Laser-assisted machining of hardened steel parts with surface integrity analysis

Machining of hardened steel components has traditionally been the domain of grinding. A laser-assisted machining (LAM) process with a larger material removal rate is developed to replace the currently used hard turning and grinding operations for machining hardened steel shafts. A three-dimensional transient thermal model is developed to predict the temperature field in the hollow shaft of varying thickness undergoing laser-assisted turning. The laser-assist effect on surface quality and subsurface integrity is investigated in terms of surface finish, size control, microhardness, microstructures and residual stresses. LAM produces the parts of a good surface finish of Ra less than 0.3 μm, a more uniform surface hardness distribution and no microstructure change. The thermal expansion effect on the actual depth of cut is experimentally studied to achieve accurate size control in LAM. It is shown that LAM produces about 150 MPa more compressive surface axial residual stresses than hard turning and reduces the variation in hoop stress than those produced by hard turning.