19 07 18

Page 1

Exercise n. 2 – technological problem Your Company is asked to performed laser cutting of a carbon steel component, using a Nd:YAG laser source with a maximum power of 5.5 kW. The laser source is equipped and it can be used with two different fibers in order to deliver the laser beam. The characteristics of employed laser source are reported in Table 1. . The carbon steel component is characterized by a thickness, t, of 6 mm and the thermal properties of employed material are reported in Table 2. You are the person in charge of this activity and it is asked you to determine the optical configuration of your laser head in order to realize a correct cutting of the component. 1. It is asked to determine the correct collimations lens, considering the fact that the diameter of collimation lens (Dc ) is bigger than the collimated beam (Df ) of 20% (referring to the scheme of figure below). Table 1 Characteristics of employed laser source Symbol Value Unit Laser source - Nd:YAG fiber laser - Maximum power P 5.5 kW Refractive index of cladding ncladd 1.34 - Refractive index of core ncore 1.38 - Fiber core diameter 1 dcore1 50 µm Fiber core diameter 2 dcore2 100 µm Diameter of collimation lens Dc 48 mm Table 2 Thermal properties of carbon steel Symbol Value Unit Density r 7810 kg/m3 Thermal capacity cp 450 J/kg°C Thermal conductivity k 55 W/m K Melting temperature Tm 1500 °C Environment temperature Tair 20 °C Latent heat of fusion Lf 275000 J/kg Latent heat of vaporization Lv 63620000 J/kg K It is asked to mark the correct answer and justify it with a numerical resolution. o fc1=57 mm o fc2=100 mm 2. It is asked to determine the correct optical configuration in terms of employed fiber and focalization lens in order to realize the cutting of the carbon steel component. It is…