Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(vol.43 no.496 May 2002)
Influence of Predeformation on the Workability Limit in Cold Upsetting
Yutaka NEISHI, Satoru WATANABE, Yoshifumi HARUHATA,
Takashi KUBOKI and Kouichi KURODA
(Received on May 10, 2001)
An experimental investigation was carried out using a cold compression test to clarify the influence of predeformation on the workability limit in cold upsetting using a typical cold-forged steel, S45C. The predeformation process selected was cold drawing. In order to apply various amounts of strain to test pieces, the reduction of area by drawing was changed. The strain paths of both axial and circumferential strain in the cold working process were calculated by finite element method (FEM). As a result, it was found that the workability limit was improved with the addition of the predeformation. The occurrence criterion of the workability limit was expressed as a function of the Vickers hardness before cold working and the final values of both axial and circumferential strains in cold working. This criterion is expressed by the same equation established in the previous study. A prediction of the workability limit was made using the criterion and strain path in cold working calculated by FEM, and its validity was checked experimentally using the forging test.
Key words : cold upsetting, predeformation, workability limit, FEM, S45C, Vickers hardness, axial strain, circumferential strain
Measurement of Contact Pressure Distribution between Rolling Rolls Using Pressure Measureing Film
Takashi TATSUKAWA, Ken MORINAGA and Shigeru SHIDA
(Received on May 30, 2001)
In this study, contact pressure distributions between rolls in cold rolling are examined experimentally. In cold rolling in which the thickness of the strip tends to decrease, it is difficult to roll flat strips because the elastic deformation of the roll is larger than the plastic deformation of the strip and the configuration of deformed rolls in complex. To examine such complex deformation of a roll, it is of cardinal importance to determine the contact pressure distributions between rolls experimentally. In this report, the method of measuring the contact pressure between rolls using a pressure measuring film is examined. The elastic deformation of rolls and a film in contact, where the film is held between two rolls, is analyzed. As a result, it is found that plastics have to be used as the material of rolls for the measurement of the contact pressure distribution between rolls, so that the roll deformation is not disturbed by the insertion of the film. Finally, it is confirmed that the experimental results, on the contact pressure determine using the 6-high mill models made of acrylic plastic, agree with the theoretical ones, and the pressure measuring film is suitable for examining the contact pressure distributions between rolling rolls.
Key words : Cold rolling, Contact pressure, Roll flattening, Pressure measuring film, Numerical analysis
Effects of Solid Lubricants Mixed with Grease on Hot Rolling Lubrication
Tsuyoshi INOUE, Hiroyasu YAMAMOTO, Matsuo ATAKA,
Hideki TAKAHASHI, Yasuyuki NISHIYAMA and Ryuro KURAHASHI
(Received on July 27, 2001)
Solid lubricants mixed with Li grease for hot rolling process are developed. Frictional coefficient and wear resistance of solid lubricants are investigated in a hot rolling wear simulator under the frictional conditions of the hot rolling process. Mica and KPO3 powders mixed with Li grease are effective in reducing wear loss of work roll without problems such as rolling slip. It is clear that the characteristics of Mica and KPO3 solid lubricants are produced by the melting reaction between Mica and KPO3 powders under the temperature of roll bite in a hot finishing mill.
Key words : tribology, lubrication, wear, friction, lubricants, strip rolling
Elastic-Plastic-Damage Constitutive Equations for Cold Tool Steel
Taking into Account Unilateral Behavior under Tension and Compression
Kunio HAYAKAWA, Tamotsu NAKAMURA and Shigekazu TANAKA
(Received on August 6, 2001)
Elastic-plastic-damage constitutive equations for cold tool steel are proposed, taking into account salient unilateral stress-strain behavior under tension and compression. First, a second-rank symmetric tensor is employed as a damage variable to describe the mechanical effects of microscopic cracks at the interface between inclusion/carbide and the matrix of tool steel. A modified stress tensor is introduced to express the unilateral behavior due to damage activation/deactivation. Conventional irreversible thermodynamic theory is used to derive the constitutive and damage evolution equations. Next, the derived equations are applied to calculate the uniaxial tension, uniaxial compression and torsion of cold tool steel SKD11 in JIS. Material constants are determined using the experimental results of uniaxial loading and fatigue tests. Calculated results show good agreement with experimental ones. Finally, the calculated locus of the initial yield surface is compared with that of the typical von Mises yield surface.
Key words : cold forging, tool steel, constitutive equation, damage, uniaxial loading, torsion, fatigue, yield surface
Mechanical Properties of Al-Si-Fe Alloy Consolidated by Powder Forging
Toshikatsu KOIKE, Hiroshi YAMAGATA and Naoyuki KANETAKE
(Received on September 6, 2001)
Direct consolidation by powder forging and mechanical properties were investigated for an Al-Si-Fe alloy in order to fabricate forging billets efficiently. The alloy powder was cold-compacted and subsequently consolidated to Diameter79mm~H20mm billets though one-step and two-step hot forging processes. Tensile strength and elongation of the powder-forged billets were measured and compared to those of the bar consolidated by hot extrusion. The strength and elongation of the billets increased with forging temperature between 723K and 793K. The billets made by the one-step forging (compressive strain was 0.5) showed an equivalent strength to that of the extruded bar only in the central region. The billets made by the two-step forging (total compressive strain was 1.3) showed the same strength and elongation as the extruded bar both at the center and near the surface region. The two-step forging with compressive strain of around 0.5 in the first step was useful to obtain a sound billet without any cracks.
Key words : forging, Al-Si-Fe powder, powder forming, hot pressing, consolidation, extrusion, tension test
Prevention of Seizure in Multi-Stage Deep Drawing
Using Colored Pure Titanium Sheets
Takuji MURAO, Ken-ichiro MORI, Yasunori HARADA,
Koji KATO and Fujio OKUBO
(Received on September 10, 2001)
Long pure titanium cups were formed by preventing seizing in multi-stage deep drawing processes due to use of commercial colored pure titanium sheets. The colored pure titanium sheets were treated by electrochemical coating so as to have oxide surface layer that effectively prevents the seizing. By the use of commercial colored sheets, the investment in coating machines is avoided in sheet metal forming makers. The effects of the coating voltage, die materials and lubricants on the occurrence of seizure in multi-stage deep drawing were examined. It was found that the colored pure titanium sheets have sufficient ability in preventing the seizure in multi-stage deep drawing processes.
Key words : sheet metal forming, deep drawing, multi-stage drawing, colored titanium sheet, seizure, tribology
Evaluation of Springback Analysis Accuracy
for Pure Bending Simulation Using Four-Node Shell Element
-- Springback Simulation Using the Static Explicit FEM Code,
Using a New Algorithm for Canceling Nonequilibrated Forces T --
Naoto YAMAMURA, Toshihiko KUWABARA,
Akitake MAKINOUCHI and Cristian TEODOSIU
(Received on September 12, 2001)
The advancement of computer technologies enables the numerical simulation of sheet metal forming processes using finite-element codes to be employed in an industrial environment. Springback simulation by the finite-element method (FEM) has been attempted using various codes, for example, dynamic explicit, static implicit and static explicit codes. However, due to the difficulty in treating quasi-static processes by dynamic explicit codes and the convergence problems frequently encountered with implicit codes, no code has yet found wide acceptance for springback analysis. In this study, this problem is approached using the static explicit FEM code, ITAS3D, in conjunction with a new algorithm for canceling the nonequilibrated forces arising during the deformation process. This new algorithm does not require any iteration. Numerical examples of springback simulation are given for pure bending tests. The results obtained show that the new algorithm considerably improves the geometry at the end of the deformation process and accordingly, the accuracy of the springback analysis.
Key words : finite-element method, sheet metal, bending, static explicit FEM, elastoplasticity, nonequilibrated force, springback
Effects of Numerical Expression of Stress-Strain Curve
on Curvature of Material of Roller Leveling Process
Tsuyoshi HIGO, Hiromi MATSUMOTO
and Shigeru OGAWA
(Received on September 18, 2001)
A numerical model to calculate the curvature of leveling material in roller leveler is presented. The features of this numerical model are 1 accurate expression of stress-strain relationship based on actual measurement, and 2 precise modeling of contact condition between the roll and leveling material. The curvature of leveling material in roller leveler derived by means of accurate expression of stress-strain relationship is less than that of elasto-perfect plastic material. The influence of precise modeling of contact condition between roll and leveling material increases larger when thickness of leveling material decreases and/or the intermesh increases.
Key words : roller leveler, numerical analysis, residual stress, curvature, bending