Numerical ControlNumerical control can be defined as a form of programmableautomation in which process is controlled by numbers, letters andsymbols.In NC,the numbers form a programme of instructions designed fora particular work part or job.Basic components of NC system1. Program of instructions.2. Controller unit, also called machine tool unit.3. Machine tool or other controlled process.The program of instructions serves as input to the controller unit,which in turn commands the machine tool or other process to becontrolled.
CNC : Computer Numeric Control• In Conventional m/c , an operator decides and adjusts various machines parameters like feed , depth of cut etc depending on type of job , and controls the slide movements by hand.• In a CNC, Machine functions and slide movements are controlled by motors using computer programs.In a CNC machine, machine control unit (MCU) decides cuttingspeed, feed, depth of cut, tool selection , coolant on offand tool paths. The MCU issues commands in form of numeric data to motors that position slides and toolaccordingly.
•All CNC machining begins with a part program, which is asequential instructions or coded commands that direct the specificmachine functions.• The part program may be manually generated or, morecommonly, generated by computer aided part programmingsystems.
Advantages of CNC :• High Repeatability and Precision e.g. Aircraft parts• Volume of production is very high• Complex contours/surfaces need to be machined. E.g. Turbines• Flexibility in job change, automatic tool settings, less scrap• More safe, higher productivity, better quality• Less paper work, faster prototype production, reduction in lead times• Easier to program;• Easy storage of existing programs;• Easy to change a program• Avoids human errors
Automatic Part Programming Software programs can automatic generation of CNC data Define Tool CNC dataMake 3D model Simulate cutting
DNC –Direct Numerical ControlIt can be defined as a manufacturing system in which a number ofmachines are controlled by a computer through direct connectionand in real time.In principle, one computer can be used to control more than 100separate machines.The system consists of four components.1. Central computer2. Bulk memory which stores the NC part programs.3. Telecommunication lines.4. Machine Tools.
CNC DNC1. CNC computers control only one DNC computers distribute instructionalmachine or a small number of data & collect from a large number ofmachines. machines2. CNC computers are located very DNC computers occupy a location thatnear their machine tools. is typically remote from the machines under their control3. CNC software is developed to DNC software is developed not only toincrease the capabilities of a particular control individual pieces of productionmachine tool. technology, but also to serve as part of management information system in the manufacturing sector of the firm