Characteristics of force generation on C-, R-, A- and M- planes of single-crystal sapphire during ultra-precision machining

Single-crystal sapphire can be used in various fields in the industry due to its superior material properties, but it has been challenging to fabricate sapphire parts with high accuracy and complexity because of its high hardness and brittleness, which lead to crack generation during the machining process. Ultra-Precision Machining (UPM) has been studied as one of the solutions to overcome this issue as it is able to cut brittle ceramics in ductile mode for small depth of cuts. However, only a few studies have focused on the force generation in UPM of single-crystal sapphire, which has significant impact on ductile mode cutting. This study focused on the characteristics of force response during UPM of single-crystal sapphire considering the average likelihood of plastic deformation based on material crystallographic structure. With a feed rate of 5 mm/min and 1/500 slope, orthogonal plunge cuts were implemented on four different crystal planes in terms of various cutting orientations. The force characteristics during machining were observed in given machining conditions. In the ductile region, it was found that the magnitude of the force response showed isotropic characteristics regardless of cutting orientation by being approximately linearly proportional to the depth of cut. However, the direction of the force showed an anisotropic characteristic that is highly dependent on the average likelihood of slip/twinning activations. The results of this study will contribute to establishing a force prediction model during ultra-precision machining of single-crystal sapphire. (C) 2022 Society of Manufacturing Engineers ( SME). Published by Elsevier Ltd. All rights reserved.