WHAT IS CNC?

– CNC may be defined as the numerical control system where in a dedicated programs in a computer are used to replace some or all of its control functions.

– In CNC the program is read once by he tape reader as the input device & is stored in the controller’s random access memory.

PRINCIPLE OF OPERATION OF CNC:-

In CNC the program is read once by the tape reader and stored in the controller’s random access memory. When a stored program has to be executed in the CNC machine the instruction blocks in the part program are implemented by the micro processor with the help of the control programs resident in ROM. The output from the controller may be either as a sequence of reference phase or as a binary word in sampled data system, with the first type of system the microprocessor helps in generate a sequence of reference phase for each axis of motion; each phase producing CNC small unit of motion (sum).

ADAPTIVE CONTROL:-

Adaptive control implies that he CNC system is

responsive to adapt. Itself operate at those

machining parameter which result in higher

productivity of part programmer.

so by the ADAPTIVE CONTROL below

mentioned control selection can be apply named as

ADAPTIVE CONTROL with constraints ACC.

1)Use the available spindle power to maximum.

2)Limit the deflection of the cutter.

3)Limit the cutting tool temperature.

4)Limit the vibrating amplitude of the cut.

FEATURE OF CNC:-

A CNC system provides all the above functions

through with the help of software based control

principle.

1)Interpolation (Linear & Circular)

2)Tool compensation using dedicated switches.

3)Speed & feed ever ride.

4)Repeated program start for batch manufacture.

5)Minor imaging.

6)Sealing.

7)Suppression of NC block.

8)Online part programming through difficult & time

consuming.

INTERACTIVE CNC:-

Programming and machine operation has been further

made easier and speedier by the following developments in

this direction.

Automatic preparation of part program with minimum

essential data input in the form of familiar words.

Easier input data definition with the help of callous,

graphical, special familiar character and multiple windows on

the screen.

Automatic tool selection according to the shape of work

piece to be machined and the machining process.

Automatic determination of machining condition such as

spindle speed, depth of cut and feed rate on the basis of

material data

Automatic geometric calculation of dimension like those of

inter section and tangent on data input from the work piece.

CNC SYSTEM FOR FACTORY

AUTOMATION:- There has been a growing need for CNC system

which can be operated unnamed for long long

hours.

1) Stand alone CNC machining, turning and working

centers for unnamed operation.

2) Flexible manufacturing modules (PMM) which consists of

one of the above mentioned centers and a material

handling device line that of robot.

3) computer controlled machine tool inspection machines

and materials handling device like robots and

automatically guided vehicles (AGV) etc. in an integral

fashion bringing about flexibility in automated storage

handling and processing and flow of the materials

namely tooling and work pieces.

DIRECT NUMERICAL CONTROL :-

DNC is the first stop towards the factory of future. It is a manufacturing system in which a central computer communicates with the controllers of several machine tools by as direct connection in real time. Its essential functions in addition to the earlier mentioned NC/CNC capabilities of the machine tools are.

1) To used the memory of the central computer far working programs meant for several NC/CNC machines. In principle programs hundred of machines may be stored. This function includes input, output, editing, updating, copying and erasing of programs at DNC computer.

2) To transfer or download directly the part programs from central computer to individual machine control units of machine.

3) To provide software for processing of the above mentioned shop floor data for management purposes. This may includes real time rescheduling of operations on several machine.

4)To provide downloading in real time on the floor shop. In the earlier type of DNC the part program data was transferred block by block to the hard wired MCUS of NC machines as if it were on a punched tape.

5)To establish two way communication I.e. in addition to downloading of programs the control computer can also receive message and other manufacturing information in real time.

6)To provide for unloading I.e. entry of part program from CNC systems to the central computer.

7)To post process part program which are written in higher languages like APT. this may also includes additional software for assistance accordingly this DNC system can be viewed to out as an interface between “higher level language process planning” and “lower level” machine planning.

8)To provide for integration of the central computer with other systems like those of CAD/CAM.

MODEM:-

It is a device which converts digital data from computer & other DTE ( data terminal equipment) like CNC controller and computers into signal which can be transmitted over long distances over telephone lines. The term modem into analog signals of light signals in case at fiber optic telephone lines. The modem can be viewed as an interface between digital equipment and analog line. At the sending side the modem modulates (conditions) the digital signal making it suitable for transmission over the line. At the receiving den it demodulates the signal and converts it look into original digital signal for the receiving equipment. The public service telephone lines can be thus used to transmit data over long distances above 10 km with the help of long haul modems. The short haul modems may of course be used for distances within a range of 2-10 km. typical data transfer rates (also called BAUD rate of locally available modems range from 300 bps (bits per seconds) to 19.2 kbps.

HOW OF DNC?

The hardware and software requirements of DNC have been shown in fig. the essential components are:

1) DNC computer which could be mainframe. A mini or now even personal computer (Pc)

2) Computer memory which is RAM, ROM and mainly the magnetic disc drive.

3) Input/output CRI terminal and other desired I/O devices like line printers, plotters Tape road and punch magnetic drives and floppy drives etc.

4) Communication line between the DNC computer and the machine controller.

5) DNC system software and enhanced functions software for management, processing higher level language part programs and linking DNC with other systems.