Investigation on minimum uncut chip thickness and size effect in micro milling of glow discharge polymer (GDP)

Glow discharge polymer (GDP) is used as the ablator material in inertial confinement fusion (ICF) applications. Its machining surface quality and geometric accuracy directly affect its high energy performance. Minimum uncut chip thickness (MUCT) and size effect are the keys to obtain higher surface quality during micro cutting. In this work, a hybrid analytical model of MUCT using cutting forces and effective rake angle based on minimum energy method (Model A), and micro milling experiment are applied to determine the MUCT of GDP. Furthermore, a specific cutting energy-based model (Model B), considering the mechanical properties, strain evolution, and tool geometry, is established to verify model A. Additionally, the material removal mechanism and size effect are also studied. It is found that the MUCT value of GDP determined by model A is between 0.268 and 0.532 μm, and the normalized MUCT value is between 0.148 and 0.295. These results are verified by the specific cutting energy obtained from model B. It is also proved that model B could preliminarily evaluate the MUCT value of GDP without conducting milling experiment. Moreover, below the MUCT threshold, the severe size effect and ploughing effect cause nonlinearly increase of specific cutting energy, and the random variation of cutting force and surface roughness. When the ratio of feed per tooth to cutting edge radius is larger than 0.61, the size effect could be ignored since the cutting mode is shearing.