2. Numerical Control
Numerical control can be defined as a form of programmable
automation in which process is controlled by numbers, letters and
symbols.
In NC,the numbers form a programme of instructions designed for
a particular work part or job.
Basic components of NC system
1. 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 be
controlled.
3.
4. 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 cutting
speed, feed, depth of cut, tool selection , coolant on off
and tool paths. The MCU issues commands in form of
numeric data to motors that position slides and tool
accordingly.
5. •All CNC machining begins with a part program, which is a
sequential instructions or coded commands that direct the specific
machine functions.
• The part program may be manually generated or, more
commonly, generated by computer aided part programming
systems.
6. 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
8. Automatic Part Programming
Software programs can automatic generation of CNC data
Define Tool
CNC data
Make 3D model
Simulate
cutting
9. DNC –Direct Numerical Control
It can be defined as a manufacturing system in which a number of
machines are controlled by a computer through direct connection
and in real time.
In principle, one computer can be used to control more than 100
separate machines.
The system consists of four components.
1. Central computer
2. Bulk memory which stores the NC part programs.
3. Telecommunication lines.
4. Machine Tools.
10. CNC DNC
1. CNC computers control only one DNC computers distribute instructional
machine or a small number of data & collect from a large number of
machines. machines
2. CNC computers are located very DNC computers occupy a location that
near their machine tools. is typically remote from the machines
under their control
3. CNC software is developed to DNC software is developed not only to
increase the capabilities of a particular control individual pieces of production
machine tool. technology, but also to serve as part of
management information system in
the manufacturing sector of the firm
