Finite element analysis and experimental validation of high-speed laser surface hardening process

Abstract

In this study, a finite element method is presented with an aim to predict the temperature distribution for optimizing laser surface hardening process on a cylindrical steel solid rod. The proposed quasi-stationary laser beam processing technique utilizing high-speed rotation was employed to obtain a uniform hardened layer along the entire workpiece surface with complete elimination of deleterious inter-pass softening effects in the overlapped regions and melting. The simulated model has been validated with actual experimentation on En-31 steel rod employing a fiber-coupled diode laser and high-speed rotating mini-lathe. Two principal quality-determining factors of laser surface hardened layer, namely, total hardened case depth and hardness distribution, across and along its depth and length of the rod are correlated and compared. The most important output factor—differential hardness—a measure of variation in hardness distribution obtained longitudinally along the processed rod length—was analyzed in terms of its variation with processing parameters such as laser power, linear speed, and rotary axis speed. The simulated thermal history with temperature distribution and thermal contours simulated facilitated in correlating the hardened surface profile with hardness distribution. Indeed, the temperature distribution profiles simulated along the treated layer longitudinally and through thickness, processed with high rotary axis speed and appropriate linear speed, exhibited uniform treated layer with complete elimination of inter-pass tracking softening effects with surface temperature being above critical temperature throughout the processed length. A good agreement could be realized between actual experimental values and that of optimized values using the finite element model.