This document provides an overview of numerical control (NC) and CNC machine tools, detailing their essential components, input methods, and programming processes. It explains the structure of NC systems, including the control unit, input programs, and machine tools, while also discussing different motion control types and the associated advantages and limitations. Additionally, the document highlights various applications for NC technology in machining processes, emphasizing its role in enhancing manufacturing flexibility and accuracy.

1. Numerical control
&CNC Machine Tools
By:
Siddesh Kumar N M
Assistant Professor
PESCE Mandya

2. Basic
component of
NC Systems

3. An operational
numerical control
system consists of
the following three
basic components
Program of
Instruction
01
Control Unit
also called
as machine
control unit
02
Machine tool
or other
controlled
process
03

4. Basic component of
NC control system
• The general relation of
the three components is
shown in the figure
• The Program of
instruction serves as input
to the control unit, which
in turn commands the
machine tool

5. Program of
Instructions
• It’s the detail step by step set of directions
which tell the machine tool what to do
• It is coded in numerical or symbolic form on
some type of input medium that can be
interpreted by the control unit
• The most common input device is 1-in. wide
tape, in older days other form of input media
includes punched cards, magnetic tape and
even motion picture film
• There are two methods of input to the NC
system
• MDI(Manual data input)

6. Program of
Instructions
There are two methods of input to the NC
system
MDI(Manual data input)
• In MDI the data is entered manually
• MDI is an appropriate method
• Suitable for particular type of production
unit where change in design is not much
required
DNC(Direct numerical control)
• The program of instructions are prepared
by some called part programmer
• The programmer job is to provide a set of
detailed instruction

7. Controller
Unit
•This consits of the electronics and hardware that
read and interpret the program of instruction, which
converts the input into mechanical actions of the
machine tool
•Elements of controller unit includes the tape
reader, data buffer, signal output channels to the
machine tool, feed back channel etc.
•In modern NC systems micro computer is used as
a control unit
•Tape reader is an electromechanical device for
winding and reading the punched tape

8. Controller
Unit
•The data contained on the tape are read into the
data buffer.
•The purpose of the device is to store the input
instruction in logical form of instruction
•A block of instructions usually represents one
complete set of infromation
•The signal output channels are connected to the
servomotors and other controls in the machine
tools
•Through these channels the instruction are sent to
the machine tool, feed back unit will be present to

9. Machine
tool
•This is the system which performs the useful work
•The machine tool consists of the work table and
spindle as well as motors and controls necessary to
drive them
•It also includes cutting tools, work fixture and other
auxillary equipments

10. NC Procedure

11. Steps to be
accomplished
to utilize NC in
manufacturing
Process
planning
Part
programming
Tape
preparation
Tape
verification
Production

12. Process planning
• The engineering drawing of the
workpart must be interpreted in
terms of the manufacturing process
• It is concerned with the preparation
of a route sheet
• The route is listing of sequence
operations to be performed

13. Part
Programming
• Part programmer plans the process for the portions of the
job to be accomplished
• Part programmer shloud be knowledgeable about the
machining process and they have been trained for NC
• The two ways to program of NC are
Manual part programming
• The machining instructions are prepared on a form called
as part program manuscript
• Part program manuscript is a listing of the relative
cutter/workpiece position must be followed
Computer assisted part Programming
• In this computer is used for programming which saves a lot
of time and money

14. Tape
preparation
• A punched tape is prepared from the part
programmer's NC process plan
• In manual part programming, the puncehd tape
is prepared directly from the part program
manuscript
• In computer assisted part programming, the
computer interprets the list of part programming
instruction
• Computer performs the calculation to covert this
into a detailed set of machine tool motion

15. Tape
verification
• After the punched tape has been
prepared, a method is usually provided
for checking the accuracy of the tape
• Sometimes the tape is running it through
a computer program which plots the
various tool movement
• A foam or plastic material is sometimes
used for verification
• Programming errors are not uncommon

16. Production
• This involves ordering the raw workparts,
speifying and preparing the tooling and
any special fixtures
• The machine tool operators function
during production is to load the raw
workpart in the machine
• When the part is completed, the operator
removes it from the machine and loads
the next part

17. Coordinate System

18. Coordinate
systems
• Two axes X and Y are defined in
the plane of the table as shown
• The z axis is perpendicular to this
plane and movement in the Z
direction is controlled by the
vertical motion of the spindle
• The positive and negative direction
of the motion of tool relative to
table along these axes is shown
• NC drilling press are classified into
two axis or three axis machine
depending on the capability to
control z axis

19. Right hand rule
• Three rotational axes are defined
in NC
• The a, b & c axes, these axes
specify about X, Y & Z axes
respecively
• To differentiate the positive and
negative angular motions the
RIGHT HAND RULE can be
used
• Using right hand rule with the
thumb pointing in the positive
linear rotational direction

20. Coordinate
system
• For turning operation, two axes
are normally required to
command the movement of the
tool
• The Z axis is the axis of rotation
of the workpiece
• The main purpose of the co
ordinate system is to provide a
means of locationg the tool in
relation to the workpiece

21. NC motion control
system

22. NC motion control system
The basic types of motion control system are as follows
• Point-to-point
• Straight cut
• Contouring
Point to point system represt the lowest level of motion control
between the tool and workpiece. Contouring represents the
highest level of control

23. Point to point
NC (PTP)
• It is also called as positioning
system
• In PTP the objective of the machine
tool is to move the cutting tool to a
predefined location
• The speed or path is not important
• Once the tool reaches the desired
position the machining operation is
performed

24. Point to point
NC
• NC drill presses are good example of PTP
system
• The spindle must be positioned at a particular
location on the workpiece
• Then the drilling of the hole is performed
• No need of controlling the speed of the
relative motion
• These are simplest tools and less expensive
• For drilling and spot welding PTP is best
suited where higher level control is not
necessary

25. Straight cut NC
• Straight cut control systems are capable of moving the cutting
tool parallel to one of the major axes at the controlled rate
• It is not possible to combine movements in more than a single
axis direction
• Angular cuts on the workpiece is not possible

26. Contouring NC
• Contouring is most complex, the most flexible and the most expensive type
of machine tool control
• The motion can be controlled in more than one axis simultaneously
• The path of the cutter is continuously controlled to generate the desired
geometry
• It is also called as continuous path NC system
• Straight, plane surface at any orientation, circular paths, conical shapes and
any shapes can be defined in contouring
• Milling and turning operations are common example

27. Contouring NC
• In order to obtain the curved geometry, the segments are braked
into many number of lines (very short lines)
• The tool is commanded to machine each segment in succession
• Results in the curve geometry inside and outside tolerance are
predefined and tolerance bands are maintained

28. Advantages &
Limitations of NC

29. Advantages of NC
• Greater manufacturing flexibility – NC can easily adapt to the engineering design changes
and a shift in the production schedule.
• Reduced manufacturing lead time – the job can easily and quickly set up with NC.
• Reduced non-productive time – In case of complex machining NC seems helpful to reduce
the non-productive time. Because of quick/ automatic tool changing, quick setting up, and
reduced workpiece handling time.
• Reduced fixturing – the fixture required in NC operation are simpler and less costly
because NC tape does positioning instead of jig and fixture.
• Reduced inventory - this is the result of fewer setup reduced lead time.
• Quality control improved – No risk of human mistakes. It produces the part with high
accuracy. It also reduce the man-hour for inspection.
• Greater operator safety.
• Reduce the scrap – the high accuracy of NC machine helps to reduce scrap material.
• Reduced floor space requirement – since the one NC can do variety of operation it
replaces several conventional machines.

30. Limitations of NC
• High investment cost and Maintenance cost –
most complex and sophisticated technology cost
more than the conventional machine.
• Require skilled operator – finding and training of
NC personnel should be considered.
• Tearing and wearing of punch tape and less
reliable punch tape component.
• Part programming mistake in punched tape.
• No optimal feed and speed – conventional NC
machine does not provide an option to change the
cutting speed and feed during the operation.

31. Application of
NC

32. Applications of NC
• The NC technology is suitable to sequence/series of machining
process.
• Job geometry is complex, expensive. Mistakes in the process
lead to high loss.
• It is expected engineering design changes in future.
• High metal removal is required.
• The work part required 100% inspection.
• There must be close tolerance on work part.
• When many operations need to be done when processing. It is
frequently processed in batches of small lot sizes.

33. Thank you
Reference
CAD/CAM Computer Aided Design and Manufacturing by M Groover & E.
Zimmers