Thermomechanical Optimization of Drill Margin Geometry in Drilling of Ti-6Al-4V: A Coupled FEM-RSM Investigation

Abstract

Drilling of titanium alloys generates extreme temperatures, cutting forces, and torque due to their poor thermal conductivity and strong tool–workpiece interaction. These extreme thermomechanical outputs could shorten drill span, reduce hole quality, and increase costs. The drill margin dimensions control frictional contact between the tool and the hole wall. However, the influence of drill margin on thermo-mechanical responses has been scarcely investigated in titanium drilling. In this study, a thermomechanical finite element model (FEM) was developed to analyze the effects of drill margin width (M_w) and margin height (M_h) on drilling temperature, thrust force, and torque. A face-centered central composite design was employed to evaluate the influence of the margin parameters. Response surface methodology (RSM) was used to develop predictive models of temperature, thrust force, and torque. The developed FEM was validated against the experimental results of Chatterjee et al. (2016) at various rotational speeds and feeds in the ranges of 400-600 rev/min and 30-50 mm/min, respectively. The force results produced an average prediction error of 2.5 %, which indicates the simulation model is sufficiently accurate to predict the drilling outputs. The results revealed that both M_w and M_hsignificantly influence drilling performance by varying the frictional contact between the drill margin and the hole wall. Increasing the margin dimensions increases temperature, thrust force, and torque due to intensified rubbing contact. Response surface analysis unveiled a strong interaction between M_w and M_h. The optimal configuration within the investigated design space was identified at M_w = 9% and M_h = 2%. The findings provide useful insights for optimizing drill margin geometry to improve drilling efficiency in titanium alloy (Ti-6Al-4V) machining.