introduction to nc,cnc and dnc

5/26/2018 Introduction to NC,CNC and DNC

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Introduction to NC machine

DIFINATION:

EIA(Electronic Industries Association) A system in whichactions are controlled by direct insertion of NumericalData at some point. The system must automatically

interpret latest some portion of this data

The control of a machine tool by means ofrecorded information on punched tape or card is

known as Numerical Control Numerical control is defined as a form of software

controlled automation, in which the process iscontrolled by alphanumeric characters or symbols.


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Introduction to DNC machine

Definition

Direct numerical control can be

defined as a manufacturing system in which a

number of machine are controlled by a computer

through direct connection in real time


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Cont

The tape reader is omitted in DNC, thus relieving thesystem as its latest reliable component

Instead of using tape reader, the part programming istransmitted to the machine tool directly from the computer

memory. In principle one large computer can be used to control

more then 100 separate machine.

The DNC computer is designed to provide instruction to

each machine tool on demand. When machine tool need control commands, they are

communicated to it immediately.

DNC also involves data collection and processing fromthe machine tool back to the computer.


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Components of DNC System

Central Computer

Bulk memory

Telecommunication

Lines

Machine Tools

Central

computerBulk memory


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Types of DNC machine

There are two types of DNC machines

1. Behind the tape reader (BTR) system

2. Special Machine control unit


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Types of DNC machine

Behind the tape reader system

In this arrangement computer is linked directly to theregular NC controllerunit.

DNC ComputerBulk memory

NC programs

NC ControllerTwo

Storage

Buffers

Tape reader replaced by

Telecommunication lines


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The replacement of the tape reader bytelecommunication lines to the DNC computer is whatgives the BTR configuration its name.

The connection with the computer is made betweenthe tape reader and the controller unit

behind the

tape reader.

Except for the source of the command instructions, theoperation of the system is very similar to conventionalNC.

The controller unit use to temporary storage buffer toreceive block of instructions from the DNC computerand convert them in to machine actions.

While one buffer is receiving a block of data, the otheris providing control instructions to the machine tool.


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Special Machine Control Unit

The other strategy in DNC is to eliminate the regularNC controller all together and replace it with special

machine control unit.

DNC ComputerBulk memory

NC programs

Special MCU

Conventional NC controllerReplaced by special MCU


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The special MCU is device that is specificallydesigned to facilitates communication between themachine tool and the computer.

The special MCU configuration achieve a superiorbalance between accuracy of the interpolation and fastmetal removal rates then is generally possible withBTR system.

The special MCU is soft wired, while the conventional

NC controller is hard wired.

The advantage of soft wired is its flexibility

Its control function can be altered with relative ease tomake improvements.


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Function of DNC

NC with out punched tape

NC part program storage

Data collection, processing and reporting

Communications


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Advantages of DNC

Elimination of punched tapes and tape

readers.

Grater computational capability and flexibility.Convenient storage of NC part program in

computer files.

Program stored as CLFILE.

Reporting of shop performance.

Establishes the framework for the evolution of

the future computer automated factory.


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Introduction to CNC machine

Definition

CNC is a self-contained NC system for a

single machine tool which uses a dedicated mini

computer, controlled by the instruction stored in its

memory, to perform all the basic numerical control

functions.

As per EIAThe numerical control system

where a dedicated stored program computer is used to

perform some or all basic functions in accordance withcontrol programs stored in Random Access Memory of

the computer


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The control unit and panel is somewhat similar toNC controls. Only difference being that is worksin on-line mode and NC in batch processingmode.

It can be mounted or stand alone type as in NCs.

A typical CNC may need only the drawingspecifications of a part to be manufactured and

the computer automatically generates partprogram for loaded parts.

CNC offers flexibility and computational capacityalong with option.


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Computerized Numerical Control

Tape Reader

for Initial

Program

Entry

Minicomputer or

Microcomputer

For

Software Functions

Part program

Storage

Computer

Hardware

Interface

And

Servo

System


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Functions of CNC

The Principle Functions of CNC are:

Machine Tool Control

In-process Compensation

Improved programming and Operating feature.

Diagnostics


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Advantages of CNC

The advantages of CNC over NC machines are:

More flexibilityReduce data reading error

Online editing of program

Diagnostic

Conversion of units

Integration with DNC systems


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Disadvantages of CNC

The disadvantages of CNC over NC machines are:

High initial cost

Higher maintenance cost

Skilled CNC personal

Not suitable for long run applications

Machine have to be installed in air-conditioned places

introduction to nc,cnc and dnc

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