Today at The Mechanical post we’ll learn about What is a CNC ? its construction, working, its types, advantages, limitations and applications.
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What is a CNC ?
The full form of CNC machine is Computer Numerical Control. A CNC machine is a computer-controlled machine used for performing various functions automatically which were once done on conventional machines like drilling, milling, turning etc, with the help of a computer.
The CNC machine can be said to be a robot that acts according to the program. The CNC machine is programmed or controlled by a computer and has a wide range of applications.
The CNC machine performs the required task as specified by the numeric code entered into the machine. These codes are the set of commands with the help of which the operator can instruct the machine what function is to be performed.
These codes are called G-codes and M-codes. Each code has a specific function.
CNC machining can be defined as, ” The manufacturing process in which a computer code commands the machine to perform various machining processes on the workpiece “
The CNC machine is capable of machining in 3 axes simultaneously. Some advanced CNC machines are capable of machining in 5 axes at the same time.
Basic components of CNC machine
The basic structure or components of a CNC machine are :
The machine control unit (MCU)
Input devices are those devices that are used to feed the program into the machine. Older CNC’s used punch tapes or magnetic tapes for program input, however, they have been replaced by digital ones called CNC controllers.
The machine control unit is the brain of the system which receives input, processes it, and then executes the program accordingly. The MCU is capable of controlling the tool movement, control the driving system, turn ON/OFF the various functions like turn ON/OFF spindle, turn ON/OFF the coolant etc.
For eg: if the operator has specified that the coolant must be switched OFF after completion of a certain process, the MCU then sends signals to switch OFF the coolant.
The machine tool is one of the basic components of the CNC machine. It is the component that performs the operations to convert the raw material into the finished product. The machine tool is controlled by the MCU.
The machine tool moves forward, upwards, downwards etc; thus removing the material from the workpiece little by little. How much should be the spindle speed, when shall the coolant turn ON / OFF, how much should be the feed rate? all of these parameters are specified by the operator in the form of code and thus the machine tool operates accordingly.
The driving mechanism consists of a drive motor and ball leadscrew arrangement with a feedback mechanism. The MCU signals the motor to rotate, this in turn rotates the ball leadscrew which is connected to the drive motor.
The table slide upon which the workpiece is placed for machining is mounted on the leadscrew. So as the leadscrew rotates the table slide moves to and fro accordingly.
A feedback mechanism is placed at the end of the leadscrew to signal the MCU about the changes. This enables higher accuracy in the table slide movement.
It is a monitor that displays the input, output, and other useful system information and settings.
Working of CNC machine
The following are the steps on how a CNC machine works:
The operator enters the G-codes and M-codes into the CNC controller and starts the process.
This program is then processed by the Machine Control Unit.
The MCU then instructs the machine tool and dive mechanism to take positions.
Then the workpiece is machined according to the program entered into it.
The feedback system gives feedback to the MCU.
The MCU also switches ON/OFF the different components according to the program.
The MCU also sends the output or feedback to the operator via the display.
The CNC router is an upgrade to the handheld router. It is capable of cutting materials like steel, aluminum, foam, plastics, brass etc. Most of the routers can machine in 3 axes (i.e X, Y, Z) Also there are 4, 5 and 6 axes CNC Routers available in the market.
The CNC plasma cutter uses a plasma torch to cut metals by melting them. It is usually used to cut metal sheets. It can easily cut heavy metals like steel. These machines are similar to CNC Routers, however, they are restricted to 2 axes only.
This machine uses electric sparks to melt the metal and thus machine it. The tool here in this case is an electrode. There is a gap between the tool and the workpiece. A dielectric fluid is continuously passed through the gap. The whole process is computer-controlled.
CNC laser cutting machine
The CNC laser cutting machine is similar to the CNC plasma except that instead of plasma a laser beam is used to cut the workpiece. They are generally used for cutting metals, wood, and plastic.