Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(Vol.39 No.445 February 1998)
Effect of Bottoming on Change of Bent Part Angles
with Three-Point Air Bending
Hideo OGAWA, Takuma GOTO and Akitake MAKINOUCHI
(Received on February 17, 1997)
The three-point air bending method is one means of reducing the change of bent part angles due to thickness
differences. The object of this study is to further enhance this effect. In the procedure for reducing the
change of bent part angles, the punch is descended slightly further after the outer surface of the bent
workpiece has come into contact with the base block surface and then the bent part of the workpiece is
effected by compression between the punch and the base block surface. The investigation is carried out
through experiments and simulation of the elastic-plastic finite element method. The results demonstrated that
when a compressive deformation (bottoming deformation) of 3 . 5-4 . O% of the workpiece thickness was applied
to the bent part, the change of the bent part angle due to variation of the workpiece thickness was reduced
to minimum. It is also shown that under that condition, the bent part angle change is approximately 80% of
that under the condition without applied compressive deformation.
Key words : bending, die bending, air bending, three-point air bending, bent part angle, accuracy, elasto-
plastic FEM
The Effect of the Billet Microstructure on Formability and
Product Quality in the Mushy-State Forming of Al-Si-Mg Alloy
Mitsuru MORITAKA Shuuji FUJISAWA, Yuuichi ANDOU,
Chisato YOSHIDA and Shigeo HATTORI
(Received on March 31, 1997)
In order to understand the characteristics of practical mushy-state metal forming, the mushy-state formability
of an automotive brake system master cylinder of aluminum alloy which is conventionally gravity cast and the
product qualities are investigated using a 250 ton vertical-squeeze cast machine. Continuous cast billets with
electromagnetic stirring and metallic mould cast billets, both with globular structures, and conventional
continuous cast billets with equi-axed dendritic structures are used as the raw material. All the billets are
A357 (AlSi7Mg) and are formed into the required near net shape in the mushy state. Although a shrinkage
defect is observed in the final solidified portion in the flange of the formed parts regardless of the billet
microstructure, the amount of defect is smaller in the billets with globular structures than in those with
equi-axed dendritic structures. The tensile strength of product reaches 300MPa with JIS-T6 heat treatment in
the case with globular structure billets. On the other hand, in the case with equi-axed dendritic structure
billets, the tensile strength does not reach the level of the globular structures. Therefore, the globular billet
structure is favorable and indispensable to mushy-state forming. It is determined that mushy-state forming is a
more effective forming method than conventional gravity casting for enhancing the degree of the near net
shape.
Key words : mushy-state forming, aluminum alloy, billet structure, mechanical property
Influence of Scrap Width on Burr Free Shearing Characteristics
Isamu AOKI and Toshinori TAKAHASHI
(Received on April 1, 1997)
In this paper, we describe the influence of scrap width on burr-free blanked products. The push-back method
is used for obtaining burr-free blanked products. In order to use the sheet metal economically, the optimum
blank layout should be considered and the scrap width minimized as much as possible. Consequently, the
influence of scrap width on the burr-free range, shearing force and sheared surface quality was investigated in
the circular blanking of aluminum sheet metal. The results showed that an excessively small scrap width
produces a small burr-free range. A fractured surface could also have been seen even with negative clearance
under a small scrap width. Shearing force and stripping force were also found to be influenced by the scrap
width. These results indicate that an optimum width exists. Piling up was also observed along the blanking
contour when the scrap width is large, confirming that it is caused by surplus material generated at the
negative clearance with an increasing punch penetration.
Key words : shearing, burr-free blanking, negative clearance, shearing force, stripping force, scrap width
Experiment and FEM Simulation on Strain Rate Control
in the Superplastic Bulge Forming of a Ti-Alloy Tube
Nihat AKKUS, Ken-ichi MANABE, Masanori KAWAHARA and Hisashi NISHIMURA
(Received on April 4, 1997)
This study evaluates the effect of strain rate in the superplastic bulge forming process of a Ti-alloy tube and
proposes a pressure formulation to maintain a constant strain rate at the apex of the bulged tube. Under
constant pressure, large variation in strain rate causes a considerable change in the strain rate sensitivity index,
m , and unfavorably affects the deformability of the material. A pressure control formulation was proposed to
optimize the strain rate and to obtain higher m value at the apex of the bulged tube. A Ti-alloy tube was used
to form a spherical shell at the temperature of 825 Cels. under two different modes of pressure control : constant
pressure and constant apex strain rate. The results of experiments under constant apex strain rate showed that
bulge forming was successful for deforming to a diameter five or more times greater than the initial diameter.
FEM simulation was conducted to predict the pressure path, thickness distribution and bulging time. The
agreement between the experimental results and the FEM simulation verified the effectiveness of the proposed
pressure algorithm.
Key words : superplastic bulge forming. , Ti-alloy tube, formulation, FEM simulation
Consolidating Parameter in Compressive Torsion Forming
for an Aluminum and SiC/Al Powder Mixture
Eiji MAEDA, Naoyuki KANETAKE and Takao CHOH
(Received on May 9, 1997)
Compressive torsion forming, which simultaneously utilizes hydrostatic pressure and shear stress to directly
consolidate metal powder, was applied to pure aluminum powder and a powder mixture consisting of pure
aluminum and SiC. The effects of forming conditions (temperature, compressive pressure, frequency, cycle and
time) on the radial distribution of tensile strength of the consolidated specimen were measured. At 773K
above the recrystallization temperature, the specimen with homogeneous strength can be fabricated at pressures
above 25MPa for pure aluminum powder and 75MPa for the powder mixture, and the strength is increased
with the frequency. At 573K below the recrystallization temperature, the strength of the center point cannot
be increased with pressure and cycle (time), although the specimen has sufficient strength in the outer regions
at pressures above 75MPa.
Key words : powder forming, consolidating parameter, composite material, new forming process, shear stress
An Analysis for Predicting the Punch Fracture Limit
of Deep-Drawn Irregularly Shaped Prismatic Shells
Wen-hua SI and Toshihiko KUWABARA
(Received on May 16, 1997)
A numerical analysis method is proposed for predicting the punch fracture limit of irregularly shaped
prismatic shells deep-drawn from arbitrary shaped blanks. The punch load is assumed to consist of three
required components : (a) to draw the flange part of the blank (FFL ) , (b) to overcome the bending-unbending
deformation at the die lip (FBU) and (c) to overcome the friction forces between the blank and die (FFR ) . The
drawing stress is determined by two methods : Method I assumes that all stress components due to FFL , FBU
and FFR distribute uniformly along the die lip ; Method 2 assumes that the stress components due to FFL and
FBU distribute uniformly along the die lip, while the stress component due to FFR concentrates at the corner
arcs of the die lip. The punch fracture is considered to occur when the drawing stress exceeds the tensile
strength of the material under a plane strain condition. Several experimental results of the forming limit of
square shells are found to be between the calculated results by method I (giving the upper bound of the
maximum drawable blank size) and method 2, verifying the validity of the calculation method.
Key words : sheet metal forming, deep-drawing, punch fracture limit, numerical analysis, slip-line field theory,
kinematically admissible velocity field, prismatic shell, experimental verification
Effect of Rolling Conditions on Cross-sectional Shape of Rolled Tube
and Forward Slip Ratio for Single Stand Rolling of the Mandrel Mill
Shuji YAMAMOTO, Yasuhiro WADA, Shin-ichi TAMURA,
Kenji YAMADA, Shuichi HAMAUZU and Tatsuo OZAKI
(Received on May 28, 1997)
In the Mandrel rolling process, the set-up model of roll peripheral speed, essentially determined by two
factors i. e., cross-sectional shape of the tube at the exit of the roll-bite and the forward slip ratio, is very
important for the accuracy of tube dimensions and the surface quality of the tube. The above two factors
depend on various rolling conditions. Here, the relationships between the five rolling conditions (thickness
reduction at groove center, ratio of thickness to diameter (t/D) of inlet tube, mandrel bar speed, friction
coefficient with the mandrel bar and flange diameter of rolls) and each of the two factors have been
investigated by the rigid-plastic finite element method and by rolling experiments with a single stand model
mill. As a result, the mathematical models for the cross-sectional shape of the tube at the exit of the roll-bite
and the forward slip ratio for single stand rolling are derived. The validity of the model for the forward slip
ratio is verified in the commercial mill.
Key words : tube rolling, mandrel rolling, numerical analysis, rigid-plastic, FEM, forward slip ratio
Prediction of Limit Strain in Sheet Metal Forming Processes
by 3-D Analysis of Localized Necking
Koichi ITO, Koichi SATOH, Moriaki GOYA and Tohru YOSHIDA
(Received on June 5, 1997)
A theoretical prediction of the forming limit strain of sheet metal is developed in the framework of the
3-dimensional general bifurcation theory. The onset of 3-D discontinuous velocity field under biaxial uniform
stretched sheet is predicted. Three fundamental bifurcation mode vectors, i.e. shear horizontal, shear vertical
and normal mode are introduced and any bifurcation mode is represented by a linear combination of them.
The linear comparison solid based on the constitiutive equation proposed by authors which incorporates the
directional dependence of the plastic strain rate on the stress rate is adopted and numerical calculations of
FLD are performed using the presented theory. The results show that forming limit strains by 3-D mode are
higher than Stoeren and Rice's limit strains and that the bifurcation mode which occurs first on any strain path
changes according to the sign of the stress ratio.
Key words : sheet metal forming, forming limit strain, FLD, bifurcation, discontinuous velocity fields,
numerical analysis, localized necking, 3-D theory
Deep Drawing Properties of High-Purity Ferritic Stainless Steel Sheets
Hidehiko SUMITOMO and Hiroaki SAKURAI
(Received on July 23, 1997)
The press formability of high-purity ferritic stainless steel sheets was examined by a multi-stage cylindrical
deep drawing test. The deformation behavior and the characteristics of press forming techniques were studied.
The results obtained are as follows. (1) High-purity ferritic stainless steels have a high r-value and show
excellent deep drawability compared with conventional stainless steels of SUS430 and SUS304. (2) High-purity
ferritic stainless steels are susceptible to secondary working embrittlement, however, their susceptibility of
embrittlement is reduced by the addition of a small amount of boron. (3) It is important that any multistage
cylindrical deep drawing process should be designed to ensure metal flow from the flange to the center of the
cylindrical cup. (4) A redrawing ratio of 1.16 produced good results for high-purity ferritic stainless steel
sheets.
Key words : sheet forming, deep drawing, multistage drawing, material property, secondary working embrittlement, stainless steel sheet, boron
High Accuracy V-bending by Uniform Force Controlling
Tetsuya ANZAI, Katsumi KOYAMA Jun-ichi ENDOH
Tsutomu MIZUNO and Hajime YAMADA
(Received on , 1997)
Machine parts manufactured by cutting or casting are being replaced by sheet metal parts due to their light
weight and rigidity. In sheet metal fabrication, high accuracy bending is required. The panel industry, in
which switch boxes and automatic vending machines are manufactured, and the construction industry require
high longitudinal accuracy. The authors developed a uniform force controlling method to obtain high
accuracy, and experimentally verified its effects. The following conclusions were obtained. I ) The bending
force can be detected by piezo sensors placed in intermediate blocks, and force ratios are calculated. The
uniform force controlling method is performed using these ratios. In the case of center bending, longitudinal
accuracy is 5' using this method compared to 1 deg. 45'. Therefore, high longitudinal accuracy is obtained using
this method. 2) In the case of offset bending, longitudinal accuracy is 13' by the same method. Compared
to the conventional method, high longitudinal accuracy is obtained
Key words : bending, press-brake, sheet metal bending, controlling bending force, uniform force controlling