Let me first introduce you about what is CNC machine, so CNC stands for Computer Numerical Control. When computers are used to control a Numerical Control (NC) machine tool than the machine is called CNC machine. In other words the use of computers to control machine tools like lathe, mills, shaper etc is called CNC machine.
The cutting operations performed by the CNC is called CNC machining, in CNC machining, programs are designed or prepared first and then it is fed to the CNC machine. According to the program, the CNC controls the motion and speed of the machine tools.
Block Diagram of CNC Machine
Main Parts of CNC Machine
The main parts of the CNC machine are
(i) Input Devices: These are the devices which are used to input the part program in the CNC machine. There are three commonly used input devices and these are punch tape reader, magnetic tape reader and computer via RS-232-C communication.
(ii) Machine Control Unit (MCU): It is the heart of the CNC machine. It performs all the controlling action of the CNC machine, the various functions performed by the MCU are
- It reads the coded instructions fed into it.
- It decodes the coded instruction.
- It implements interpolation ( linear, circular and helical ) to generate axis motion commands.
- It feeds the axis motion commands to the amplifier circuits for driving the axis mechanisms.
- It receives the feedback signals of position and speed for each drive axis.
- It implements the auxiliary control functions such as coolant or spindle on/off and tool change.
(iii) Machine Tool: A CNC machine tool always has a slide table and a spindle to control of the position and speed. The machine table is controlled in X and Y axis direction and the spindle is controlled in the Z axis direction.
(iv) Driving System: The driving system of a CNC machine consists of amplifier circuits, drive motors and ball lead screw. The MCU feeds the signals (i.e. of position and speed) of each axis to the amplifier circuits. The control signals are than augmented (increased) to actuate the drive motors. And the actuated drive motors rotate the ball lead screw to position the machine table.
(v) Feedback System: This system consists of transducers that acts like sensors. It is also called as measuring system. It contains position and speed transducers that continuously monitor the position and speed of the cutting tool located at any instant. The MCU receives the signals from these transducers and it uses the difference between the reference signals and feedback signals to generate the control signals for correcting the position and speed errors.
(vi) Display Unit: A monitor is used to display the programs, commands and other useful data of CNC machine.
How CNC Machine Works
- First the part program is inserted into the MCU of the CNC.
- In MCU all the data process takes place and according to the program prepared, it prepares all the motion commands and sends it to the driving system.
- The drive system works as the motion commands are send by MCU. Drive system controls the motion and velocity of the machine tool.
- Feedback system, records the position and velocity measurement of the machine tool and sends a feedback signal to the MCU.
- In MCU, the feedback signals are compared with the reference signals and if there are errors, it corrects it and sends new signals to the machine tool for the right operation to happen.
- A display unit is used to see all the commands, programs and other important data. It acts as the eye of the machine.
Advantages and Disadvantages
1. It can produce jobs with highest accuracy and precision than any other manual machine.
2. It can be run for 24 hours of a day.
3. The parts produced by it have same accuracy. There is no variation in the parts manufactured by a CNC machine.
4. Highly skilled operator is not required to operate a CNC machine. A semi-skilled operator can also operate accurately and more precisely.
5. Operators can easily make changes and improvements and reduces the delay time.
6. It has the capability to produce complex design with high accuracy in minimum possible time.
7. The modern design software, allows the designer to simulate the manufacturer of his/her idea. And this removes the need of making a prototype or model and saves time and money.
8. Fewer workers are required to operate a CNC machine and saves labour cost.
Despite of having so many advantages, a CNC machine has some disadvantages too. And these are:
1. The cost of the CNC machine is very high as compared with manually operated machine.
2. The parts of CNC machines are expensive.
3. The maintenance cost in the case of CNC is quite high.
4. It does not eliminate the need of costly tools.
Application of CNC Machine
Almost every manufacturing industry uses CNC machines. With increase in the competitive environment and demands, the demand of CNC usage has increased to a greater extent. The machine tools that comes with the CNC are lathe, mills, shaper, welding etc. The industries that are using CNC machines are automotive industry, metal removing industries, industries of fabricating metals, electrical discharge machining industries, wood industries etc.
This is all about what is CNC machine-parts, block diagram, working, advantages and disadvantages and application. If you find any thing missing than comment us. And if this article looks you informative than don’t forget to share it on Facebook and Google+.