more realistically Some controls can also incorporate the surface finish

More realistically some controls can also incorporate

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formation, etc. more realistically. Some controls can also incorporate the surface finish generation process in terms of the feeds and speeds used, so that the operator can get a feel of the final surface finish to be obtained on the component. Conversational Part Programming Many of the controllers are available with some form of conversational part programming facility built in. This can be in many forms. FAPT-TURN was one of the first such system which uses a vector drawing technique for making the turning part contour in 2D on screen. Based on that the system automatically selects the tools, and generates completely the part program. Similar systems have become available in many of the systems. 2.5 DEVELOPMENTS IN CNC SYSTEMS The machine control unit (MCU) in the early NC machine tools was hardwired with all the control logic to operate the machine tool embedded in the hardware circuitry. This makes the controller really bulky, with a large amount of power consumed that used to generate a large amount of heat. In addition because of a large number of wires running through the controller, the reliability also suffered. The availability of the microprocessors from mid 1970s helped in changing that situation. The microprocessor allowed for the availability of large processing power inside the controller thereby allowing for a large number of innovations. All the control logic of the machine tool is converted into software, which allowed for a reduction in a large amount of electronic hardware used in the controller. As a result the controller is a small unit unlike the earlier NC controllers. In addition the computer is available in the controller, which can be utilized for other associated functions. Consequently the controller is now called as Computer Numerical Control or CNC to recognize the computer inside the controller. All of the controllers that are being
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20 Principles of CNC Manufacturing manufactured in the present day are CNC incorporating the latest microprocessors. Consequently the word NC that represented the earlier day controllers is strictly speaking obsolete. However, people tend to use NC now-a-days as synonymous to CNC. As mentioned earlier, the computing power built into the controller allows for providing a number of advances, which were not possible with the older NC systems. Some of these developments are detailed below : It is possible to have large part program storage compared to single blocks in the previous controllers. This would allow a number of part programs to be stored in the controller for easy job changeover. It is also possible to store large part programs, which are generally required for complex 3D surface machining. The computer present in the control can allow for part program graphical proving and editing to be carried out on the controller. This would allow for carrying out necessary changes in the part programs at the machine as well as allowing for a graphical proving of tool path directly on the controller.
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