Micro-structure evolution-based force model and surface characteristic studies of Inconel 718 during micro-endmilling

Abstract

An accurate prediction of cutting force is significant, as it plays a critical role on surface quality and tool wear. In micro-endmilling, the machined feature size and feed/tooth are comparable to the material grain size and the edge radius of the endmill. Hence, the effects of scaling issues, material micro-structure and cutting temperature on the machining performance need to be addressed. This article presents a force model for micro-endmilling by incorporating size effect, machining temperature, workpiece spring back effect and micro-structure evolution. The developed force model was validated with experimental results on Inconel 718 and the prediction error was found to be less than 10%. An experimental study to understand the influence of size effect on cutting force, micro-hardness and surface defect during micro-endmilling on Inconel 718 was carried out. Minimum uncut chip thickness was observed adjacent to 0.9 µm. For a feed/tooth less than 0.9 µm, both cutting force and micro-hardness of the endmilled surface shows a nonlinear trend. Higher value of cutting force at feed/tooth less than 0.9 µm was observed due to high strain hardening, and significant plowing effect on the micro-endmilled surfaces.