Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(vol.43 no.493 February 2002)
Strip Width Control Using Strip Tension of Hot Strip Finishing Mill
Kazuyoshi KIMURA and Kouichi SAKAGAMI
(Received on March 9, 2001)
Strip width control using strip tension of a hot strip finishing mill, the so-called tension AWC (automatic width control), has been studied. The tension AWC manipulates the looper torque between forward interstands in response to the same interstand strip width deviation measured by a width meter. This tension AWC has large width control capability and a quick response of the feedback control without dead time. Furthermore, the tension AWC is equipped with a looper multivariable control in order to compensate for the tension and the looper angle fluctuations. The looper multivariable control consists of the minor feedback controls of tension and looper angular velocity and the feedforward control of the velocity disturbances estimated by a disturbance observer. The effects of the control are verified using computer simulations and experiments.
Key words : hot rolling, hot strip finishing mill, automatic width control, tension AWC, multivariable control, observer
Shear Band Bifurcation and Post-Bifurcation Analyses of FCC
Polycrystals under Plane Strain Compression
-- Ductile Fracture of FCC Crystals by Shear Band Formation 3 --
Yoshihiro KAMADA, Shokichi KANNO, Akinori SATO,
Jun NITTA, Koichi ITO and Taketoshi SAGAWA
(Received on March 15, 2001)
A numerical analysis, based on crystal plasticity, of the formation and the propagation of localized shear bands in FCC polycrystals is studied in order to establish the fundamental basis for predicting the forming limit of sheet metals. A deformation analysis is performed using the finite element polycrystal model. The critical state of shear band formation and the direction of the shear band of each element are predicted using the bifurcation theory. For the post-bifurcation analysis, a hypothetical 13th slip system is introduced into the element that satisfies the bifurcation condition. The results of the numerical analysis show that shear bands weaken the formation of deformation texture. Moreover, there are two different types of shear band formation. One is that shear bands propagate across grain boundaries, and the other is that they do not, which agrees qualitatively with the experimental results.
Key words : sheet metal forming, numerical analysis, crystal plasticity, shear band, deformation texture
Development of a Helical Coil Forming Machine for Nuclear Fusion Devices
Naozumi HATADA, Keii UENO, Makoto TATEMURA,
Shinobu WATANABE,
Keiichi NAKAMURA, Michio TAKAHASHI,
Shinsaku IMAGAWA and Osamu MOTOJIMA
(Received on March 15, 2001)
A superconducting helical coil is a main component of the fusion devices. Because the helical coil is wound on the donut-shaped winding core, the shapes of the superconductors have bending curvature and a torsion angle. The aim of this study is to develop a high-precision helical coil winding machine whose forming head can bend and twist the conductor and which can wind the conductor continuously into a helical coil. The forming head is made compact in order to be easier to move. The position and direction of the forming head must be controlled to avoid an irregular deformation of the conductor during forming. Finite element analysis was carried out to determine the suitable position and direction of the forming head. By modifying forming conditions based on differences between desired and measured shapes during the winding, the shape errors of the conductors were reduced to within 15% of the maximum shape of in-plane and out-of-plane bending curvature and torsion angle of the coil. This machine was used for winding the helical coil of the Large Helical Device (LHD) that is a main experimental facility of the National Institute for Fusion Science (NIFS).
Key words : bending, torsion, finite element method, springback, helical coil, superconductor, LHD
Effect of Die Properties on Bending Characteristics of Push-Through Bending
-- Bending of Aluminum Extrusion Section 3 --
Hidemitsu HAMANO, Hisashi NISHIMURA,
Yasuhisa HAGIWARA and Yuichi NAGAI
(Received on December 18, 2000)
In our previous study, we reduced the slide mark on material surfaces by optimizing the lubricant for push-through bending. In this study, we investigate contact conditions of material deformation in dies upon push-through bending. We attempt to improve slide mark by investigating the die material, surface treatment of the die and roller die set. The following was clarified. Bending deformation and flange wrinkling occur in fixed die upon push-through bending. Sliding between the material and the die begins from inside the fixed die. The cemented carbide die is excellent for obtaining ideal surface roughness of the slide mark. Hard metal dies tend to have excellent sliding characteristics. However, although cold die steel (SKD11) and high-speed steel (SKH51) are of almost equal hardness, their qualities exist harmoniously between bending member and die material without the above-mentioned relationship. When we treat the die surface, the roughness may increase. When we use the above-mentioned dies, roughness of slide mark also increases. The die surface roughnesses in Diamond Like Carbon (DLC) processing and Toyota Diffusion Coating Process (TD) are minimal, and the surfaces of their bening members are also smooth. However, their efficiency is nearly equal to that of cemented carbide die without surface teatment. The use of a roller die is effective for the improvement of the slide mark. However, roller die is in contact locally with the bending member and the contact pressure is higher than that with normal die. Thus, roller die is inferior to normal die in its curvature, deformation and flange wrinkling. The structure of the roller die is most suitable for a part to use for the appearance that is small curvature.
Key words : push-through bending, tube forming, lightening, aluminum extrusion section, square tube, die material, surface treatment, roller die, friction, Al-Mg-Si, forming property
Effect of Forming Conditions on Bending Characteristics in Push-Through Bending
-- Bending of Aluminum Extrusion Section 4 --
Hidemitsu HAMANO, Hisashi NISHIMURA and Yasuhisa HAGIWARA
(Received on March 30, 2001)
In this study, we initially investigated the clearance between the die and the extrusion section in order to clarify the influence of processing conditions on cross-sectional deformation and slide marks in push-through bending. Next, we determined that the value of the die bending angle relative to the stroke of the gyro die affects the cross-sectional deformation. For the slide mark improvement, the effect of delaying the die bending angle operation was also investigated as the large cross-section. Finally, we examined the effect of the distance between the fixed die and the gyro die. As a result, the following was revealed. As the clearance between the die and the extrusion section increases with an identical gyro die stroke, the curvature decreases. Longitudinal-section dimension change rate, wrinkling and roughness of the slide mark increase when the die bending angle is not correct. By delaying the die bending angle operation to the transfer start of the gyro die, it was proven that the cross-sectional deformation and slide marks were reduced when the distance between the dies was large. Although the maximum load of the bending axis decreases as the distance between the dies increases, the cross-sectional deformation increases, therefore an optimum value exists.
Key words : push-through bending, tube forming, lightening, aluminum extrusion section, square tube, forming condition, friction, Al-Mg-Si
Separate Measurements of Frictional Coefficients on Die Profile
and Flange Part in Cylindrical Cup-Drawing
Minoru YAMASHITA, Manabu GOTOH and Jun SUZUKI
(Received on April 5, 2001)
We attempt to measure the frictional coefficient on the die profile separately from that on the flange part in cylindrical cup-drawing. Both the die and the blank holder are divided into two parts along a radial line and the repulsive forces acting on these parts are measured during the process. Frictional coefficients on the die profile and the flange part are evaluated separately using the newly derived theoretical formulae which use the measured repulsive forces. Three kinds of sheet materials whose thicknesses are 0.5 and 1.0mm are tested. Three kinds of lubricants are tested, i.e., ¬graphite in tallow', ¬molybdenum grease' and an oil lubricant. Two die profile radii, 1.0 and 4.0mm, are tested, the former of which is severe for the tested sheet thickness. The frictional coefficient on the die profile is found to be higher than that on the flange region. ¬Graphite in tallow' shows the lowest frictional coefficient. Friction on the die profile is found to be greater for the smaller profile radius. Typically, the frictional coefficient is about 0.3 on the die radius of 4mm, whereas it is about 0.1 or less on the flange. It is as high as 0.7 when a titanium sheet of 1mm thickness is deep-drawn using the die radius of 1mm.
Key words : frictional coefficient, cup-drawing, split die, split blank holder, separate measurement
Development of a Method of Prediction
of the Workability Limit in Cold Upsetting
Yutaka NEISHI, Satoru WATANABE, Yoshifumi HARUHATA,
Takashi KUBOKI and Kouichi KURODA
(Received on May 7, 2001)
An investigation into the behaviour of cracking on the surface in cold upsetting of typical cold-forged steels of S45C and SCM435 was carried out with a crank press. The dominant factors of the occurrence criterion regarding the surface cracking are both axial strain and circumferential strain, and it seems that the criterion may be expressed by the Vickers hardness of the mother material before cold working. In order to confirm this, further experiments were carried out using S25C, SCr420 and boron steel after several heat treatments. As a result, it was found that the criterion can be expressed as a function of the Vickers hardness, axial strain and circumferential strain, and that the criterion is applicable for a wide range of cold-forged steels. A prediction of the workability limit in cold forging was made using the criterion and strain path calculated by finite element method (FEM), and its validity was checked experimentally using the forging test.
Key words : cold upsetting, workability limit, FEM, S45C, SCM435, Vickers hardness, axial strain, circumferential strain
Coining Bend of Sheet Metal
Hideo OGAWA
(Received on May 9, 2001)
V-bends of sheet metal are classified, according to the number of contact points of the sheet with the bending die, into air bends, bottoming bends and coining bends. The former has 3 contact points with the bending die at the punch top and die shoulders, and there have been many experimental and analytical research works reported on it. The latter two are in contact at a greater number of points. To clarify the bending characteristics, it is necessary to fully understand the stress state in the bent part. However, at the bottoming bend and coining bend, the stress state in the bent part becomes complex, and by the conventional experimental method, it is very difficult to full understand the stress state in the bent part. In this study, elastic-plastic FEM simulation was employed in order to understand the stress state of the bent part. The boundary between bottoming bend and coining bend was clarified and the characteristics of bending load and spring-back, the adequate dimensions of the bending die, and the distributions of the contacting force acting on the surface of the bending die were clarified.
Key words : bending, die bending, air bend, bottoming bend, coining bend, forming property, deformation-load property, accuracy, spring-back, FEM bending simulation
Longitudinal Buckle in Temper Rolling of Double Reduced Ultrathin Strips
-- Development of Dieless Bending Process for Precision-Bent Tube 2 --
Hideo KIJIMA and Masanori KITAHAMA
(Received on June 4, 2001)
It is known that longitudinal buckles appear in temper rolling of double reduced ultrathin strips with large- diameter work rolls. This phenomenon has not been thoroughly experimented on nor discussed in comparison with cross buckles. Also, the mechanism of the phenomenon has not been clearly explained thus far. In this paper, the effect of several rolling conditions on the buckling phenomenon is investigated in laboratory rolling. Results show that roll roughness predominantly affects the phenomenon. The buckling form does not change with delivery tension, and the buckling appears more clearly depending on the delivery angle. It is hypothesized that compressive stress in the width direction, due to constraints in the roll bite, affects the longitudinal buckling phenomenon. The difference between longitudinal and cross buckles as functions of mother strips and rolling condition is clarified. The two types of buckle must be treated as different phenomena, and the methods of preventing buckling in operations differ from each other.
Key words : strip rolling, temper rolling, experimental analysis, model simulation, flatness, buckling, undulation, longitudinal buckle, cross buckle