Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(vol.43 no.492 January 2002)
Blank Design of Anisotropic Sheets for Deep Drawing Cups
of Arbitrary Convex Shape
Kunio ISOBE
(Received on November 16, 2000)
The slip line field method for anisotropic sheets is employed to design blank shapes for deep drawing cups with an arbitrarily shaped flange. The relationships between the ear height Δh/d, drawing ratio D/d and Hill's anisotropic parameter c in deep drawing circular cups are determined by the method, where D and d are blank and circular cup diameters, respectively. In order to estimate anisotropy of a certain material, a circular cup is drawn from a circular blank of the material and the ear height is measured. Then, the anisotropic parameter of the material can be determined by plotting the measured ear height in the figure showing the relationship. The optimum blank shape for a tested steel is determined by the method using the determined parameter c. The reduction in the ear height of the cup drawn from the blank is confirmed. Then, the procedure is applied to rectangular and diamond-shaped cups of some steels. Based on the results, it is concluded that the procedure is applicable to practical blank design.
Key words : deep drawing, blank shape, sheet metal forming, anisotropy, slip line field method
Formation of Spinning Rings by Ring Rolling
||Formation of Rings with Asymmetric Shapes by Ring Rolling I||
Hiroaki KANAI, Kiyohide YAGYU, Akira MARUTA, Kouji SASAHARA and Masaru NAKAZAWA
(Received on November 8, 2000)
The ring rolling process generally enlarges a tube and forms a symmetrical and comparatively simple shape from it. We formed high-carbon chromium steel and studied the method of ring rolling to achieve the finished asymmetric and complicatedly structured spinning rings, Which were previously formed by two turning processes. The application of the ring rolling method has been limited to vertically symmetric shapes. Because it was considered impossible to process asymmetric rings as they always shifted or tilted while rolling. Compared with the previous turning processes, the ring rolling method has many advantages, such as better yield rate, shorter processing time and more precise processing because the conditions can be adjusted correctly. We determined suitable conditions to manufacture shape. As a result, an excellent spinning ring was developed which satisfied the desired specifications for the shape and surface.
Key words : ring rolling, mandrel, forming roll, hlgh carbon chromium steel, spinning ring, asymmetric shape, turning
Analysis of Hydrostatic Tube Bulging with Cylindrical Die
||Characteristic of Hydroforming Using
Elastoplastic FEM by Static Explicit Method I||
Takayuki HAMA, Motoo ASAKAWA, Sadakatsu FUCHIZAWA and Akitake MAKINOUCHI
(Received on January 30, 2001)
Tube hydroforming (THF) is getting an increasing amount of attention in industry. THF has advantages such as weight reduction, high dimensional accuracy, and high rigidity. However, this foming process requires precise control of internal pressure and axial feeding. Additionally, in most cases prebending processes must be performed on the tubes before the hydroforming process can be carried out, and the forming ability of the hydroforming processes is influenced by the outcome of this prebending process. We describe the development of the Finite element method (FEM) code for THF analysis and a comparison of experimental and analytical results. The elastoplastic FEM code for THF analysis has been developed based on ITAS3D which is a sheet-metal-forming simulation program using the static explicit method. The algorithm of hydrostatic internal pressure has been newly implemented in ITAS3D. Hydrostatic copper tube bulging with a cylindrical die was calculated with the code, and analytical results show good agreement with experimental ones. In this calculation, there is only a very small difference between the solid element and shell element results.
Key words : tube forming, elastoplastic FEM, static explicit method, discretization of internal pressure
The Method of Predicting the Shape Freezing Property for Automobile Sheet Steel
||The Proposal of a New System for Unified Evaluation||
Kunio OHYA, Hideto SUZUKI, Souichiro NISHINO, Kazuyasu TAKADA and Ikuya MASAKI
(Received on February 22, 2001)
Since today's automobile body needs to be both lightweight and safe, the employment of high-tensile steel for automobile parts is increasing in the manufacturing industry. Therefore, the prediction and reduction of springback error has long been a key issue for obtaining accurate shapes and dimensions in forming automobile parts. In this study, we examined the new method of predicting the shape freezing property by combining V-bending test data with Finite Element Method (FEM) simulation results. In the V-bending test, air or pressure bending and measurement of springback error were carried out employing various types of automobile sheet steel that had different tensile strengths and thicknesses. We investigated the influences of steel strength, thickness, radius of die curvature and bending angle on the shape freezing property. The ratio of the equivalent elastic strain inside the material was calculated using FEM simulation. The amount of springback, which indicated the shape freezing property, was linearly related to the ratio elastic strain irrespective of differences of steel type, bending method and condition. Due to the introduction of this strain parameter, we could consistently evaluate the shape freezing property under various conditions. This hybrid system will help to predict the shape and dimensions of parts in advance and to determine the bending condition corresponding to material type and press capacity.
Key words : material testing, bending, FEM, forming property, springback, hybrid evaluation system
Transcription Mechanism of Minute Surface Pattern in Injection Molding
Toshiyuki YASUHARA, Kazunori KATO, Hiroshi IMAMURA and Naoto OHTAKE
(Received on March 1, 2001)
In injection molding of an optical disk, toric lens, and so forth, their quality depends on the preciseness of the transcription of a minute structure on a mold surface. However, transcription mechanism has not yet been charified, because transcription is carried out in a very short time and the structure is very small. In this paper, transcription properties have been examined using V-grooves of various sizes, machined on mold surfaces, and the following results are obtained. (1) Transcription properties have been clarified. (2) Transcription height changes with compression time tc, when tc is short. Therefore, tc should be more than 2.0s for fine transcription. (3) A mechanical model of the transcription process, in consideration of the strain recovery due to the viscoelasticity the property of polymer, is proposed. (4) Simulation results agree fairly well with experimental ones, indicating that the proposed transcription model is useful for brief estimation of the transcription propertieS prior to an actual injection molding trial.
Key words : Injection molding, Transcription property, Minute pattern, Viscoelasticity, Strain recovery
Reduction of Wall Thickness in Flange Region of Disks of Automobile
Steel Wheels Using Combined Forming of Deep Drawing and Ironing
Osamu EBIHARA, Ken-ichiro MORI, Kenji YOSHII, Kishiro ABE and Yushi IWAKURA
(Received on March 28, 2001)
In the present study, a combined forming process of deep drawing and ironing is developed to form blanks into wheel disks having an optimum thickness distribution. A model experiment for the forming of wheel disks was carried out to examine the ironing limit. It was found from the model experiment that the critical ironing ratio is 40%. The optimum forming conditions under the ironing ratio of 40% are determined from the axisymmetric rigid-plastic finite-element simulation. In the optimization, the contact pressure on the die surface is minimized to prevent the occurrence of defects. It was found that the conditions of α=25 and R=6mm are optimum for the prevention of galling and necking. In the actual forming process, disks are formed without defects under the optimum conditions obtained from the simulation.
Key words : ironing and drawing, wall thickness reduction, defects, finite-element method, wheel disk, forming conditions, forming limit
Characteristics of Controlling Edge Drop by Tapered Work Roll
Shifting and Crossing Mill in Tandem Cold Strip Rolling
Jun-ichi TATENO, Kazuhito KENMOCHl, Masanori KITAHAMA, Tomohiro KANEKO, Teruhiro SAITO and Yasuhiro YAMADA
(Received on April 6, 2001)
Based on a series of investigations on controlling edge drop in cold strip rolling, a tapered work roll shifting and crossing mill has been proposed as an advanced method to increase the edge drop control capability. In this paper, characteristics of controlling edge drop in a commercial tandem cold strip mill are discussed. The tapered work roll shifting and crossing method yields a much higher capability of controlling edge drop than the sum of shifting's and crossing's capabilities. The amount of improvement of edge drop increases quadratically with an increase in the effective roll gap, which is defined as the difference of roll gap between 100mm from the strip edge and an arbitrary point. With this method, sufficient accuracy in transverse thickness after the final stand's rolling is achieved by improving edge drop at only the first stand. This new concept in this advanced method decreases the required number of rolling stands equipped with edge drop control functions in tandem cold strip mill.
Key words : cold rolling, rolling mill, thickness, edge drop, work roll shifting, work roll crossing
Superplastic Isothermal Forging of TiAl-Based Intermetallic Compound
Shin KAGUCHI, Kei ECHIZEN, Masayuki SUGAWARA and Kiyoyuki OHUCHI
(Received on April 16, 2001)
TiAl-based intermetallics have excellent characteristics, such as low density, high strength and good resistance to oxidation, but they also have some weak points, such as low ductility and poor workability. Isothermal forging offers the potential of forming materials from basic-shaped performs to near-net-shaped products in a single process because of the superplasticity of the materials. In order to study the hot work ability of γ-Met 300, a TiAl-based intermetallic, isothermal compression tests were carried out. As a result, it was found that the material shows superplasticity in the strain rate range of 5X10-4s-1 to 2X10-3s-4 at 1423K, and a 1X10-4s-1 to 2X10-3s-1 at 1473K. A forging test of the material from a cylindrical preform to a disk shape with a boss and rim was also carried out. As the result, a sound product that perfectly filled up the die cavity was obtained by isothermal forging at a temperature of 1473K and at 1X10-4s-1.
Key words : forging, intermetallics, TiAl, isothermal forging, superplasticity.
Strain and Strain-Rate Hardening Effects on Forming Limit Diagrams
of 5083 Aluminum Alloy Sheet under Warm Stretching
Tetsuo NAKA, Gaku TORIKAI, Ryutaro HINO and Fusahito YOSHIDA
(Received on June 8, 2001)
Forming limit diagrams (FLDs) of an aluminum alloy (5083-O) sheet were obtained by performing Punch stretch-forming tests at various forming speeds (0.2 to 200mm.min-1) at several temperatures between 293 and 573K. The forming limit strain drastically increased with decreasing speed for any strain path at high temperatures ranging from 423 to 573K, while at room temperature the FLDs were less sensitive to speed. In order to clarify the effects of strain and strain-rate hardening, namely, the influences of the n-value and m-value in the Backofen-type constitutive equation (σ=Cε nεE m), on the FLD, the Marciniak-Kuczynski analysis was conducted. By comparing the experimentally obtained FLDs with the numerical predictions, it is concluded that the improvement in formability at high temperatures and low forming speeds is due specifically to the high strain-rate hardening characteristic (high m-value) of the material. Even at high temperatures, the formability is comparatively low at high forming speeds because of the low n-value at high strain rates.
Key words : forming limit diagram, 5083 aluminum sheet, warm forming, strain hardening, strain-rate hardening, M-K analysis