Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(Vol.39 No.454 November 1998)

Temperature Simulation Model of Wire Rod and Bar Rolling and Simulation Results

Yukio NOGUCHI, Koshiro AOYAGI, Matsuo ATAKA, Koe NAKAJIMA and Takao KAWANAMI

(Received on October 30, 1997)

We have developed a simulation model for calculating interstand tension, height, width, temperature, load and torque of a rolled material in continuous wire rod and bar rolling. In this paper, we deal with a temperature simulation model and its results. In order to calculate the temperature, the material is converted into one with a circular cross section, and the finite difference equation for radial heat flow through a wire is used. In roll bite, the heat generated by plastic deformation and friction, and the conduction of heat by thermal contact resistance between material and roll are considered using several models. At interstand, heat transfer by radiation is calculated using a theoretical formula, and mean heat transfer coefficients of cooling water for roll and cooling trough are assumed based on the measured values of the material temperature at entries and exits of roll bite and cooling trough. The computed temperatures at wire rod mill showed good agreement with the measured values.
Key words : wire rod and bar rolling, modeling of rolling temperature, FDM

Multiaxial Yield Behavior of Mild Steel in Stress Aging Process

Takenobu TAKEDA, Zhongchun CHEN, Shin-ichi KIKUCHI and Youichi TANIMURA

(Received on November 26, 1997)

Tubular specimens of mild steel are subjected to a torsional prestrain and then aged under reverse loading at 150℃ for 1 hr. The stress-aged steel has the same yield stress for both forward and reverse torsions when it undergoes stress aging at a stress level of 74% of the prestress. By applying a combined loading of axial load, internal pressure and torsion to the prestrained, the stress-reversed and the stress-aged specimens, the changes in yield surface and anisotropy which occur during the stress aging process are examined. In the tension-torsion stress field, the yield surface of the prestrained steel forms a rounded nose in the prestress direction and flattens on the opposite side. This flattened yield surface expands during reverse loading. The yield surface of the stress-aged steel is symmetric with respect to the tensile stress axis. However, the stress-aged steel exhibits somewhat severe anisotropy compared with the stress-reversed (unaged) steel. In order to measure such anisotropic yield behavior, a new test method, i.e., off-axis torsion test by the combined loading, is developed.
Key words : material testing, ferrous metal (Fe-C), deformation-load property, yield surface, torsional prestrain, stress aging, combined stress

Analysis of Surface Properties of Cold-Rolled Stainless Steel Sheet in Soluble Rolling Oil

Fumio FUDANOKI, Jun ARAKI, Shuichi INOUE and Kazuhiro YANAI

(Received on December 10, 1997)

In this work, the surface properties of a cold-rolled stainless steel sheet as a result of the effect of the mother sheet surface and rolling speed in an emulsion-type soluble rolling oil is analyzed. The mother sheet surface influences the transudation of the rolling oil mechanically trapped in the micropits. Therefore the surface of the sheet rolled with emulsion oil cannot easily be made smoother than with neat oil. In rolling with emulsion oil, surface brightness irregularity of the cold-rolled sheet begins to occur with increasing rolling speed, because the emulsion phase is inhomogeneously supplied in the roll bite. Accordingly, the surface smoothness of the sheet rolled with emulsion oil is the same as with neat oil, with control of the rolling speeds based on “the rolling oil transudation model”, which was proposed by the authors.
Key words : cold rolling, stainless steel, soluble rolling oil, micropit, lubrication mechanism

Finite-Element Analysis of Blanking Process

Nobuki YUKAWA, Yoshihiko INUKAI, Yoshinori YOSHIDA, Takashi ISHIKAWA and Takashi JIMMA

(Received on December 11, 1997)

Element size control and the remeshing technique are developed and applied to rigid-plastic finite-element analysis of blanking processes. The shearing behavior of materials before crack initiation is successfully simulated. The simulated results are obtained for various clearances and shapes of the punch and/or die corner. The influences of these parameters on the shape of the deformed plate, and on the strain and stress distribution, especially near the punch and dies edges, are obtained. Furthermore, using the distribution of the tensile part of the mean normal stresses, which indicates the position where crack initiation mostly occurs, the amount of barr is predicted.
Key words : shearing, finite element method, blanking, remeshing, barr, shear droop

Effect of Accumulated Equivalent Plastic Strain on Grain Coarsening Phenomenon in Multistage Hot Deformation Process

Yutaka NEISHI, Masayoshi AKIYAMA and Kouichi KURODA

(Received on December 18, 1997)

Experiments were carried out using a hot deformation simulator to investigate the effect of accumulated equivalent plastic strain on the grain-coarsening phenomenon. Specimens of a typical medium carbon steel, S45C, were tested by double deformation method. It was found that the ratio of accumulated strain depends on interpass time between the first and the second deformation, working temperature. It was also found that the accumulated strain is completely conserved if the working temperature is below 1173K and the interpass time is shorter than 1s. The results were verified using a model bar mill. In a previous paper1）, it was revealed that the grain-coarsening phenomenon is affected by the equivalent plastic strain and working temperature. Consequently, complete prediction of the grain size, after sizing by tandem stands, can be made using the criterion proposed in the previous paper and the results of the present work.
Key words : grain-coarsening phenomenon, S45C, hot-deformation simulator, prediction of grain size, interpass time, accumulated equivalent plastic strain

Experimental Verification of Finite Element Analysis using a Wire-Rope Laying Process

Takuya MURAKAMI, Shinji KURASHIGE, Guilan WANG, Tatsuhiko AIZAWA and Junji KIHARA

(Received on January 12, 1998)

P-type wire rope laying experiments were performed for 1×7 ropes to validate the calculated geometry and residual stress using a three-dimensional FEM analysis developed by us. The inverse ratio of the wire-supply bobbin was parametrically varied to investigate the sensitivity of the laying process on the inverse ratio(y). The geometry and dimensions of the deformed wire could be predicted by the present finite element analysis with sufficient accuracy. When y＝0, the measured residual stress distribution was in quantitative agreement with the calculated value; for y＝1.0, the finite element analysis can qualitatively predict the residual stress pattern after the laying process.
Key words : wire rope forming, elasto-plastic FEM, stress and strain analysis, inverse ratio, X-ray diffraction, residual stress

Deformation-Mode-Dependent Constitutive Modeling of TRIP Steels

Takeshi IWAMOTO, Toshio TSUTA and Yoshihiro TOMITA

(Received on January 12, 1998)

TRIP steel possesses favorable mechanical properties such as high strength, ductility and toughness and is frequently employed as a structural material. In order to realize the expected mechanical properties of TRIP steels during cold-working conditions, prediction and control of the material characteristics during the deformation processes are indispensable. Here, to evaluate characteristics such as the stress-strain relationship and the volume fraction of martensite of the specimen, uniaxial tension and compression tests for SUS304 have been carried out under various environmental temperature conditions. On the basis of the experimental results, the deformation mode dependence of martensitic transformation and deformation behavior of TRIP steels are discussed. Next, a deformation-mode-dependent transformation kinetics model and the corresponding constitutive equations are presented. Finally, the validity of the proposed constitutive equations is examined by a comparison of the predicted stress ― strain and volume fraction of martensite ― plastic strain relations with the experimentally obtained ones.
Key words : constitutive equation, transformation-induced plasticity steels, strain-induced martensitic transformation, deformation mode dependence

Metal Flow Behavior of Wide Flat Bar by Spreading Extrusion ――Study of Spreading Extrusion ProcessⅠ――

Yoshinobu IMAMURA, Norio TAKATSUJI, Kenji MATSUKI, Mitsugu TOKIZAWA, Kazuo MUROTANI and Hiroaki MARUYAMA

(Received on March 5, 1998)

To experimentally examine metal flow behavior in the spreading extrusion process, a round billet is spread by means of a spread ring and extruded through a die opening wider than the internal diameter of the container. In spreading extrusion, the extrusion load is reduced by about 30% in comparison with basic extrusion. However, the metal flow balance in this extrusion worsens, because of the high friction generated at the interface of the billet and spread ring during the filling process. As the flat bar is wide or height of the spread ring is low, the geometry of the plastic deformation zone on the die face changes from an ellipse into at the wide zone at both ends of the die opening. As a result, the metal flow balance markedly worsens, due to the increase of the plastic deformation zone and frictional resistance acting on the spread ring wall.
Key words : extrusion, wide shape, spread ring, metal flow

Copper Powder Compaction by Differential Speed Rolling

Saiji MASAKI, Tetsuya HIROHATA, Shuji MITAMURA and Susumu SHIMA

(Received on March 25, 1998)

When differential speed rolling is applied for powder roll compaction, the stress state in the powder or strip between the rolls may be different from that found in conventional rolling, and this difference affects both rolling load relative density and strip thickness. Differential speed rolling of electrolytic copper powder is conducted under the condition of carefully controlled powder feed rate. Roll speed ratios are changed in the range of 1.00 to 1.33 by choosing combinations of the number of roll revolutions. The rolling load increases on increasing the ratio of powder feed volume to strip speed and is slightly smaller compared with that of conventional rolling. The decrease in the rolling load is about 25% of what specify when roll speed ratio is 1.33. The relative density of the strip is about 15% larger than that of conventional rolling under the same rolling load. The strip thickness increases with an increase in the rolling load for each roll gap, regardless of the roll speed ratio.
Key words : powder metallurgy, differential speed rolling, copper powder, rolling load, relative density, strip thickness

High-Accuracy V-Bending of Stainless Steel and Aluminum Plates

Katsumi KOYAMA, Tetsuya ANZAI, Jun-ichi ENDOH, Tsutomu MIZUNO and Hajime YAMADA

(Received on March 30, 1998)

High-accuracy bending of sheet-metal parts, which have recently been used in many industrial products, is required. In particular, a highly accurate bending angle and longitudinal accuracy of SPCC, stainless steel and aluminum plate is demanded for applications in the panel industry and the construction industry. To obtain longitudinal accuracy, a uniform force controlling method effective for SPCC, SPHC or SECC has been developed. However, this method cannot be applied to stainless steel and aluminum plates because of the differences between their bending force curves from those of SPCC. This paper describes high-accuracy V-bending using a combination of the improved uniform force controlling method and the bending-angle detector. The following conclusions are arrived at. (1) The bending angles of stainless steel and aluminum plates which thickness have dispersions have been observed to range from 89°52' to 90°05' using the bending-angle detector. Therefore, the bending-angle detector is effective for obtaining high-accuracy. (2) At the center bending and offset bending too, the bending angle has been observed to range from 89°45' to 90°10'. Highly accurate bending angle and longitudinal accuracy of stainless steel and aluminum plates have been obtained using a combination of improved uniform force controlling method and the bending-angle detector.
Key words : bending, press-brake, uniform force controlling, bending-angle detector, stainless steel, aluminum plate