1. Applications of CAD Systems
Chapter 11: Numerical Control
Ζήσης Κ. Πλίτσης

2. Computerized process planning without human intervention realized by adding Numerical Control (NC) capabilities to machine tools.
Numerical Control refers to the use of coded numerical information in the automatic control of equipment positioning and have to do with motion (of cutting tools or the part against a rotating tool), positioning, inserting etc.
The production steps stored in a Part Program.

3. Περιεχόμενα Introduction Hardware Configuration of an NC Machine Tool
Types of NC System
NC/CNC/DNC
Basic Concepts for Part Programming
Manual Part Programming
Computer Assisted Part Programming

4. Περιεχόμενα Introduction Hardware Configuration of an NC Machine Tool
Types of NC System
NC/CNC/DNC
Basic Concepts for Part Programming
Manual Part Programming
Computer Assisted Part Programming

5. Introduction / History
In 1940s John Parsons devised a method for manufacture of smooth shapes, relied on recording the location of the center of large number of holes and feeding this information to a machine tool to drive the cutter. The Air Corps was impressed by the idea and the task was subcontracted to the Servomechanisms Laboratory of MIT
In 1952 a modified 3-axis Cincinnati Hydrotel milling machine was demonstrated by MIT, the term numerical control was coined

6. Introduction According to Electronic Industries Association (EIA):
“Numerical Control is a system in which actions are controlled by direct insertion of numerical data at some point. The system must automatically interpret at least some portion of this data.”
The part program is a set of statements that a machine control system can interpret and converted them into signals that move the spindles and drive the machine tool
Today the part program can be generated directly from the CAD database by NC software and then can be the input for a NC machine tool

7. Περιεχόμενα Introduction Hardware Configuration of an NC Machine Tool
Types of NC System
NC/CNC/DNC
Basic Concepts for Part Programming
Manual Part Programming
Computer Assisted Part Programming

8. Hardware Configuration of an NC Machine Tool
A typical NC machine tool contains the Machine Control Unit (MCU) and the machine tool itself.
The MCU includes
the Data Processing Unit (DPU) and
the Control Loop Unit (CLU)

9. Hardware Configuration of an NC Machine Tool
DPU reads the part program, decodes it, processes the information and passes it to the CLU
CLU convert the information to control signals and drives the mechanism, receives feedback (about position and velocity) and instructs DPU to read new instructions
Axis of a machine tool is defined as a path along which relative motion between the cutting tool and the workpiece occurs and a machine can have more than one axis.

10. Περιεχόμενα Introduction Hardware Configuration of an NC Machine Tool
Types of NC System
NC/CNC/DNC
Basic Concepts for Part Programming
Manual Part Programming
Computer Assisted Part Programming

11. Types of NC System Used Point-to-Point NC controllers – PTP
When the path of the tool relative to the work piece is not important, maybe when the tool is not in contact with the workpiece
Contouring (continuous) NC systems
When the motion of the tool relative to the part being machined is important

12. Περιεχόμενα Introduction Hardware Configuration of an NC Machine Tool
Types of NC System
NC/CNC/DNC
Basic Concepts for Part Programming
Manual Part Programming
Computer Assisted Part Programming

13. NC/CNC/DNC
Third generation of machine tools uses integrated circuits and memory technology wildly used in computer hardware
Computer Numerical Control (CNC, about 1970) program needs loading into the MCU once, the controller resembles a personal computer, it is a special-purpose computer for control of machine tools with CPU, ROM, RAM, hard disk communication ports, key pad, display monitor etc.
Today PC-based NC are available which use general-purpose PC with servo-control board.

14. NC/CNC/DNC
Direct Numerical Control is a system that uses a central computer to control several machines at the same time
Distributed Numerical Control (DNC): the central computer downloads complete programs to the CNC machines, which can be workstations or PCs, and can get the information for the machine operations.
The speed of the system is increased, large files can be handled and the number of machine tools used is expanded.

15. Direct numerical control

16. DNC

17. Περιεχόμενα Introduction Hardware Configuration of an NC Machine Tool
Types of NC System
NC/CNC/DNC
Basic Concepts for Part Programming
Manual Part Programming
Computer Assisted Part Programming

18. Basic Concepts for Part Programming
Part programming contains geometric information about the part and motion information to move the cutting tool with respect to the workpiece
The first thing to be defined is the
Coordinate System and then some-one can continue with the Syntax of Part Programming

19. Coordinate System
Main 3 Axes forming a right-hand coordinate system, by convention z axis moves the cutting tool away from the workpiece, in details:
The z axis, parallel to the spindle for rotating workpiece, and parallel to the machine tool axis for rotating tool, as a milling, drilling, or boring machine
The x axis, in the direction of the tool movement for the first case, and points to the right when some-one is facing the machine.

22. Coordinate System
There can be more axes because of secondary slide motions in addition to the primary x, y and z directions, and the rotary motions around axes parallel to x, y and z axes.
These axes can be labeled u, v and w (for the first case) and a, b and c (for the second).
The machine tools can be classified according to the number of axes they provide to control position and orientation. For example, there are 2-axis, 3-axis and 5-axis milling machines.

23. Syntax of Part Programming
Various formats and well defined syntax with variations due to differences between machines
Use of a sequence of blocks containing commands to set machine parameters as speed etc
Each command has an identifying letter followed by an associated number

24. Syntax of Part Programming
Some identifying letters for the commands:
Sequence number (N code)
Preparatory command (G code)
Dimension words (X, Y, Z, A and B words)
Feed commands (F code)
Speed commands (S code)
Tool selection (T code)
Miscellaneous (M code)

25. Syntax of Part Programming
Formats for the commands arranged to form a block:
Fixed sequential format
Block address format
Tab sequential format
Word address format
For example: N040 G00 X0 Y0 Z300 T01 M06
N: identifier number, G: preparatory commands,
X,Y and Z: coordinates along the x, y and z axis
T: the tool number and M: miscellaneous commands

26. Περιεχόμενα Introduction Hardware Configuration of an NC Machine Tool
Types of NC System
NC/CNC/DNC
Basic Concepts for Part Programming
Manual Part Programming
Computer Assisted Part Programming

27. Manual Part Programming
Part program manuscript

28. Manual Part Programming Example:

29. Manual Part Programming Answer:
N001 G91 EOB
N002 G71 EOB
N003 G00 X0.0 Y0.0 Z40.0 T0.1 M06 EOB
N004 G01 X65.0 Y0.0 Z-40.0 F950 S717 M03 EOB
N005 G01 X10.0 F350 M08 EOB
N006 G01 X110.0 EOB
N007 G01 Y70.0 EOB
N008 G01 X EOB
N009 G02 X Y0.0 I14.14 J5.0 EOB
N010 G01 X EOB
N011 G01 Y-70.0 EOB
N012 G01 X-75.0 Y0.0 Z40.0 F950 M30

30. Περιεχόμενα Introduction Hardware Configuration of an NC Machine Tool
Types of NC System
NC/CNC/DNC
Basic Concepts for Part Programming
Manual Part Programming
Computer Assisted Part Programming

31. Computer Assisted Part Programming
The alternative to manual part programming is the use of high-level programming language, which:
Defines the geometry part in terms of basic geometry elements (points, lines …)
Instructs the machine about the cutting tool

32. Computer Assisted Part Programming
So the following procedures must be used to obtain the G-code:
The programmer identifies the part geometry, cutter motions, feeds, speeds and cutter parameters
The programmer codes the part geometry, cutter motion, feed etc and this is the source using a programming language
The source is then compiled to produce the machine independent list of cutter movements and other machine control information (the cutter location control data file or CL data file)
The CL data are processed by post-processor to generate machine control data for the particular machine

33. APT Language
The most comprehensive and widely used language is Automatically Programmed Tool (APT) – the first prototype of the APT system was developed at MIT in 1956.
The APT statements belong to one of the five types:
Identification statements
Geometry statements
Motion statements
Post-processor statements
Auxiliary statements

34. APT Language
Geometry statements, the general form of geometry statement is:
Symbol = geometry_word/descriptive data
In the case of points:
P1 = POINT/X, Y, Z
P2 = POINT/L1, L2
P3 = POINT/CENTER, C1
P4= POINT/YLARGE, INTOF, L1, C1
P5= POINT/XLARGE, INTOF, L1, C1
P6= POINT/XLARGE, INTOF, C1, C1
P7= POINT/YLARGE, INTOF, C1, C1

35. APT Language In the case of lines: L1 = LINE/X1, Y1, Z1, X2, Y2, Z2
L2 = LINE/P1, P2
L3 = LINE/P1, PARLEL, P2
L4 = LINE/P1, PERPTO, L0
L5 = LINE/P1, LEFT, TANTO, C1
L6 = LINE/P1, RIGHT, TANTO, C1
L7 = LINE/LEFT, TANTO, C1, LEFT, TANTO, C2
L8 = LINE/LEFT, TANTO, C1, RIGHT, TANTO, C2
L9 = LINE/RIGHT, TANTO, C1, LEFT, TANTO, C2
L10 = LINE/RIGHT, TANTO, C1, RIGHT, TANTO, C2
L11 = LINE/P1, ATANGL, L0

36. APT Language In the case of circles: C1 = CIRCLE/X, Y, Z, R
C2 = CIRCLE/CENTER, P1, RADIOUS, R
C3 = CIRCLE/CENTER, P1, TANTO, L0
C4 = CIRCLE/P1, P2, P3
C5 = CIRCLE/XSMALL, L1, XSMALL, L2, RADIOUS, R
…And the same with XLARGE, YLARGE or YSMALL
In the case of planes:
PL1 = PLANE/P1, P2, P3
PL2 = PLANE/PARLEL, PL0, XLARGE, D
…And the same with XLARGE, YLARGE, YSMALL, ZLARGE or ZSMALL

37. APT Language
Motion statements, with regard to point-to-point operation there are three motion statements for positioning the tool at a desired point:
FROM/point_location
GOTO/point_location
GODLTA/Δx, Δy, Δz

38. APT Language Example 1:

39. APT Language Answer: P0 = POINT/0.0, 3.0, 0.1 P1 = POINT/1.0, 1.0, 0.1
FROM/P0
GOTO/P1
GODLTA/0, 0, -0.7
GODLTA/0, 0, 0.7
GOTO/P2
GOTO/P0

40. APT Language Other Motion statements:
GO/{TO}, Drive surface, {TO} Part surface, {TO}, Check surface Or
GO/{TO}, Drive surface, {TO} Part surface, {TANTO}, Check surface
…And the same with PAST or ON instead of TO
GOLFT/
GORGT/
GOUP/
GODOWN/
GOFWD/
GOBACK/
For example:
GO/TO, L1, TO, PS, TANTO, C1
GO/PAST, L1, TO, PS, TANTO, C1

41. APT Language Example 2:

42. APT Language Answer: FROM/SP GO/TO, L1, TO, PS, ON, L4
GORGT/L1, PAST, L2
GOLFT/L2, PAST, L3
GOLFT/L3, PAST, C1
GOLFT/C1, PAST, L3
GOLFT/L3, PAST, L4
GOLFT/L4, PAST, L1
GOTO/SP

43. APT Language Example 3:

44. APT Language Answer: FROM/SP GO/TO, L1, TO, PS, ON, L6
GORGT/L1, PAST, L2
GORGT/L2, TANTO, C1
GOFWD/C1, TANTO, L3
GOFWD/L3, PAST, L4
GOLFT/L4, PAST, L5
GOLFT/L5, PAST, L6
GOLFT/L6, PAST, L1
GOTO/SP

45. APT Language Additional statements: MACHIN/DRILL, 2 COOLNT/
For example: COOLNT/MIST COOLNT/FLOOD COOLNT/OF
FEDRAT/
SPINDL/
For example: SPINDL/ON SPINDL/1250, CCLW
TOOLNO/
TURRET/
END

46. APT Language P0 = POINT/0.0, 0.3, 0.1 FROM/P0
Other capabilities of APT, the macro facility, with use variable argument as in a FORTRAN subroutine, for example:
P0 = POINT/0.0, 0.3, 0.1
FROM/P0
CALL/DRILL, X=1.0, Y=1.0, Z=0.1, DEPTH=0.7
CALL/DRILL, X=2.0, Y=1.0, Z=0.1, DEPTH=0.7
GOTO/P0
when the definition of the macro DRILL is:
DRILL = MACRO/X, Y, Z, DEPTH
GOTO/X,Y,Z
GODLTA/0,0, -DEPTH
GODLTA/0,0, DEPTH
TARMAC

47. APT Language Example 4 (1/2):

48. APT Language Example 4 (2/2):

49. APT Language Answer (1/4):
PARTNO PART11
MACHIN/MILL, 3 ;machine selection
CLPRINT ;prints out CL data file
OUTTOL/0.002
SP =POINT/5,0,1
P1 =POINT/1,2,0.5
P2 =POINT/4,2,0.5
P3 =POINT/6,4,0.5
P4 =POINT/8,5,0.5
P5 =POINT/9,7,0.5
P6 =POINT/2,7,0.5
PL1 = PLANE/P1, P2, P3
PS = PLANE/PARALEL, PL1, ZSMALL, 0.5
;define part surface to be z = 0

50. APT Language Answer (2/4):
C1 = CIRCLE/CENTER, P4, RADIOUS, 1.0
L1 = LINE/P2, P3
L2 = LINE/P3, RIGHT, TANTO, C1
L3 = LINE/P5, LEFT, TANTO, C1
L4 = LINE/P5, P6
L5 = LINE/P6, P1
L4 = LINE/P1, P2
MILL = MACRO/CUT, SPIN, FEED, CLNT
CUTTER/CUT
FEDRAT/FEED
SPINDL/SPIN
COOLNT/CLNT
FROM/SP

51. APT Language Answer (3/4):
FROM/SP
GO/TO, L1, TO, PS, ON, L6
GORGT/L1, TO, L2
GORGT/L2, TANTO, C1
GOFWD/C1, TANTO, L3
GOFWD/L3, PAST, L4
GOLFT/L4, PAST, L5
GOLFT/L5, PAST, L6
GOLFT/L6, PAST, L1
GOTO/SP
TERMMAC
TURRET/4

52. APT Language Answer (4/4):
TURRET/4
CALL/MILL, CUT=0.52, SPIN=600, FEED=3.0, CLNT=ON
TURRET/6
CALL/MILL, CUT=0.5, SPIN=900, FEED=2.0, CLNT=ON
SPINDL/0
COOLNT/OFF
END
FINI

53. Other Part Programming Languages
ADAPT (ADaptation APT) was the first attempt to adapt APT programming system for smaller computers
AUTOSPOT (AUTOmatic Sytem for POsitioning Tools) was developed by IBM and first introduced in 1962
EXAPT (EXtended subset of APT) was developed jointly in German in about 1964 by several universities to adapt APT for European use. It is compatible with APT and thus can use the same processor as APT
COMPACT was developed by Manufacturing Data Systems, Inc. (MDSI)
SPLIT (Sundstrand Processing Language Internally Translated) was developed by Sundstrand Corporation, intended for its own machine tools
MAPT (Micro-APT) is a subset of APT, to be run on the microcomputers

54. Τέλος