cnc- cad-cam mach.shp final

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.



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



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



History: Continued1990s - Price drop in CNC technology1997 - PC- Windows/NT based Open Modular Architecture Control (OMAC) systems introduced to replace firmware controllers.



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



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



Control SystemsClosed-Loop ControlVariable DC motors - ServosPositioning sensors -ResolversFeedback to control unit Position information compared to target locationLocation errors corrected



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



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



Three Basic Categories of Motion Systems



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.



CNCAdvantagesIncreased Program storage capability at the machine toolProgram editing at the machine toolControl systems upgrades possibleOption -resident CAM system at machine toolTool path verification



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.



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



Machining CentersMachine motion is programmableServo motors drive feed mechanisms for tool axissPositioning feedback is provided by resolvers to the control system



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.



Machining Centers



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.



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



Programming Methods-APTRequires excellent 3D visualization skills

Capable of generating machine code for complicated part programs5 axis machine tools



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



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



Programming Methods-CAMTool & material librariesTool path simulationTool path editingTool path optimization Cut time calculations for cost estimating



Programming Methods-CAMImport / export capabilities to other systemsExamples: Drawing Exchange Format (DXF) Initial Graphics Exchange Standard (IGES)



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)



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)



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)



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)



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



Output: NC CodeNumerical Control (NC) LanguageA series of commands which direct the cutter motion and support systems of the machine tool.



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



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



Example of CNC Programming What Must Be Done To Drill A Hole On A CNC Vertical Milling Machine



Top ViewFront ViewTool Home1.) X & Y Rapid To Hole Position



Top ViewFront View2.) Z Axis Rapid Move Just Above Hole3.) Turn On Coolant4.) Turn On Spindle.100



Top ViewFront View5.) Z Axis Feed Move to Drill Hole



Top ViewFront View6.) Rapid Z Axis Move Out Of Hole



Top ViewFront View9.) X&Y Axis Rapid Move Home7.) Turn Off Spindle8.) Turn Off Coolant



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!



Top ViewFront ViewTool At HomeO0001O0001 Number Assigned to this program



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



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



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



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.



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



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



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



Output: NC Code - Canned Cycles



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



Advantages of CNC Machine ToolsEase of part duplicationFlexibilityRepeatabilityQuality control through process control



Advantages of CNC Machine ToolsAccommodates simple to complex parts geometryImproved part aestheticsIncreased productivityTechnology costs are decreasing



Advantages of CNC Machine ToolsReduced set-up timeReduced lead timesReduced inventoryBetter machine utilizationJob advancement opportunities



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.**************

cnc- cad-cam mach.shp final

Documents

machine toolprogram

machine toolsintro

numerical control system

control sequences

cut control

loop limitationscostintro

stepper motors

cnc technology1997 pc