Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(Vol.38 No.437 June 1997)
Confirmation of Pressure Dependence of Coefficient of Friction by means of
Direct Observation of Micro Contact Behaviors at Interface
between Tool and Workpiece
Tribology in Sheet Metal Forming lll
Akira AZUSHIMA and Masatoshi SATO
(Received on June 28, 1996)
Determination of the relationship between the coefficient of friction and the average pressure was previously
investigated for application to numerical process simulation. The author found experimentally that the
coefficient of friction was constant in the low pressure range, while in the high pressure range, it decreased
with increasing average pressure. In the present work, a flat tool drawing apparatus which consists of a
transparent die made of quartz, a microscope with a CCD camera and a video system is newly developed in
order to directly observe in situ the contact behavior at the interface. The model workpicoe material chosen is
commercially pure annealed aluminum sheets having two rough surface levels. The flat tool drawing experi-
ments are carried out at a constant speed of 0.14mm/s at eleven levels of average pressure within a range from
19 to 72MPa. Paraffinic mineral oil having a viscosity of 1460mm2/s with 5% oleic acid is used as the
lubricant.The results obtained are as follows.
(1) At low average pressure. the coefficient of friction is constant and the regime is characterized by the
isolated contact area according to the boundary lubrication model.
(2) At medium average pressure, the coefficient of friction decreases with increasing average pressure and
the regime is characterized by closed lubricant pools in which the hydrostatic pressure is generated
according to the hydrostatic-boundary lubrication model.
(3) At high average pressure, the coefficient of friction also decreases with increasing average pressure and
the regime is characterized by oil permeation into the real contact area according to the boundary,
hydrostatic and micro-plasto-hydrodynamic lubrication model.
Key words : sheet metal forming, coefficient of friction, direct observation, lubrication model, real contact
area, lubricant pool, hydrostatic pressure. lubricant permeation
Bending of Thermo Plastic Resin Pipe Using Floating
Expanding Plug
Kiyotaka HAYASHI, Masao NAKAMURA,
Seijiro MAKI and Yasunori HARADA
(Received on August 8, 1997)
Application of plastic pipes is performed using the pipe bending method with a floating expanding plug.
Preliminary tensile and expansive tests are conducted for several plastic pipes for the application. Bending
characteristics of the polycarbonate pipe, whose good bendability is estimated from the tests, is investigated.
The results indicate the following features. 1) Bendability can be estimated from residual strain using an
expansive test, whereas an estimation from a tensile test would not provide an accurate result. 2) Measures
such as an increase of expansion ratio and/or heating to increase residual strain enhance bendability. 3) A
polycarbonate pipe can be bent severely without cross-sectional distortion at room temperature. Its wall
thickness difference and flattening are both negative at a large bending radius in contrast to metallic pipes. 4) When
a hot pipe is bent, the bending moment. pipe thrust and plug tension decrease, and the shape freezability rises.
Key words : tube forming, bending, expanding. new forming process, plastics, forming property
Characteristics of the Pair-Cross Cold Rolling Mill
Applied to a Production Mill
Development of Technology for Reducing Edge-drop of
Cold Rolled Strips by Pair-Cross Mill V
Ryuji HAMADA, Shunji KAMADA, Manabu ETO,
Tetsuo KAJIHARA, Shoichi HASHIMOTO and Yutaka MATSUDA
(Received on September 20, 1996)
The N0.2 5-stand tandem cold strip mill at Sumitomo Metal Industries. Ltd., Kashima Steel Works, which
contains a pair-cross mill in stands 1-3 for the first time in a cold strip mill, was recently constructed. For
application of a pair-cross mill to a continuous mill, a new flat bearing to be located between the back-up roll
chocks and the mill housing was developed and used in order to change the roll cross angle under the rolling
force during flying gage change. From the result of an experiment performed using a production mill, it was
confirmed that the rolling force and torque remained almost constant and were nearly completely unaffected by
the cross angle. Even the maximum roll thrust force was 5% to 6% of the rolling force, which was a
permissible range for the mill. As to terms of edgedrop reductions in cold-rolled strips, it was found that the
edgedrop was greatly reduced and strips with nearly uniform thickness in cross section could be produced by
appropriate cross angle control in a pair-cross mill at stands 1-3. Further more, it was proved that the
edgedrop in a cold-rolled strip was reduced by increase of the thickness of the hot strip and high-reduction
rolling in the upper stands.
Key words : cold strip rolling, cross rolling, flat bearing, roll thrust force, edgedrop, pair-cross mill
A Coupling Analysis of Temperatures, Rolling Loads and
Metallurgical Properties in Hot Strip Mills
Hiroshi YOSHIDA
(Received on October 17, 1996)
An integrated mathematical simulator from the exit of a reheating furnace to the coiler in hot strip mills has
been developed. This Hot Integrated Mathematical Simulator (HIMS) can simultaneously estimate temperatures
of both the rolled material and the roll as well as the rolling loads and the metallurgical properties of rolled
material. The HIMS consists of three simulators related to temperature, rolling and metallurgy. (1) The
temperature simulator is used for predicting temperature changes of both the rolled material and the roll (2)
The rolling simulator is used for predicting the forces, the torques and the motor powers during rolling. (3)
The metallurgy simulator is used for predicting changes of the austenite grain size and the phase transforma-
tion, and the mechanical properties such as yield strength, tensile strength, elongation and Vickers hardness in
hot final products. The HIMS takes a coupling relation between the above three simulators into consideration
to obtain accurate results. At present, the HIMS is utilized as an effective tool for solving various problems of
hot strip mills, because of its very wide application field .
Key words : strip rolling, hot strip mill, numerical analysis, temperature, rolling load. metallurgical property
Springback Analysis of Sheet Metal Subjected to
Biaxial Stretch-bending
- Springback Analysis Of Sheet Metal IV -
Toshihiko KUWABARA, Norio SEKI and Susumu TAKAHASHI
(Received on October 18, 1996)
An elastic-plastic strain incremental analysis method for predicting the springback of sheet metal formed into
a cylindrical surface under biaxial stretching forces is developed to clarify the effects of stretching forces and
material properties on the magnitude of springback. Hill's quadratic yield criterion and its associated flow rule
are assumed. Stresses in the thickness direction and the Bauschinger effect are not considered. The whole
stretch-bending process is assumed to consist of an initial stretching process, bending process, unloading process
and springback process. A linear strain path is assumed in each process, although the proposed analysis method
is applicable to arbitrary stress/strain paths. The following results were obtained: i) springback generally
decrease$ with increasing circumferential tensile stress sigmaTx0. ii) when sigmaTx0 is small enough, springback decreases
with increasing transverse tensile stress sigmaTx0, iii) springback becomes minimum under plane-strain stretch-
bending (no change in sheet width). provided that sigmaTx0 is large enough so that the sheet is in a plastic state
in the initial stretching process, iv) springback generally increases with decreasing n-value and increasing
r-value, and v) the larger the ratio of bending radius to sheet thickness, the more marked the effect in
decreasing springback with increasing sigmaTx0.
Key words : stretch bending, biaxial stretching. cylindrical surface, springback, elastic-plastic strain incremental analysis