NC PART PROGRAMMING IE 550 Fall 2001 IE

NC PART PROGRAMMING IE 550 Fall 2001 IE 550

HISTORICAL DEVELOPMENT • 15 th century - machining metal. • 18 th century - industrialization, production-type machine tools. • 20 th century - F. W. Taylor - tool metal - HSS Automated production equipment Screw machines Transfer lines Assembly lines. . . using cams and preset stops Programmable automation NC PLC Robots IE 550

NEW NCs or CNCs high speed spindle (> 20, 000 rpm) high feed rate drive ( > 600 ipm) high precision ( < 0. 0001" accuracy) IE 550

NC MACHINES • Computer control MCU - Machine control unit • Servo axis control • Tool changers • Pallet changers • On-machine programming CLU - Control-loops unit • Data communication • Graphical interface Machine Tool MCU CLU DPU IE 550 DPU - Data processing unit

NC MOTION-CONTROL IE 550

NC MACHINE CLASSIFICATIONS 1. Motion control: point to point (PTP) and continuous (contouring) path 2. Control loops: open loop and closed loop 3. Power drives: hydraulic, electric, or pneumatic 4. Positioning systems: incremental and absolute positioning 5. Hardwired NC and softwired Computer Numerical Control (CNC) IE 550

POINT TO POINT • Moving at maximum rate from point to point. • Accuracy of the destination is important but not the path. • Drilling is a good application. IE 550

CONTINUOUS PATH IE 550 • Controls both the displacement and the velocity. • Machining profiles. • Precise control. • Use linear and circular interpolators.

MAJOR COMPONENTS OF AN NC MACHINE TOOL IE 550

NC MACHINE RATING Accuracy Repeatability Spindle and axis motor horsepower Number of controlled axes Dimension of workspace Features of the machine and the controller. IE 550

NC ACCURACY AND REPEATABILITY • Accuracy = control instrumentation resolution and hardware accuracy. • Control resolution: the minimum length distinguishable by the control unit (BLU). • Hardware inaccuracies are caused by physical machine errors. IE 550

HARDWARE INACCURACIES Component tolerances: inaccuracies in the machine elements, machinetool assembly errors, spindle runout, and leadscrew backlash. Machine operation: Tool deflection (a function of the cutting force), produces dimensional error and chatter marks on the finished part. Thermal error: heat generated by the motor operation, cutting process, friction on the ways and bearings, etc. Use cutting fluids, locating drive motors away from the center of a machine, and reducing friction IE 550

REPEATABILITY IE 550

LEADSCREWS Converting the rotational motion of the motors to a linear motion. Nut Leadscrew Pitch pitch (p): the distance between adjacent screw threads the number of teeth per inch (n): n=1/p BLU: Basic Length Unit (machine resolution) BLU = p / N e. g. an NC machine uses a 0. 1" pitch leadscrew and a 100 pulse/rev encoder. IE 550 BLU = p / N = 0. 1 (in/rev) /100 (pulses/rev) = 0. 001"

CONTROL LOOPS Open loop - No position feedback. Use stepping motor. pulses table motor A machine has 1 BLU = 0. 001". To move the table 5" on X axis at a speed (feed rate) of 6 ipm. pulse rate = speed/BLU = 6 ipm/0. 001 ipp = 6, 000 pulse/min pulse count = distance/BLU = 5/0. 001 = 5, 000 pulses IE 550

CLOSED LOOP Closed-loop control mechanism IE 550

INTERPOLATION Control multiple axes simultaneously to move on a line, a circle, or a curve. Point-to-point control path IE 550 Linear path

INTERPOLATORS Most common interpolators are: linear and circular Since interpolation is right above the servo level, speed is critical, and the process must not involve excessive computation. Traditional NC interpolators: Digital Differential Analyzer (DDA) Higher order curves, such as Bezier's curve, use offline approximation algorithms to break the curves into linear or circular segments. IE 550

COORDINATE SYSTEMS • Right hand rule • Z axis align with the spindle - +Z moves away from the workpiece or the spindle. • X axis - Lathe: perpendicular to the spindle. Horizontal machine: parallel to the table. Vertical machine: +X points to the right. IE 550

MACHINE COORDINATES Z X - Primary Feed axis Z - Spindle axis Y - Remaining axis Y X IE 550

PROGRAM STORAGE • Paper tape Paper or Mylar coated paper. • Diskettes • From other computers through RS 232 or local area network (LAN) IE 550

SYMBOLIC CODES • ASCII or ISO, use even parity • EIA - Binary Coded Decimal (BCD), RS 244 A standard, use odd parity. IE 550

TAPE INPUT FORMATS EIA RS-274 standard • Fixed sequential format 0010 01 07500 06250 00000 612 • Tab sequential format T 0010 T 01 T 07500 T 06250 T T T 612 • Word-address format N 0010 G 01 X 07500 Y 06250 S 612 IE 550

NC WORDS A G-code program consists the following words: N, G, X, Y, Z, A, B, C, I, J, K, F, S, T, R, M An EIA standard, RS-273 defines a set of standard codes. IE 550

BASIC REQUIREMENT OF NC MACHINE CONTROL a. Preparatory functions: which unit, which interpolator, absolute or incremental programming, which circular interpolation plane, cutter compensation, etc. b. Coordinates: three translational, and three rotational axes. c. Machining parameters: feed, and speed. d. Tool control: tool diameter, next tool number, tool change. e. Cycle functions: drill cycle, ream cycle, bore cycle, mill cycle, clearance plane. f. Coolant control: coolant on/off, flood, mist. g. Miscellaneous control: spindle on/off, tape rewind, spindle rotation direction, pallet change, clamps control, etc. h. Interpolators: linear, circular interpolation IE 550

NC WORDS N code. sequence number N 0010 G code. preparatory word. * * * IE 550

NC WORDS (continue) X, Y, Z, A, B, C Codes. coordinate positions of the tool. The coordinates may be specified in decimal number (Decimal Programming), or integer number (BLU Programming). BLU programming: leading zero, trailing zero. In the leading zero format: X 00112 Y 002275 Z 001 In the trailing zero format, the program looks like: X 11200 Y 22750 Z 10000 IE 550

NC WORDS (continue) Circular Interpolation: Full circle ON (5. 000, 4. 000) N 0100 G 02 X 7. 000 Y 2. 000 I 5. 000 J 2. 000 Cut from (5. 000, 4. 000) to (7. 000, 2. 000) CW (5. 000, 2. 000) IE 550 (7. 000, 2. 000)

NC WORDS (continue) F Code. feed speed. inch/min (ipm), or ipr. F code must be given before either G 01, G 02, or G 03 can be used. N 0100 G 02 X 7. 000 Y 2. 000 I 5. 000 J 2. 000 F 6. 00 S Code. cutting speed code. It is programmed in rpm. S code does not turn on the spindle, spindle is turned on by a M code. N 0010 S 1000 IE 550

NC WORDS (continue) T Code. tool number. Actual tool change does not occur until a tool change M code is specified. R Code. cycle parameter. The cycle may be programmed in one block, such as: (cycle programming is vendor specific. ) N 0010 G 81 X 1. 000 Y 2. 000 Z 0. 000 R 1. 300 IE 550

NC WORDS (continue) M Code. miscellaneous word. IE 550

MANUAL PART PROGRAMMING Example 9. 1 Machined from a 5" x 4" x 2" workpiece. low carbon steel. The process plan: 1. Set the lower left bottom corner of the part as the machine zero point (floating zero programming). 2. Clamp the workpiece in a vise. 3. Mill the slot with a 3/4" four flute flat end mill made of carbide. From the machinability data handbook, the recommended feed is 0. 005 inch/tooth/rev, and the recommended cutting speed is 620 fpm. 4. Drill two holes with a 0. 75" dia twist drill. Use 0. 18 ipr feed and 100 fpm speed. IE 550

PART DRAWING 2 ho les ø 0. 7 5 ± 0. 00 1. 7 5 ø 0. 0 0 1 M MA BC 4. 0 0 0 R 1. 0 0 0 3. 0 0 0 2. 0 00 1. 0 0 0 A 1. 7 5 B 3. 0 0 0 5. 0 0 0 . 5 00 2. 0 0 0 C All dimension in inches. A ll t olerance ± 0. 00 1 " IE 550

SOLUTION TO EXAMPLE Solution: The cutting parameters need be converted into rpm and ipm. IE 550 Milling: 12 x 620 fpm 12 V RPM = = = 3, 157 rpm BD B 0. 75 inch Drilling: 12 x 100 fpm RPM = 12 V = = 509 rpm BD B 0. 75 inch

SETUP AND CUTTER PATH IE 550

CUTTER LOCATIONS The coordinates of each point (cutter location) are calculated below: p 1': ( 1. 75+0. 375, -0. 1 -0. 375, 4. 00) = (2. 125, -0. 475, 4. 000) p 1: (2. 125, -0. 475, 2. 000 -0. 500) = (2. 125, -0. 475, 1. 500) p 2: (2. 125, 4. 000+0. 100, 1. 500) = (2. 125, 4. 100, 1. 500) p 3: (3. 000 -0. 375, 4. 100, 1. 500) = (2. 625, 4. 100, 1. 500) p 4: (2. 625, 1. 375, 1. 500) p 5: (3. 000, 2. 000 -1. 000+0. 375, 1. 500) = (3. 000, 1. 375, 1. 500) p 6: (3. 000, 2. 625, 1. 500) p 7: (3. 000, 2. 000, 1. 500) p 8: (2. 625, 2. 000, 1. 500) p 9: (2. 625, -0. 100, 1. 500) p 9': (2. 625, -0. 100, 4. 000) IE 550

PART PROGRAM Part program Explanation N 0010 G 70 G 90 T 08 M 06 Set the machine to inch format and absolute dimension programming. N 0020 G 00 X 2. 125 Y-0. 475 Z 4. 000 S 3157 Rapid to p 1'. N 0030 G 01 Z 1. 500 F 63 M 03 Down feed to p 1, spindle CW. N 0040 G 01 Y 4. 100 Feed to p 2. N 0050 G 01 X 2. 625 To p 3. N 0060 G 01 Y 1. 375 To p 4. N 0070 G 01 X 3. 000 To p 5. N 0080 G 03 Y 2. 625 I 3. 000 J 2. 000 Circular interpolation to p 6. N 0090 G 01 Y 2. 000 To p 7. N 0100 G 01 X 2. 625 To p 8. N 0110 G 01 Y-0. 100 To p 9 N 0120 G 00 Z 4. 000 T 02 M 05 To p 9', spindle off, tool #2. N 0130 F 9. 16 S 509 M 06 Tool change, set new feed and speed. N 0140 G 81 X 0. 750 Y 1. 000 Z-0. 1 R 2. 100 M 03 Drill hole 1. N 0150 G 81 X 0. 750 Y 3. 000 Z-0. 1 R 2. 100 Drill hole 2. N 0160 G 00 X-1. 000 Y-1. 000 M 30 Move to home position, stop the machine. IE 550

CNCS VERIFICATION IE 550

CNCS 3 D DRAWING IE 550

TOOL-RADIUS COMPENSATION Start of Compensation. G 41 (or G 42) and G 01 in the same block ramp takes place at block (0. 5, 1. 7) N 0010 G 01 G 42 X 0. 500 Y 1. 700 N 0020 G 01 X 1. 500 (1. 5, 1. 7) G 41 G 42 G 41 (or G 42) and G 01 in separate blocks the compensation is effective from the start. N 0010 G 41 N 0020 G 01 X 0. 500 Y 1. 700 N 0030 G 01 X 1. 500 IE 550

TOOL-RADIUS COMPENSATION Inside Corner. Cutter path is inside a corner, stops at the inside cutting point (1. 5, 2. 0) N 0010 G 41 N 0020 G 01 X 1. 500 Y 2. 000 N 0030 G 01 X 0. 000 Y 1. 600 (0, 1. 6) Use of M 96 and M 97. Cutting tool that is larger than the height of the step, M 97 must be used N 0010 G 41 N 0020 G 01 X 1. 000 Y 1. 000 N 0030 G 01 Y 0. 800 M 97 N 0040 G 01 X 2. 000 IE 550

TOOL-RADIUS COMPENSATION Cancel Tool Compensation. G 40 in the same block ramp off block. N 0060 G 40 X 2. 000 Y 1. 700 M 02 (2. 000, 1. 700) G 40 in a block following the last motion, the compensation is effective to the end point (2. 000, 1. 700). N 0060 X 2. 000 Y 1. 700 N 0070 G 40 M 02 (2. 000, 1. 700) IE 550

EXAMPLE A square 2. 0 in. x 2. 0 in. is to be milled using a 1/2 in. end milling cutter. Write an NC part program to make the square. Solution Let us set up the lower left corner of the square at (6. 0, 6. 0). Using tool-radius compensation, the square can be produced. IE 550

PART PROGRAM IE 550

TURNING Part design Cutter path IE 550

Programming tool point TURNING No compensation needed. Surfaces cut Programmed tool path Surface created IE 550

COMPUTER ASSISTED PART PROGRAMMING Machine-oriented languages - machine specific General-purpose languages - use post processors to generate machine specific code Translate input symbols Arithmetic calculation Part program Language Processor Cutter offset calculations Post processing CL BCL CL data Post Processor RS-494 N-G code IE 550 RS-273