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Egekwu_nc1 ISAT 331 Manufacturing Control - Numerical Control.

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Presentation on theme: "Egekwu_nc1 ISAT 331 Manufacturing Control - Numerical Control."— Presentation transcript:

1 egekwu_nc1 ISAT 331 Manufacturing Control - Numerical Control

2 egekwu_nc2 Numerical Control (NC) is the use of coded numerical data (information) in the automatic control of equipment positioning. NC controls Applications: –motion of cutting tool –moving part being machined or assembled –fiber placement in filament winding composites –chip placement and assembly in electronic component manufacturing.

3 egekwu_nc3 NC system An NC system is made of (Fig 8.1)

4 {Rabie}4 NC system An NC system is made of (Fig previous slide) Program of instructions (part program) Machine Control Unit (MCU) Hardware (and software) that converts program instruction into electrical signals that in turn control the mechanical actions of the machine Machine (Processing equipment)

5 egekwu_nc5 NC/CNC/DNC NC – numerical control –Control functions controlled by “inflexible physical electronic components e.g. punched paper tape readers; no memory MCU and program cannot be stored. CNC – computer numerical control –Microprocessor is an integral component of MCU –Motion interpolation handled by ‘soft-wired” features –Program editing and use of canned cycles (preprogrammed functions e.g. tapping of holes) possible

6 egekwu_nc6 NC/CNC/DNC continued DNC – distributed numerical control –Facilitated by existence of LANs (Ethernet, etc.) –Jobs are centrally processed (tool motion commands for all parts in facility developed) post-processed and stored in host computer; then sent to specific machines for machining –Facilitates efficient assignment of jobs to machines, and improves other performance metrics ?? E.G.

7 {Rabie}7 The purpose is to provide a means of locating the tool in relation to the work piece NC Coordinate System

8 egekwu_nc8 NC process steps fig Receive part definition from design engineering 2.Generate a process plan –specify machines (processes) –define operational sequence –specify standard time estimates- setup & others –tooling required –raw materials

9 egekwu_nc9 NC Process steps contd. 3.Generate NC program or code –geometry and motion statements. 4.Process NC code –develop cutter location data set (CLDATA) –APT language is one example of a processor –generic processing of NC code is produced

10 egekwu_nc10 NC process steps contd. 5.Post processing –CLDATA is further processed to conform to specific machine tools –machine tools differ in the way they respond to the dynamic behavior of a particular machine ( e.g. coolant flow rate) 6.Input numerical information to machine.

11 { Zarrugh }11 NC Programming Methods NC- words Language-based Graphics-based Programmer Language Processor machine code High-level language APT Drawing geometry CL Data Programmer machine code Drawing geometry machine code CAD System NC Graphic Processor geometry IGES DXF Language Processor CL Data Programmer

12 { Zarrugh}12 NC in CAD/CAM Environment Design (CAD) CAD file Develop full product definition including geometry, tolerance, surface finish and material callout. Process Planning Process & routing instructions Develop mfg steps and sequence NC Processor Part program & CL DATA Generate generic instructions for running the NC cutter along the path prescribed by the geometry. Usually language- based statements. Post- processing Convert generic instructions to specific machine commands in low level machine language. Execute machine code on the NC machine tool to produce the part. machine code Process is fully automated for simple applications

13 [Zarrugh]13 NC Programming Methods The part program may be developed using low-level language (NC –words) >> Manual Language based (high-level language e.g APT- Automatically Programmed Tools) >> partially develops geometry Graphics-based >> Fully develops geometry (Auto CAD) CAD/CAM system >> Fully automated? (MasterCAM)

14 [Zarrugh]14 Manual NC Programming Blocks & Words The part programmer prepares a list of machine coded statements arranged in lines. Each line is called a “block” and contains a string of “words” having coded numerical data to move the tool from one location to another. A block also contains machining instructions (speed, feed rate, tools, coolant, etc) to be executed. The order of execution depends on the type of word.

15 [zarrugh]15 Types of Words N_ G _ X_ Y_ F_ S_ T_ M_ N = statement sequence number G = preparatory functions dealing with motion control parameters X, Y, Z = dimensional words followed by absolute or relative positions F = feed rate code used for contouring and straight cut followed by feed rate in inch/min S = spindle speed code followed by speed in rev/min (rpm) T = tool word to specify a particular tool by number M = miscellaneous functions (e.g control of coolant, clamp, etc) Cod e Number Word Block N110 G04 X Y0.901 F60 S710 T650 M03

16 [Zarrugh}16 General Guidelines 1 The sequence of words (address character plus parameters) must appear in the following order: N, G, X, Y, Z, F, S, T, M. Only one of each address character can be used per block, except for G-codes, which can occur more than once, if the words are of different G-word types Example N1 G01 G90 X.20 Y.25 is valid. N1 G01 G00 X.20 Y.25 is not valid.

17 [Zarrugh]17 General Guidelines (cont.) Some words (usually dimensional words) do not have to be repeated in every block. The controller will use the latest value for each word type until it changes. Example N3G1X.5Y2.25F30 N4Y3.5 Spaces and insignificant zeroes are optional

18 [zarrugh]18 General Guidelines (cont.) The first block in any program should move the tool to a safe location HOME. The location should allow the removal of the finished part and/or put another part: N0G0Z.1 ;move rapidly to z=0.1 inches (away from part) N1M3 ;turn spindle on The second block will prompt the operator to start the spindle ON. The third block will move the tool to a START location to be ready for machining. N2G00G90X.5Y.5 ;move rapidly to absolute coordinates (.5,.5) The end of a part program should move the tool back to the HOME location N92G0Z.1 ;move tool rapidly to z=0.1, away from part N93X.5Y.5M5 ;move tool rapidly to coordinates (.5,.5) and turn spindle off. N94M2 ;end of program

19 egekwu_nc19 Motion Control (machining plan)  Point –To-Point (PTP)  Contouring  Straight-Cut: motion along one major axis e.g. sawing operation

20 [ Zarrugh}20 Point-To-Point (PTP) Control P1P1 P2P2 Many paths are possible P1P1 P2P2 Stationary tool workpiece motion u Relative motion between the tool and the work piece is controlled u In PTP control, only the final destination is controlled, but not the actual path (no contact between tool and work piece) u Typically a work piece is moved with respect to the tool (at full speed) until the desired location is reached. u The tool performs the required action, such as drill a hole, spot weld or punch a shape with the work piece stationary.

21 [Zarrugh]21 Contouring Control In contouring systems, such as NC mills and NC lathes, all axes can be moved simultaneously to generate a continuous smooth path in space. In general, the axes do not move at constant velocity so that curvilinear (not a straight line) motion, such as circular motion, can be generated.

22 Zarrugh22 Interpolation Scheme An interpolator is necessary to generate intermediate points on the path between the points. Most common is linear interpolation. The tool moves on series of straight lines between these two points (linear interpolation?) The interpolation scheme influence tolerances (accuracy) on tool path (Figure 8.8-next slide) Others - Circular, Helical, etc

23 Zarrugh23 Interpolation Scheme Others - Circular, Helical, etc

24 egekwu_nc24 APT Organization Structure APT organization structure contain following sub-divisions: 1.Part Definition: contain elements of geometry that physically describe the part 2.Machining Specification: defines characteristics specific to a machine e.g. coolant flow rate 3.Machining plan: specifies tool motions that control the removal of material in relation to defined part geometry in

25 egekwu_nc25 Language-Based Programming: APT Part Definition Two major types of motion statements –Point to Point –Contouring Point-To-Point –FROM/ Defines initial cutter center; may be x, y, z coordinates PTA = POINT/4,3,6 FROM/PA –GOTO/ Rapid move of cutter to a point GOTO/P1 OR GOTO/0.3,2.0,3.6 –GODTA/dx,dy,dz Incremental move of cutter from current position GODLTA/0,0,+0.9

26 egekwu_nc26 APT (Automatically Programmed Tool) Programming Typical APT geometry statements: Geometric typeAPT Word PointPOINT LineLINE PlanePLANE CircleCIRCLE Pattern (of parts)PATERN CylinderCYLDR

27 egekwu_nc27 APT Prog. - Machining Plan contd. Contouring For contouring, three surfaces have to be defined to guide the tool (see figs and 9.35) –Part surface: On top of which the tool rides –Drive surface: Against which the tool moves –Check surface: At which motion must stop Tool must be brought in contact with the control surfaces using Initial Motion Statements:

28 egekwu_nc28 Contouring Motion Statements Initial Motion Statement: GO/, drive surface,, part surface,, check surface – is a cutter specifier parameter E.G: TO, ON, PAST, OR TANTO GO/TO,CIR1,ON,PLN1,TO,LN1 Initial motion statements are not repeated in the program, but regardless defines the part surface for the entire APT program.

29 egekwu_nc29 Contouring Motion Statements Intermediate Motion Statements - control the actual part cutting –Motion Word/drive surface,,check surface –c.p. are as defined for initial motion statements –Motion Words are: GOLFT, GOFWD, GORGT, GOBACK, GOUP, GODOWN

30 egekwu_nc30 APT Programming - Machining Specification Part Definition (Geometric) and Motion statements constitute approx. 70% of an APT program, while Marching statements the remaining 30%. Machining Specification statements are grouped into: –Postprocessor statements - to control specific auxiliary functions e.g. spindle speed, feed rate, etc –Tolerance and cutter specifications - specify cutter size and permissible deviations from of cuts from ideal –Initial and Termination - these specify the beginning and end of an APT program.

31 egekwu_nc31 Postprocessor statement example MACHIN/, Defines post processor and specific machine to be used COOLNT/ON - Turns coolant ON or OFF SPINDLE/ON - Turns spindle ON or OFF SPINDLE/3000,CCLW - set spindle at 3000 RPM CCW FEEDRAT/4 - feed rate set at 4 in/min TOOLNO/381,4 - use tool #381having 4 units of length TURRET/6 - selects tool in the #6 position of the automatic tool changer END - the end statement of the CNC program

32 egekwu_nc32 Machining Spec.- Tolerance and Cutter Specifications OUTTOL/ outer tol. or maximum over cutting error. INTOL/ inner tolerance or maximum undercutting error TOLER/ maximum outer and inner tolerance CUTTER/ specifies size of cutter - diameter = units.

33 egekwu_nc33 Machining Specs. - Initial and Termination statements PARTNO DF first statement identifying part no. FINI - stops compilation of APT part program; is always last statement of an APT program.


35 egekwu_nc35 APT program for sample part Bedworth Fig 9.44

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