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Learning more about Computer Numerical Control (CNC)

10/1/2013 11:52:59 AM | by Anonymous

Controls: Cnc

Computer Numerical Control also known as CNC is one of the functions and motions of a machine tool. They are controlled by means of a program containing prepared coded alphanumerical data. CNC controls the motion of the work piece, the input parameters, tool, depth of cut, speed and the functions of turning the spindle and coolant on and off.


Applications


The application of the Computer Numerical Control includes both machine tool as well as non machine tool areas. Under the machine tool category, CNC is widely used for lathe, milling machine, drill press, laser, sheet-metal press working machine, grinding unit, tube bending machine and etc. The machine tools are usually highly automated by the various machines such as the machining center and turning center. They change the cutting tools automatically under the control of the CNC development. Under the non-machine tool category, CNC applications would include coordinate measuring machine, tape laying, electronic assembly, welding machine and filament winding machines for composites.


Advantages and Limitations of the CNC


The benefits of CNC are as follows: It wields high accuracy rate in the manufacturing process, incurs shorter production time, greater flexibility in the manufacturing process, contours machining approximately two to five under the axis machining, simpler fixturing and significantly reduced human error. The drawbacks however are high cost, maintenance and the requirement of skilled part programmers might not be realistic.


Elements of the CNC


The Computer Numerical Control system consists of three components which are: the part program, machine control unit (MCU) and machine tool


1. Part Program


The part program is a set of detailed commands that is to be followed by the machine tool. Each of the command specifies a position in the Cartesian coordinate system (X, Y, Z) or motion (work piece traveling or cutting tool travel), machining parameters as well as the on/off function. Part programmers are generally well versed with machining processes, machine tools, effects of process variables and limitations of CNC controls. The part program is written either manually or by an assisting language from the computer such as the automated programming tool.


2. Machine Control Unit


The machine control unit is a computer that stores programs and executes commands into feasible actions by the machine tool. The Machine Control Unit mainly consists of two units namely the data processing unit and the control loops unit. The DPU software includes the calculation algorithms, control system software, translation software that aids in the conversion of the part program into useable formats for MCU. The interpolation algorithm helps to achieve smoother motion of the cutter and editing of the part program just in case of errors and changes to be made. The DUP processes data transmitted from the part program and passes it on to the CLU. The CLU then operates the attached drive to the lead screws of the machine. Additionally, it receives feedback signals of the original position and the velocity of the axes. The driver and feedback devices are attached to the lead screw. The CLU consists of circuits for position and velocity control, backlash take up, deceleration and function controls. The machine tools could also be one of the following: milling, lathe, laser, plasma, machine, coordinate measuring machine and etc.


3. Machine Tool


The machine cool could be in the form of the following: lathe, laser, milling machine, plasma, coordinate measuring machine etc. The machine tool typically has three linear axes (X, Y, Z) and three rotational axes (I, J, K). Additionally, it also has other axes such as the tilt 9 axe.


All of these three elements make up what the Computer Numerical Control.

 

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