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Numerical control (NC) is the precursor of computer numerical control (CNC). Computer numerical control is the automation controller for machine tools and the cutting tool process of stock removal. The CNC machine tool is the servo actuator of the CAD/CAM (Computer Assisted Design/Computer Assisted Manufacturing) process both literally and figuratively.
CNC inherits from NC its essential character of by-the-numbers interpolation of transition points in the work envelope of a motion platform based on the separation of programming from operations. The program - usually an ASCII text file
The need of the U.S. Air Force for templates more precise than could be done by methods representative of the state of the art in the late 1940s inspired a gentlemen by the name of John Parsons, President of the Parsons Works of Traverse City, Michigan, to propose that a by-the-numbers technique commonly used in machining be put under servo control with position data generated by a computer (in order to have many more points that would defy the practicability of hand calculations). His concept was to machine to setpoints as guides for subsequent manual finishing, that is, to speed up a manual process so more points could be included. His project was taken over by the Servo Mechanisms Laboratory of the Massachusetts Institute of Technology and redefined as interpolated position control that has the cutting tool traverse a straight line between points at a prescribed rate of travel. Thus, the tool would be constantly on the programmed contour and not spending most of
At the time when M.I.T. was developing numerical control, engineers at General Motors were putting position transducers on the lead screws of a conventional engine lathe and recording the motion of the axes as the machinist put the machine through its paces to make a workpiece. The machine was also fitted with a servo system that took data from the recording to reproduce the same sequence of motion to produce a second, third and more parts. This technique is called record/playback and it is reminicent of a musician making music on a piano that has been modified to record his keystrokes on a paper chart to be read by a player piano to reproduce the music. The popular novel, "The Player Piano", is inspired by this machine. The author [[Kurt Vonnegut]] was exposed to the machine when he worked as a publicist for General Electric. Record/playback is different from numerical control in that the program is produced by the machinist in the process of making the first part.
The Air Force wanted numerical control and not record feedback because the latter put the machinist in charge of program production. This was the same machinist who was a union member; thus union strikes could result in delays in military production. Also, numerical control represented the ability to produce parts that were not possible by conventional, manual means. The Air Force used its deep pockets to get its way and while American manufacturing may have been better served with the simpler Parson concept or with record/playback, today this is a mute issue. An entire manufacturing process known as CAD/CAM has developed around the NC concept and, in addition, CNC with its powerful microprocessors and other enabling technologies proffered from the personal computing phenomenon has enabled the NC concept to branch into
If there is a difference in concept, it is that CNC is not just for the spindle and cutting tool process of stock removal anymore. It is for any process that can be carried on a machine tool motion platform that benefits from the separation of programming from operations, that is, from the CAD/CAM process. This includes lasing, welding, friction stir welding, ultrasonic welding, flame cutting, bending, spinning, pinning, gluing, fabric cutting, sewing, tape and fiber placement, routing, sawing and processes not yet invented.
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