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When basic and even on some machines all features are controlled using the instruction program is stored on a computer, then the numerical control system is known as computer numerical control systems. The growing trend of the downsizing of machine equipment led to the sale of CNC systems equipped with microcomputer-based controller units. CNC systems are also equipped with minicomputers and thus saving space.
CNC machining systems look very similar in appearance to those of conventional numerical controlled systems. The instruction program has inserted the machine using the perforated tape readers.
The difference between conventional numerical control and computerized numerical control systems is that in the case of conventional systems, the tape goes through the reader for each job, however, in the case of computer systems, the program is entered once and then stored permanently in the computer’s memory. Additional and computational flexibility capability is offered by CNC systems compared to conventional control systems.
For the addition of new functionalities to the system, only the reprogramming of the control unit is required. CNC systems are also called soft-wired NC because of CNC reprogramming capability.
Functions of CNC Machine:
1. Controlling Machine Tool:
The main function of CNC systems is the control of machine tools. Control of the machine tool is done through part programs that are fed through the computer interface to the machine tool. There are two variants of a CNC system:
Hybrid CNC and straight CNC
In the case of hybrid CNC systems, the control unit is composed of soft-wired computers and hard-wired logic circuits. Functions such as feed rate generation and circular interpolation are performed using hard-wired components. The other functions that are not performed using the wired components are performed using the computer of the wired components.
In addition, there are certain components that are common to conventional NC systems and therefore these components are connected logic circuits that can be produced in large quantities and at a relatively lower cost. These also save the computer to run any other additional task and thus saving computational expenses.
Therefore, to make CNC systems more cost-effective, lower-cost computer systems are provided with hybrid CNC systems. However, in the case of a straight CNC variant, all functions are performed via a computer. Only the machine tool interface with the computer is done using the wired elements.
Therefore, a more powerful computer is needed for straight CNC compared to a hybrid CNC system. The added flexibility is one of the main advantages of a straight CNC system. Interpolation programs can be changed easily; however, you cannot change the logic contained in the wired circuits.
2. In-Process Compensation:
In-process control is one of the functions closely related to machine tool control. In-process compensation helps dynamically verify machine movements and change errors that may occur during the machining process. Compensation in the process consists of the following:
• Error adjustment, the error is detected by gauges and probes.
• Offset adjustments for tool length and radius.
• Axis position recomputation.
• Adjustments for speed or feed control.
• Tool life forecast and use of alternative tooling when indicated.
3. Diagnostics
CNC machining systems are capital intensive. The complex structure of machine systems increases the risk of system component failure and thus leading to system shutdown. To make the necessary repairs, the necessary personnel must be highly trained so that the necessary repairs can be made.
Therefore, employees are motivated to properly care for CNC machining systems to avoid machine shutdown. CNC machines are also equipped with diagnostic features that assist personnel in system maintenance and repair. The diagnostic features serve to identify the reason for a failure in the machining system. This could help personnel make repairs faster.
Any signs of intermittent failure of any component of the machine will also be alerted to the operator in advance by the diagnostic feature. This will help to replace the failed component within the scheduled downtime and thus lead to uninterrupted production.
The CNC system’s diagnostic capability also allows you to switch to another spare component if the main operating component fails. This is only possible if the CNC machining system has provisions for waiting components.
Advantages of CNC Systems
CNC systems have a number of advantages. The following discussion lists some of the advantages of CNC systems over conventional NC systems:
• In-place machining tape editing: the instruction program on the tape can be optimized for parameters such as feed, speeds and tool path during machine tool operation.
• Limited tape usage: the tape is read once and the instruction program written on it is stored in the computer’s memory. Reliability is therefore increased as a result of limited tape usage.
• Metric Conversion: CNC machining systems have the ability to convert tape to international systems of units starting from inches.
• Greater flexibility: CNC machining systems are flexible compared to conventional NC systems. New control features, such as new interpolation schemes, can be adopted easily and at the lowest cost. Furthermore, the risk of CNC systems becoming obsolete is also reduced.
• Total fabrication systems: CNC systems can be conveniently used with factory-wide computerized fabrication systems, which is one of the main advantages of CNC over conventional NC systems.
