The document provides an overview of manufacturing processes, specifically focusing on numerical control (NC) and its evolution into computer numerical control (CNC) systems. It details the components, advantages, and applications of NC technology, including its relevance in modern manufacturing for precision and efficiency. Additionally, it explores different programming methods and the operational principles of numerical control systems, such as open-loop and closed-loop configurations.

1. MANUFACTURING PROCESSES-II
Engr. Umair

2. What is Manufacturing?
 The word manufacturing is derived from two latin words, manus (hand) and factus (make), the
combination means made by hand.
 Manufacturing, in its broadest sense, is the process of converting raw materials into products.
 Manufacturing can be defined two ways, one technologic and other economic.
- Technologically, manufacturing is the application of physical and chemical processes to alter the
geometry, properties and appearance of a given starting material to make parts or products;
manufacturing also includes assembly of multiple parts to make products.
- Economically, manufacturing is the transformation of materials into items of greater value by
means of one or more processing and/or assembly operations.
Production vs Manufacturing
 Production engineering is a complete cycle as it involves procurement of raw material, storing
that raw material as inventory, conversion of raw into semi finished or finished goods,
dispatching, sales forecasting etc. but manufacturing is a part of production engineering which
just involves in the value addition of raw materials (conversion of raw into semi finished or
finished goods).

3. Chapter No. 06
CONTROL OF MACHINE TOOLS

4.  NC is a method of automatically operating a manufacturing machine based on a code of letters,
numbers, and special characters.
 A complete set of coded instructions for executing an operation is called a program.
 The program is translated into corresponding electrical signals for input to motors that run the
machine.
 NC machines can be programmed manually. If a computer is used to create a program, the process
is known as computer-aided programming.
 NC has been used in industry for more than 40 years.
 Traditionally, NC systems have been composed of the following components:
 Tape punch: converts written instructions into a corresponding hole pattern. The hole pattern is
punched into tape which is passed through the tape punch. Much older units used a typewriter
device called a Flexowriter, and later devices included a microcomputer coupled with a tape punch
unit.
 Tape reader: reads the hole pattern on the tape and converts the pattern to a corresponding
electrical signal code.
 Controller: receives the electrical signal code from the tape reader and subsequently causes the
NC machine to respond.
 NC machine: responds to programmed signals from the controller. Accordingly, the machine
executes the required motions to manufacture a part (spindle rotation on/off, table and or spindle
movement along programmed axis directions, etc.).
Control Of Machine Tools
NUMERICAL CONTROL DEFINITION, ITS CONCEPTS
AND ADVANTAGES

5. Control Of Machine Tools
Components of traditional NC systems
 Components of an NC System
1. Program of instructions
 Part program in machining
2. Machine control unit
 Controls the process
3. Processing equipment
 Performs the process

6. Control Of Machine Tools
 NC systems offer some advantages over manual production methods:
 Higher precision: NC machine tool are capable of machining at very close tolerances, in some
operations as small as 0.005 mm;
 Machining of complex three-dimensional shapes:
 Better quality: NC systems are capable of maintaining constant working conditions for all parts
in a batch thus ensuring less spread of quality characteristics;
 Higher productivity: NC machine tools reduce drastically the non machining time. Adjusting
the machine tool for a different product is as easy as changing the computer program and tool
turret with the new set of cutting tools required for the particular part.
 Multi-operational machining: some NC machine tools, for example machine centers, are
capable of accomplishing a very high number of machining operations thus reducing significantly
the number of machine tools in the work shops.
 Low operator qualification: the role of the operator of a NC machine is simply to upload the
work piece and to download the finished part. In some cases, industrial robots are employed for
material handling, thus eliminating the human operator.

7.  Types of NC systems
 Machine controls are divided into three groups,
 Traditional numerical control (NC);
Œ
 Computer numerical control(CNC);
 Distributed numerical control (DNC)
 The original numerical control machines were referred to as NC machine tool. They have
“hardwired” control, whereby control is accomplished through the use of punched paper
(or plastic) tapes or cards. Tapes tend to wear, and become dirty, thus causing
misreading.
 CNC refers to a system that has a local computer to store all required numerical data. The
advantages of CNC systems include but are not limited to the possibility to store and
execute a number of large programs (especially if a three or more dimensional machining
of complex shapes is considered), to allow editing of programs, to execute cycles of
machining commands, etc.
 Distributed numerical control is similar to CNC, except a remote computer is used to
control a number of machines. An off-site mainframe host computer holds programs for all
parts to be produced in the DNC facility. Programs are downloaded from the mainframe
computer, and then the local controller feeds instructions to the hardwired NC machine.
Control Of Machine Tools

8. Control Of Machine Tools
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)

9. Control Of Machine Tools
Absolute and Incremental Positioning
 Absolute positioning
 Locations defined relative to origin of axis system
 Incremental positioning
 Locations defined relative to previous position
 Example: drilling
 The workhead is presently at point (20, 20) and is to be moved to point (40, 50)
 In absolute positioning, the move is specified by x= 40, y= 50
 In incremental positioning, the move is specified by x= 20, y= 30.

10. Control Of Machine Tools
 Computer Numerical Control (CNC) –Additional Features
 Storage of more than one part program
 Various forms of program input
 Program editing at the machine tool
 Fixed cycles and programming subroutines
 Interpolation
 Communications interface
 Diagnostics
Configuration of CNC Machine Control Unit

11. Control Of Machine Tools
 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
 Two way communication
System Connection to MCU is behind the tape reader (BTR). In distributed NC, entire programs are
downloaded to each MCU, which is CNC rather than conventional NC

12. Control Of Machine Tools
Distributed Numerical Control Configurations

13. Control Of Machine Tools
 Applications of NC
 Machine tool applications:
 Milling, drilling, turning, boring, grinding
 Machining centers, turning centers, mill-turn centers
 Punch presses, thermal cutting machines, etc.
 Other NC applications:
 Component insertion machines in electronics
 Drafting machines (x-y plotters)
 Coordinate measuring machines
 Tape laying machines for polymer composites
 Filament winding machines for polymer composites

14. Common NC Machining Operations
Control Of Machine Tools

15. Control Of Machine Tools
 NC Application Characteristics
(Machining)
 Where NC is most appropriate ?
1) Batch production
2) Repeat orders
3) Complex part geometries
4) Much metal needs to be removed from the starting workpart
5) Many separate machining operations on the part
6) The part is expensive

16. Control Of Machine Tools
 Advantages of NC
 Nonproductive time is reduced
 Greater accuracy and repeatability
 Lower scrap rates
 Inspection requirements are reduced
 More complex part geometries are possible
 Engineering changes are easier to make
 Simpler fixtures
 Shorter lead times
 Reduce parts inventory and less floor space
 Operator skill-level requirements are reduced

17. Control Of Machine Tools
 Disadvantages of NC
 Higher investment cost
 CNC machines are more expensive
 Higher maintenance effort
 CNC machines are more technologically sophisticated
 Part programming issues
 Need for skilled programmers
 Time investment for each new part
 Repeat orders are easy because part program is already available
 Higher utilization is required

18. Control Of Machine Tools
NC Positioning System
 Typical motor and lead screw arrangement in an NC positioning system for one linear axis
 For x-y capability, the apparatus would be piggybacked on top of a second perpendicular axis

19. Control Of Machine Tools
 Analysis of Positioning NC Systems
 Two types of NC positioning systems:
1) Open-loop -no feedback to verify that the actual position achieved is the desired position
2) Closed-loop -uses feedback measurements to confirm that the final position is the specified
position
 Precision in NC positioning -three measures:
1) Control resolution
2) Accuracy
3) Repeatability

20. Control Of Machine Tools
 Open-Loop Motion Control System
Operates without verifying that the actual position achieved in the move is the desired position

21. Control Of Machine Tools
 Closed-Loop Motion Control System
Uses feedback measurements to confirm that the final position of the worktable is the location
specified in the program
 Optical Encoder
 Device for measuring rotational position and speed
 Common feedback sensor for closed-loop NC control

22. Control Of Machine Tools
NC Part Programming
1) Manual part programming
2) Computer-assisted part programming
3) Part programming using CAD/CAM
4) Manual data input

23. Control Of Machine Tools
1) Manual part programming
 The programmer first prepares the manuscript in a standard format. Manuscripts are typed with
a device called flexo writer, which is also used to type the program instructions. After the
program is typed the punch tape is prepared on the flexo writer. Complex shaped components
require tedious calculations. This type of program is carried out for simple machining parts
produced on point-to-point machine tool.
 To be able to create a program manually, need the following information
a) Knowledge about various manufacturing processes and machines.
b) Sequence of operations to be performed for a given component.
c) Knowledge of the selection of cutting parameters.
d) Editing the part program according to the design changes.
e) Knowledge about the codes and functions used in the part programs.
 In manual part programming the programmer prepares the NC code using the low-level
machining language (G-M Codes)

24. Control Of Machine Tools
Binary Coded Decimal System
Each of the ten digits in decimal system 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
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)

25. Control Of Machine Tools
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
Example: Word Address Format
 N001 G00 X07000 Y03000 M03
 N002 Y06000

26. Control Of Machine Tools
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

27. Control Of Machine Tools
Computer-Assisted Part Programming
 Manual part programming is time-consuming, tedious, and subject to human errors for complex
jobs
 Machining instructions are written in English-like statements that are translated by the computer
into the low-level machine code of the MCU
 APT (Automatically Programmed Tool)
 The various tasks in computer-assisted part programming are divided between
 The human part programmer
 The computer
Computer-Assisted Part Programming
Sequence of activities in computer-assisted part programming

28. Control Of Machine Tools
Part Programmer's Job
Two main tasks of the programmer:
1) Define the part geometry
2) Specify the tool path
1) Defining Part Geometry
 Underlying assumption: no matter how complex the part geometry, it is composed of basic
geometric elements and mathematically defined surfaces
 Geometry elements are sometimes defined only for use in specifying tool path
 Examples of part geometry definitions:
P4 = POINT/35,90,0
L1 = LINE/P1,P2
C1 = CIRCLE/CENTER,P8,RADIUS,30
2) Specifying Tool Path and Operation Sequence
 Tool path consists of a sequence of points or connected line and arc segments, using
previously defined geometry elements
 Point-to-Point command:
GOTO/P0
 Continuous path command
GOLFT/L2,TANTO,C1

29. Control Of Machine Tools
 Other Functions in Computer-Assisted Part Programming
 Specifying cutting speeds and feed rates
 Designating cutter size (for tool offset calculations)
 Specifying tolerances in circular interpolation
 Naming the program
 Identifying the machine tool

30. Control Of Machine Tools
Computer Tasks in Computer-Assisted Part Programming
1) Input translation –converts the coded instructions in the part program into computer-usable form
2) Arithmetic and cutter offset computations –performs the mathematical computations to define
the part surface and generate the tool path, including cutter offset compensation (CLFILE)
3) Editing –provides readable data on cutter locations and machine tool operating commands
(CLDATA)
4) Post processing –converts CLDATA into low-level code that can be interpreted by the MCU

31. Control Of Machine Tools
NC Part Programming Using CAD/CAM
 Geometry definition
 If the CAD/CAM system was used to define the original part geometry, no need to recreate
that geometry as in APT
 Automatic labeling of geometry elements
 If the CAD part data are not available, geometry must be created, as in APT, but user gets
immediate visual feedback about the created geometry
Tool Path Generation Using CAD/CAM
 Basic approach: enter the commands one by one (similar to APT)
 CAD/CAM system provides immediate graphical verification of the command
 Automatic software modules for common machining cycles
 Profile milling
 Pocket milling
 Drilling bolt circles

32. NC Part Programming Using CAD/CAM

33. Control Of Machine Tools
Examples of Machining Cycles in Automated NC Programming Modules
Pocket milling
Contour turning
Facing and shoulder facing
Threading (external)

34. Control Of Machine Tools
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

35. Control Of Machine Tools
Example

36. Example of CNC Programming
What Must Be Done To Drill A Hole On A CNC Vertical
Milling Machine?
Control Of Machine Tools

37. Top
View
Front
View
Tool Home
1.) X & Y Rapid To Hole Position

38. Top
View
Front
View
2.) Z Axis Rapid Move
Just Above Hole
3.) Turn On Coolant
4.) Turn On Spindle
.100”

39. Top
View
Front
View
5.) Z Axis Feed Move to
Drill Hole

40. Top
View
Front
View
6.) Rapid Z Axis Move
Out Of Hole

41. Top
View
Front
View
9.) X&Y Axis Rapid
Move Home
7.) Turn Off Spindle
8.) Turn Off Coolant

42. Top
View
Front
View
Tool At Home
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N030 G91 G28 X0 Y0 Z0
N035 M30
N025 G00 Z.1 M09
Here’s The CNC Program!

43. Top
View
Front
View
Tool At Home
O0001
O0001
Number Assigned to this program

44. Top
View
Front
View
Tool At Home
O0001
N005 G54 G90 S600 M03
N005 Sequence Number
G54 Fixture Offset
G90 Absolute Programming Mode
S600 Spindle Speed set to 600 RPM
M03 Spindle on in a Clockwise Direction

45. Top
View
Front
View
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
G00 Rapid Motion
X1.0 X Coordinate 1.0 in. from Zero
Y1.0 Y Coordinate 1.0 in. from Zero

46. Top
View
Front
View
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
G43 Tool Length Compensation
H01 Specifies Tool length compensation
Z.1 Z Coordinate .1 in. from Zero
M08 Flood Coolant On

47. Top
View
Front
View
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
G01 Straight Line Cutting Motion
Z-.75 Z Coordinate -.75 in. from Zero
F3.5 Feed Rate set to 3.5 in./min.

48. Top
View
Front
View
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
G00 Rapid Motion
Z.1 Z Coordinate .1 in. from Zero
M09 Coolant Off
N025 G00 Z.1 M09

49. Top
View
Front
View
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N030 G91 G28 X0 Y0 Z0
G91 Incremental Programming Mode
G28 Zero Return Command
X0, Y0, Z0
X,Y,& Z Coordinates at Zero
N025 G00 Z.1 M09

50. Top
View
Front
View
O0001
N005 G54 G90 S600 M03
N010 G00 X1.0 Y1.0
N015 G43 H01 Z.1 M08
N020 G01 Z-.75 F3.5
N035 M30
N030 G91 G28 X0 Y0 Z0
N025 G00 Z.1 M09
M30 End of Program

51. programmable logic controller (PLC) - History
 The control of manufacturing operation has traditionally been performed by devices such as
timers, switches, relays, counters, and similar hard-wired devices that are based on
mechanical, electromechanical, and pneumatic principles.
 In 1968 programmable logic controllers (PLCs) were introduced to replace these devices.
 PLC or Programmable Controller is a digital computer used for automation
of electromechanical processes, such as control of machinery on factory assembly lines.
 PLCs are used in many industries and machines.
 Unlike general-purpose computers, the PLC is designed for multiple inputs and output
arrangements, extended temperature ranges.
 Programs to control machine operation are typically stored in battery-backed-up or non-
volatile memory.
 A PLC is an example of a hard real time system since output results must be produced in
response to input conditions within a limited time, otherwise unintended operation will
result.
Control Of Machine Tools

52. Control Of Machine Tools
PLC

53.  Areas of PLC Applications
 Motor Winding
 Baking
 Oil Fields
 Blending
 Painting
 Boring
 Palletizers
 Polishing
 Casting
 Reactors
 Chemical Drilling
 Robots
 Color Mixing
 Rolling
 Compressors
 Security Systems
 Stretch Wrap
 Conveyors
 Cranes
 Crushing
 Sorting
 Cutting
 Electronic Testing
 Threading
 Elevators
 Engine Test Stands
 Heat Treating
 Traffic Control
 Extrusion
 Textile Machine
 Forging
 Generators
 Turning
Control Of Machine Tools

54. Control Of Machine Tools
 PLC and Computer
 A PLC and a computer both are electronic processor unit. The architecture of a PLC’s CPU is
basically same as that of a general purpose computer; however, some important characteristics
set them apart.
 Unlike computer, PLCs are specifically designed to survive the harsh conditions of the
industrial environment. A well-designed PLC can be placed in an area with substantial amounts
of electrical noise, electromagnetic interference, mechanical vibration, and non condensing
humidity.
 Distinction of PLCs is that their hardware and software are designed for easy use by plant
electricians and technicians. The hardware interfaces for connecting field devices are actually
part of the PLC itself and are easily connected.
 The modular and self-diagnosing interface circuits are able to pin point malfunctions and
moreover, are easily removed and replaced.
 Software programming uses conventional relay ladder symbols, or other easily learned
languages, which are familiar to plant personnel.
 A computer can execute a complex programming task and also multitasking. An standard PLC
is designed to executes a single program in an orderly fashion. As PLCs are rapidly changing,
modern PLCs have multitasking capabilities.

55.  Why PLCs are so Popular?
 Programmable logic controller have made it possible to precisely control large process
machines and driven equipment with less physical wiring and wiring time than it
requires with standard electro-mechanical relays, pneumatic system, timers, drum
switches, and so on.
 The programmability allows for fast and easy changes in the relay ladder logic to meet
the changing needs of the process or driven equipment without the need for expensive
and time consuming rewiring process.
 Modem PLCs are "electrician friendly", PLC can be programmed and used by plant
engineers and maintenance electricians without much electronic and computer
programming background. They can programmed by using the existing ladder
diagrams.
Control Of Machine Tools

56.  Advantages of PLC
 Flexibility
 Universal Controller - can replace various independent/ standalone controller.
 Implementing Changes and Correcting Errors
 Do not have to rewiring relay panel.
 Change program using keyboard.
 Large Quantity of Contact
 Large number of' Soft Contact' available.
 Lower Cost
 Advancement in technology and open architecture of PLC will reduce the
market price.
 Pilot Running (Simulation Capability)
 A program can be simulated or run without actual input connection.
 Visual Observation
 Can observe the opening and closing of contact switch on CRT .
 Operator message can be programmed for each possible malfunction.
Control Of Machine Tools

57.  Speed of Operation
 Depends on scan time -millisecond.
 Asynchronous operation.
 Ladder or Boolean Programming Method
 Easy for 'Electrician’.
 Reliability
 In general -very reliable
 Simplicity of Ordering Control Sys. Components
 One package with Relay, Timers, Control Block, etc.
 Documentation
 Printout of ladder logic can be printed easily
 Security
 Software lock on a program (Password)
 Ease of Changes by Programming
 Ability to program and reprogram, loading and down loading
Control Of Machine Tools

58.  Disadvantages of PLC
 New Technology
 Change from ladder and relay to PLC concept
 Fixed program Application
 Not cost effective for single- function application
 Environment Consideration
 Not adapted for very high temperature, high humidity level, high vibration, etc.
 Fail-safe operation
 Does not start automatically when power failure ( can be programmed into )
 Not "Fail-safe" -Fail-shorted rather than OPEN
 Fixed-circuit operation
 Fixed control system -less costly
What is a Ladder Diagram?
 A complete control scheme normally drawn as a series of contacts and coils arranged between two vertical
control supply lines so that the horizontal lines of contacts appear similar to rungs of a ladder. The control
contacts (input devices) are to left and coils (output devices) on the right. Ladder diagrams are an industrial
standard for representing relay-logic control system
Control Of Machine Tools

59. Programming terminal
 Programming is done through programming terminal
 Programming terminal translates engineering language (logic control) to
machine language (binary code)
Programming through standard computer
 Most PLC manufacturers offer software packages that allow a standard
computer to be used as a programming terminal
Control Of Machine Tools

60. An application example 1: Gate Control
 PLC can sense a vehicle at the entrance or exit, and open and close the gate automatically
 The current vehicle count is easily determined by programming a simple counter
Control Of Machine Tools

61. An application example 2: Conveyor System
 PLC can be used to start/stop latching logic for motor control
 Counters can be used for monitoring product amounts
Control Of Machine Tools