Investigation of surface integrity in the laser-assisted turning of AISI 4340 hardened steel

The use of laser-assisted turning (LAT) can improve different aspects of the machinability of high hardness/strength materials. The heat applied in this process reduces the strength of the material and upon a proper selection of laser heat source and machining process parameters, a significant improvement in the machining process can be achieved. This research studies the effect of machining and laser heat source parameters on the surface integrity of the LAT process of AISI 4340 hardened steel with a hardness of 560 HV using Response Surface Methodology (RSM). The effect of machining process parameters (feed rate, depth of cut and cutting speed) and laser power on the surface integrity characteristics of the machined surfaces (white layer thickness, microhardness, surface roughness, and surface chemical composition) are investigated. A detailed finite element simulation of the process has been performed to better understand the physics of the process and to interpret the experimental results. Laser power and feed rate are shown to be the most significant parameters affecting the surface integrity of the machined surfaces. It has been shown that a proper selection of machining and laser heat source parameters makes it possible to minimize the adverse effect of laser heating in the LAT process. This can pave the way for the widespread application of the LAT process by eliminating one of the most important obstacles of this process by controlling the laser heat diffusion into the workpiece.