Modelling and experimental analysis of exit burr height and studies on size effect during micro endmilling on Inconel 718

Micro endmilling is considered as a preferred precision micromachining technique to produce complex 3D micro features due to the high material removal rate (MRR) and flexibility. In micromachining, feed/tooth is comparable to tool edge radius and material grain size. The scaling issues, material microstructure, flow stress and cutting temperature has a significant influence on the cutting mechanism and machined surface quality. This work proposes a mathematical model to predict the exit burr height during micro end milling by considering size effect, material microstructure, oblique cutting principle, cutting temperature, chip formation and flow stress. The model is based on the continuity principle and burr formation geometry. The proposed exit burr height model was validated by conducting micro endmilling experiments on Inconel 718. It was found that the exit burr height model based on the Johnson–Mehl–Avrami–Kolmogorov (JMAK) grain evolution model gives a good matching with experimental results and the proposed model could predict the exit burr height with a maximum percentage error of 6.4%. Size effect in exit burr height was observed. The exit burr height was observed to be higher at feed/tooth (f/t) much below cutting edge radius due to high ploughing on the workpiece material. The exit burr height at f/t above edge radius increases with f/t similar to conventional milling. The minimum exit burr height was observed in the ploughing to shearing transition region. The proposed model can be utilized for the optimization of machining parameters to control and minimize the exit burr size.