1. Unit 5 Numerical Control
Sections:
Fundamentals of NC Technology
Computer Numerical Control
Distributed Numerical Control
Applications of NC
NC Part Programming

2. Numerical Control (NC) Defined
Programmable automation in which the mechanical actions of a ‘machine tool’ are controlled by a program containing coded alphanumeric data that represents relative positions between a work head (e.g., cutting tool) and a work part
Program
Instructions
Machine
Control Unit
Transformation
Process
Power

5. NC Coordinate Systems For flat and prismatic (block-like) parts:
Milling and drilling operations
Conventional Cartesian coordinate system
Rotational axes about each linear axis
For rotational parts:
Turning operations
Only x- and z-axes

6. Motion Control Systems
Point-to-Point systems
Also called position systems
System moves to a location and performs an operation at that location (e.g., drilling)
Also applicable in robotics
Continuous path systems
Also called contouring systems in machining
System performs an operation during movement (e.g., milling and turning)

7. Interpolation Methods
Linear interpolation
Straight line between two points in space
Circular interpolation
Circular arc defined by starting point, end point, center or radius, and direction
Helical interpolation
Circular plus linear motion
Parabolic and cubic interpolation
Free form curves using higher order equations

8. Absolute vs. Incremental Positioning
Absolute positioning
Move is: x = 40, y = 50
Incremental positioning
Move is: x = 20, y = 30.

9. Computer Numerical Control (CNC)
Storage of more than one part program
Various forms of program input
Program editing at the machine tool
Fixed cycles and programming subroutines
Interpolation
Acceleration and deceleration computations
Communications interface
Diagnostics

10. Machine Control Unit

11. DNC
Direct numerical control (DNC) – control of multiple machine tools by a single (mainframe) computer through direct connection and in real time
1960s technology
Two way communication
Distributed numerical control (DNC) – network consisting of central computer connected to machine tool MCUs, which are CNC
Present technology

12. Distributed Numerical Control
Central
Computer
NC Pgms
Computer Network
BTR
BTR
BTR
Machine
Control Unit
Machine
Control Unit
Machine
Control Unit
Transformation
Process

13. Applications of NC

14. NC Application Characteristics (Machining)
Batch and High Volume production
Repeat and/or Repetitive orders
Complex part geometries
Mundane operations
Many separate operations on one part

15. Cost-Benefits of NC Costs High investment cost High maintenance effort
Need for skilled programmers
High utilization required
Benefits
Cycle time reduction
Nonproductive time reduction
Greater accuracy and repeatability
Lower scrap rates
Reduced parts inventory and floor space
Operator skill-level reduced

16. Precision

17. NC Part Programming Manual part programming Manual data input
Computer-assisted part programming
Part programming using CAD/CAM

18. Manual Part Programming
Binary Coded Decimal System
Each of the ten digits in decimal system (0-9) is coded with four-digit binary number
The binary numbers are added to give the value
BCD is compatible with 8 bits across tape format, the original storage medium for NC part programs
Eight bits can also be used for letters and symbols

19. Creating Instructions for NC
Bit - 0 or 1 = absence or presence of hole in the tape
Character - row of bits across the tape
Word - sequence of characters (e.g., y-axis position)
Block - collection of words to form one complete instruction
Part program - sequence of instructions (blocks)

20. Block Format Organization of words within a block in NC part program
Also known as tape format because the original formats were designed for punched tape
Word address format - used on all modern CNC controllers
Uses a letter prefix to identify each type of word
Spaces to separate words within the block
Allows any order of words in a block
Words can be omitted if their values do not change from the previous block

21. Types of Words N - sequence number prefix G - preparatory words
Example: G00 = PTP rapid traverse move
X, Y, Z - prefixes for x, y, and z-axes
F - feed rate prefix
S - spindle speed
T - tool selection
M - miscellaneous command
Example: M07 = turn cutting fluid on

22. Example: Word Address Format
N001 G00 X07000 Y03000 M03
N002 Y06000

23. Cutter Offset
Cutter path must be offset from actual part outline by a distance equal to the cutter radius

24. Issues in Manual Part Programming
Adequate for simple jobs, e.g., PTP drilling
Linear interpolation
G01 G94 X050.0 Y086.5 Z100.0 F40 S800
Circular interpolation
G02 G17 X088.0 Y040.0 R028.0 F30
Cutter offset
G42 G01 X100.0 Y040.0 D05

25. Example

26. Manual Data Input Machine operator does part programming at machine
Operator enters program by responding to prompts and questions by system
Monitor with graphics verifies tool path
Usually for relatively simple parts
Ideal for small shop that cannot afford a part programming staff
To minimize changeover time, system should allow programming of next job while current job is running

27. Computer-Assisted Part Programming
Write machine instructions using natural language type statements
Statements translated into machine code of the MCU
APT (Automatically Programmed Tool) Language

28. Sample Statements
Part is composed of basic geometric elements and mathematically defined surfaces
Examples of statements:
P4 = POINT/35,90,0
L1 = LINE/P1,P2
C1 = CIRCLE/CENTER,P8,RADIUS,30
Tool path is sequence of points or connected line and arc segments
Point-to-Point command: GOTO/P4
Continuous path command: GOLFT/L1,TANTO,C1

29. NC Part Programming Using CAD/CAM

30. YouTube CNC Milling CNC Punching CNC Adhesive Bonding
CNC Drug Insertion
CNC Bioprocessing
CAD/CAM
Etc.