Definition of Numerical Control

AN INTRODUCTION TO THE
CONCEPT OF COMPUTER
NUMERICAL CONTROL

Definition of Numerical Control

Numerical control (NC) is the term used to describe the control of machine movements and various other functions by instructions expressed as a series of numbers and initi­ated via an electronic control system.

Computerized numerical control (CNC) is the term used when the control system uti­lizes an internal computer. The internal computer allows for the following: storage of ad­ditional programs, program editing, running of programs from memory, machine and control diagnostics, special routines, and inch/metric-incremental/absolute switchability.

Ihe two systems are shown diagrammatically in Figure 1.1. The control units may be free-standing or built into the main structure of the machine. The operating panel of an integrated control unit is shown in Figure 1.2.

The Application of Computer Numerical Control

Computer numerical control is applied to a wide range of manufacturing processes such as metal cutting, woodworking, welding, flame cutting, sheet metal forming, sheet metal punching, waterjet cutting, electrical discharge machining and laser cutting. The text that follows is restricted to its application to common machine-shop engineering processes, namely, turning, milling, and drilling, where it has been particularly successful.

The Advantages of Computer Numerical Control
over Conventional Machining

Computer numerical control is economical for mass, batch, and, in many cases, single­item production. Many factors contribute to this economic viability, the most important of these being as follows:

  • high productivity rates
  • uniformity of the product
  • reduced component rejection
  • reduced tooling costs
  • less operator involvement
  • machining of complex contours can now be produced.

It is also found in most cases that fewer machine operators will be required as conven­tional machines are replaced by modem CNC technology, but those employees that re­main will of necessity be high caliber technicians with considerable knowledge of metal-cutting methods, cutting speeds and feeds, work-holding, and tool-setting tech­niques and who are familiar with the control systems and programming for computer numerical control.