Experimental validation of cutting forces modeling in micromilling of Inconel 718 considering material heterogeneity and wear-induced tool edge rounding

Abstract

The process of chip formation in micromilling is fundamentally different from traditional machining in macro scale, because of the size effect. The workpiece cannot always be treated as homogeneous, since the small dimensions of the cutting-edge radius of a micromill can be in the same order of magnitude as the microstructure of the machined material. Microtools become rounded and rapidly lose their cutting capacity as a consequence of the high wear rates encountered in micromilling. In the present work, a numerical simulation of micromilling of Inconel 718 was performed, considering the heterogeneity of the workpiece material (homogeneous and heterogeneous assumptions) and the wear-induced increase in the cutting-edge radius of the microtool (edge radius 1 μm or 5 μm). Machining experiments were conducted to validate the simulation. The experiments consisted in fabricating microslots on a sample of Inconel 718 using a 400 μm diameter WC micromill coated with AlTiN. The cutting forces obtained from the numerical model were compared to those obtained from the experiments. The results showed a small variation between the experimental and numerical forces varying from 0.5 N to 1.0 N and from 0.2 N to 1.4 N, for experimental and numerical, respectively. The wear of the microtool, simulated by the larger edge radius, led to an increase in experimental forces, as expected. The simulated cutting forces, however, increased in 700 %. Finally, it was concluded that lower values of fz (0.5 μm and 1.0 μm) could not properly form chips on the simulations and resulted in plowing marks on the experiments, indicating that higher values (fz = 2.5 μm and 4.0 μm) might be above the minimum uncut chip thickness and are more adequate for the micromilling of Inconel 718.