著者

鈴本 雄也 梶川 翔平 久保木 孝

出版者

公益社団法人 日本材料学会

雑誌

材料 (ISSN:05145163)

巻号頁・発行日

vol.70, no.12, pp.912-917, 2021-12-15 (Released:2021-12-20)

参考文献数

10

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Wood materials are attracting attention as an alternative material to plastics for solving environmental problems, such as sea microplastic. An effective wood processing method should be developed for producing products with various shapes, which leads to an effective use of the wood. This paper proposed extrusion of the wood powder mixed with a natural binder composed of sucrose and citric acid, which effectively forms products with same cross-sectional shape in the extruding direction. Circular tube was extruded in this experiment. It was important to solidify the wood powder inside an extrusion die for molding the tube without cracks and fracture. Therefore, influence of the extrusion die length, the punch speed and the heating temperature, which concern solidification with cooling, were investigated for improving the dimensional accuracy and the mechanical property of the tube. At first, the fracture of the molded product was prevented by setting an appropriate die length. High punch speed caused the tube expansion due to insufficient cooling before extruding, while low punch speed caused the fracture due to long time heating. Density and strength of the molded product increased with the decrease in the temperature, although the cracks easily occurred on the tube surface under the low temperature of 140°C. The tube surface state became smooth by setting the molding temperature to 160 or 180°C. From the above results, the circular tube, which has good dimensional accuracy and mechanical property, was molded by controlling the extruding condition.

著者

山根 康嗣 下田 一宗 黒田 浩一 梶川 翔平 久保木 孝

出版者

一般社団法人 日本塑性加工学会

雑誌

塑性と加工 (ISSN:00381586)

巻号頁・発行日

vol.62, no.720, pp.1-7, 2021 (Released:2021-01-25)

参考文献数

25

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This paper discusses the effect of inclusions on internal fracture in skew rolling. The prediction of internal fractures is crucial given that internal fractures cause loss of product strength and are difficult to detect. Our previous report, published in 2019, proposed a new ductile fracture criterion that considers the effect of shear stress on void coalescence in a cylindrical coordinate system. This paper covers the following three points: (1) the evaluation of the hot workability of materials with different inclusions in tensile testing, (2) the relationship between the hot workability and the damage value determined using the proposed criterion, and (3) the effect of inclusions on void evolution in skew rolling. Given that the critical damage value decreased with decreasing hot workability, internal fractures are more likely to occur in a material that contains numerous large inclusions. The experimental results led to the hypotheses that the plastic strain nucleates the voids originating from inclusions and that shear stress allows the voids to coalesce. This study has demonstrated that decreasing the diameter and number density of inclusions is effective toward suppressing internal fractures.

著者

梶川 翔平 荒木 聖人 渡辺 雅人 崩岡 久敏 土屋 昭則 久保木 孝

出版者

一般社団法人 日本塑性加工学会

雑誌

塑性と加工 (ISSN:00381586)

巻号頁・発行日

vol.64, no.750, pp.123-128, 2023 (Released:2023-07-25)

参考文献数

15

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The small diameter bending of thin-walled copper tubes which are used for heat exchanger is desired to reduce the size and weight of products. In this study, a series of experiments were conducted to investigate appropriate tool shapes, such as that of a mandrel, for preventing wrinkling, cracking and flattening in rotary draw bending. A C1220 tube with a diameter of 7 mm and a thickness of 0.21 mm was used in the experiments. The bending radius was twice the tube diameter. Plug and ball mandrels were used. The effects of the mandrel position, the mandrel shape, and the clearance between the tube and the mandrel were investigated. As a result, moving the mandrel position forward prevented wrinkling and flattening, but moving the mandrel position excessively caused cracking. The mandrel position at which the wrinkle and crack occurred varied depending on the mandrel shape and clearance. By optimizing the tool shape, wrinkling and cracking were prevented, and flatness was reduced to less than 15% for the plug mandrel and 5% for the ball mandrel.

著者

張 世良 川口 光 久保木 孝 赤坂 勇 寺下 雄三 秋山 雅義 梶川 翔平

出版者

一般社団法人 日本塑性加工学会

雑誌

塑性と加工 (ISSN:00381586)

巻号頁・発行日

vol.63, no.743, pp.174-179, 2022 (Released:2022-12-25)

参考文献数

9

被引用文献数

2

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In the present paper, we describe a tube drawing method with diameter expansion for the effectively formation of thin-walled tubes. The proposed method makes the tube thickness easier to reduce than the conventional method, because the tube wall stretches biaxially in the axial and hoop directions. The effects of the plug half-angle on the forming limit, drawing load, thickness reduction, the precision of the inner diameter, and the strength of the formed tube were investigated by a series of experiments and finite element method (FEM) analysis. As a result, the forming limit was the highest at a plug half-angle α of 36˚, and then the maximum thickness reduction ratio γ max of 32 % was obtained by increasing the expansion ratio. In addition, the thickness reduction ratio increased with the plug half-angle owing to the increase in drawing load. On the other hand, the dimensional precision of the tube inner diameter deteriorated with the increase in plug half-angle because of an overshoot of the tube wall, indicating a gap between the tube wall and the plug. The effect of the plug half-angle on the strength was small, while elongation changed with the plug half-angle. The above results suggest that the plug half-angle should be selected appropriately to obtain the target dimension and mechanical properties.

著者

久保木 孝夫

出版者

中古文学会

雑誌

中古文学 (ISSN:02874636)

巻号頁・発行日

vol.59, pp.19-27, 1997-05-26 (Released:2019-05-18)

著者

柴田 隆浩 金 英俊 小山 純一 久保木 孝 村田 眞

出版者

一般社団法人 日本塑性加工学会

雑誌

塑性と加工 (ISSN:00381586)

巻号頁・発行日

vol.53, no.612, pp.64-68, 2012 (Released:2012-01-25)

参考文献数

8

被引用文献数

1

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Recently, the adjustment of working conditions in a manufacturing process is indispensable for realizing manufacturing accuracy in the V bending of a sheet metal. This adjustment is called "Trial Processing", and is a factor for lowing productivity. Therefore, "Trial Processing Free", a method that can obtain accuracy within tolerance but without the adjustment, is required. In the V bending of a sheet metal, there are two types of bending process, i.e., (i) air bending and (ii) bottom bending, using two types of punch control, i.e., (a) stroke control and (b) force control. In this research, a series of analysis and experiments were carried out to clarify that (ii) bottom bending with (b) force control is most appropriate for achieving Trial Processing Free. It was also established that bottom bending at an appropriately controlled force can absorb the effect of uncontrollable factors such as the dispersion of thickness and material properties of sheet metals and bend sheets within a certain tolerance, because the bending angle is stable even in a very wide range of bending forces. This bending method with force control was called the "FCSS (Force Control to Sweet Spot) method" and the advantage of this new process was verified experimentally.

著者

グダラズィ モハマド 久保木 孝 村田 眞

出版者

一般社団法人日本機械学会

雑誌

年次大会講演論文集 : JSME annual meeting

巻号頁・発行日

vol.2005, no.1, pp.619-620, 2005-09-18

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In order to minimize the space of bent tubular parts, a bending technology with small bending radii is requested. Tube shear bending is a suitable technology to realize a considerable small bending radius, which is very difficult to be manufactured with common cold-bending methods. It can be applied as an effective means when space limitation is a main design factor. Utilizing the shear bending process, production of compact and unified elbow tubular parts is feasible. In this paper, the procedure of tube shear bending has been introduced. Also, an elasto-plastic 3D simulation analysis for shear bending process of circular tubes was undertaken. As the result, the deformation behavior of tube as well as the effect of pushing force have been clarified.