This paper describes the difficult machinability of nickel titanium alloy (NiTi alloy) and its mechanism. As a result of examining the difficult cutting machinability via a turning experiment, NiTi alloy cutting showed larger cutting force, higher cutting temperature, and severe tool wear with plastic deformation of the tool compared to Ti-6Al-4V. In addition, the discharged chips were tangled with the jaw chuck and the cutting tool. As a result of investigating the cause of these difficult machining properties by orthogonal cutting, it was found that the progression of severe flank wear is affected by the elastic recovery due to the super elasticity of the material. The verification of the results according to the shear plane theory suggest that the large deformation resistance of the material is the cause of the increase in cutting temperature. Furthermore, because the cutting temperature exceeds the shape memory transformation temperature, the generated chips are shape memory processed. It was also found that because the generated chips are super elastic, chips are not easily broken and they are lengthened, and are easily entangled with a cutting tool and a jaw chuck.

Background and Objectives: Although there have been research on bone cutting, there have been few research on bone grinding. This study reports the measurement results of the experimental system that simulated partial laminectomy in microscopic spine surgery. The purpose of this study was to examine the fluid lubrication and cooling in bone grinding, histological characteristics of workpieces, and differences in grinding between manual and milling machines. Materials and Methods: Thiel-fixed human iliac bones were used as workpieces. A neurosurgical microdrill was used as a drill system. The workpieces were fixed to a 4-component piezo-electric dynamometer and fixtures, which was used to measure the triaxial power during bone grinding. Grinding tasks were performed by manual activity and a small milling machine with or without water. Results: In bone grinding with 4-mm diameter diamond burs and water, reduction in the number of sudden increases in grinding resistance and cooling effect of over 100 °C were confirmed. Conclusion: Manual grinding may enable the control of the grinding speed and cutting depth while giving top priority to uniform torque on the work piece applied by tools. Observing the drill tip using a triaxial dynamometer in the quantification of surgery may provide useful data for the development of safety mechanisms to prevent a sudden deviation of the drill tip.

This study describes a new surface treatment method that involves immersing sintered cutting tools into a high-pressure, high-temperature processing liquid. Cutting experiments were performed, and the results show that oil-immersion treatment helps reduce tool wear. However, this treatment limits the applications of treated carbide tools, e.g., they become unsuitable for heavy-cutting conditions. After the cutting test, surface analyses of the treated carbide tools were performed using FT-IR, SEM, EPMA, and XPS to verify the effect of oil-immersion treatment on tool-wear reduction. FT-IR analysis showed that, following oilimmersion treatment, trace quantities of the coolant remained on the tool surface, which could be readily removed by ultrasonic cleaning. Despite the removal of the processing liquid, the tool subjected to oil immersion exhibited less wear than the non-treated tool. SEM and EPMA examinations revealed that oilimmersion treatment reduced the amount of cobalt on the tool surface, forming sulfur deposits. EPMA analysis indicated that less cobalt binder was found on the surface after oil-immersion treatment, suggesting that the reduction in the amount of cobalt caused tungsten carbide particles to be exposed.