Plasma arc machining
When a free-flowing gas is heated to a very high temperature, it becomes partially ionized. This ionized gas is called plasma. With this process, metal is removed from the surface of the work piece with the help of high-temperature plasma. Metal is also moved as a result of electron bombardment.
This plasma arc machining has a gas chamber which is fitted with a copper nozzle at the bottom. A tungsten electrode is held vertically in the gas chamber. The tungsten carbide is connected to the negative terminal of the DC supply, and the nozzle is connected to the positive terminal of the power supply.
When the power supply is given, an arc is produced between the tungsten electrode and the copper nozzle. A di-atomic gas is passed through the gas chamber. Hydrogen, nitrogen, and oxygen are the most commonly used di-atomic gases. This gas is permitted through the arc. The arc heats up the gas and it gets ionized due to the high temperature.
This ionized gas flows out of the nozzle in the form of a flame known as a plasma flame. This plasma flame is forced on to the surface of the work piece. The high temperature of the plasma flame melts down the metal. As a result of the action of the bombardment of the ions on the surface of the work piece, the metal is eroded.
The metal removal rate is controlled by controlling the flow of the diatomic gas. Vast use of the tungsten electrode in the same position leads to the erosion of the electrode, so it has to be frequently adjusted. The wear of the nozzle is minimized by cooling with the help of water.
Laser beam machining
A laser is an electromagnetic radiation source. A beam of the same wavelength is focused by a lens on a very small spot on a work piece. The laser beam emits high heat, which can melt and vaporize any type of material.
This equipment consists of a ruby crystal. The crystal is placed inside a flash lamp coil. The flash lamp is filled with xenon gas. When the flash lamp is switched on, it gives a high intensity light. The ruby crystal is stimulated and emits the laser beam. By using a lens, the beam is focused on the work piece. The work piece is fed past the beam. The portion of the metal is melted and vaporized.
This type of machining is also known as the “micromachining method,” which is used for producing very fine and minute holes. It is also used for milling very hard materials. Holes in surgical needles, oil or gas orifice are drilled using this method. Complex profiles in thin materials like ceramic can be cut using this machine.