Page 139 - Module DMV20173

7.0 NON CONVENTIONAL PROCESSES

EXERCISE 7.2

A wire EDM operation is used to cut out die components from 25 mm thick
tool steel plates. However, initial cut give the poor surface finish on the cut
edge. What changes in discharge current and frequency of discharges should
be made to improve the finish?

7.4 LASER BEAM MACHINING

1. Laser beam machining (LBM) uses the light energy from a laser to remove
material by vaporization and ablation.
2. A schematic diagram of LBM is illustrated in Figure 7.5

3. The types of lasers used in LBM are carbon dioxide gas lasers and solid state
lasers. In laser beam machining process, the energy of the coherent light beam
is concentreted not only optically but also in terms of time.
4. The highly focused, high-density energy source melts and evaporates portions of

the workpiece in a controlled manner.
5. The melted material evacuate the surface at a very high velocity.
6. LBM can cut a through and blind holes depending on the requirement.
7. Important physical parameters in LBM are the reflectivity and thermal conductivity

of the workpiece surface and its specific heat and latent heats of melting and
evaporation.
8. More efficient process can be achieved if the parameters mentioned above is
reduced.

9. The cutting depth can be calculated by this formula;

t = CP/vd 8 . 2

where t is the depth, C is a constant for the process, P is the power input, v is the

cutting speed, and d is the laser-spot diameter.
10. LBM is used to perform various types of drilling, slitting, sloting, scribing, and
marking operations. LBM is not considered a mass production process, and it is
generally used on thin stock.

11. Example of workpiece in LBM are ceramic, glass, plastics, rubber, wood and
cloth.

BPLK 171 DMV 20173