Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(vol.42 no.488 September 2001)
Yield Improvement by Partial Welding of Bars of Different Thickness
Hiroyuki HINO and Masaki KOJI
(Received on August 21, 2000)
In hot-strip rolling, the head and tail ends of a single transfer bar undergo deformations such as overlap, flare, tongue or fishtail, resulting in numerous problems in terms of quality, yield and threading stability. Endless hot-strip rolling, namely, joining of the head and tail ends of each bar is performed to obtain a steady-state condition so as to prevent the occurrence of these problems. A miniature model test using plasticine slabs has been carried out in order to investigate the effect of partial welding of bars of different thickness on crop loss. On the basis of the results of this investigation, the following can be concluded; 1) the width-edges weld is highly effective for reducing crop loss, 2) a smaller thickness difference, results in a better yield, and 3) a rolling schedule with increasing thickness is more effective than that with decreasing thickness.
Key words : rhot-strip rolling, transfer bar, partial welding, different thickness, overlap, plane view, crop loss, yield, plasticine, model mill
Simulation System Based on New Constitutive Equation Incorporating
Stress Increment Dependence on the Direction of Strain Increment
for Estimation of Sheet Metal Formability
Tohru YOSHIDA, Koichi ITO, Yukihisa KURIYAMA and Matsuo USUDA
(Received on September 7, 2000)
The J2-flow rule is commonly used in FEM software for sheet forming processes. However, it is known that the J2-flow rule is not suitable for predicting the phenomenon of plastic instability, for example, fractures and wrinkles. Thus in this paper, a new constitutive equation incorporating stress increment dependence on the direction of strain increment is introduced into FEM software for sheet metal forming, and the effect of this constitutive equation on analytical results is investigated. In a stretching test with hemispherical punch, localized strain distribution before fracture is affected by the parameter Kc of the constitutive equation. The practical use of measuring Kc is proposed from a simplified stretching test. Finally, analytical results for maximum major strain are compared with experimental results; it is clarified that a new FEM program applying this constitutive equation enables prediction of the fracture more accurately than the J2-flow rule.
Key words : sheet metal forming, stretch forming, constitutive equation, yield criterion, elastoplastic FEM
Effect of Material Properties on Cross Section Deformation
――Bending of Aluminum Extrusion SectionT――
Hidemitsu HAMANO, Hisashi NISHIMURA,Yasuhisa HAGIWARA and Yuichi NAGAI
(Received on September 12, 2000)
In the process of push-through bending of a square extrusion pipe, the effects of proof stress, r value, wall thickness and cross section size on the cross-sectional shape change were investigated. The extruded shape of A6063 aluminum alloy was used in the experiment, and the fundamental section size was 40×40×2.0 mm. The push-through bending machine used has a six-axes NC controller, but in this study, the bending shape adapted was two-dimensional single curvature in order to investigate the fundamental bending property. A high proof stress material with severe bending workability was examined in the course of this experiment. The aim was to clarify the effect of bending workability on the material property value. Workability was evaluated by examining wrinkles and shape change of the cross section. The change in thickness was evaluated as a mechanical property. Moreover n and r values were evaluated as material properties. The obtained results are as follows. The material with high proof stress was bent, resulting in large cross section deformation was large, the size of wrinkles caused by internal bending increased due to the large bending radius, and the wrinkles produced were deep. The effect of the r value on the cross section deformation after bending could not be determined. In the present experimental range, the bending limit was determined by the size of wrinkles in the case of internal bending. In A6063-T1, the effect of the wall thickness was large and the forming limit of the thin-walled material was low. The bending limit was low for A6063-T5, and the effect of the wall thickness was slight. The bending limit of 60×60mm cross sectional size was considerably lower than that of a 40×40mm cross sectional one, for the same wall thickness, and in particular, it was significant in A6063‐T5.
Key words : push-through bending, tube forming, lightening, aluminum extrusion section, square tube, forming limit, Al-Mg-Si, forming property
Lubrication in Push-Through Bending
――Bending of Aluminum Extrusion Section U――
Hidemitsu HAMANO, Hisashi NISHIMURA, Yasuhisa HAGIWARA, Yuichi NAGAI and Ken-ichi AOKI
(Received on September 12, 2000)
The push-through bending process can be regarded as a bending mechanism with two fixed die points and two movable die points, resulting in a total of four points. It can also be regarded as a continuous four-points bending. As compared to other bending processes, there is severe friction at the contact area between the material and die in push-through bending. In this paper, we clarify different aspects of lubrication and research excellent lubrication oil in push-through bending. Based on the results obtained, it was found that adhesion occurs depending on the lubricant used and the occurring force. It was also confirmed, that olefin is effective as a remedy for oiliness, in case of using a mineral oil-based lubricant. In addition, it was confirmed that excellent lubrication oil could be obtained by increasing the alcohol content and adjusting the content of synthetic ester. This is a good alternative to the more expensive olefin.
Key words : push-through bending, tube forming, lightening, aluminum extrusion section, square tube, lubrication, friction, abrasion, galling, Al-Mg-Si, forming property
Bulging of Aluminum Square Tube by Electromagnetic Forming
Shoubin ZHANG and Hideaki NEGISHI
(Received on September 12, 2000)
Magnetic flux density in the gap between the coil in the electromagnetic forming and the external surface of a square tube is measured, and shows that the magnetic flux density for a given charging voltage is almost identical along the gap, and decreases with increasing gap distance. The profiles and strain distribution of the deformed square tube are affected by the charging voltage of the condenser bank of electromagnetic forming, the dimensions of bulging width and the corner radius. A uniform profile can be obtained when the deforming of the plane part of the square tube is confined by a metallic block placed around the square tube. Simulation of deforming is performed by the finite element method. The results of simulation agree well with the experimental ones.
Key words : electromagnetic forming, bulging, aluminum, impulsive pressure, square tube
Effect of Deformation of Thin Strip Material under Leveling Process upon Residual Stress
――Research for Improvement of Residual Stress Quality of Thin Strip Product T――
Shusuke YANAGI, Shigeo HATTORI and Takashi ISHIKAWA
(Received on September 13, 2000)
In order to evaluate the residual stress of thin strip material after roller leveler in terms of the deformation of the strip, the effects of the working curvature and leveling tension on residual stress are examined using copper alloy sheet material with a thickness of 0.15mm and proof stress of 430MPa after tension leveling process. The working curvature of the strip imposed on work roll of the leveler is estimated based upon the image of the strip in contact with the work roll recorded by a CCD camera. Residual stress is estimated by measuring the residual curvatures after successively removing the surface part of the specimen which if cut out from the test material. Numerical simulation of leveling process is also conducted to obtain the theoretical solution of the residual stress. The results obtained here are as follows:(1)Compressive residual stress with the same order of leveling tension is uniformly formed to a certain depth of the strip. (2)The depth coincides with that of the plastic deformation region through the leveling process. (3)The compressive residual stress level increases with large tension loss through the leveling process.
Key words : roller leveler, residual stress, thin strip, leveling tension, working curvature, tension loss
Accuracy of Formed Product in Axisymmetric
Shrink Flanging of Steel Sheet
Shigeo ICHIKAWA, Yasuhisa TOZAWA and Naoyuki KANETAKE
(Received on October 2, 2000)
The accuracy of a formed product is investigated experimentally in the axisymmetric shrink flanging of a cold-rolled steel sheet. By ironing of the flange, the nonuniformity of the flange thickness is improved, the flange profile becomes straight, the flange angle is reduced, and the diameter of the flange comes close to that of a die. When the flange thickness is ironed over 10%, an accurate product can be obtained. However, the thickness of the ironed flange is larger than the clearance of the tools due to the elastic deformation of the tools or elastic recovery of the flange, and this difference increases with decreasing the clearance of the tools and increasing die shoulder radius. The influence of web width on the flange thickness and the flange angle is negligibly small. However, the warp of the web generated by the springback of the punch shoulder bending increases with decreasing web width.
Key words : shrink flanging, axisymmetric flanging, ironing, thickness, accuracy, steel sheet
Prediction of Internal Defect in
Cold Multistage Extrusion
Takashi ISHIKAWA, Satoshi TAKAYANAGI, Yoshinori YOSHIDA,
Nobuki YUKAWA, Katsuhiro ITO and Minoru IKEDA
(Received on October 5, 2000)
Internal defects such as Shevron crack occasionally occur in the process of cold extrusion or cold drawing. The purpose of this research was to propose an accurate procedure to predict internal defects in cold multistage extrusion by finite element simulation. The testing method to obtain the accurate fracture limit of a material was investigated by considering the center segregation or nonuniformity of the microstructure in the billet. The tensile test of the notched specimen is useful to obtain the fracture limit. The equation for expression of the ductile fracture limit is required for prediction of the defect. The equations of Cockroft & Latham，McClintock，Oyane, Ayada and Brozzo were examined. The equation of Cockroft & Latham obtained the best results for the prediction of internal fracture in cold multistage extrusion.
Key words : FE simulation, extrusion, internal defects, ductile fracture limit
Effects of Flow Guide Configuration on Material Flow
Characteristics in Extrusion of C-Channel Product
――Die Design Aided by Physical Simulation System U――
Hirofumi KOBA, Kenji NAKANISHI and Shunpei KAMITANI
(Received on October 13, 2000)
A series of extrusion experiments of a C-channel product were carried out using a flat die and dies with flow guides of various configurations and dimensions. A cylindrical plasticine billet was employed as a model material of aluminum alloy in hot extrusion in the experiments, and the three-dimensional plastic flow conditions during the steady state extrusion process were measured and analyzed by applying the visioplasticity method. Three-dimensional dead zone configurations were also calculated from the steady state flow line patterns and graphically displayed in the present investigation. We could confirm that the distribution of flow out velocity on the cross-sectional plane of a product becomes almost uniform at the die exit section in steady state extrusion by using a die with a flow guide of optimum configuration and dimensions. The experimental and analytical data provide useful information for optimum design of the die with a flow guide.
Key words : extrusion, flat die, flow guide, die design, visioplasticity method, dead zone, physical simulation，material flow
Residual Stress and Sheet Flatness in Manufacturing
of Tin-Gauge Steel Sheets
Tetsu MATOBA, Kazuo NAGAHIRO, Fumio TAKI, Matsuo ATAKA and Itaru AOKI
(Received on October 23, 2000)
The residual stress distribution in tin-gauge steel sheets as a function of the depth from the sheet surface is measured by the conventional method, which measures the curvature changes after the removal of thin layers from the specimen step by step. In the case of the temper-rolled sheets, compressive stress ranging from 100MPa to nearly one half of the yield stress of the specimen remains near the surface, while tensile stress is found in the center of thickness. The distribution pattern is similar to a parabolic curve. The sheets stretched by a tension leveler have larger residual stress than those of a temper-rolling mill. Large residual stress and its large dispersion are causes of the degradation of the sheet flatness in the manufacturing process. The prediction of the residual stress is indispensable. However, measuring the residual stress by the conventional method requires enormous effort, thus we propose a simple and quantitative method which employs the stress distribution similar to a parabolic curve. This method is applied in the factory experiments attempting to reduce the residual stress. The usefulness and the practical accuracy of the method are confirmed.
Key words : finishing・shape correction, straightening, stress measurement, residual stress, tension leveling, temper rolling, tin-gauge steel sheet, reduction of residual stress
Effect of Rolling Direction and Stress-Relief Annealing
on Ferromagnetic Property in Austenitic Stainless Steel
Satoshi SUGIYAMA, Takashi ISHIKAWA and Yuuhi TONOHATA
(Received on November 14, 2000)
In the press-forming of a ferromagnetic/nonmagnetic composite material, the process of obtaining a ferromagnetic property was developed using the deformation-induced martensitic transformation taking place in 304 austenitic stainless steel. The partial application of induction heat treatment, causing a portion to return to the nonmagnetic state, yields a one-piece part comprising nonmagnetic and ferromagnetic portions. Without an increase in the volume fraction of martensite, the ferromagnetic property of the magnetic flux density B4K
(induction at H of 4000A/m) was improved for the advantageous rolling direction and the stress-relief annealing. When the prior annealing temperature was about 700K the magnetic flux density along the rolling direction that has no connection with the former rolling direction had a maximum value, and it conformed to a (200) texture. With no stress-relief annealing, the magnetic flux density had a minimum value due to residual stress. Through the experiment based on this assessment, a magnetic circuit matched in the magnetic easy direction shall be designed.
Key words : rolling, forming property, rolling direction, stress-relief annealing, ferromagnetic property