CNC : Computerised Numerical Control (Computer + Numerical Control)

What is a CNC Machine?

CNC : Computerised Numerical Control (Computer + Numerical Control)
Numerical control is a programmable automation in which process is controlled by Numbers, Letters, and symbols. CNC Machining is a process used in the manufacturing sector that involves the use of computers to control machine tools like lathes, mills and grinders.

Why is CNC Machining necessary?

 To manufacture complex curved geometries in 2D or 3D was extremely expensive by mechanical means (which usually would require complex jigs to control the cutter motions). Machining components with high Repeatability and Precision. Unmanned machining operations. To improve production planning and to increase productivity. To survive in global market CNC machines are must to achieve close tolerances.

 CNC program structure:-

There are four basic terms used in CNC programming
 Character -> Word -> Block -> Program
Character is the smallest unit of CNC program. It can have Digit / Letter / Symbol. Word is a combination of alpha-numerical characters. This creates a single instruction to the CNC machine. Each word begins with a capital letter, followed by a numeral. These are used to represent axes positions, federate, speed, preparatory commands, and miscellaneous functions. A program block may contain multiple words, sequenced in a logical order of processing. The program comprises of multiple lines of instructions, „blocks‟ which will be executed by the machine control unit (MCU).

Structure of an NC part program :-

An NC part program is made up of a series of commands that are input into the MCU in a serial manner. The MCU interprets these commands and generates the necessary signals to each of the drive units of the machine to accomplish the required action. The NC program is required to have a particular structure that the controller can understand and it must follow a specific syntax. Commands are inputs into the controller in units called blocks or statements. Each block is made up of one or more machine commands. In general, several commands are grouped together to accomplish a specific machining operation, hence the use of a block of information for each operation. Each command gives a specific element of control data, such as dimension or a feed rate. Each command within a block is also called a word. The way in which words are arranged within the block is called block format. Three different block formats are commonly used, (Fixed sequential format, Tab sequential format and Word address format)

Commonly used word adresses:-

N-CODE: Sequence number, used to identify each block with in an NC program and provides a means by which NC commands may be rapidly located. It is program line number. It is a good practice to increment each block number by 5 to 10 to allow additional blocks to be inserted if future changes are required.
 G-CODE: Preparatory Word, used as a communication device to prepare the MCU. The G-code indicates that a given control function such as G01, linear interpolation, is to be requested.
X, Y & Z-CODES: Coordinates. These give the coordinate positions of the tool.
 F-CODE: Feed rate. The F code specifies the feed in the machining operation.
 S-CODE: Spindle speed. The S code specifies the cutting speed of the machining process.
T-CODE: Tool selection. The T code specifies which tool is to be used in a specific operation.
 M-CODE: Miscellaneous function. The M code is used to designate a particular mode of operation for an NC machine tool.
 I, J & K-CODES: They specify the centre of arc coordinates from starting.

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