Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(Vol.38 No.435 April 1997)

Effects of Pressure Distribution and Boundary Condition on
Deformation Mechanism of a Circular Metal
Plate Subject to Shock Pressure

Masahiro FUJITA, Yasuo ISHIGORI, Minoru MOCHIHARA, Hiroo OSAKA, Rui ZHANG and Hirofumi IYAMA

(Received on January 30, 1996)

To investigate the deformation mechanism of a circular metal plate subjected to shock pressure, the effect of pressure distributions and the constraint boundary conditions have been numerically analyzed using the finite differential method. The analytical result showed noteworthy differences in the deformation mechanism due to the difference in shock pressure distributions. When the pressure distribution is uniform, the plate is formed into a conical shape with a rounded top due to an inward movement of the bending wave produced near the constrained periphery. When the pressure decreases linearly from the plate center to its periphery, the plate is formed into a shallow spherical dome shape due to the movement of the bending wave from the center to the periphery. Moreover, other analytical results clarify the several effects of the constraint boundary conditions on the deformation mechanism. Finally, the deformation mechanism for die forming is numerically analyzed using a die with a shallow spherical cavity.
Key words : sheet metal forming, high-energy-rate forming, explosive forming, numerical analysis, FDM, shock loading, bending wave, deformation process, die forming

Analysis of Circular Tube Forming by
MOS Bending Method

Makoto MURATA

(Received on May 14, 1996)

A new, flexible tube bending method, the MOS bending method, has been developed by the author. When tubes are inserted into a guide cylinder and bending die, they are bent by shifting the relative position of the tube. The bending radii are controlled by the relative distance between the die and the tube, while the bending angle are controlled by the penetrated tube length. A CNC bending machine which can bend tubes using the MOS bending method has been built. In this paper, the author presents the properties of the MOS bending method both experimentally and analytically. The penetration, the bending force and the amount of springback of bent tubes are analyzed in order to clarify the bending. Finally, the experimental and analytical value are compared and are shown to agree with one another.
Key words : tube forming, MOS bending, bending moment, bending radius.

Plastic Flow of a Material Plate in the Shearing
Process under Shock Pressure

Minoru MOCHIHARA, Masahiro FUJITA, Yasuhiro NAKIYAMA, Kazuyuki HOKAMOTO and Shigeru ITOH

(Received on June 5, 1996)

We experimentally and analytically investigated the plastic flow of a copper plate during the shearing process under a mild shock pressure too low to cut through the plate. Explosively welded multilayered copper plates were used to examine the plastic flow. Fine and uniform waves, which were generated at the welded interfaces in the material, were used as markers inside the material. Also, the positions of each wave before and after shearing were experimentally measured to identify the plastic deformation process. Thus, by comparing the experimental results with those of an analytical simulation using the finite difference method, the validity of the calculated results for plastic flow during the shearing process was confirmed. Furthermore, based on the analytical simulations, the deformation mechanism with time was identified, because we were unable to reproduce this deformation mechanism in our experiments. The analytical results showed the transformations of the plastic flow, the fluctuations in the concentrations of plastic strain around the die edges and the effects of the strain hardening of the material on the deformation mechanism during the shearing process.
Key words : shearing, high-energy-rate forming, numerical analysis, blanking, shearing process, FDM, plastic flow, strain-hardening metal, elastic-perfectly plastic solid, shock pressure.

Fuzzy Adaptive Control of Circular-Cup Deep-Drawing Process
Using Variable Blank Holder Force Technique

Shoichiro YOSHIHARA, Ken-ichi MANABE, Ming YANG and Hisashi NISHIMURA

(Received on June 26, 1996)

A new fuzzy BHF adaptive control method was developed to improve the reliability and flexibility of the circular-cup deep-drawing process. The new fuzzy method adds a new constraint function to the former fuzzy model which is constructed by two evaluation functions. The constraint function, which is given as a gradient of the drawing stress, /dDR, obtained from the punch load-flange reduction ratio curve, is introduced for determining the progress of deep-drawing. A multifunction computer-controlled deep-drawing simulator with above fuzzy controller was used for experiments. The materials tested were aluminum alloy, cold rolling steel and brass sheets. Using the new fuzzy method, all experimental results showed that the lifting-up and wrinkle behaviors at the flange part of the blank were suppressed. Furthermore, we evaluated the wall thickness distribution using the thickness difference between the end site and punch shoulder of a drawn cup. As a result, the maximum and minimum wall thicknesses in the case of new fuzzy model were got better than ones in the case of the former model. It was confirmed that the new fuzzy BHF adaptive control method improved the reliability and flexibility of the process for various materials and blank sizes.
Key words : sheet metal forming, deep drawing, variable blank holder force, fuzzy control, on-line adaptive control, flexible forming

Method for Calculating Punch Stroke-Punch Load Curves
in Deep-Drawing lrregularly Shaped Cylindrical
Shells with Arbitrarily Shaped Flanges

Wen hua SL Toshihiko KUWABARA and Masayuki SHUUNO

(Received on June 27, 1996)

A method for calculating punch stroke-punch load curves in deep-drawing irregularly shaped cylindrical shells with arbitrarily shaped flanges is proposed. It is assumed that the blank is an isotropic, work hardening material and that its thickness remains constant during the deep-drawing process. A kinematically admissible velocity field for the metal flow on the die surface is quantitatively predicted using the slip-line field theory. This velocity field is utilized to evaluate the rate of plastic work dissipated by the flange deformation. From this energy dissipation rate, a punch load-punch stroke curve is predicted by the energy method. The increase of the punch load due to the bending-unbending deformation at the die lip and the friction forces between the blank and die are also considered. A deep-drawing experiment is conducted for square shells with two different flange shapes and uniform wall height, using an aluminum alloy sheet A5182-O 1.0 mm thick and a cold rolled steel sheet SPCE 0.5mm thick. The mode of the blank deformation and the measured values of maximum punch load are in good agreement with those predicted for both materials.
Key words : sheet metal forming, deep drawing, cylindrical shell, maximum punch load, slip-line field theory

Powder Forging of Combined Al-Si Alloy Powder and I/M Alloy

Nobukazu HAYASHI

(Received on June 28, 1996)

To consolidate aluminum powder, a powder forging process is sometimes employed. In previous studies, however, the properties of powder metallurgy (P/M) alloy made by the forging process were usually discussed under ideal conditions, i.e., at a uniformly strained area and under high pressure. In practice, however, strain does not distribute uniformly in all parts with complicated shapes, especially in small-strain low-strength regions. In this report, I present two methods for producing parts with no defects. One method is to forge a combination of powder and alloy by the ingot metallurgy (I/M) process. The I/M alloy is placed in the part where a small strain is applied and which becomes weak over time. The other method is warm forging with a good lubricant to enable high formability and uniform straining. For the former, joining strength between powder forged alloy and I/M alloy was investigated.
Key words : powder forging, powder metallurgy, Al-Si alloy, consolidation, joining strength, warm forging

Consideration on the Relationship Between Breakthrough
and Noise During Press Blanking

Jianhua Mo, Masao KONDOH, Nobuhiro KOGA and Masao MURAKAWA

(Received on July 11, 1996)

This paper concerns consideration on the relationship between breakthrough and the blanking noise. First, we investigated a method for determining the point of breakthrough either by measuring various relevant blanking parameters, such as blanking force or load (F), degree of breakthrough or rate of deceleration of blanking force (dF / dt), actual punch speed (v), acceleration of press ram (a) or sound pressure level (SPL), or by observing the progress of cracks as the punch penetration increases. This enabled us first to define the start of breakthrough as the time when the material to be blanked has just been completely separated into a product and its blanking waste, and then to define the time of maximum breakthrough as when the above parameters, dF / dt, v and a, become maxima just after the start time of breakthrough. Next, we analyzed the relationship quantitatively based on the measurements of the various parameters at the maximum point of breakthrough and on a theoretical prediction of the relationship between the blanking noise power, or release rate of elastic energy, and the various parameters in question. Our theoretical prediction agreed well with actuality.
Key words : shearing, blanking, breakthrough, blanking speed, noise level, noise power, elastic energy.

Experiment on Rectangular Cup Drawing of Sheet Metal

Takaji MIZUNO and Daixin ER

(Received on September 17, 1996)

Rectangular (36mm~72mm) cups with different corner radii ( 1, 3 and 9 mm) are deep-drawn from a rectangular blank sheet of copper 0.2mm thick. Strain distributions are measured in three positions : namely, along the periphery of the flange, on the rectangular axes and on the centerline of the flange corner. Next, the states of stress are estimated. The stress and strain in the flange corner are very different from those in an axisymmetric radial drawing ; the tensile stress and strain prevail along the periphery of the flange corner, while in the middle region of the flange corner, a compressive stress acts in radial direction. This compressive This compressive stress combined with "strain relief effect" enables successful forming of a very large value of the local drawing ratio.
Key words : sheet metal forming, deep drawing, rectangular cup, experiment, strain distribution, stress distribution, forming load, forming limit.

Synthesis of Ti-Al Intermetallic Compounds by Pressure Infiltration

Tohru SHIROTA Tasuku DENDO, Kenki HASHIMOTO, Haruo DOHI Takashi KIMURA and Morihiko NAKAMURA

(Received on September 20, 1996)

The synthesis of Ti-AI intermetallic compounds by means of a pressure infiltration process has been studied. Molten Al was poured into a die in which a preform made of Ti powder had been set after pre-heating, and infiltrated into the preform at a pressure of 130MPa under various thermal conditions. Three kinds of compounds i.e., Ti3Al, TiAl and TiA13, are synthesized by this process, and each of their fractions is affected mainly by thermal conditions such as the pre-heating and pouring temperatures. Reactivity for the synthesis is promoted with a decrease in the particle size of Ti powder. Unreacted Ti core remains in the central portion of the infiltrated preform under conditions of higher pre-heating temperature and higher preform density.
Key words : material, Ti-AI intermetallics, pressure infiltration, synthesis.

Development of an Assembly for Hot Dynamic Compaction
of Powders Using a Converging Underwater Shock Wave

Kazuyuki HOKAMOTO, Seiichiro TANAKA, Takahiro KUGIMOTO, Masahiro FUJITA, Shigeru ITOH and Akira CHIBA

(Received on August 5, 1996)

A new system for the dynamic compaction of hard powders at an elevated temperature is developed. In the system, a converging underwater shock wave assembly is used to obtain a higher and longer shock pulse, and the use of a high temperature enhances the deformation and bonding of powders. For the compaction of high-speed steel powders, samples were successfully recovered and the high temperature experiments showed an increased melting fraction of powder surfaces and a decreased number of cracks in comparison with the experiments performed at room temperature. C-BN/TiB2 mixed powders were also compacted at a high temperature for producing ceramic composites, and the samples were successfully recovered with few voids and cracks by the use of heating.
Key words : high-energy rate forming, powder metallurgy, dynamic compaction of powders, explosive powder compaction, underwater shock wave, hot dynamic compaction.