechnic Institute
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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History: Continued
1959 - MIT announces Automatic Programmed
Tools (APT) programming language
1960 - Direct Numerical Control (DNC). This
eliminates paper tape punch programs and allowsprogrammers to send files directly to machine
tools
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History: Continued
1968 - Kearney & Trecker machine tool builders
market first machining center
1970s - CNC machine tools & Distributed
Numerical Control
1980s - Graphics based CAM systems
introduced. Unix and PC based systems available
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History: Continued
1990s - 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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Intro to CAM
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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 ofthe motor001 is possible
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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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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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Control Systems
Closed-Loop Advantages
DC motors have the ability to reverse instantly to adjust
for position error
Error compensation allows for greater positionalaccuracy (.0001)
DC motors have higher torque ranges vs.. stepper
motors
Closed-loop limitations Cost
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Intro to CAM
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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 axiss controlledsimultaneously
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Intro to CAM
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Three Basic Categories of
Motion Systems
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Intro to CAM
ChiapponeRensselaer Polytechnic Institute
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 atthe machine tool.
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Intro to CAM
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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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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 arereferred to as hardwire controls and were popular
from the 1950s to 1970s.
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Intro to CAM
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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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Intro to CAM
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Machining Centers
Machine motion is programmable
Servo motors drive feed mechanisms for tool axiss
Positioning feedback is provided by resolvers to the
control system
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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 havemultiple spindles.
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Intro to CAM
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Machining Centers
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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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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 allprogramming in the defense and aerospace industries
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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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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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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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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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Programming Methods-CAM
Import / export capabilities to other systems Examples:
Drawing Exchange Format (DXF)
Initial Graphics Exchange Standard (IGES)
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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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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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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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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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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, rpms, etc.
G & M function capabilities
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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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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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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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Example of CNC
Programming What What Must Be Done To Drill A Hole On A
CNC Vertical Milling Machine
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TopView
FrontView
Tool Home
1.) X & Y Rapid To Hole Position
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TopView
FrontView
2.) Z Axis Rapid Move
Just Above Hole
3.) Turn On Coolant
4.) Turn On Spindle
.100
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TopView
FrontView
5.) Z Axis Feed Move toDrill Hole
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TopView
FrontView
6.) Rapid Z Axis Move
Out Of Hole
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TopView
FrontView
9.) X&Y Axis Rapid
Move Home
7.) Turn Off Spindle
8.) Turn Off Coolant
Tool At HomeHeres The CNC Program!
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TopView
FrontView
Tool At Home
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08N020 G01 Z-.75 F3.5
N030 G91 G28 X0 Y0 Z0N035 M30
N025 G00 Z.1 M09
Heres The CNC Program!
Tool At Home
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TopView
FrontView
Tool At Home
O0001O0001
Number Assigned to this program
Tool At Home
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Intro to CAM
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TopView
FrontView
Tool At Home
O0001
N005 G54 G90 S600 M03N005 Sequence Number
G54 Fixture Offset
G90 Absolute Programming Mode
S600 Spindle Speed set to 600 RPM
M03 Spindle on in a Clockwise Direction
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TopView
FrontView
O0001
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
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TopView
FrontView
O0001
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
M08 Flood Coolant On
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TopView
FrontView
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08N020 G01 Z-.75 F3.5
G01 Straight Line Cutting Motion
Z-.75 Z Coordinate -.75 in. from Zero
F3.5 Feed Rate set to 3.5 in./min.
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TopView
FrontView
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08N020 G01 Z-.75 F3.5
G00 Rapid MotionZ.1 Z Coordinate .1 in. from Zero
M09 Coolant Off
N025 G00 Z.1 M09
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TopView
FrontView
O0001
N005 G54 G90 S600 M03N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N030 G91 G28 X0 Y0 Z0G91 Incremental Programming Mode
G28 Zero Return Command
X0, Y0, Z0
X,Y,& Z Coordinates at Zero
N025 G00 Z.1 M09
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Intro to CAM
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TopView
Front
View
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N035 M30
N030 G91 G28 X0 Y0 Z0
N025 G00 Z.1 M09
M30 End of Program
O t t NC C d C d
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Output: NC Code - Canned
Cycles
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CAD to NC CodeGeometry
Direct input
Tool Path GenerationWhat you want to cutHow you want to cutTool TypeRpms FeedsMethodCanned cyclesCut direction
Post Process
DXF
IGES
Import
File
CL
File
NC CodeN1 G80 G90
N3 G0 T01 M06N5 G0 X0 Y0
OEMCustom
Language
Advantages of CNC Machine
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Advantages of CNC Machine
Tools
Ease of part duplication
Flexibility
Repeatability
Quality control through process control
Advantages of CNC Machine
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Advantages of CNC Machine
Tools
Accommodates simple to complex parts geometry
Improved part aesthetics
Increased productivity
Technology costs are decreasing
Advantages of CNC Machine
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Advantages of CNC Machine
Tools
Reduced set-up time
Reduced lead times
Reduced inventory
Better machine utilization
Job advancement opportunities
Advantages of CNC Machine
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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 Rpms and feeds