02_introduction to nc_cnc and dnc
TRANSCRIPT
INTRODUCTION TO NC, DNC AND CNC
Chirag p patelU v patel college of engineering
Lecture 2
Introduction to NC machine DIFINATION:
EIA(Electronic Industries Association) ”A system in which actions are controlled by direct insertion of Numerical Data at some point. The system must automatically interpret latest some portion of this data”
The control of a machine tool by means of recorded 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 is controlled by alphanumeric characters or symbols.
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 ”
Cont… The tape reader is omitted in DNC, thus relieving the
system as its latest reliable component
Instead of using tape reader, the part programming is transmitted 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 from the machine tool back to the computer.
Components of DNC System
Central Computer
Bulk memory
Telecommunication
Lines
Machine Tools
Central
computerBulk memory
Types of DNC machine
There are two types of DNC machines
1. Behind the tape reader (BTR) system
2. Special Machine control unit
Types of DNC machine Behind the tape reader system
In this arrangement computer is linked directly to the regular NC controller unit.
DNC ComputerBulk memory
NC programs
NC ControllerTwo
Storage
Buffers
Tape reader replaced by
Telecommunication lines
Cont…
The replacement of the tape reader by telecommunication lines to the DNC computer is what gives the BTR configuration its name.
The connection with the computer is made between the tape reader and the controller unit – behind the tape reader.
Except for the source of the command instructions, the operation of the system is very similar to conventional NC.
The controller unit use to temporary storage buffer to receive block of instructions from the DNC computer and convert them in to machine actions.
While one buffer is receiving a block of data, the other is providing control instructions to the machine tool.
Cont… Special Machine Control Unit
The other strategy in DNC is to eliminate the regular NC controller all together and replace it with special machine control unit.
DNC ComputerBulk memory
NC programs
Special MCU
Conventional NC controller
Replaced by special MCU
Cont…
The special MCU is device that is specifically designed to facilitates communication between the machine tool and the computer.
The special MCU configuration achieve a superior balance between accuracy of the interpolation and fast metal removal rates then is generally possible with BTR 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 to make improvements.
Function of DNC
NC with out punched tape
NC part program storage
Data collection, processing and reporting
Communications
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.
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 EIA “The numerical control system
where a dedicated stored program computer is used to
perform some or all basic functions in accordance with
control programs stored in Random Access Memory of
the computer”
Cont… The control unit and panel is somewhat similar to
NC controls. Only difference being that is works in on-line mode and NC in batch processing mode.
It can be mounted or stand alone type as in NCs.
A typical CNC may need only the drawing specifications of a part to be manufactured and the computer automatically generates part program for loaded parts.
CNC offers flexibility and computational capacity along with option.
Computerized Numerical Control
Tape Reader
for Initial
Program
Entry
Minicomputer or
Microcomputer
For
Software Functions
Part program
Storage
Computer
Hardware
Interface
And
Servo
System
Functions of CNC
The Principle Functions of CNC are:
Machine Tool Control
In-process Compensation
Improved programming and Operating feature.
Diagnostics
Advantages of CNC
The advantages of CNC over NC machines are:
More flexibility
Reduce data reading error
Online editing of program
Diagnostic
Conversion of units
Integration with DNC systems
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
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