LASER BEAM MACHINING PROCESS-
What is Laser Beam Machining?
First of all what is meant by a LASER?
LASER is abbreviated as Light Amplification for Stimulated Emission of Radiation.
The above figure illustrates the principle of laser beam machining process. This machining method mainly comprises ruby laser tube, a pair of mirrors, an amplifying source, a flash tube, a cooling system, a lens and the main setup is incorporated in an enclosure (with high reflective inside surface). Depending upon the application, the lasers employed can be solid or gaseous type. The solid type provides shorter duration of laser beam while the gaseous type provides continuous laser beam and are best suited for cutting and welding operations.
When a light (i.e., optical energy) is projected on a laser tube by a flash lamp, the atoms get excited and absorb the radiation of incoming light energy. This causes to and fro motion of light in between the reflecting mirrors. Since partial reflecting mirror does not reflect the total light back at each travel that comes from a laser tube. Thus, a lens incorporated (in between work piece and partial reflecting mirror) converges the coherent stream of monochromatic light and focuses it to a particular point on the work piece surface. Therefore, the material gets melted and vapourised at the point where the converged laser beam of high intensity falls on work piece. The process continues to obtain the desired shape of the work piece.
Since the process is accomplished by melting and vapourising the work piece, this process is also known as “Thermal cutting process”.
Mechanism of Machining Rate in Laser Beam Machining Process –
In an Laser Beam Machining the mechanism of machining involves the removal of material by melting and evaporation processes. It uses an intense and unidirectional laser beam for accomplishing these processes. In certain materials, the mechanism for material removing is purely by evaporation process.
Drilling process by using Laser Beam Machining technique involves few uncertainties. They are:
1. Irregular shape of the hole.
2. Tapered hole.
3. Recast structure in heat affected zone.
In this process, for every 10 mm depth of drill there will be a taper of 0.5 mm. In order to minimize the taper and obtain high accuracy the component is rotated as the hole is drilled. The material is placed within a tolerance of 0.2 mm of focal point to obtain better surface finish. High accuracy (about 0.1 mm) in profile cutting can be obtained by using numerical control or a photoelectric tracer unit. However, for drilling in thicker materials. the focal point is moved down the hole.
The important characteristics of Laser Beam Machining process–
1. All the materials can be machined except Aluminum, copper and their alloys.
2. Maximum Metal Removal Rate ( Material Removal Rate ) for Laser Beam Machining technique is 5 mm^3/min.
3. High aspect ratio (hole depth/diameter of hole) holes (up to 250 pm) can be easily drilled.
4. Tapered holes can also be drilled using this technique.
5. The rays of a laser beam are perfectly parallel and monochromatic.
6. Laser Beam Machining technique minimizes the fatigue strength of the components.
7. It is capable of producing very high power density (about W/mm^2) with the use of powerful focused laser.
8. Specific power consumed by this process is 1000 W/mm^3/min.
9. The process is carried out in normal atmospheric conditions.
10. The dimensional accuracy of the technique is + 0.025 mm.
Advantages of LaserBeam Machining –
1. Machining Of any material (i.e., including its structural and material properties) can be performed easily.
2. In this process, there is no physical contact between the tool and work piece, which reduces the large forces.
3. Tool wear does not occur in this process.
4. Heat affected zone around the machined part is very small.
5. Machining of holes and cuts can be performed with greater accuracy.
6. Welding of dissimilar metals can be performed effectively.
Disadvantages of Laser Beam Machining –
1. Capital investment is very high.
2. Experienced and skilled operators are required.
3. Rate of production is low.
4. Applicable to thin cross sectional materials.
5. Metal removal rate is very slow.
6. Machining of heat conductive and reflective materials is not efficient.
Applications of Laser Beam Machining –
1. Drilling small holes in hard metals such as tungsten and ceramics.
2. Trimming of sheet metal, plastic parts and carbon resistors.
3. Machining of complicated profiles (or) geometry on thin and hard metals.
4. For dynamic balancing of rotating components.
5. Engraving patterns on thin films.
This is all about Laser Beam Machining.