Thermal addition is an obvious physical field to have a great impact on dislocation mobility by increasing the kinetic energy within the system of atoms and destabilize the bonds to ease deformation. Most research in this area stop at this explanation for the enhanced machinability but our motivation was based on the notion that such atomistic occurrences result from the activation of secondary slip systems that promote ductile mode cutting of brittle materials. The activation of secondary slip systems was theoretically validated in crystal plasticity finite element method (CPFEM) numerical simulations to enhance the machinability of brittle materials with reductions in cutting forces as an indicator of enhanced plasticity [1]. We experimented with this concept to identify the reduction in anisotropy of the single-crystal materials during micro-indentations [2] and the delay in ductile–brittle transition during micro-cutting [3]. The symbolic mitigation of asymmetric micro-cracking features on the machined surface suggests that heat addition could address the great challenge in ultra-precision machining of anisotropic brittle materials. Molecular dynamics (MD) simulations further reiterate the influence of thermal-excitation on the reduction in hardness [4] and improved crack mitigation [5], which allows us to believe in the enhancement of dislocation activity on a larger scale in globalized heating as compared to localized heating of the work material [6]. Our heating method also called for the improvisation of advanced tool holder systems with internal cooling to prevent undesirable heat transfers on the machine tool [7].

Publications

[1] Wang, A. Senthil Kumar, O. Riemer, On the theoretical foundation for the microcutting of calcium fluoride single crystals at elevated temperatures, Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 232 (2018) 1123–1129.

[2] A. Chaudhari, et al., Thermal effect on brittle-ductile transition in CaF2 single crystals, in: 17th International Conference of the European Society for Precision Engineering and Nanotechnology (Euspen), Hannover, Germany, 2017.

[3] Y.J. Lee, et al., Thermally assisted microcutting of calcium fluoride single crystals, in: Simulation and Experiments of Material-Oriented Ultra-Precision Machining, Springer Singapore, 2019: pp. 77–127.

[4] J. Chua, et al., High-temperature nanoindentation size effect in fluorite material, International Journal of Mechanical Sciences, 159 (2019) 459–466.

[5] Y.J. Lee, Thermal expansion control in heat assisted machining of calcium fluoride single crystals, in: 19th International Conference of the European Society for Precision Engineering and Nanotechnology (Euspen), Bilbao, Spain, 2019.

[6] J. Zhan, et al., Investigation of the temperature effect on cutting of calcium fluoride single crystal using molecular dynamics simulation, Procedia CIRP, 117 (2023) 438–443.

[7] A. Chaudhari, et al., Tool design and implementation for thermally assisted ultraprecision diamond turning, in: The 7th International Conference of Asian Society for Precision Engineering and Nanotechnology, Seoul, Korea, 2017.

Acknowledgements

This research is proudly supported by the National University of Singapore (R-265-000-564-133).