Computer Numeric Control
Numerical Control of machine tools may be defined as a method of automation in which various fuctions of machine tools 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 the movements.For example what tool is to be used.at what speed,at what feed and to move from which point to 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.
a) Starting and stopping of machine tool spindle.
b) Controlling the spindle speed.
c) Positioning the tool tip at desired locations and guiding it along desired paths by automatic control of the motion of slides.
d) Controlling the rate of movement of the tools tip.(i.e.feed rate)
e) Changing of tools in the spindle.
The principle of operation of a NC machine tool is the basic information that has to be inputted into the system consists of the part geometry,cutting process parameters followed by the cutting tools used.This program is then entered into the controller of the machine,which in turn runs the machine tool to make the part.Each of the machine axes is connected to a servo motor which works under the control of the machine control unit(MCU).The movement of the cutting tool with respect to the workpiece is given in terms of the coordinates,which are used to control the motion of the servo motor which drives the individual axes.
The part program consist of instructions written in the numerical codes that constitutes the basic operations to be carried out in machining of the part.These instructions entered into an input medium.
This instructions are sent through computer NC program.This new control systems are termed computer Numerical Control (CNC) which are characterised by availability of an embedded computer and enhanced memory in the controller These may also be termed as softwired Numerical control.
