Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(vol.44 no.504 January 2003)

Changes in Friction Force of Surface-Coated Steels Owing to Sliding Distance and Influence of the Friction Force on Deep Drawability
-- Assessment of Sheet Formability by Nonlinear Friction Model ts --

Koji HASHIMOTO, Yukihisa KURIYAMA and Koichi ITO

(Received on December 26, 2001)

Highly functional sheet steels such as surface-coated steel sheets sometimes suffer from instabilities such as rupture, particularly under long-distance sliding. This phenomenon can be explained as a surface topology change induced by the softer coated layer rather than the base metal resulting in changes in the friction coefficients. To analyze the evolutional friction phenomena, an original friction test machine was developed and the changes in the friction coefficients during long-distance sliding were measured. In the case of an electrogalvanized steel sheet, the friction coefficient increases rapidly in spite of a decreasing friction coefficient at the initial sliding stage. Cylindrical cup deep-drawing tests in which the tool sets have similar shapes but different diameters were carried out. In these experiments, the formability of each coated steel sheet was affected by both the sliding distance and normal pressure. It was shown that the deep-drawing results could not be explained according to the Coulomb friction law, by a comparison of the measured punch load with the calculated load using simple theory.
Key words: friction/wear test, formability test, deep drawing, ferrous metal, friction, adhesion, surface roughness

Fundamental Study on Incremental Shearing

Masahiro SASADA, Takao KABURAGI and Isamu AOKI

(Received on April 10, 2002)

It is possible to obtain a free-form sheet product by using a turret punch press. The principle of the procedure is so-called incremental shearing which depends on the positioning of the material to be sheared and the use of selected tool fits for the product shape. The characteristics of the incremental shearing are not known, although the method is already used widely in the sheet metal working industry. In order to apply the incremental shearing method to the manufacturing of precise and fine parts, the shearing mechanism should be investigated in detail. We studied the influence of shearing conditions on the product quality through experiments. Furthermore, some defects of incrementally sheared products are improved by the techniques developed.
Key words: shearing, blanking, incremental shearing, sheared surface, product quality

Finite-Element Analysis of Strip Rolling and Regression Formulas of Temperature Distribution
-- Formulation of Temperature Distribution of Workpiece in Hot Rolling 1 --

Eiji WAKAMATSU, Manabu KIUCHI and Jun YANAGIMOTO

(Received on April 19, 2002)

It is important to control the strip temperature during hot rolling, thus the combined use of a heater and cooler during the process is desirable to achieve rolling at optimal temperature. Therefore it is necessary to determine the best combination from the viewpoint of the whole process. Three-dimensional finite element analysis can be carried out for a single stand of rolling, but it is excessively time-consuming to calculate all stands and all combinations. It is convenient if there is a formula to predict the temperature of a strip from the rolling conditions. By carrying out calculations under various conditions for analysis, regression formulas can be constructed for temperature at a specific point, such as the middle on the top surface at the exit of the stand of concern. In this paper, the basic reasoning behind a regression formula is introduced, and then a concrete procedure to construct it and a list of formulas are presented for the first and the last pass of the rough and finish rolling, respectively.
Key words: hot rolling, finite element method, thermal analysis, regression analysis, regression formula

Finite-Element Analysis of Bar and Wire Rolling and Regression Formulas of Temperature Distribution
-- Formulation of Temperature Distribution of Workpiece in Hot Rolling 2 --

Eiji WAKAMATSU, Manabu KIUCHI and Jun YANAGIMOTO

(Received on April 19, 2002)

In hot rolling, the prediction of temperature distribution is very important because this parameter directly influences the flow stress, the microstructure and the deformation behavior of the workpiece. In addition, knowing this parameter permits working of the material at temperatures above Ar3 and precise determination of the reheating temperature. In these respects, it is very important to analyze the temperature of hot rolling. In this paper, a three-dimensional finite-element method of thermal analysis of hot rolling is presented. A new mesh system, which was implemented in the simulation, is described and applied to obtain the temperature distribution in bar and wire rolling. The reliability of the proposed method is confirmed by comparison with results reported by other researchers. Finally, we present the results of numerical simulations as mathematical formulas that permit us to know and calculate the temperature simply from the parameters of the rolling conditions. An equivalent rectangular method is employed to generalize the cross-sectional shapes of workpieces and the roll caliber, and dimensionless parameters are employed to generalize the formulas.
Key words: numerical analysis, finite-element method, wire/bar rolling, thermal analysis, regression analysis

Prevention of Seizure by Nitride Coating in Multi-Stage Deep Drawing of Pure Titanium Sheets

Takuji MURAO, Ken-ichiro MORI,
Yasunori HARADA and Fujio OKUBO

(Received on April 30, 2002)

Seizing in multi-stage deep drawing processes of pure titanium sheets was prevented by nitride coating. The nitride coating was performed by annealing pure titanium sheets in nitrogen atmosphere. The titanium substrate was not in direct contact with the die during the forming due to the existence of the nitride layer. The effects of die materials and lubricants on the occurrence of seizure in multi-stage deep drawing were examined. It was found that the nitride coating is effective in preventing the seizure in multi-stage deep drawing processes of pure titanium sheets. In addition, the surface roughness of the side wall of drawn titanium cups was improved by a deep drawing and ironing process in the final stage of forming.
Key words: sheet metal forming, deep drawing, multi-stage drawing, drawing and ironing, nitride coating, seizure, tribology, surface roughness

Effects of Forming Methods on Deformation Features of Circular Seamless Tubes Reshaped into Square-Shaped Tubes by Hot Roll Forming Mill

Yoshitomi ONODA and Eiji WAKAMATSU

(Received on May 10, 2002)

In order to manufacture a heavy gauge square steel pipe, a hot roll forming process is introduced because of the difficulty in manufacturing a pipe with sharp corners by cold roll forming and with high strength and high productivity by a casting process. In this paper, the effects of forming methods on a cross-sectional shape are discussed based on the results obtained by the rigid-plastic finite element method. The corners of the product become sharper as the total reduction increases, and the depth of the hollow at the side is small when the incremental reduction at each forming roll is high at an early reshaping stage with large bending curvature (D0/(2RiT), RiT:bending radius, D0:initial external diameter of a circular seamless pipe) and when it is low at a late reshaping stage with small bending curvature, for both the two-roll and four-roll type. Under the condition of the same pass schedule, the corners of the product are sharper and the depth of the hollow at the side is smaller in the four-roll type than in the two-roll type.
Key words: hot roll forming, tube forming, seamless pipe, heavy gauge square pipe, rigid-plastic FEM

Investigation of Simple Method to Predict Cross-Sectional Shape of Square Steel Pipes Reshaped by Extroll-Forming

Yoshitomi ONODA and Eiji WAKAMATSU

(Received on May 29, 2002)

Characteristics of the cross-sectional shape of finished square steel pipes (69, 72 and 75mm wide) reshaped from circular pipes (t0/D0q 3.4, 8.4q2, where t0 denotes initial wall thickness and D0 denotes initial outer diameter) by die pushing are investigated to evaluate the reliability of die pushing as a simple method to predict the cross-sectional shape of finished square pipes reshaped by extroll-forming, with reference to the results of rigid-plastic FEM analysis. These are also compared with the results of roll pushing. Deformation behavior of a circular pipe reshaped by die pushing can be treated as a 2-dimensional problem so that the calculation load will be much smaller than the analysis of roll pushing or extroll-forming, which must be treated as a 3-dimensional problem. Owing to uniform deformation of a circular pipe in the longitudinal direction by die pushing, corners of a pipe are sharpened excessively and therefore the rates of increase of wall thickness, inner curvature and outer curvature at the center of the corner become much greater than those based on the experimental results of extroll-forming.
Key words: roll forming, tube forming, extroll-forming, roll pushing, die pushing, rigid-plastic FEM

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