Introduction to computer numerical control

Computer numerical control or CNC refers to any machine tool, e.g. drilling machine, milling machine or lathe, which uses a computer to electronically control the motion of one or more axes on the machine through the use of coded instructions. 

Simply put, instead of turning handwheels as is required by conventional machines the CNC machine control unit (MCU) sends a motion signal via a controller board to a servo motor attached to each machine axis. This causes the servo motor to rotate a ballscrew attached to the table, cross-slide or column, causing it to move. The actual position of the axis is continuously monitored and compared to the commanded position with feedback from a transmitter attached to the ballscrew. The ballscrews have almost no backlash, so when the servo reverses direction there is almost no lag between a commanded reversing motion and corresponding change in slide direction. 

The use of CNC machine tools has radically changed the manufacturing industry. Curves are as easy to machine as straight lines, as well as parts with complicated contours and complex 3D shapes. The increased automation has resulted in improvements in consistency and quality together with a reduced frequency of errors. CNC also allows for more flexibility in the way workpieces are held, often avoiding the use of expensive jigs or fixtures required on conventional machines. Dimensional modifications can be done quickly and the time required to change over to a different part is reduced. Small batches or short production runs as well as parts needed in a hurry can be easily accommodated. 

All CNC machine tools have two or more programmable directions of motion called axes. An axis of motion can be linear, i.e. in a straight line, or rotary, i.e. along a circular path. The more axes a machine system is capable of simultaneously controlling, the more complex the machine tool. 

A body in space has six degrees of freedom. Motion can therefore be resolved into six axes, namely three linear referred to as X, Y and Z and three corresponding rotational axes referred to as A, B and C as shown in Fig. 12.1. 

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Introduction to computer numerical control 12.2.2 Part programming... 

Since the introduction of TQGs in 1993, the DOD has introduced new 100 and 200 kW versions to power weapons systems, command posts (CPs), command, control, communications, computers, intelligence, surveillance, and reconnaissance (C4ISR) systems, and numerous other battlefield systems throughout the DOD. In terms of development, the TQGs represent the minimum benchmark that fuel-cell development needs to reach. 

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