Presentation on theme: "Machining Centers General Manufacturing Processes Engr"— Presentation transcript:
1 Machining Centers General Manufacturing Processes Engr.-20.2710 Instructor - Sam Chiappone
2 HistoryJohn 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.
3 History: ContinuedMIT announces Automatic Programmed Tools (APT) programming languageDirect Numerical Control (DNC). This eliminates paper tape punch programs and allows programmers to send files directly to machine tools
4 History: ContinuedKearney & Trecker machine tool builders market first machining center1970’s - CNC machine tools & Distributed Numerical Control1980’s - Graphics based CAM systems introduced. Unix and PC based systems available
5 History: Continued 1990’s - Price drop in CNC technology PC- Windows/NT based “Open Modular Architecture Control (OMAC)” systems introduced to replace “firmware” controllers.
6 Control Systems Open-Loop Control Stepper motor system Current pulses sent from control unit to motorEach pulse results in a finite amount of revolution of the motor001” is possible
7 Control Systems Open-Loop Limitations Open-Loop Advantages Control unit “assumes” desired position is achievedNo positioning compensationTypically, a lower torque motorOpen-Loop AdvantagesLess complex, Less costly, and lower maintenance costs
8 Control Systems Closed-Loop Control Variable DC motors - Servos Positioning sensors -ResolversFeedback to control unitPosition information compared to target locationLocation errors corrected
9 Control Systems Closed-Loop Advantages Closed-loop limitations DC 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 motorsClosed-loop limitationsCost
10 Three Basic Categories of Motion Systems Point to Point - No contouring capabilityStraight cut control - one axis motion at a time is controlled for machiningContouring - multiple axis’s controlled simultaneously
12 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.
13 CNCAdvantagesIncreased Program storage capability at the machine toolProgram editing at the machine toolControl systems upgrades possibleOption -resident CAM system at machine toolTool path verification
14 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 1950’s to 1970’s.
15 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
16 Machining Centers Machine motion is programmable Servo motors drive feed mechanisms for tool axis’sPositioning feedback is provided by resolvers to the control system
17 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.
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.
20 Programming Methods-APT Developed as a joint effort between the aerospace industry, MIT, and the US AirforceStill used today and accounts for about 5 -10% of all programming in the defense and aerospace industries
21 Programming Methods-APT Requires excellent 3D visualization skillsCapable of generating machine code for complicated part programs5 axis machine tools
22 Programming Methods-APT Part definitionP1=Point/12,20,0C1=Circle/Center,P1,Radius,3LN1=Line/C1. ATANGL,90Cutter CommandsTLRT,GORT/LN1.TANTO,C1GOFWD/C1,TANTO,L5
23 Programming Methods-CAM Computer Aided Machining (CAM) SystemsGraphic representation of the partPC basedIntegrated CAD/CAM functionality“Some” built-in expertiseSpeed & feed data based on material and tool specifications
24 Programming Methods-CAM Tool & material librariesTool path simulationTool path editingTool path optimizationCut time calculations for cost estimating
25 Programming Methods-CAM Import / export capabilities to other systemsExamples:Drawing Exchange Format (DXF)Initial Graphics Exchange Standard (IGES)
26 The Process CAD to NC File Start 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)
27 The Process CAD to NC File Define cutter path by selecting geometryContoursPocketsHole patternsSurfacesVolume to be removed(At this point the system knows what you want to cut)
28 The Process CAD to NC File Define 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)
29 The Process CAD to NC File Execute 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)
30 The Process CAD to NC File Post 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, rpm’s, etc.G & M function capabilities
31 Output: NC Code Numerical Control (NC) Language A series of commands which “direct” the cutter motion and support systems of the machine tool.
32 Output: NC Code G-Codes (G00, G1, G02, G81) Coordinate data (X,Y,Z) Feed Function (F)Miscellaneous functions (M13)N - Program sequence numberT - Tool callS - Spindle command
36 Advantages of CNC Machine Tools Ease of part duplicationFlexibilityRepeatabilityQuality control through process control
37 Advantages of CNC Machine Tools Accommodates simple to complex parts geometryImproved part aestheticsIncreased productivityTechnology costs are decreasing
38 Advantages of CNC Machine Tools Reduced set-up timeReduced lead timesReduced inventoryBetter machine utilizationJob advancement opportunities
39 Advantages of CNC Machine Tools CNC machine tools are more rigid than conventional machine tools$$$- Climb milling requires about % less horsepower vs. conventional cutting, but requires a ridged machine tool with no backlashIncreased Rpm’s and feeds