NC Machining: A Definition and Complete Guide

What is NC Machining?

Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, and 3D printers) by means of a computer.

A CNC machine processes a piece of material (metal, plastic, wood, ceramic, or composite) to meet specifications by following a coded programmed instruction and without a manual operator directly controlling the machining operation.

A CNC machine is a motorized maneuverable tool and often a motorized maneuverable platform, which are both controlled by a computer, according to specific input instructions. Instructions are delivered to a CNC machine in the form of a sequential program of machine control instructions such as G-code and M-code, then executed.

The program can be written by a person or, far more often, generated by graphical computer-aided design (CAD) software and/or computer-aided manufacturing (CAM) software. In the case of 3D printers, the part to be printed is “sliced”, before the instructions (or the program) are generated. 3D printers also use G-Code.

CNC is a vast improvement over non-computerized machining that must be manually controlled (e.g. using devices such as hand wheels or levers) or mechanically controlled by pre-fabricated pattern guides (cams). In modern CNC systems, the design of a mechanical part and its manufacturing program is highly automated.

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The part’s mechanical dimensions are defined using CAD software and then translated into manufacturing directives by computer-aided manufacturing (CAM) software. The resulting directives are transformed (by “post processor” software) into the specific commands necessary for a particular machine to produce the component and then are loaded into the CNC machine.

Since any particular component might require the use of a number of different tools – drills, saws, etc. – modern machines often combine multiple tools into a single “cell”. In other installations, a number of different machines are used with an external controller and human or robotic operators that move the component from machine to machine.

In either case, the series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD drawing.

What is NC machine?

Numerical control is defined as the form of programmable automation in which numbers letters and symbols control the operation. This instruction is designed to do a particular job. NC machines have the capability to change the program for each job i.e. when the job changes the program instruction is also changed. It is easier to change the program instruction than to modify the production equipment. This flexibility reduces the overall production cost.

Types of NC Systems

The two major types of NC systems are:

1. Point-to-point (PTP) system,

PTP is an NC system, which controls only the position of the components. In this system, the path of the component motion relative to the workpiece is not controlled. The traveling between different positions is performed at the traverse speed allowable for the machine tool and following the shortest way.

2. Contouring system.

Contouring NC systems are capable of controlling not only the positions but also the component motion, i.e., the traveling velocity and the programmed path between the desired positions.

Applications of numerical control technology

Numerical control technology has application in a wide variety of production operations such as metal cutting, automatic drafting, spot welding, press working, assembly, inspection, etc. However, NC finds its principal application in metal machining operations. It is built to do virtually the entire metal removing process. (Example for metalworking Turning, sawing, Grinding, Milling, Drilling, boring).

The production jobs where the numerical control machines are most appropriate are listed below.

  • The NC technology is suitable to sequence/series of machining process.
  • Job geometry is complex, expensive. Mistakes in the process lead to high loss.
  • It is expected engineering design changes in future.
  • High metal removal is required.
  • The work part required 100% inspection.
  • There must be close tolerance on work part.
  • When many operations need to be done when processing. It is frequently processed in batches of small lot sizes.

Advantages of NC Machine

  • Greater manufacturing flexibility. NC can easily adapt to the engineering design changes and a shift in the production schedule.
  • Reduced manufacturing lead time. The job can easily and quickly set up with NC.
  • Reduced non-productive time. In case of complex machining NC seems helpful to reduce the non-productive time. Because of quick/ automatic tool changing, quick setting up, and reduced workpiece handling time.
  • Reduced fixturing. The fixture required in NC operation are simpler and less costly because NC tape does position instead of jig and fixture.
  • Reduced inventory. This is the result of fewer setup reduced lead time.
  • Quality control improved. No risk of human mistakes. It produces the part with high accuracy. It also reduces the man-hour for inspection.
  • Greater operator safety.
  • Reduce the scrap. the high accuracy of NC machine helps to reduce scrap material.
  • Reduced floor space requirement. since the one NC can do variety of operation it replaces several conventional machines.

Disadvantages of NC Machine

  • High investment cost and Maintenance cost. Most complex and sophisticated technology cost more than the conventional machine.
  • Require skilled operator. Finding and training of NC personnel should be considered.
  • Tearing and wearing of punch tape and less reliable punch tape component.
  • Part programming mistake in punched tape.
  • No optimal feed and speed. Conventional NC machine do not provide an option to change the cutting speed and feed during the operation.