An experimental and numerical study on the influence of not uniform beam energy distribution in laser steel hardening

In this work the influence of the beam not-uniform energy distribution, typical of new sources such as diode lasers, was investigated in the laser hardening of carbon steels. A transient numerical model, based on the Finite Element Method, was implemented in order to analyse the process in these particular conditions, and to provide a tool for the off line design and simulation of the treatment. An experimental set up was prepared to have beam characteristics similar to those that will be offered when high power diode lasers will be available for industrial applications: an elliptical beam with a not uniform energy distribution was obtained operating with an integrator mirror on a CO2 CW laser. The heat treatment was performed with various parallel beam tracks, also by experimenting different degrees of overlapping; the numerical results were compared with the microstructures and the measured micro-hardness obtained on the specimens. The study shows that the FEM simulation can give prediction in good agreement with the experimental observation, considering how the microstructures and the obtainable hardness are influenced by the beam.