Numerical evaluation of the reflectivity coefficient in laser surface hardening simulation

This paper reports the results concerning the simulation of a laser surface hardening process of a cylindrical surface. In particular it focuses on the problems related to the definition of the physical parameter values necessary in order to achieve an accurate and reliable simulation. The strict dependency of laser process simulation results on the physical parameters describing the target material is, in fact, a well known matter, especially considering that the values of these parameters change during the process dependently on temperature and time. Moreover in laser surface hardening this problem is even more important because melting of the target material should be avoided, surface roughness plays an important role and, sometimes, the surface is coated with absorbent layers. These factors increase the complexity of the simulations and make the evaluation of the physical parameters more difficult and critical. The results presented in this paper are obtained on AISI420B steel, coated with graphite and treated with a direct diode laser. Considering the above mentioned conditions, a plausible temperature dependent reflectivity coefficient was evaluated and its robustness was investigated. This reflectivity coefficient can be used with a good approximation for the simulation of laser hardening treatments of many carbon steels.