Force Modeling in Laser-Assisted Microgrooving Including the Effect of Machine Deflection

Abstract

Laser assisted mechanical micromachining is a process that utilizes highly localized thermal softening of the material by continuous wave laser irradiation applied simultaneously and directly in front of a miniature cutting tool in order to produce micron scale three-dimensional features in difficult-to-machine materials. The hybrid process is characterized by lower cutting forces and deflections, fewer tool failures, and potentially higher material removal rates. The desktop-sized machine used to implement this process has a finite stiffness and deflects under the influence of the cutting forces. The deflections can be of the same order of magnitude as the depth of cut in some cases, thereby having a negative effect on the dimensional accuracy of the micromachined feature. As a result, selection of the laser and cutting parameters that yield the desired reduction in cutting forces and deflection, and consequently an improvement in dimensional accuracy, requires a reliable cutting force model. This paper describes a cutting force model for the laser-assisted microgrooving process. The model accounts for the effect of elastic deflection of the machine X-Y stages on the forces and accuracy of the micromachined feature. The model combines an existing slip-line field based force model with a finite element based thermal model of laser heating and a constitutive material flow stress model to account for thermal softening. Experiments are carried out on H-13 steel (42 HRC (hardness measured on the Rockwell ‘C’ scale)) to validate the force model. The effects of process parameters, such as laser power and cutting speed, on the forces are also analyzed. The model captures the effect of thermal softening and indicates a 66% reduction in the shear flow stress at 35 W laser power. The cutting force and depth of cut prediction errors are less than 20% and 10%, respectively, for most of the cases examined.