Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(vol.44 no.506 January 2003)

Superplastic Forming of Aluminum Alloy Tailored Blank Sheet Joined by Electron Beam Welding

Shoitsu SEO, Satoshi Toru JINISHI and Nobuyuki SUZUKI

(Received on April 30, 2002)

Bulging is a typical type of deformation for superplastic blow forming of sheet metal, and it often causes undesirable thickness reduction in the formed part. Therefore, the control of thickness distribution in the formed part is strongly desired for making aerospace structures. A new technology called "Tailored Blank " was proposed to control the thickness distribution, and some forming experiments were couducted. Two kinds of tailored blank sheets were assembled from 1.0mm-thick 5083 aluminum alloy as the base metal, using electron beam welding. One base sheet was joined with the same alloy of 1.6mm thickness, and the other was joined with 5052 aluminum alloy of 1.0mm thickness. Pressurization schedules were analyzed considering suitable forming condition of the tailored blank (maximum strain rate of 5*10-4sec-1 at 788K) for the forming of a slender and rectangular pan. As a result, forming trials of these sheets were completed successfully, and these weld lines maintained their microstructure without harmful defects or local necking. This result shows a potential in the application of tailored blank technology with different thicknesses and different materials to superplastic forming.
Key words: sheet metal forming, superplastic forming, bulge forming, 5083 aluminum alloy, welding, tailored blank sheet

Lubricity Characteristics of Particles Mixed with Organic and Inorganic Powders and their Seizure Prevention Effect at High Temperature

Tsuyoshi INOUE, Hiroyasu YAMAMOTO, Kazuo WATANABE, Kiyoshi NISHIDA and Tsutomu SUGIURA

(Received on February 18, 2002)

Effect of characteristics of organic (polyphenylene sulfide (PPS), polyethylene (PE)) and inorganic (graphite, potassium phosphate (KPO3)) powders on lubricity and the effect of seizure prevention at high temperature were studied. A mixture of PPS powder and inorganic ones shows good lubricity and the effect of seizure prevention in comparison with a mixture of PE powder and inorganic ones. The reason seems to be that PPS powder has better heat resistance than PE powder. It is clarified that the excellent effect of seizure prevention is caused by the formation of a lubricating film consisting of graphite particles, softened PPS, and melted and solidified KPO3.
Key words: lubrication, solid lubricant, powder, polymer, grease, hot rolling, wear, friction coefficient

Residual Stress of Thin Strip Product after Leveling Process
-- Research for Improvement of Residual Stress Quality of Thin Strip Product 2 --

Shusuke YANAGI, Shigeo HATTORI, Yasushi MAEDA, Takashi ISHIKAWA

(Received on April 10, 2002)

The residual stress after leveling process in the actual processing line is examined in this study to evaluate the influence of variation in the ordinary leveling process, and the following results are verified:(1)When the proportion of plastic deformation to the entire cross section under the leveling process is small, residual stress is determined by both initial residual stress and the leveling condition, and as the proportion of plastic deformation increases, the residual stress converges into a certain distribution determined only by the leveling condition. (2)In residual stress after tension leveling with multiroller unit, the influence of variation in the intermesh condition of the multiroller unit effectively emerges at a shallow depth. Furthermore, in order to improve the numerical prediction of residual stress after leveling process, the equation for the stress-strain relation which considers the gradual transition from elastic to plastic state is derived based on the uniaxial tensile and compressive loading tests. The calculated results using the new constitutive equation showed better agreement with actual residual stress.
Key words: leveling process, residual stress, thin strip, constitutive equation, residual stress prediction

Forming Limits of AZ31 Magnesium Alloy Sheets at Room and Elevated Temperatures

Eitaro YUKUTAKE, Junichi KANEKO and Makoto SUGAMATA

(Received on June 11, 2002)

Forming limit diagrams of AZ31-O and AZ31-H24 magnesium sheets were constructed at temperatures between RT and 573K and their forming limits were compared with those of A1100-O sheet. Tensile properties, such as tensile strength, elongation, n-value and r-values, were also evaluated for these sheet materials at these temperatures and correlated to the forming limits. The AZ31 sheets, with strong basal plane textures, exhibited high r-values at RT, indicating a high plastic anisotropy. This caused significantly low forming limits in the AZ31 sheets in plane strain and biaxial tension. However, the r-value of the AZ31 sheets decreased with rising temperature and became nearly isotropic at temperatures above 473K. Thus, the forming limits of the AZ31 sheets under such deformation conditions improved remarkably at higher temperatures. At RT, the AZ31 sheets showed much lower forming limits than the A1100-O sheets in plane strain and biaxial tension. But the forming limits of the AZ31 sheets at temperatures above 423K became comparable to or higher than those of A1100-O at room temperature. It is implied that sheet metal forming at temperatures above 423K is recommended for AZ31 magnesium sheets.
Key words: magnesium sheet, formability, sheet metal forming, forming limit diagram, texture, mechanical property

Measurement and Analysis of Work Hardening Characteristics of 5000 Series Aluminum Alloy Tubes Subjected to Axial Force and Internal Pressure

Toshihiko KUWABARA, Kohji NARIHARA, Kengo YOSHIDA and Susumu TAKAHASHI

(Received on July 8, 2002)

There is a strong demand for the establishment of an accurate simulation technology for tube hydroforming using a finite-element method. In order to accomplish accurate simulations, it is crucial to use accurate constitutive models for tube materials. In the present study, a novel servo-controlled tension-internal pressure testing machine for metal tubes is developed. This testing machine is capable of applying arbitrary stress or strain paths to a tubular specimen using an electrical, closed-loop control system. Under linear stress paths in the principal stress space, the initial yield locus and contours of plastic work are determined for 5000 series aluminum alloy tubes (A5154-H112) of 76mm outer diameter and 3.8mm wall thickness. The shapes of the initial yield locus and work contours are found to be in good agreement with those calculated on the basis of the Hosford or Yld2000 yield criteria. Moreover, the directions of the measured incremental plastic strain vectors are found to be almost constant under linear stress paths, and are in good agreement with those of local outward normals to these yield loci. Thus, we have confirmed that the Hosford and Yld2000 yield criteria are effective phenomenological plasticity models for predicting the plastic deformation behavior of the present aluminum alloy tubes.
Key words: material testing, tube forming, material property, aluminum alloy, contours of plastic work, yield criterion

Seizure Avoidance in Deep-Drawing of Titanium Sheet for Mass Production

Manabu GOTOH, Minoru YAMASHITA and Joji SATOH

(Received on September 4, 2002)

It is well known that seizure on a tool surface renders press-forming of titanium sheets almost impossible. In this study, a few methods are developed to avoid such difficulty. When an oil lubricant is used, a beryllium-copper die hardened by heat treatment is found to be most preferable among all tested die materials. The SKD11 die with thermal spray-coating of Cu-Ni powder is the best among all tested spray-coating materials. As for the lubricant, the liquid used in the spray-coating process is the best anti-seizure material. This liquid is used to prevent any selected portion of the die surface from undesirable spray-coating, and is composed of carbon-graphite, carbon-black and others mixed in water. This lubricant seems to allow us to operate endlessly the cup forming of a titanium sheet.
Key words: deep drawing, die design, titanium sheet, lubricant, seizure, die material, mass production



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