Y. Kamada

Bio: Y. Kamada is an academic researcher from University of Tokyo. The author has contributed to research in topics: Regeneration (biology) & Reynolds number. The author has an hindex of 1, co-authored 1 publications receiving 4 citations.

Mechanism to suppress regenerative chatter vibration due to the effect of air-cutting and multiple regeneration during low frequency vibration cutting

Abstract: Recently, the application of low frequency vibration has been attempted in the turning process. The tool is vibrated in the feed direction by numerical control to break up long continuous chips that adversely affect the surface quality and tool wear, etc., by generating a duration of cutting edge leaving workpiece. In order to achieve higher machining efficiency in vibration cutting, however, it is necessary to focus on chatter stability. When chattering occurs, a higher frequency chatter vibration is superimposed on the low-frequency tool vibration caused by the feed motion of the servo drive. However, the chatter amplitude decreases due to system damping, because the cutting force does not act in the air-cutting section of vibration cutting. In addition, tool displacement is regenerated not only before one spindle rotation, but also before two or more rotations in vibration cutting. Therefore, the application of low frequency vibration has an important influence on the chatter stability. The purpose of this study is to reveal the detailed effects of vibration conditions on the stability limit, and identify the vibration conditions that achieve high chatter stability. We consider the effect of the air-cutting and multi-rotation delayed regeneration described above, in which chatter displacement occurring more than two spindle rotations before is regenerated, and analyze regenerative chatter vibration during vibration cutting in the frequency domain. In this study, the phase difference φ of tool motion in vibration cutting is focused as an important vibration condition parameter that affects the stability limit. In the conventional condition ( φ = π ), the air-cutting ratio is limited to a relatively low value, and only the dynamic displacements before one and two spindle revolutions are regenerated. On the other hand, setting φ appropriately under the condition φ ≠ π , the air-cutting ratio is increased. Furthermore, the dynamic displacement is regenerated not only before one and two spindle rotations but also before three or more spindle rotations. These results indicate that proper setting of the phase difference φ is effective in suppressing regenerative chatter vibration due to the effects of both the air-cutting phenomenon and multi-rotation delay. Finally, cutting experiments show that the phase difference φ specified by the analysis was effective in suppressing chatter vibration. In summary, the application of low frequency vibration with an appropriately set phase difference φ is an effective strategy for suppressing chatter vibration without reducing the material removal rate in the turning process. • We performed chatter stability analysis in low frequency vibration cutting. • Chatter stability is affected by vibration cutting parameters. • Phase difference φ and amplitude ratio A / F heavily impact chatter stability. • Using the specific φ depending on A / F is an effective chatter-suppression strategy.

Parametric analysis of interfacial friction factor for liquid film dynamics sheared by turbulent gas flow

Abstract: Water droplet impingement on a low-pressure steam turbine blade causing erosion has been recognized as a crucial issue. It is essential to elucidate a comprehensive droplet detachment mechanism, not only from the trailing edge but also from the liquid film surface. In the present paper, we investigate the influence of interfacial friction factor against liquid film dynamics on a wall sheared by a turbulent gas flow, including the liquid film thickness, liquid film velocity and entrained droplet detached from liquid surface for both pipe flow and plate flow conditions. We conduct the analyses by using a liquid film dynamics model, recently established, considering the three-dimensional destabilized waves and droplet entrainment from the liquid surface. As a result, the film thickness and velocity greatly depends on the interfacial friction factor. Interestingly, the rate of entrained droplet to initial liquid film has a minimum value when the interfacial friction factor equals to the inverse of the liquid film Reynolds number, while the remaining liquid film flow rate becomes maximum.

The Properties of Selected Spinodally Strengthened Copper Alloys Following High-Temperature Neutron Irradiation

Abstract: Three spinodally strengthened copper alloys were irradiated with fast neutrons to 34 displacements per atoms (dpa) at 414{degrees} C, 50 dpa at 411{degrees} C, and 32 dpa at 529{degrees} C in order to assess their suitability for high-temperature service in neutron environments. Density, electrical conductivity, tensile property, and fracture behavior changes were determined with emphasis on the microstructural reasons for the changes observed. This paper reports on these spinodally strengthened alloys which were found to exhibit improved properties following irradiation, and they show merit for use in high-temperature neutron environments, although their low initial conductivity may be a limitation. The results are compared to those of high-purity, unalloyed copper.

Cutting Chatter in Ultrasonic Elliptical Vibration Cutting and Its Influence on Surface Roughness and Tool Wear

Abstract: Ultrasonic elliptical vibration cutting has a wide range of applications in the field of precision cutting of difficult-to-machine metal materials. However, due to its intermittent cutting characteristics and the weak rigidity of the horn, cutting chatter is prone to occur during its cutting process, which has an important impact on cutting surface quality and tool wear. In this paper, the rigid/viscoplastic rod model is used to simulate the horn in the ultrasonic elliptical vibration cutting device, and the influence factors of the amplitude-frequency response of the horn are analyzed. The influence of cutting speed and cutting depth on cutting chatter was studied by ultrasonic elliptical vibration cutting experiment of tungsten heavy alloy, and the influence of cutting chatter on cutting surface morphology and diamond tool wear was studied. The research shows that cutting speed will change the excitation frequency of the horn, and reasonable cutting speed can inhibit the occurrence of cutting chatter and avoid resonance of the horn. The cutting depth will affect the excitation amplitude and amplify the vibration amplitude when chatter or resonance occurs. The experimental results show that in ultrasonic elliptical vibration cutting of heavy tungsten alloy, chatter suppression can significantly improve the quality of the cutting surface and reduce the wear of diamond tools.