CNC Machine is Computer Numerical Control, while NC is numerical control.The user interface in both vary, in NC the input given is by punched cards or magnetic tapes. And the program cannot be edited immediately, to do the same the cards should be changed and the whole process was slower.In case of CNC, the interface is through the computer, hence any changes to the program can be made immediately through editing it on the spot. This adds to more convenience.
Firstly, NC is not a machining method, It is a concept in which a machine is controlled by programs.
These programs are written using machine codes usually numerical data, symbols or alphabets which are then fed into punch cards. Punch cards are basically storage device. They hold data in small punched holes. These holes are aligned in such a way that that can be read by computers or machines.
In NC method mostly the program is written using numerical codes so the name for the machine is given as numeric control machine. This method is widely used in various machining processes like milling, shaping,turning etc.
The program written gives proper description of the job, tool, cutting speed, feed rate etc required by the machine for the manufacturing operation.
Working Of The NC Machine-
The components of an NC machine are Program of instructions, machine control unit(MCU) and the machine tool.
As the name says program of instructions, the programmer plans the sequence of operations to be taken place and writes it using numerical codes. These codes are punched in the punch cards also called tape readers. These codes are sent to the machine control unit that continuously converts the codes into machine tool movement. The machine tool is the main component of the NC machine as it executes the program written. The block diagram for NC machine is shown below.
Just like the NC machine, CNC machine is used for the various manufacturing process, mostly metal cutting processes. The machine tool in CNC is controlled by the programs written just like the NC machine.
Now, the difference is that in NC machine the programs are fed into the punch cards and in CNC machine the programs are written with the help of keyboard that is directly fed to the computers.
These programs are stored in the computer memory which can be used for different parts and these are not needed to be repeated many times. The programs can be easily edited according to the requirement. The block diagram for CNC machine is as shown.
Working Of CNC Machine-
The CNC machine works with the execution of the programs at the machine tool. The program is customized with CNC machining language called G-codes or M codes. Using these codes the description of the operation that is to be perform is written. The description of coordinates, the location of the machine tool, speed and feed rates.
At first from the 2D drawing the program is written and loaded in the computer for a trial run which is called cutting air. In this trial run program, the mistakes of a programmer can be rectified thereby saving the time and machine work, wastage of metal. If the trial run runs successfully, the program is run for the final machining operation.
You can refer to this paper for more concept about NC and CNC machine:- Paper
|DESCRIPTION||NC MACHINE||CNC MACHINE|
|FULL FORM||Numeric Control Machine||Computer Numeical Control Machine|
|CONCEPT||Programs are stored in punch card and the MCU processes it for the movement of machine tool||Programs are written through the computer and stored in the memory for machine tool operation|
|STORAGE||Punch cards are used||Directly stored in computer memory|
|CODES||Numeric, symbols, letters||G-codes and M-codes|
|MAINTENANCE AND COST||Less maintenance so the the maintenance cost is less||High maintenance so the the maintenance cost is high|
|PROGRAM EXECUTION||Requires more time for executing the program||Requires less time for the program execution|
|ACCURACY||Less compared to CNC||High|
|OPERATOR SKILL||Highly skilled operator is required||Semi-skilled operators|
|RUNNING TIME||Cannot run continously||Can run for 24 hours|