cnc- cad-cam mach.shp final
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CAM Systems & CNC Machine Overview - Lecture 3
Computer Aided Manufacturing Mechanical Engineering UNC=EA
Intro to CAMChiappone
Rensselaer Polytechnic Institute
History1955 - 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.
Intro to CAMChiappone
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History: Continued1959 - MIT announces Automatic Programmed Tools (APT) programming language1960 - Direct Numerical Control (DNC). This eliminates paper tape punch programs and allows programmers to send files directly to machine tools
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History: Continued
1968 - Kearney & Trecker machine tool builders market first machining center1970s - CNC machine tools & Distributed Numerical Control 1980s - Graphics based CAM systems introduced. Unix and PC based systems available
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History: Continued1990s - Price drop in CNC technology1997 - PC- Windows/NT based Open Modular Architecture Control (OMAC) systems introduced to replace firmware controllers.
Intro to CAMChiappone
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Control SystemsOpen-Loop ControlStepper motor systemCurrent pulses sent from control unit to motorEach pulse results in a finite amount of revolution of the motor001 is possible
Intro to CAMChiappone
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Control Systems Open-Loop LimitationsControl unit assumes desired position is achievedNo positioning compensationTypically, a lower torque motorOpen-Loop AdvantagesLess complex, Less costly, and lower maintenance costs
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Control SystemsClosed-Loop ControlVariable DC motors - ServosPositioning sensors -ResolversFeedback to control unit Position information compared to target locationLocation errors corrected
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Control SystemsClosed-Loop AdvantagesDC motors have the ability to reverse instantly to adjust for position errorError compensation allows for greater positional accuracy (.0001)DC motors have higher torque ranges vs.. stepper motors Closed-loop limitationsCost
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Three Basic Categories of Motion SystemsPoint to Point - No contouring capability Straight cut control - one axis motion at a time is controlled for machiningContouring - multiple axiss controlled simultaneously
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Three Basic Categories of Motion Systems
Intro to CAMChiappone
Rensselaer Polytechnic Institute
CNC vs. NC Machine ToolsComputer 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.
Intro to CAMChiappone
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CNCAdvantagesIncreased Program storage capability at the machine toolProgram editing at the machine toolControl systems upgrades possibleOption -resident CAM system at machine toolTool path verification
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NCNumerical 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 1950s to 1970s.
Intro to CAMChiappone
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Machining CentersA machining center can be defined as a machine tool capable of:Multiple operation and processes in a single set-up utilizing multiple axisTypically has an automatic mechanism to change tools
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Machining CentersMachine motion is programmableServo motors drive feed mechanisms for tool axissPositioning feedback is provided by resolvers to the control system
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Machining CentersExample - 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.
Intro to CAMChiappone
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Machining Centers
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Programming MethodsAutomatically 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.
Intro to CAMChiappone
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Programming Methods-APTDeveloped 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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Programming Methods-APTRequires excellent 3D visualization skills
Capable of generating machine code for complicated part programs5 axis machine tools
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Programming Methods-APTPart definitionP1=Point/12,20,0C1=Circle/Center,P1,Radius,3LN1=Line/C1. ATANGL,90Cutter CommandsTLRT,GORT/LN1.TANTO,C1GOFWD/C1,TANTO,L5
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Programming Methods-CAMComputer Aided Machining (CAM) SystemsGraphic representation of the partPC basedIntegrated CAD/CAM functionalitySome built-in expertiseSpeed & feed data based on material and tool specifications
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Programming Methods-CAMTool & material librariesTool path simulationTool path editingTool path optimization Cut time calculations for cost estimating
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Programming Methods-CAMImport / export capabilities to other systemsExamples: Drawing Exchange Format (DXF) Initial Graphics Exchange Standard (IGES)
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The Process CAD to NC FileStart with graphic representation of partDirect inputImport from external systemExample DXF / IGES2D or 3D scanModel or Blueprint (At this point you have a graphics file of your geometry)
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The Process CAD to NC FileDefine cutter path by selecting geometryContoursPocketsHole patternsSurfacesVolume to be removed(At this point the system knows what you want to cut)
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The Process CAD to NC FileDefine cut parametersTool informationType, Rpm, FeedCut methodExample - Pocket mill zig-zag, spiral, inside-outRough and finish parameters(At this point the system knows how you want to cut the part)
Intro to CAMChiappone
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The Process CAD to NC FileExecute cutter simulationVisual representation of cutter motionModify / 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 FilePost ProcessingCL file to machine specific NC codeFilters CL information and formats it into NC code based on machine specific parametersWork envelopeLimits - feed rates, tool changer, rpms, etc. G & M function capabilities
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Output: NC CodeNumerical Control (NC) LanguageA series of commands which direct the cutter motion and support systems of the machine tool.
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Output: NC CodeG-Codes (G00, G1, G02, G81)Coordinate data (X,Y,Z)Feed Function (F)Miscellaneous functions (M13)N - Program sequence numberT - Tool callS - Spindle command
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Output: NC CodeNC Program Example N01G90 G80N03 GOO T12 M06N05 GOO X0 Y0 Z.1 F10 S2500 M13N07 G1Z-.5N09 G02 X-10. I0J0F20N13 X0Y10N17 X10Y0N19 X0Y-10N21 X-10Y0N23 M2
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Example of CNC Programming What Must Be Done To Drill A Hole On A CNC Vertical Milling Machine
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Top ViewFront ViewTool Home1.) X & Y Rapid To Hole Position
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Top ViewFront View2.) Z Axis Rapid Move Just Above Hole3.) Turn On Coolant4.) Turn On Spindle.100
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Top ViewFront View5.) Z Axis Feed Move to Drill Hole
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Top ViewFront View6.) Rapid Z Axis Move Out Of Hole
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Top ViewFront View9.) X&Y Axis Rapid Move Home7.) Turn Off Spindle8.) Turn Off Coolant
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Top ViewFront ViewTool At HomeO0001N005 G54 G90 S600 M03N010 G00 X1.0 Y1.0N015 G43 H01 Z.1 M08N020 G01 Z-.75 F3.5N030 G91 G28 X0 Y0 Z0N035 M30N025 G00 Z.1 M09Heres The CNC Program!
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Top ViewFront ViewTool At HomeO0001O0001 Number Assigned to this program
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Top ViewFront ViewTool At HomeO0001N005 G54 G90 S600 M03N005 Sequence NumberG54 Fixture OffsetG90 Absolute Programming ModeS600 Spindle Speed set to 600 RPMM03 Spindle on in a Clockwise Direction
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Top ViewFront ViewO0001N005 G54 G90 S600 M03N010 G00 X1.0 Y1.0G00Rapid MotionX1.0X Coordinate 1.0 in. from ZeroY1.0Y Coordinate 1.0 in. from Zero
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Top ViewFront ViewO0001N005 G54 G90 S600 M03N010 G00 X1.0 Y1.0N015 G43 H01 Z.1 M08G43Tool Length CompensationH01Specifies Tool length compensationZ.1 Z Coordinate .1 in. from ZeroM08Flood Coolant On
Intro to CAMChiappone
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Top ViewFront ViewO0001N005 G54 G90 S600 M03N010 G00 X1.0 Y1.0N015 G43 H01 Z.1 M08N020 G01 Z-.75 F3.5G01Straight Line Cutting MotionZ-.75Z Coordinate -.75 in. from ZeroF3.5Feed Rate set to 3.5 in./min.
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Top ViewFront ViewO0001N005 G54 G90 S600 M03N010 G00 X1.0 Y1.0N015 G43 H01 Z.1 M08N020 G01 Z-.75 F3.5G00Rapid MotionZ.1Z Coordinate .1 in. from ZeroM09Coolant OffN025 G00 Z.1 M09
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Top ViewFront ViewO0001N005 G54 G90 S600 M03N010 G00 X1.0 Y1.0N015 G43 H01 Z.1 M08N020 G01 Z-.75 F3.5N030 G91 G28 X0 Y0 Z0G91Incremental Programming ModeG28Zero Return CommandX0, Y0, Z0 X,Y,& Z Coordinates at ZeroN025 G00 Z.1 M09
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Top ViewFront ViewO0001N005 G54 G90 S600 M03N010 G00 X1.0 Y1.0N015 G43 H01 Z.1 M08N020 G01 Z-.75 F3.5N035 M30N030 G91 G28 X0 Y0 Z0N025 G00 Z.1 M09M30End of Program
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Output: NC Code - Canned Cycles
Intro to CAMChiappone
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CAD to NC Code
Import
File
Geometry
Direct input
Post Process
Tool Path Generation
What you want to cut
How you want to cut
Tool Type
Rpms Feeds
Method
Canned cycles
Cut direction
DXF IGES
OEM
Custom
Language
NC Code
N1 G80 G90
N3 G0 T01 M06
N5 G0 X0 Y0
CL
File
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Advantages of CNC Machine ToolsEase of part duplicationFlexibilityRepeatabilityQuality control through process control
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Advantages of CNC Machine ToolsAccommodates simple to complex parts geometryImproved part aestheticsIncreased productivityTechnology costs are decreasing
Intro to CAMChiappone
Rensselaer Polytechnic Institute
Advantages of CNC Machine ToolsReduced set-up timeReduced lead timesReduced inventoryBetter machine utilizationJob advancement opportunities
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Advantages of CNC Machine ToolsCNC 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 backlashIncreased Rpms and feeds
**********************************An example of creating a CNC program using a simple hole drilled on a computer numerical controlled (CNC) vertical milling machine.*In this case, we are using a simple analogy to stress how a programmer must be able to visualize a CNC programs execution. We first look at how a machinist would machine a hole in a work piece held in a vise on a milling machine. Then well show how the same operation will be performed with a CNC program.
The machinist standing in front of the milling machine has everything they need right in front of them. They wouldnt forget something as simple as turning the spindle on before trying to drill the hole. On the other hand, a CNC programmer must typically work with nothing more than a blueprint, a pencil, a calculator, and a blank piece of paper. They must be able to visualize every motion and function of the programs execution in their minds.*****Here is the same operation (drilling a hole) performed by a CNC program. Each step will be explained.**************