Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(vol.43 no.498 July 2002)
Microstructual Prediction of Ferrite-Pearlitic Microalloyed Steel in Controlled Forging
-- Process Modeling in Controlled Forging 1 --
Hiroaki YOSHIDA, Sachihiro ISOGAWA, Yoshinori KANEKO,
Yasuhiro YOGO and Takashi ISHIKAWA
(Received on August 20, 2001)
Controlled forging is greatly effective in the weight reduction of automobile components as mentioned in the previous report, because of very fine microstructure. It's fine microstructure can be obtained by the control of forging temperature, strain and cooling rate. Thus, the optimization of the forging process is very important. Process modeling using finite element method (FEM) is very effective for the optimization of forging process, which has been widely used in controlled rolling. In the process modeling of controlled forging, austenite microstructure prediction and ferrite-pearlite microstructure prediction transformed from recrystallized and work-hardened austenite must be discussed respectively. Moreover, it is also necessary to predict yield strength, tensile strength, fatigue strength and ductility for the purpose of weight reduction. However, there are few process modeling systems which satisfy these requirements. In this attempted study, the construction of a process model of controlled forging which can predict the above-mentioned microstructure have been attempted. In the prediction of the austenite microstructure, Sellers' model showed a good result. In the prediction of the ferrite-pearlite microstructure transformed from recrystallized austenite, good results were obtained by using an effective austenite interfacial area. On the other hand, concerning the ferrite-pearlite microstructure transformed from work-hardened austenite, it was confirmed to be predicted precisely by the use of 'effective retained strain' which is newly suggested.
Key words : forging, material property, thermomechanical heat treatment, microalloyed steel, process modeling
Effects of Blade Tip Shape on Thread Dross Occurrence
in Paperboard Die Cutting
Shigeru NAGASAWA, Yasushi FUKUZAWA, Takashi YAMAGUCHI,
Mitsuhiro MURAYAMA, Daishiro YAMAGUCHI and Isamu KATAYAMA
(Received on September 14, 2001)
This study deals with the fundamental characteristics of coated paperboard die cutting. The cross-sectional profile of sheared paperboard and the occurrence of thread dross were investigated experimentally in terms of blade tip thickness. The features of the cutting line force, such as the variation of initial yielding point, the saturated shearing resistance and the final breaking point, were discussed and compared with the blade tip thickness. The correlation between room humidity and thread dross occurrence was shown. It was clarified that the occurrence probability of thread dross distributes continuously in a certain region from the lower bound through the upper bound of blade tip thickness. By observing the length, height and width of the thread dross, the mechanical conditions for generating the thread dross were derived. The results were as follows:1) the thread dross height to blade tip thickness ratio is the primary factor contributing to the occurrence of thread dross. 2) In a room with humidity ranging from 44.0 to 56.4%, the maximum cutting resistance and the width of thread dross are almost not varied. However, the percentage occurrence of thread dross depends on the room humidity. 3) By observing the response curve between the blade stroke and the cutting line force, the occurrence of thread dross could be inferred.
Key words : shearing, die cutting, humidity, tip thickness, paperboard, thread dross, wood/paper
Changes of Shape and Stress Distribution during Free-Bulging
in Axi-Symmetrically Blow-Formed Superplastic Sheet
Masahide KOHZU, Nobuyuki SUZUKI and Kenji HIGASHI
(Received on September 19, 2001)
Changes of the shape and stress distribution during free-bulging in axi-symmetrically blow-formed superplastic sheet are analyzed. Usually, the shape has been assumed to be a spherical surface while the stress distribution has been assumed to be a function satisfying only boundary conditions without any theoretical bases, because of nonlinear constitutive equations of superplasticity. An assumed stress distribution function gives a peculiar pressure to radius position of the workpiece. If the pressure distribution is uniform, it is proved that the function represents the true distribution of stress. Such a function is proposed in this paper and is also verified by the analysis without these surplus assumptions. With progress of forming, all areas except in the neighborhood of the periphery approach the equi-biaxial tensile stress state and the entire shape approaches that of a semi-sphere.
Key words : sheet metal forming, numerical analysis, free-bulging, axi-symmetric blow forming, superplasticity, formed shape, stress distribution
Shaping of Helical Gear by Cold Extrusion
Yozo SAWAKI and Hajime YOSHIDA
(Received on October 19, 2001)
The conditions for shaping a helical gear by cold extrusion are examined experimentally. The specifications of the helical gear examined is as follows:module m=1.5, number of teeth Z=18, pressure angle alpha=20, tooth depth h=2.25m, helix angle beta=20. The tested materials are low-carbon steel, S15C, S45C and alloy steel, SCM415. The inner diameter of workpiece is varied in order to examine the effect of reduction in area. It was found that a well-shaped helical gear can be produced, and that the shaping condition is closely related to the punch pressure. Thus a stepped mandrel, which expands the inner diameter of the specimen, is effective because of the increasing in the punch pressure. The required pressure of the punch and the stepped mandrel for shaping is far below the strength of the punch and mandrel materials.
Key words : extrusion, helical gear, reduction in area, formability index, mean pressure, complete tooth,carbon steel
Importance of Appropriate Modeling of the Bauschinger Effect
in Springback Analysis
Takeshi UEMORI, Tatsuo OKADA and Fusahito YOSHIDA
(Received on October 25, 2001)
FE analysis of springback after hat-shaped draw-bending for various die radii were conducted using the following four types of material models:a) the isotropic hardening model (IH model);b) the linear kinematic hardening model (LK model);c) the IH{Armstrong-Frederick-type nonlinear kinematic hardening model (IH{NLK(AF)model);and d) the present authors' original model which is characterized by the accurate description of the transient Bauschinger effect (Yoshida-Uemori model). Experiments were also performed on high-strength steel sheets to enable comparison of the analytical predictions with the experimental results. It was found in the present work that proper modeling of the Bauschinger effect is of vital importance as well as the prestrain dependency of Young's modulus for accurate prediction of springback. Among these material models, the Yoshida-Uemori model gave the most accurate predictions of springback.
Key words : springback, hat-bending, constitutive model, elasto-plastic analysis, finite element
Prediction of Free Surface Profiles of Sheet-Formed
Products Using a Fractal Approach
Masahito MATSUI, Yasushi KUROSAKI,
Mir Behdad KHAMESEE and Ken-ichi MURAI
(Received on November 9, 2001)
Free surface profiles of aluminum sheets deformed under three kinds of loading tests (uniaxial and equi-biaxial tensions and shrink flanging) are examined by employing the power spectrum fractal analysis. A method for simulating the surface roughening phenomenon caused by plastic deformation is presented, and its validity is confirmed. The strain dependence of the fractal parameters required for the simulation can be unifiably expressed with the equivalent strain, irrespective of the strain (or stress) ratio. From this, a CAE system for predicting the surface profiles of any press-formed products is proposed and shown to be valid.
Key words : sheet metal forming, measurement, free surface, surface roughening, fractal analysis, self-affinity, power spectrum, fractal dimension, surface prediction, computer simulation
Production of Aluminum Ultrathin-Walled Cylinder
by the DI Method Using a Floating Die
Nobuhiro KOGA and Haruhiko UENO
(Received on November 13, 2001)
With the currently commercially available laser printers with copying functions, users themselves must perform maintenance work and replace units; thus, the structure must be designed keeping this point in mind. Therefore, these laser printers have simple structures with a seamless belt. However, to date, metal seamless belts are manufactured by the electroforming method; thus, the cost is high, and waste generated during electroforming must be properly processed, which increases the environmental burden. In this study, we experimentally studied the feasibility of manufacturing the above-mentioned seamless belts by the drawing and ironing (DI) method, which is a plastic processing method widely used for manufacturing soft drink cans. The results of our study indicated that the DI method is applicable to the manufacture of sensitizing belts and fixing belts; it has been clarified that the manufacture of long ultrathin-walled cylinders of 50 micro meter thickness with an effective length of 380 mm is possible.
Key words : sheet metal forming, ironing, deep drawing, accuracy, DI, seamless belt, floating die
Production of Shaped Tubes with Various Curvatures Using
Extrusion Process through Inclined Die Aperture
Makoto NIKAWACMitsunobu SHIRAISHI, Yoshitaka MIYAJIMA
Hiroyuki HORIBE and Yoshihiro GOTO
(Received on December 11, 2001)
We have recently developed a flexible extrusion process, in which the billet is extruded through a die aperture tilted at an adequate angle from the central axis of the container, for manufacturing various profiles curved along their length. In this paper, an application of the extrusion process to rectangular tubes with/without flanges is attempted and the curvature of the extruded tube is assessed. It is clarified that the curvature of the extruded tube increases with an increase in the inclination angle of the die independently of the cross-sectional shape of the die, the dimension of the die aperture and the extrusion ratio. The results confirm that the extrusion process is useful for producing shaped tubes with various curvatures.
Key words : extrusion, production system, plasticine, metal flow control, profile, bending, inclined die