Numerical analysis of the influence of sequential cuts during micro-milling of wrought and LPBF Ti6Al4V alloys

Abstract

This study investigates the distribution of stresses, plastic strains, and temperatures in the machined surface and subsurface during micro-milling of wrought and Laser Powder Bed Fusion (LPBF) Ti6Al4V alloys considering the effects of sequential cuts using modeling approach. A series of micro-milling tests and numerical simulations were performed at two spindle rotational speeds (12000, 24000 rpm), two feeds per tooth (2, 4 µm/tooth), and a constant depth of cut (100 µm) under dry conditions. A 3D finite element model was developed, and simulation of micro-milling process was performed using Coupled Eulerian Lagrangian (CEL) approach. The experimentally measured machining forces and surface residual stresses were used to validate the developed 3D micro-milling model. It was shown that the model can reasonably simulate the machining forces (2.51–14.53 % error) and surface residual stresses (0.7–29.3 % error) for both wrought and LPBF Ti6Al4V alloys under different cutting conditions. To investigate the effects of intermittent cutting (i.e. sequential cuts) during micro-milling, the numerical model was developed to simulate three sequential cuts by considering the process of entry and exit of each tool tooth as one cut. In addition, unloading and cooling of the work material were also simulated to compare the state of the material during and after the process. The numerical results showed that sequential cuts resulted in increased stresses and temperature after the first cut and affected the material state during and after the micro-milling process. Machining-induced surface and subsurface residual stresses increased with the number of cuts due to accumulated stresses and strains, leading to greater plastic deformation and mechanical loads. Furthermore, LPBF Ti6Al4V alloy led to higher stresses and temperatures during micro-milling than the wrought material. This was attributed to the specific microstructure and higher mechanical properties of the LPBF Ti6Al4V alloy.