Laser Beam Machining: Definition, Parts, Working Principle, Advantages, Application

 

Laser Beam Machining: Definition, Parts, Working Principle, Advantages, Application

Laser Beam Machining (LBM) is a form of machining process in which laser beam is used for the machining of metallic and non-metallic materials. 

In this process, a laser beam of high energy is made to strike on the workpiece, the thermal energy of the laser gets transferred to the surface of the workpiece. The heat so produced at the surface heats, melts and vaporizes the materials from the workpiece. Light amplification by stimulated emission of radiation is called LASER.

Laser Beam Machining Construction or Parts:

Laser Beam Machining consists of following main parts:

1. Power Supply

2. Capacitor

3. Flash Lamps

4. Reflecting Mirror

5. Laser Light Beam

6. Ruby Crystal

7. Lens

8. Workpiece

1. Power Supply:

The electric current or power is supplied to the system. A high voltage power system is used in laser beam machining. It will give initial power to the system after that reaction starts in a laser that will machine the material. There is a high voltage supply so that pulses can be initiated easily.

2. Capacitor:

During the major portion of the cycle, a capacitor bank charges and releases the energy during the flashing process. The capacitor is used for the pulsed mode for charging and discharging.

3. Flash Lamps:

It is the electric arc lamp that is used to produce extremely intense production of white light which is a coherent high-intensity beam.

It is filled with gases that ionize to form great energy that will melt and vaporizes the material of the workpiece.

4. Reflecting Mirror:

Reflecting Mirror are two main types of internal and external. Internal mirrors also called a resonator that is used to generate maintain and amplify the laser beam. It is used to direct the laser beam towards the workpiece.

5. Laser Light Beam:

It is the beam of radiation produced by the laser through the process of optical amplification based on the coherence of light created by the bombarding of active material.

6. Ruby Crystal:

Ruby laser produces a series of coherent pulses which is deep red in color. It achieves by the concept of population inversion. It is a three-level solid-state laser.

7. Lens:

Lenses are used to focus the laser beam onto the workpiece. First laser light will enter into the expanding lens and then into the collimating lens which makes the light rays parallel, and the expanding lens expands the laser beams to the desired size.

8. Workpiece:

The workpiece can be metallic or non-metallic. In this machining process, any material can be machined.

Working Principle:

It works on the principle that when a high energy laser beam strikes the surface of the workpiece. The heat energy contained by the laser beam gets transferred to the surface of the workpiece. This heat energy absorbed by the surface heat melts and vaporizes the material from the workpiece. In this way the machining of material takes place by the use of laser beam.

How is Laser Beam Produced?

In normal condition, the electrons present in atoms lies in the ground state (lowest energy level). When some source of energy is provided to the atoms in the form of radiation, the electrons of the atoms absorbs energy and excited to higher energy level. After a short duration, these electrons automatically jump back to the ground state and while doing so they emit photons of light. This emission of photons by the electrons is called spontaneous emission.

When the electron in the excited state do not jumps back to the ground state by its own. This situation is called meta-stable state. When a photon is fired to the meta- stable state of atoms, this stimulates an electron at excited state, and it jumps back to its ground state giving of two photons (one photon that we fired and other produced by the electron). These two photons stimulate other atoms electrons and produces more photons- a chain reactions start, and number of photons increases. This process is called stimulated emission as we are stimulating other electrons to get photons. Here we are getting two light photons from a single photon i.e., amplifying the light (increasing the light).

Hence the light beams produced by this method is called laser (light amplification by stimulated emission of radiation).

Working:

A high voltage power supply is applied across the flash tube. A capacitor is used to operate the flash tube at pulse mode. As the flash is produced by the flash tube, it emits light photons that contain energy.

These light photons emitted by the flash tube is absorbed by the ruby crystal. The photons absorbed by the atoms of the ruby crystals excite the electrons to the high energy level and population inversion (situation when the number of exited electrons is greater than the ground state electrons) is attained. After short duration, these excited electrons jump back to its ground state and emits a light photon. This emission of photon is called spontaneous emission. The emitted photon stimulates the excited electrons and they start to return to the ground state by emitting two photons. In this way two light photons are produced by utilizing a single photon. Here the amplification (increase) of light takes place by stimulated emission of radiation. Concentration of the light photon increases and it forms a laser beam.

100 % reflecting mirror bounces back the photons into the crystal. Partially reflecting mirror reflects some of the photons back to the crystal and some of it escapes out and forms a highly concentrated laser beam. A lens is used to focus the laser beam to a desired location. When the laser beam strikes the surface of the w/p, the thermal energy of the laser beam is transferred to the surface of the workpiece. this heats, melts, vaporizes and finally removes the material form the workpiece. In this way laser beam machining works.

Process Parameters:

Important physical parameters in LBM are reflectivity and thermal conductivity of the workpiece surface and its specific heat and latent heat of melting and evaporation; the lower these quantities, the more efficient is the process.

The cutting depth t may be expressed as-

t µ 𝐏/𝐯𝐝

Where p = Power input

v = cutting speed

d= laser beam spot diameter

The surface produced by LBM is usually rough and has a heat affected zone.

Laser Beam Machining Advantages:

The following advantages of Laser Beam Machining are:

1. In Laser Beam Machining any material including non-metal also can be machined.

2. Extremely small holes with good accuracy can be machined.

3. The tool wear rate is very low.

4. There is no mechanical force on the work.

5. Soft materials like plastic, rubber can be machined easily.

6. It is a very flexible and easily automated machine.

7. The heat-affected zone is very small.

8. Laser Machining gives a very good surface finish.

9. Heat treated, and magnetic materials can be welded, without losing their properties.

10. The precise location can be ensured on the workpiece.

Laser Beam Machining Disadvantages:

Disadvantages of Laser Beam Machining are:

1. Laser Machining cannot be used to produce a blind hole and also not able to drill too deep holes.

2. The machined holes are not round and straight.

3. The capital and maintenance cost are high.

4. There is a problem with safety hazards.

5. The overall efficiency of the Laser beam machining is low.

6. It is limited to thin sheets.

7. The metal-removing rate is also low.

8. The flash lamp life is short.

9. There is a limited amount of metal removing during the process.

Laser Beam Machining Application:

Uses or Application of Laser Beam Machining are:

1. Laser Machining is used for making very small holes, Welding of non-conductive and refractory material.

2. It is best suited for brittle material with low conductivity and Ceramic, Cloth, and Wood.

3. Laser Machining also used in surgery, micro-drilling operation.

4. Spectroscopic Science and Photography in medical science.

5. It is also used in mass macro machining production.

6. Cutting complex profiles for both thin and hard materials.

7. It is used to make tiny holes. Example: Nipples of the baby feeder.