Computer numerical control: Difference between revisions

Revision as of 04:01, 5 May 2005

Revision as of 04:30, 5 May 2005

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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 representeddemonstrated 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 many variants, even a variant that is essentially record/playback. In the industry, these machines are called teach lathes. In addition, powerful and well crafted human/machine interfaces allow the machine operator to prepare programs by means of interactive displays which request only the definition of the machining operation and its required parameters (such as the dimensions of a pocket) and not the actual tool path with all the calculations that are there required. Anyone today who knows machining concepts and blueprint interpretation can produce programs at the machine without the need for CAD/CAM. Nonetheless, the vast majority of programs are produced with CAD/CAM and for most users, CNC today, for all its gigahertz microprocessors and megabytes of real time kernel software, is conceptually no different from the first NC demonstrated by the M.I.T. in 1952.

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.