Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(vol.44 no.508 May 2003)

Material Model That Considers Material Property during Unloading
and Numerical Method Using This Model
-Numerical Prediction of Springback Behavior of a Stamped Metal Sheet 2-

Hideo TSUTAMORI, Noritoshi IWATA and Naomori SUZUKI

(Received on June 13, 2002)

In this study, the springback behavior of a sheet bent into a hat shape has been investigated in order to establish a prediction system for all the geometrical defects in formed sheet products. The most notable feature of this study is that the nonlinear property of the sheet material during unloading is taken into consideration. The material model to express its characteristic behaviors (i.e., the strain-dependent pseudoelastic modulus and the Bauschinger effect around the stress reversal point) is proposed. Results of the present calculation are compared with the experimental ones. It is confirmed that the proposed method can precisely predict the springbacked shape.
Key words: sheet metal forming, springback behavior, strain-dependent elastic modulus, finite element, hat bending, Bauschinger effect

Development of Forming Allowance Test for Hydroforming
-A Research of Forming Allowance for Hydroforming 1-

Masaaki MIZUMURA and Yukihisa KURIYAMA

(Received on July 4, 2002)

Hydroforming of an expanded to a rectangular cross section was investigated by an experiment and finite element analysis. In this research, a simple loading path was selected. After loading of initial internal pressure, axial feeding was loaded under holding pressure, and finally internal pressure was increased until burst occurred. We expressed the hydroforming range with only two parameters, holding pressure pH and final axial stroke ¢®F, in this loading path. Namely, in the map expressed by pH and ¢®F, the hydroforming range was defined as the range surrounded by four forming limit lines, burst limit, limit for the corner radius, limit for the wrinkle which occurs at a forming site and limit for buckling at tube ends. The burst limit indicates the holding pressure when burst occurs during axial loading, and then the hydroforming allowance of a tube could be evaluated by comparison of hydroforming ranges obtained by this method.
Key words: tube forming, hydrostatic forming, hydroforming, formability test, forming property, forming limit, finite element method

Theoretical Analysis of Three-Point Bending
with Flattening of Tube

Masaaki MIZUMURA, Yukihisa KURIYAMA, Hiroyuki MIMURA and Hisashi NAOI

(Received on July 4, 2002)

Three-point bending behavior of a tube is calculated by the energy method. This calculation includes not only flattening by the bending moment but also flattening by pressing of the punch at a loading point. The calculated results agree with the results obtained by the three-point bending test. In particular, the maximum bending load can be estimated accurately by this calculation method. The optimum size of the tube under the same cross section area was determined by this calculation method. The maximum bending load increases with increasing diameter, but it is smaller in the case of extremely large diameter because of flattening. This optimum size of the tube is not influenced by the cross section area but by the span of bending.
Key words: tube forming, die bending, bend test, energy method, deformation-load property

Measurement of Friction in Cold Upsetting with Mist Lubrication

Ryo MATSUMOTO and Kozo OSAKADA

(Received on July 29, 2002)

Frictional behavior under the semi-dry condition is measured with the ring compression test. A small quantity of mist lubricant is sprayed onto the cemented tungsten carbide (WC) tool surfaces polished to mirror surfaces, and the pure aluminum specimens are compressed. It is found that spraying a small quantity of lubricant (0.5g/m2) is effective in reducing the friction in comparison with that for compression without lubrication. The roughness of workpieces after compression increases as the quantity of the lubricant increases and becomes Ra¡á0.20¡Ý1.0 *********** m which is of the same order as the lubricant film thickness. The mist lubrication leaves very small dots of lubricant particles on the tool surface; the lubrication mechanism of mist lubricant is discussed.
Key words: friction, upsetting, forging, MQL (minimal quantity lubricants), semi-dry condition, ring compression test

Metal Flow Behavior to Fill Grooved Die by Rotary Forging

Shinsaku KATAYAMA, Masakazu KAKIUCHI,Tooru KAWABE and Tomoyuki WADA

(Received on August 23, 2002)

Metal flow behavior in a rotary forging process, particularly deformation in the lower part of a workpiece, has been studied experimentally by using two types of lower grooved dies. By observing the metal flow to the lower grooved dies, it was confirmed that the axial metal flow vector increased as the feed of upper die per revolution was increased, and the radial and circumferential metal flow vector shifted to the axial direction as the feed of upper die per revolution was increased. The filling rate to the grooved dies increased as the feed of upper die per revolution was increased, and the filling rate was equal to that of conventional forging in the feed range 1.0 to 1.5mm¡¦rev.¡Ý1. The circumferential metal flow caused a deviation of form; however, a decrease in the deviation rate of 90% could be realized by increasing the feed from 0.19 to 1.88mm¡¦rev.¡Ý1. The metal flow vector shifted to the radial, circumferential and axial directions as the feed of upper die per revolution varied; therefore, a three-dimensional model is required to design a rotary forging process.
Key words: rotary forging, experimental formability test, three¡¾dimensional deformation property, process design

Possibility of Nosing of Bamboo

Kimiyoshi KITAZAWA, Masahiro TAKAHAMA and Hisashi OGAWA

(Received on August 8, 2002)

Bamboo is considered to be a sustainable resource material substitute for wood, because it grows rapidly and can be harvested in three to four years. Although a forming technique for flatting out a split bamboo has been developed from the viewpoint of bamboo utilization, tube forming techniques, such as nosing and reducing, have not been applied to bamboo materials as natural tubular resources. Here we report the possibility of the nosing of bamboo (Madake, Phyllostachys bambusoides Sieb. et Zucc.). Water-saturated bamboo specimens are irradiated with microwaves and then are axially compressed using nosing dies, followed by cooling to set their form. The deformation behavior and nosing limits are investigated experimentally. It is found that nosing limits are governed by the occurrence of splits in the epidermis;these splits grow into cracks, which propagate to the pith cavity and finally lead to the rupture of the bamboo culm wall. When the nosing ratio reaches about 0.15, the split occurs in the epidermis. The occurrence of the split is slightly affected by the ratio of the wall thickness to the diameter of the bamboo culm and the apex angle of nosing dies. Experimental results suggest that both split initiation and crack growth are attributed to the mechanism of shear band formation. Furthermore, it is elucidated that this nosing process enables us to engineer tubular parts of bamboo culms.
Key words: tube forming, nosing, bamboo, formability, crack, shear band



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