Computer Numerical Control (CNC) Study Materials for Mechatronics

Computer Numerical Control (CNC) is a specialized and versatile form of Soft
Automation and its applications cover many kinds, although it was initially
developed to control the motion and operation of machine tools.
Computer Numerical Control may be considered to be a means of operating a
machine through the use of discrete numerical values fed into the machine, where
the required 'input' technical information is stored on a kind of input media such
as floppy disk, hard disk, CD ROM, DVD, USB flash drive, or RAM card etc. The
machine follows a predetermined sequence of machining operations at the
predetermined speeds necessary to produce a workpiece of the right shape and
size and thus according to completely predictable results. A different product can
be produced through reprogramming and a low-quantity production run of
different products is justified.
1.1 Control Systems
1.1.1 Open Loop Systems
Open loop systems have no access to the real time data about the performance of
the system and therefore no immediate corrective action can be taken in case of
system disturbance. This system is normally applied only to the case where the
output is almost constant and predictable. Therefore, an open loop system is
unlikely to be used to control machine tools since the cutting force and loading of
a machine tool is never a constant. The only exception is the wirecut machine for
which some machine tool builders still prefer to use an open loop system because
there is virtually no cutting force in wirecut machining.

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CNC Study materials

                                             CNC MACHINING CENTERS
                     INTRODUCTION TO COMPUTER NUMERICAL CONTROL
The variety being demanded in view of the varying tastes of the consumer calls for a
very small batch sizes. Small batch sizes will not be able to take advantage of the mass
production techniques such as special purpose machines or transfer lines. Hence, the need for
flexible automation is felt , where you not only get the benefits of rigid automation but are
also able to vary the products manufactured thus bringing in the flexibility. Numerical control
fits the bill perfectly and we would see that manufacturing would increasingly be dependent
on numerical control in future.
Numerical control
Numerical control of machine tools may be defined as a method of automation in
which various functions of machine tools are controlled by letters, numbers and symbols.
Basically a NC machine runs on a program fed to it. The program consists of precise
instructions about the methodology of manufacture as well as movements. For example, what
tool is to be used, at what speed, at what feed and to move from which point to which point in
what path. Since the program is the controlling point for product manufacture, the machine
becomes versatile and can be used for any part. All the functions of a NC machine tool are
therefore controlled electronically, hydraulically or pneumatically. In NC machine tools, one
or more of the following functions may be automatic.
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CNC - 2 mark Question & Answer

1. Define NC system?

NC is defined as a form of programmable automation in which the process is controlled by alphanumeric data.

2. What is MCU?

MCU is a hardware system which reads, interprets and translates the program of instructions into mechanical action of machine tool.

3. List out any four advantage of using NC?

Ø Increased flexibility.

Ø Reduced setup time.

Ø Production of complex part.

Ø Elimination of special jigs and fixtures.

4. What are the limitations of using NC?

Ø Relatively high price.

Ø More complicated maintenance, a special crew is desirable.

Ø Highly skilled and properly trained programmers are needed.

5. What are all the problems encountered with NC system?

Ø Part programming mistakes.

Ø Non-optional speeds and feeds.

Ø Problem with punched tape and tape reader.

Ø Problem with controller and management information.

6. Define CNC?

CNC is defined as a NC system that utilizes a dedicated, stored computer program to perform some or the entire basic NC functions.

7. Write the main functions of CNC?

Ø Machine tool control.

Ø In-process compensation.

Ø Improved programming and operating features.

Ø Diagnostics 

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