Development of Slip/fracture Activation Model Based on Force Modeling of Single-Crystal Sapphire During Ultra-Precision Machining
Single crystalline sapphire (α-Al2O3) can be used in engineering applications under harsh operating conditions thanks to its superior mechanical, thermal, and chemical properties. It is manufactured with different crystal orientations depending on applications. For example, M-plane of sapphire is mostly used in the window of supersonic aircraft, while A-plane of sapphire is applicable to make high-temperature superconductors. C-plane of sapphire is mostly used in light-emitting diodes (LEDs), while R-plane of sapphire can be used in microwave devices. However, despite these beneficial properties, processing sapphire is challenging because of its high hardness and brittleness which can easily cause crack initiation and propagation during processing. In order to resolve this problem, ultra-precision machining (UPM) has been used because it can process the material at a nanometric scale where the sapphire behaves in a ductile manner. Understanding the removal mechanism of single-crystal sapphire during UPM is very important in order to establish proper machining strategy and improve throughputs. However, the mechanics during UPM of single-crystal sapphire has not been clearly understood yet. In the previous study, the authors modified the slip/fracture activation model by reflecting the resultant force signal to explain the removal behavior of single-crystal sapphire during orthogonal ultra-precision plunge cutting in terms of different cutting directions. But the exact stress distribution was not considered, and prediction from the model showed discrepancies compared to experimental results. This research extended the previous study of the removal behavior mechanism of single-crystal sapphire during UPM by developing a slip/fracture activation model with modeling cutting force. An analytical model describing the relationship between cutting force and machining inputs has been established with considering tool edge radius effect in order to consider stress distribution during processing. Plunge cutting experiments have been conducted on C-, R-, A-, M- planes of single-crystal sapphire using a polycrystalline diamond tool, and the experimental results were compared to the predictive force model for validation. The plastic deformation/fracture cleavage parameters which indicate the activation likelihood of slip/fracture systems during UPM have been newly calculated by correlating the stress distribution to critical resolved shear stress/critical stress intensity factor. Interactions between these two parameters and their effect on machinability were also studied. Through this study, the mechanism of removal behavior on single-crystal sapphire during UPM has been explained with more detail and accuracy. The developed model would help establishing a machining strategy for UPM of single-crystal sapphire practically, and also can be applied to other brittle ceramics such as zirconia and silicon.
Development of Slip/fracture Activation Model Based on Force Modeling of Single-Crystal Sapphire During Ultra-Precision Machining
Category
Poster Presentation
Description
Session: 16-01-01 National Science Foundation Posters - On Demand
ASME Paper Number: IMECE2020-25306
Session Start Time: ,
Presenting Author: Suk Bum Kwon
Presenting Author Bio: Suk Bum Kwon is a Ph.D. candidate in the Department of Mechanical Engineering, University of Wisconsin-Madison, Wisconsin, United States. He received his B.S. in 2013, and M.S. in 2015 in Mechanical Engineering from Yonsei University, Korea. His research interests include modeling material removal behavior during the ultra-precision machining of ceramics.
Authors: Suk Bum Kwon University of Wisconsin-Madison
Sangkee Min University of Wisconsin-Madison