Simulation and optimization of machining parameters in drilling of titanium alloys

The present study attempts to analyse the effect of various drilling parameters such as spindle speed, feed rate and drill bit diameter on performance characteristics such as thrust force, torque and circularity at entry and exit of the holes in drilling of titanium alloy using coated drill bit. A three dimensional machining model based on Lagrangian approach is developed using DEFORM-3D software. The performance characteristics obtained through simulation model is compared with experimental results. The simulation model closely agree with the experimental results as percentage relative error of 4.93, 9.01, 6.04 and 3.0 is observed for thrust, torque circularity at entry and circularity at exit respectively. The experimental data is used to develop valid empirical models to relate performance characteristics with drilling parameters using non-linear regression analysis. The empirical model helps to predict various performance characteristics without resorting to rigorous analysis through the numerical model. The values of various performance characteristics predicted from empirical models are compared with experimental results and the percentage relative error within 10% is observed. Finally, an improved version of latest evolutionary approach known as Harmony Search (HS) algorithm has been proposed to obtain favorable machining conditions through optimization of each performance characteristic. The optimal value of circularity at entry is obtained as 0.985 (approaching towards ideal value of one) when spindle speed, feed rate and drill bit diameter are set at 530.86 (≈531) RPM, 44.8 (≈45) mm/min and 7 mm, respectively. Similarly, optimal value of circularity at exit reaches 0.979 with same spindle speed and drill bit diameter but feed rate of 50 mm/min.