Plasma arc machining
When a free flowing gas is heated to a very high temperature it becomes partially ionized. This ionized gas is called as plasma. In 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 D.C supply d 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, oxygen are the generally used di-atomic gases. This gas is permitted through the arc. The arc heats up the gas and it gets ionized due to high temperature. This ionized gas flows out of the nozzle in the form of a flame known as 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 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 di-atomic gas. Vast using of the tungsten electrode in the same position leads to the erosion of the electrode so it has to be frequently adjusted. Ware of the nozzle is minimized by cooling with the help of water.
It is used for cutting stainless steels and aluminium alloys. Profile cutting and slitting in hard materials can be done using this method.
Laser beam machining
Laser is an electromagnetic radiation. A beam of 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 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 high intensity light. The ruby crystal is stimulated and it 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 micro machining method. Which is used for producing very fine and minute holes. It is also used to machine 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.