Papers by Author: Masahiro Fujita

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Authors: Kazumasa Shiramoto, Junki Shimizu, Akiyoshi Kobayashi, Masahiro Fujita
Abstract: A burr is most commonly created after machining operations, such as drilling. Drilling burrs, for example, are common when drilling almost any material. When burrs are broken during the operation of a machine including the parts with the created burrs, the broken piece is in fear of disturbing normal operation or damaging the parts of the machine, so that the sufficient deburring is requested because it can affect equipment performance, reliability, and durability. Several deburring method have been developed up to date. In the present report, we proposed a deburring method by means of applying underwater shock wave. The method is as follows: after all entrance of holes is closed with seal tape, the equipment is submerged, so that all passages for running fluid are filled with air. The explosive is set under water near the entrance of the main hole. As soon as the explosive is detonated, the underwater shock wave generated at the detonation point arrives at the entrance of the hole and breaks through the tape. The water flows into the hole with a high speed. The burr is broken by water hummer action of high speed. In the present investigation, the experiments of deburring are performed under some setting conditions of explosive. It is found by experimental results, that the burr is sufficiently removed with the newly proposed method. When the shock pressure is sufficiently high at the entrance of hole, the burr is broken surface is smooth as polished one. When the shock pressure is not sufficiently high, the broken surface of the burr is notched.
Authors: Kazumasa Shiramoto, Takumi Watanabe, Akihito Mizuno, Hirofumi Iyama, Masahiro Fujita
Abstract: t is well known as an important merit of the explosive forming process that the delicate figure of the die surface is precisely transferred onto the specimen of a thin metal plate, because the plate is strongly pressed against the die by the very high pressure of underwater shock wave. However, we cannot find any examples of work pieces making the best use of the merit in literatures until now. We tried to form explosively a thin copper plate into shapes of a palm and a back of human hand, as a work piece making the best use of the merit. The palm has many small delicate lines such as fingerprints and the back has interesting figures such as loose skin at the joints of fingers and the borders of fingernails. The object of the present investigation is to make work pieces just like to a real hand. In this investigation, the following process is adopted in order to perform successfully explosive forming ; real hand plaster concave model convex model of Duplicone (material for dental impression) die of Ren Cast (a kind of epoxy resin) explosive forming. Annealed copper plates of 0.3 mm thick were used in the experiments. Since the extension limit of the plate is not so large, the plate is apt to be broken. If the plate is broken, the die is modified not to break the plate. Though the die made of epoxy resin is too hard to be modified, the plaster model can be easily modified with a cutter knife or a chisel. The modified die is obtained through model of Duplicone made by using the modified plaster model. After a few times of repeating modification, the breakage of plate was scarcely produced. On the work piece of palm, a lot of small lines including finger prints clearly appeared and the work piece of the back showed the shape just like to real human hand.
Authors: Kazuyuki Hokamoto, Yasuhiro Ujimoto, Shunsuke Tanaka, Masahiro Fujita
Authors: Seiichiro Ii, Akio Kira, Ryuichi Tomoshige, Masahiro Fujita
Abstract: In the research center for advances in impact engineering established in Sojo university, advanced materials have been synthesized by using shock wave and their microstructure has been investigated. An extremely high shock pressure and a dynamic hot compaction technique were developed, and the synthesis of the advanced materials and composites was succeeded. Transmission electron microscopy observations revealed unique microstructures of such materials obtained by our original advanced technique.
Authors: Kazuyuki Hokamoto, Krishnamorthy Raghukandan, J.S. Lee, Masahiro Fujita, Ryuichi Tomoshige
Authors: Kazumasa Shiramoto, Akiyoshi Kobayashi, Kazuto Takamiya, Masahiro Fujita
Abstract: When a few branched holes are made in order to cross a main hole at right angle, burrs are produced on the sidewall of the main hole at end of each branched hole. The principle of the process is as follows. After the specimen of which all holes are closed by using sealing tape is submerged, explosive set at the position a little apart from the entrance of the main hole is detonated. As soon as the generated underwater shock wave is arrived at the entrance of the main hole, the sealing tape is broken and the water stream with very high velocity flows into the main hole. The deburring is performed by the action of the water stream with very high velocity. The deburring is sufficiently succeeded in most case. When the main hole is closed, however, the deburring could not be succeeded at the branched hole very near closed position. In order to improve the insufficiency of the process, we designed new equipment in order that underwater shock wave may be concentrated at the entrance of main hole and the water stream with very high velocity, which is caused by the shock wave, may flow along sidewall on which burr is generated. In the present report, we propose the new method and give full account of the experimental results for deburring obtained by using the equipment.
Authors: Masatoshi Nishi, Hiroko Sakaguchi, Hirofumi Iyama, Li Qun Ruan, Masahiro Fujita
Abstract: This study has investigated the plastic forming of magnesium alloys plate. It is not easy to perform the cold-worked with the usual plastic forming method although magnesium alloys have the advantages in terms of strength-to-weight ratio. Therefore, explosive forming method which is one of the plastic forming methods with a specific forming mechanism has been applied. At first, numerical simulations have been conducted to clarify the optimal combination conditions, and then we have verified practical effectiveness of this proposed method by using experimental study.
Authors: Akio Kira, Kazuyuki Hokamoto, Yasuhiro Ujimoto, Shoichiro Kai, Masahiro Fujita
Abstract: A new method has been developed to generate an extremely high impulsive pressure by using a metal jet that is discharged when a metal collides with another metal. The high pressure is used to synthesize a new material. When a metal plate was accelerated by the detonation of an explosive, it collides with the concentric circle of the conic surface of a conical concave metal block metal jets are discharged from all parts on the concentric circle. The metal jets fly toward the center while converging and collide with each other at the central axis. Because those collide at high-speed pressure becomes extremely high. The flight direction of the converged metal jet changes downward. The metal jet collides with the bottom of the block. A large hole is formed inside the bottom. The formation process of the hole was examined by the observation of the section of the block. A specimen powder that was rubbed to the conic surface is discharged with the metal jet and become the high pressure. The specimen powder is synthesized to a different material. The synthesized material is held inside the formed hole. The existence of cBN was confirmed by the X-ray diffraction of the synthesized material, in the case that BN was used as the specimen powder. Similarly, the existence of diamond was confirmed in the case of graphite powder.
Authors: Kazumasa Shiramoto, Akihisa Mori, Kazuyuki Hokamoto, Masahiro Fujita
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