Thermal Analysis of Laser Hardening for Different Moving Patterns

Transient thermal field in laser surface hardening treatment of medium carbon steel was analyzed by employing both three-dimensional analytical model and finite element model. In finite element model the laser beam was considered as a moving plane heat flux to establish the temperature rise distribution in the work-piece, while in analytical model laser beam was considered as an internal heat source. The numerical results were compared with the analytical results. In laser heat treatment of steel some methods are used to produce a wider and nearly uniform average irradiance profile. It may be achieved by rotating the beam optically, thereby producing an overlapping spiral track, or by dithering the beam (rocking the lens or mirror) perpendicular to the track, thus producing a zigzag pattern. In this paper, these models are used to cover the two mentioned patterns for laser hardening with Gaussian distribution, and to compare the results with the hardened region of bimodal and uniform distribution. The results show that dithering beam and rotating beam are useful for obtaining a uniform heat intensity distribution, if the parameters of dithering beam or rotating beam are properly chosen with the aid of these models. The diffusion process being a time dependent phenomenon, an interaction time of 15 ms was taken as a basis to determine the hardened region.