Computer numerical control (CNC) machines

CNC machine is the best and basic example of application of Mechatronics in manufacturing automation. Efficient operation of conventional machine tools such as Lathes, milling machines, drilling machine is dependent on operator skill and training. Also a lot of time is consumed inwork part setting, tool setting and controlling the process parameters viz. feed, speed, depth of cut. Thus conventional machining is slow and expensive to meet the challenges of frequently changing product/part shape and size.

Figure 1.2.1 Comparison between a conventional machine tool and a CNC machine tool

Computer numerical control (CNC) machines are now widely used in small to large scale industries. CNC machine tools are integral part of Computer Aided Manufacturing (CAM) or Computer Integrated Manufacturing (CIM) system. CNC means operating a machine tool by a series of coded instructions consisting of numbers, letters of the alphabets, and symbols which the machine control unit (MCU) can understand. 

These instructions are converted  into  electrical  pulses  of current which the machine’s motors and controls follow to carry out machining operations on a workpiece. Numbers, letters, and symbols are the coded instructions which refer to specific distances, positions, functions or motions which the machine tool can understand.

CNC automatically guides the axial movements of machine tools with the help of computers. The auxiliary operations such as coolant on-off, tool change, door open- close are automated with the help of micro-controllers. Figure 1.2.1 shows the fundamental differences between a conventional and a CNC machine tool. Manual operation of table and spindle movements is automated by using a CNC controllers and servo motors.

The spindle speed and work feed can precisely be controlled and maintained at programmed level by the controller. The controller has self diagnostics facility which regularly alarms the operator in case of any safety norm violation viz. door open during machining, tool wear/breakage etc.  Modern machine tools are now equipped with friction-less drives such as re-circulating ball screw drives, Linear motors etc. The detail study of various elements of such a Mechatronics based system is the primary aim of this course and these are described at length in the next modules.

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