Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(Vol.40 No.457 February 1999)

Improving Ironing Performance by Using Dies Subjected to Radial Vibration ――A Study of Ultrasonic Vibration Ironing Process Ⅰ――

Pongpan KAEWTATIP, Masahiko JIN and Masao MURAKAWA

(Received on February 16, 1998)

In the manufacturing of thin-walled cups by metal forming processes, the use of high viscosity lubricants, which would inevitably require strong and non-environment friendly degreasing agents such as fluorocarbons, has been restricted in order to reduce environment pollution. This problem can be solved, for example, by using low-viscosity lubricants, such as water-soluble oil. However, this generally results in poor forming (e.g. ironing) performance which must be solved in some other way. The authors, therefore, attempt to apply ultrasonic vibration to dies for ironing process both in the axial and radial directions in an effort to improve the lubricity of the die. From the experiments using aluminum and steel specimens, it is found that in the case of radial vibration ironing, despite the use of low-viscosity lubricants, the limiting reduction ratio of wall thickness (LRRWT) and product precisions are improved as compared to conventional ironing. In addition, FEM is used to investigate the mechanism of improvement of LRRWT.
Key words : ironing, radial ultrasonic vibration, lubricity, product precision

Effect of Roll Coating on Surface Brightness and Heat Streak in Cold Rolling of SUS430 Strip

Kazuhito KENMOCHI, Ikuo YARITA, Akihiko FUKUHARA and Yoshikazu SEINO

(Received on March 9, 1998)

In cold rolling of a stainless steel strip, the roll surface is colored dark brown due to the presence of a material known as the roll coating. In the past, it was expected that roll coating would affect the surface brightness of cold rolled strips and the occurrence of heat streaks in cold rolling; however, the effect was not investigated quantitatively. In this study, the effect of cold rolling conditions of a ferritic SUS430 strip on roll-coating film thickness is investigated, and the effect of the film thickness on the surface brightness of strips and on the occurrence of heat streaks in cold rolling is examined. The results obtained are as follows. (1) The roll coating is composed of iron, chromium and oxide, and consists of fine particles less than 1〓m in size. (2) The coating film thickness is affected by reduction, rolling length, lubrication conditions, chemical composition of rolling oil and roll material. (3) Surface brightness is improved slightly with increasing film thickness. (4) The limited reduction occurring heat streak increases slightly with increasing roll coating film thickness, and the limited reduction becomes almost constant in spite of increasing film thickness.
Key words : cold rolling, lubrication, roll coating, stainless steel, surface brightness, heat streak

Improvement of Erichsen Values of Titanium and Stainless Steel Sheets by Wheat Flour Lubricant

Hirofumi YOSHIMURA, Toyokazu HAYASHI, Jun-ichi KATAYAMA and Hidetsugu FUWA

(Received on March 16, 1998)

A feasibility experiment was conducted on a suspension produced by dissolving wheat flour in water for use as a lubricant that would cause no pollution and recyclable, in place of lubricants normally used in the press forming of metal sheets. In this experiment, an Erichsen cupping test was performed as one of the press-formability tests on two materials for the purpose of comparison:titanium and stainless steel sheets coated with this suspension and then dried, and those coated with a conventional lubricant. As a result, Erichsen values increased with an increase in the concentration of wheat flour in the suspension. It can be considered that this lubrication effect was due to wheat flour components such as gluten.
Key words : formability test, lubricant, Erichsen test, titanium sheet, stainless steel sheet, wheat flour, suspension, gluten

Deep-Drawing of Metal-Wire Cloth

Manabu GOTOH, Minoru YAMASHITA and Hitoshi KURIHARA

(Received on April 23, 1998)

A plainly woven metal-wire cloth exhibits extremely strong planar-anisotropic plasticity. Its principal deformation mode is the transformation of the square net into the diamond net in the 45°-direction. A Copper or brass wire cloth is deep-drawn into a circular or a square cup. A rubber sheet pad inserted between the wire cloth and the die is found to be very effective, especially in the case of circular drawing. The shape accuracy of the formed cup is high when tool clearance is narrow. The rubber sheet pad exerting an appropriate pressure on the wire cloth sliding along the die cavity wall is preferable. In the case of square cup-drawing, the wire cloth can be deep-drawn without a rubber sheet pad in both cases, where the specimen is set parallel and diagonal to the tool edges. The shape accuracy is better when the narrower tool clearance is adopted. For a wider tool clearance, the shape accuracy is better with a rubber sheet pad than without it.
Key words : deep-drawing, plastic deformation processes, metal-wire cloth, circular cup-drawing, square cup-drawing, formability, shape accuracy

Measurement and Analysis of Contours of Plastic Work in Cold Rolled Sheet Steel by Biaxial Tensile Tests Using Cruciform Specimens

Toshihiko KUWABARA and Satoshi IKEDA

(Received on April 23, 1998)

Biaxial tensile tests of cold-rolled sheet steel were carried out using newly designed cruciform specimens. The specimens were deformed under linear loading paths in a servo-controlled biaxial tensile testing machine. Plastic orthotropy remained coaxial with the principal stresses throughout every experiment. On the other hand, the successive contours of plastic work in biaxial stress space changed their shapes progressively, exemplifying differential work hardening. The geometry of the entire family of the work contours was compared with the yield loci calculated from existing yield criteria. Hill's quadratic yield criterion overestimated the measured work contours; in particular, in the neighborhood of balanced biaxial tension, the discrepancy was large, while the other yield criteria described the behavior of the work contours well. The only yield criterion that could describe the general trends of the work contours as well as the in-plane r-value distribution with good accuracy was Gotoh's biquadratic yield criterion. Moreover, it was observed that the components of an increment of logarithmic plastic strain are proportional to the components of the associated normal to the current work contour in stress space; accordingly it appears that the work contours act instantaneously as plastic potentials at least under linear loading paths.
Key words : biaxial tensile test, cruciform specimen, contours of plastic work, cold-rolled sheet steel, yield criterion

Shaping of Inner Helical Spline by Cold Extrusion

Yozo SAWAKI and Hajime YOSHIDA

(Received on April 30, 1998)

We have previously proposed a two-step cold extrusion method for internal spur gear shaping. A mandrel specially designed to form the outer diameter of a spur gear in two steps is used to expand the inner diameter of the cylindrical workpiece. In this paper, the shaping of an inner helical spline by this method is reported. The specifications of the helical splines examined are as follows:module 1.0，1.5，1.75; helix angle 10-30°; and number of teeth 10-22. It is shown that almost all the conditions examined produced a completely teethed inner helical spline even with only a few percent area reduction and under quite low compressive stress on the stepped mandrel and the punch.
Key words : cold extrusion, inner herical spline, reduction in area, complete tooth, stepped mandrel

Density Change of Al‐20Si Alloy Powder Compact in Upsetting

Nobukazu HAYASHI

(Received on May 11, 1998)

To fabricate P/M (powder metallurgy) alloy from aluminum powder, the technology of deformation processing is applied. The consolidation process of powder compact by upsetting is investigated in this paper. Past studies of upsetting have claimed that fault-free products can be obtained. It has been thought that the addition of plastic distortion under compressive stress is necessary for prefer compaction. However, the workpiece used in upsetting always has a small-pressure area. Because of these contradicting ideas, the consolidation behavior in upsetting is examined with attention. Workpieces of cylindrical and hollow cylindrical shapes were made by hot pressing, and then subjected to upsetting. The consolidation process was investigated from the density change of the workpiece because it can be measured with high precision. The relative density was low at 523K but was maintained 100% at 773K. The mechanism of the density change was examined by conducting a tensile test of the powder compact. The specimen had a small strain at low temperatures and a large one at high temperatures, because fracture stress and flow stress became equal at high temperatures. These results explain well the above-mentioned.
Key words : powder forming, powder forging, aluminum powder, hot pressing, upsetting, density measurement

Extended Mesoplasticity FEM Based on Dislocation Behavior

Masahiko YOSHINO, Toshinori SHIINA and Takahiro SHIRAKASHI

(Received on May 21, 1998)

In this paper we propose a new mesoplasticity theory that relates crystalline plasticity theory to dislocation theory. The new theory relates slip deformation in a crystal to the evolution of dislocation loops to estimate the accumulation rate of dislocations in a crystal. The theory also relates the recovery process to the dislocation annihilation mechanism, and estimates its rate from the rearrangement energy of dislocations. Based on dislocation densities calculated from the accumulation rate and the annihilation rate, the work-hardening equation for a crystal is proposed. Using this equation, we develop a new meso-plasticity FEM that can take into account effects of both plastic deformation and heat treatment on crystalline materials. Stretching and annealing processes of copper single crystal are simulated by the FEM, and results show that the FEM can simulate the effects of annealing on the mechanical properties appropriately.
Key words : finite element method, material testing, deformation-load property, plasticity theory, dislocation, crystalline theory, recovery, material property, work hardening