Explained Numerical Control Machines tools.

2. NC Machine Tool
 Numerically controlled (NC) Machine tool are the machine tool , of which the
various function are controlled by Letters, numbers and symbols
 NC machine tools run on programme fed to it, without human operator
 NC programme consist set of instruction or statement for controlling the motion of
the drives of the machine , the motion of cutting tool
Function of NC Machine
• starting and stopping of the Machine tool
• Controlling the spindle speed
• Positioning the tool at desired location and guiding it along the desired path
• Controlling the feed rate
• Changing the tool

3. NC Machine Tool
In NC machine, numbers form program of instructions and are:
1.TO Start (or) Stop the machine tool spindle .
2. To control the spindle speed.
3.To change the tool.
4.To change the feed rate.
5.To switch the coolant on/off.
6.To position the tool at a desired position

4. Historical Background
• Conventional NC is based on the pioneering work of a man named John T. Parsons.
• In late 1940, parson conceived a method of using punched cards containing coordinate
positioning data to control the machine.
• In 1948 parson demonstrated his concept to U.S. Air Force.
• The first demonstration of NC prototype was held in 1952 and in 1953 potential
usefulness of the NC concept has been proven

5. Elements of NC Machine

6. Elements of NC Machine continue…
(1) Part Drawing and Part Programming
• Part programme is set of step by step instruction to the machine tool for carrying out
the operation and which tells the machine tool what to do.
• Part program is written by using part Drawing and cutting process parameter
• The set of instruction includes
 Instruction position of machine tool spindle with respect to the work table
 Instruction for cutting operation
 Instruction for selection of spindle speed, cutting tool etc.
Method of Part Programing
I. Manual Part programming
II. Computer aided Part programming

7. Elements of NC Machine continue…
(2) Programme Tape
• Part programme is entered on the programme tape
• The tape is a long wound roll of the one inch width.
• The programme is entered on the tape in the form of punched holes ,holes punched
with the help of punching machine.
• Now a day punch-line tape is replaced with magnetic cassettes, floppy disc , pen
drive, hard drive

8. Elements of NC Machine continue…
(3)Machine control unit (MCU)
• MCU is heart of NC/CNC machine which consist of some electronics hardware that read
the NC programme, interpret it and conversely translates it for mechanical action of
machine tool
• A typical MCU consist following units
 Input or tape reader
 memory
 processor
 output channels
 control panel
 feedback channels

9. Elements of NC Machine continue…
• Functions of MCU
 Read coded instruction
 Decode coded instruction
 Implement interpolation (linier ,circular, and Helical )v to generate axis motion
commands
 Feed axis motion command to amplified circuits for driving the axis mechanism
 Received the signals of position and speed for each drive axis
 Implement auxiliary control function such as coolant or spindle on/off, and tool change.

10. Elements of NC Machine continue…
(4) Machine Tool
• The Machine tool is operated by MCU
• following function may automated by Machine tool
 Starting and stopping of the machine tool spindle
 Controlling the spindle speed
 Positioning of tool tip at desires locations and guiding it along the desired path by
automatic control of the slide motion
 Controlling the feed rate
 Changing the tool

11. Elements of NC Machine continue…
Main component of NC Machine tool
I. work Table
II. Machine tool Spindle
III. Drive unit
IV. Machine control unit
V. Feedback mechanism
VI. Manual Control
VII. Electrically operated control
equipment or magnetic box

12. Steps in NC based Manufacturing
1. Process Planning The decision are made about selection of manufacturing operation , their Sequence
,machine Requirement and tooling requirements. With the use of part drawing , data about machine tooling
,etc.
2. Part Programming for converting the sequence sheet of various machine operation, understandable
syntaxes and various control commands for machines so that machine perform exactly the way program
3. Coding of part program on suitable medium- part program converted into machine readable
coding using tape punching machine
4. Part Program Testing And Validation The accuracy of part programming is tested and modified
by using the dry run on NC Machine , and then print is taken of tool path for validation
5. NC Machining With Tool Pre-setting once testing and validation of part programme is done
operator adjust NC Machine with required tool for final batch production

13. Advantages of NC Machines
 High degree of accuracy
 Less inspection required
 Reduction of scrap and wastage
 Reduction lead time for production
 Increase productivity
 Lower tooling cost
 Reduction of human error
 Greater operation and machine tool safety
 Greater machine tool and operator efficiency
 Reduced space requirement

14. Limitation of NC Machine
Limitations:
1. High initial cost
2. High maintenance cost
3. High operation cost
4. Limited life of punching tapes
5. Limited consuming punching
tape preparation
Applications:
1. NC lathe and turning
2. NC Milling .boring , drilling and Machining
centre.
3. NC welding and Arc cutting machine
4. NC sawing Machine
5. NC pipe bending ,grinding ,inspection and
Gauging