Contrary to the typical application of coatings for cutting tools, we explore the umbrella of surface effects in micro-cutting, which include physical effects by pre-coating work materials to enhance their machinability [1]. We adopted the concept of employing the physical obstruction of the coating on the micro-cutting process with the notion of increased pressurization on the workpiece to promote plasticity of brittle materials. Significant delays in ductile–brittle transitions and reduced subsurface damage layer thickness were achieved through pre-coated brittle materials [2], which was attributed to the resistance to deformation of the coating that induced stresses back into the work material and altering the stress distribution [3]. On one hand, it was postulated that these stresses increased the resultant stress to supersede the critical resolved shear stress and promote plasticity through slip deformation. This was studied with the development of a predictive analytical model for anisotropic ductile–brittle transition under both normal micro-cutting conditions and coating-assisted cutting [4]. On the other hand, our anisotropic characterization methodology also saw cleavage associated fracture features on the machined surfaces being suppressed during coating-assisted cutting, which led to additional assertions that the induced stress sealed the cleavage planes to prolong ductile mode cutting as demonstrated in CPFEM [5]. At present, our understanding follows that practically any type of coating material that has an appropriate strength in its solid state would be able to induce these stresses for ductile mode cutting [6].

Publications

[1] Y.J. Lee and H. Wang, Current understanding of surface effects in microcutting, Materials & Design, 192 (2020) 108688.

[2] Y.J. Lee, et al., Enhancing ductile-mode cutting of calcium fluoride single crystals with solidified coating, International Journal of Precision Engineering and Manufacturing-Green Technology. 7 (2019) 1019–1029.

[3] Y.J. Lee and R.T. Tan, Compression effects of epoxy coating in microcutting of calcium fluoride single crystals, in: 20th International Conference of the European Society for Precision Engineering and Nanotechnology (Euspen), Geneva, CH, 2020.

[4] Y.J. Lee, et al., Beneficial stress of a coating on ductile-mode cutting of single-crystal brittle material, International Journal of Machine Tools and Manufacture, 168 (2021) 103787.

[5] Y.J. Lee and H. Wang, Characterizing crack morphology toward improving ductile mode cutting of calcium fluoride, Ceramics International, 47 (2021) 28543–28556.

[6] Y.J. Lee, Increasing the critical uncut chip thickness with coating-assisted microcutting on magnesium fluoride single-crystal, in: 21st International Conference of the European Society for Precision Engineering and Nanotechnology (Euspen), Copenhagen, DK, 2021.