LASER BEAM MACHINING(LBM) AND ELECTROCHEMICAL MACHINING PROCESS

LASER BEAM MACHINING(LBM)PROCESS

1. BASIC IDEA:-

Laser beam machining is a non traditional process where machining takes place without tool in contact with work piece.

2. What is laser:-

LASER means light amplified stimulated emission of radiation. It is monochromatic light or single wavelength light which is unidirectional in nature. These waves are focused on a single point by focusing lens and they become highly intense.

3. What is normal light wave and laser light wave?

A normal light waves has multiple wavelength and is multi directional in nature. This can be observed in electric bulb or rays of the sun. Whereas LASER waves monochromatic in nature (all waves have same wavelength). These are non diverging in nature and are said to be one directional. 

4. How is laser wave generated?

For amplifying light to high intensity, the gain medium (space inside the chamber) is to be supplied with energy, this is called PUMPING.

The light bounces to and fro between the two mirrors in the gain medium and each time it gets amplified and finally all the light waves acquire same wavelength. Hence it becomes monochromatic and of high intensity which is used for verity of purposes.


5. WORKING PROCESS:-

fig:-LBM PROCESS

Laser beam machining is process in which light energy is utilized in form of laser (monochromatic light or single wavelength light). This laser is directed on the work piece and material removal takes place by vaporization process. The laser is focused to very small area (since light is monochromatic) and high energy of 100 MW is applied on that area. The light energy is concentrated optically in LBM process.
         

6. Various types of laser are used. Some of them are as under.

Gas laser 

In gas laser coherent light waves are produced when current is induced through gas. This is the first known laser which produced continuous light source in infrared region by conversion of electrical energy to laser light. The various examples of gas laser are helium-neon laser, argon ion laser etc.

 

Excimer laser

It is generally formed when reactive gases like chlorine etc are added to noble gases like xenon, krypton etc. Under proper electric current and pressure we obtain excimer. It is a excited pseudo molecule which has energy and capable of producing laser beam.

Solid state laser

Solid state laser are also called semiconductor laser and it is characterized by doping of crystals with the ions. The pulses are generated in this type of laser and good beam quality is achieved.

7. APPLICATION:-

• Drilling, cladding.
• Cutting material.
• Welding

8. ADVANTAGES:-

• No heat generation problem.
• Very accurate cut/weld/drill.
• Very small diameter operation is possible.

ELECROCHEMICAL MACHINING

Basic idea

The process includes machining by indirect contact between tool and work piece. The material removal takes place by electrochemical process. The process includes one electrode as cathode, work piece as anode and the electrolyte as medium between them.

Cathode (negative charged) is Tool.
Anode (positive charged) is Work piece.
Electrolyte is Acidic (saline) medium.



         

                                  fig:-ECM PROCESS


WORKING:-

When the circuit is complete, the cathode i.e. tool is advanced towards the anode i.e. work piece.
The electrolyte is forced or pressurized from in between of tool (cathode) as shown in figure.
The gap between tool and work piece is kept between 80-800 micrometer.


USE OF ELECTROLYTE:-

The electrolyte used performs fallowing function:-

It acts as lubricant. Carries debries or metal (found between tool and work piece due to chemical reaction). Removes heat from working region. Provides good machinability. Completes circuit for reaction to take place.Material is removed and gets separated from electrolyte as metal hydroxide. As the tool advances towards the work piece the material from the work piece is removed due to reaction and the same mirror image is obtained on the work piece.

ADVANTAGES:-

• Used for extremely hard material.
• Good machinability for intricate shapes.
• Very low heat production.

LIMITATION:-

Limited for electrically conductive material only .