Plasma Arc Machining | Laser Beam Machining

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.

01 - PLASMA ARC MACHINING - UNCONVENTIONAL MACHINING PROCSS

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.

01 - LASER BEAM MACHINING - UNCONVENTIONAL MACHINING PROCESS

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.

Rocket Engines | Solid Propellant Rockets | Liquid Propellant Rockets

Jet propulsion

Jet propulsion is based on newton’s second law and third law of motion. Newton’s second law states that the rate of change of momentum in any direction is proportional to the force acting in that direction. Newton’s third law of motion states that for every action there is an equal and opposite reaction. A type of jet engine is explained below.

Rocket engines

A rocket does not depend upon the oxygen in the atmosphere for its operation. It carries all its supply of oxygen in addition to fuel with it.

01 - ROCKET ENGINE - TYPE OF JET PROPULSION.

Principles of working: In rocket engine, a large amount of gases are produced by the combustion of oxidizer and fuel. High pressure gases are created by burning the oxidizer and fuel in the combustion chamber. The gases emerge out of the exit nozzle with a supersonic velocity producing a thrust to propel the rocket.

Solid propellant rockets

In this rocket, the total mass of fuel is stored and burned within the combustion chamber. No separate fuel supply system is provided. It consists of a seamless tube made of steel. The one end of the tube is closed and the open end holds the nozzle. These rockets are classified as the following.

Restricted burning type Rocket: In this type, the propellants are burnt on only end surface and the burning of propellant takes place progressively to the other end. The burning of propellant takes place similar to that of a cigarette.

Unrestricted burning type rocket: In this type, propellant is burnt freely on all surfaces at the same time. Washers provided at the ends to prevent the ends from burning.

Nitrocellulose, ammonium nitrate, ammonium perchlorate are some of the solid propellants used in rockets.

01 - LIQUID PROPELLANT - SOLID PROPELLANT.

Liquid Propellant Rockets

Liquid propellant rockets use liquid propellants. The propellants are stored in separate containers outside the combustion chamber. It consists of

· A fuel tank,

· An oxidizer tank,

· A fuel injection system,

· A combustion chamber and

· An exit nozzle.

The oxidizer and fuel are pumped into the combustion chamber. In the combustion chamber, burning of fuel and oxidizer takes place at high pressure and at high pressure, high temperature gasses are produced. These gases expand through the exit nozzle. In the nozzle, pressure energy is transformed into kinetic energy and the gases are emerging from the nozzle to the atmosphere with a very high velocity. As a result of the increased velocity of gases coming out of the nozzle, a reaction or thrust is produced in the opposite direction. This thrust propels the rocket engine.

Application of rocket engines

· Signaling and fireworks – small solid fuel rockets are used for sending distress signal from ships and signals from the ground army. They are also used for fire work display,

· Long range artillery – rockets are used in long range artillery enemy countries may be attacked by rocket assisted shells.

· Lethal weapon – naval ships and ground forces are equipped with short and long range missiles. Rocket propelled missiles are used in modern fighter aircrafts.

· Satellites – satellites are sent by rockets into outer space.

· Space ships – these are driven out of the earth with the help of rockets.

· Future expectation-rockets may be used to carry passengers from one place to another.

· JATO – jet assisted take off enables interceptor, fighters, bombers, etc. to climb vertically rapidly