With the advent of the production of sophisticated equipment and machinery, there need to transfer instructions from man to the machine through automatic device arose. The control system used with such machines requires the instructions to be encoded in a suitable language, in a particular pattern, and on a convenient medium, so that the machine can read the instruction automatically and perform the job. The general objective behind the development of NC technology has been the reduction of cost by reducing time. This is achieved by reducing non-production time on the number of setups time.
The setup time is achieved by reducing work piece handling time, tool change time, and read time, etc. the fixture is reduced. Design changes can easily be incorporated without having to change jigs, fixtures, and tools. Accuracy is improved due to the reduction of human error. NC machining is the best suited for small batch producers.
The control of a machine tool by means of recorded information supplied to the control because of information of numbers in binary (alpha-numeric form). This numerical control system is a method and a system for controlling a machine or process by instructions in the form of numbers. Machine control functions done by the operator in conventional machines are translated into numeric instructions that can be understood by the machine control unit. The information stored in the punch tapes or cards can be read by automatic means and converted into electrical signals, which operate the electrically controlled servo system. The use of the cards and the electrically controlled servo system permits the slides of a machine tool to be driven simultaneously and at the appropriate speed with a single operation and without the need to re-orient.
In automatic control, operation right from the feeding of the stock to clamping, machining and even inspection of the work piece are carried out automatically. A particular sequence is followed depending upon the requirements of the work pieces and is achieved by using cams, stops, setting, trip dogs and another mechanical movement of the machine.
The principle of automatic control is explained below:
- The suitable feeding arrangements like feed hoppers, strip feed rolls etc. could be employed on the Orthodox machines to make them partially automatic in respect of material handling.
- The machines used for turning operation could be made automatic in the operation of feeding and turning movement by incorporation of cams and mechanical movements, the setting of which may be made for any one of a variety components within the capacity of the machine. Generally, one set at settings (cam etc) is designed to suit a given set of conditions for one particular work piece only and to change from one job to other necessitates changing of economic than employing a more standard machine.
- The third category of automatics includes machines designed especially for operations on a particular component and generally used for drilling and profiling operations.
- The fourth category includes transfer machining units assembled and used in conjunction with some form of conveyor or indexing work table so that the work may be automatically moved through the sequence of operations concerned.
- Until now, we have considered machines in which the actuation and control are based on mechanical movements. During recent years the concept of automatics has changed altogether due to the introduction of the automatics feedback control. i.e; the tool or cutter is fed back electrically into the controlling system where it is compared with the set value and the tool is accordingly moved and thus a continuous system of monitoring and correction is used.