Papers by Author: Kazuki Hiro

Abstract: The unsteady supersonic jet and the shock wave injected by the small volume shock tube are experimentally studied in this paper. The experimental was performed by the background oriented schlieren method. The main parameters for the jet are the pressure ratio by the high pressure chamber/ a back pressure 10.9-53.0 and the length of high pressure chamber/diameter ratio 1 and 10. The velocity of the shock wave and supersonic jet were estimated by using the principle of the background oriented schlieren method. The results showed that the influence of the length of the high pressure chamber on the velocity of the jet.

Abstract: Phase diagrams including absolute negative pressure regions of thermotropic liquid crystals give useful information on science and technology. A phase diagram was depicted for ca. 40mg of a thermotropic liquid crystal in a pressure vs. temperature (P-T) plane by the Berthelot method using a metal tube. N-I phase transitions occurred even under-10MPa, and a polymorphism of the crystalline phase was observed.

Abstract: In the turning of a shaft with a step of specified corner R, it is important whether the corner radiuses of the turning insert is the same as the specified corner R or lower than it. A turning tool with a large corner radius cannot adapt to cutting a shaft with a step of specified corner R. In this study, the surface roughness, cutting force, and tool wear were experimentally investigated in order to clarify the cutting performance of the turning insert with a three-arcs-shaped finishing edge. The machined surface of the insert with a three-arcs-shaped finishing edge was better than that of the normal insert. The wear progress of the insert with an arc-shaped finishing edge was slightly slower than that of the normal insert. The cutting force of the insert with an arc-shaped finishing edge was almost the same as that of the normal insert.

Abstract: Various methods of surface modification technology are available for yielding high function characteristics such as wear-resistance, lower or higher friction coefficient, corrosion-resistance and thermal-resistance on the surface of the material. Generally, the coating of a hard material like ceramic on the surface of a material is a popular surface modification technology. The physical vapor deposition (PVD) method, which is one of the coating technologies, is widely used because it can be coated at a lower treatment temperature of 470K – 870K. In cutting, e.g. turning, milling, drilling and tapping, coated cemented carbide tools, which have good fracture toughness and wear resistance, seem to be effective tool materials. In this case, the titanium based films (e.g. TiN, Ti(C,N), (Ti,Al)N) are generally used as the coating film. However, the tantalum based films (e.g. TaN, TaC) are not applied as the coating film for cutting tools because the melting point of TaC is higher than that of TiC. Moreover, it is unclear whether TaN coating film can be used as a coating film of WC-Co cemented carbide cutting tools. In this study, to clarify the effectiveness of tantalum (TaN) coating film, we measured the thickness, hardness and scratch strength (critical load measured by scratch tester) of TaN coating film formed on the surface of the substrate which was a cemented carbide ISO K10 by the magnetron sputter ion plating process. The hardened steel ASTM D2 (JIS SKD11) was turned with the TaN and the (Ti,Al)N coated cemented carbide tools. The tool wear of the TaN coated cemented carbide tool was experimentally investigated and compared with that of the (Ti,Al)N coated tool. The following results were obtained: (1) Droplets on the surface of the TaN coating film, which has the K10 substrate, were negligible. (2) The micro-hardness of TaN coating film 2510HV was higher than that of TiN coating film 2090HV, and there was little difference in hardness between the TaN 2510HV and (Ti,Al)N 2710HV. (3) The critical scratch load of TaN coating film over 130N was higher than that of TiN coating film 68N or (Ti,Al)N coating film 73N. (4) In cutting the hardened steel using TaN and (Ti,Al)N coated tools, the wear progress of the TaN coated carbide tool was almost equivalent to that of the (Ti,Al)N coated carbide tool. The above results clarify that the TaN coating film, which is a new type of coating film, has both high hardness and good adhesive strength, and can be used as a coating film of WC-Co cemented carbide cutting tools.