Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(Vol.40 No.459 April 1999)
Consideration of the Fracture Mechanism of a Metal Plate
during Shearing by an Impulsive Pressure
Minoru MOCHIHARA, Masahiro FUJITA,
Kazuyuki HOKAMOTO and Yasuhiro NAKIYAMA
(Received on December 24, 1998)
The deformation mechanism of a metal plate sheared by impulsive pressure is numerically analyzed,
and deformation and fracture processes are studied and compared with the experimental results.
At an early stage of deformation, the metal plate is sheared only around the die edge with no
appearanc of cracks. The fiber structure at the plate's lower surface seems to have been cut
from the die edge, eventually causing cracks around the die edge. Meanwhile, necking due to
tensile deformation occurs on the plate's upper surface in line with shear development,
finally causing other cracks. These two cracks appear almost simultaneously at both the die edge
and the plate's upper surface, causing the plate to be totally sheared. The effects of strain
hardening, the distance between two straight die edges, and pressure applied to the plate are
also discussed.
Key words : shearing, high-energy rate forming, numerical analysis, FDM, fracture mechanism, shock pressure
Sharp Bending of Sheet Metal with Indentation of V-Shaped Punch
Hideo OGAWA and Akitake MAKINOUCHI
(Received on July 21, 1998)
Recently bent parts of sheet metal generally require sharp bend corners
from the point of view of presenting a fine appearance. For sharp bending,
there is a method of cutting the part of the sheet in question into a V-groove
form before bending. However, this method is problematic in that the strength
of the bent part is reduced and V-groove cutting requires much time. To resolve
such problems, the present study examined the method of first forming the V-groove
by pressing a V-shaped punch onto the sheet before bending. The features of this
method are that the strength is improved through work hardening by punch indentation,
that a press machine is used for groove formation so that the work time is reduced,
and that no exclusive cutting machine is required. Sharpness of the bent corner
is nearly the same as that of the groove cut material, and the strength of the bent part
is improved to about 1.2`1.4 times that of the groove cut sheet. For groove formation,
a CNC turret punch press can also be used, and the bending radius of the obtained
product is nearly equal to that of the groove indentation sheet by means of a usual punch.
Key words : bending, die bending, sheet metal bending, forming property, accuracy, bend radius, bent part strength, press-brake, CNC turret punch press
Rolling Characteristics on Helical Rolling of Tube
Hideo TAKIZAWA and Toshio KIMURA
(Received on July 24, 1998)
In a helical rolling mill, three conical rolls are arranged periodically
around the pass line and the roll axes are inclined relative to the pass
line by a cross angle and a feed angle. The tube is driven forward by the front
tension applied on the top end of the tube and the frictional force of
rolls. Large axial elongation is achieved by reducing the diameter and
the wall thickness. In this paper, hot rolling experiments are carried out
using a carbon steel tube. The forming limit of this process is experimentally
determined. The tube can be rolled without defects by controlling the front
tension. The effects of forming conditions on rolling force, torque and specific
energy consumption are examined. To decrease specific energy consumption,
the front tension is more effective as the axial driving force than the
frictional force of rolls. Specific energy consumption in this process
is extremely large. The energy is mainly consumed for redundant deformation
which does not remain on the rolled tube. This redundant deformation
occurrs at the inlet boundary of the contact area. Therefore, specific
energy consumption becomes lower as the number of contacts decreases.
Key words : rotary forming, helical rolling, tube rolling, forming limit, forming defects, deformation-load property, specific energy consumption
Numerical Analysis of Reshaping Process from
Round Pipes to gCross-Typeh Pipes
Manabu KIUCHI, Ken SHINTANI and Hassan MOSLEMI NAEINI
(Received on August 17, 1998)
In this paper, an elasto-plastic method is extensively developed to investigate
characteristics of reshaping processes from round pipes to gcross-typeh
pipes. In this method, the plane strain condition is assumed and the shearing
deformation is neglected while the shearing force is considered in the equilibrium
equations. The peripheral equilibrium equation of forces and moments is
satisfied at each portion of the cross section of pipe whether each element is
in contact with the roll or not. In order to deal with the behavior of the pipe
during deformation, a modified contact model is suggested. By the method
developed, various reshaping processes are analyzed and the effects of the
reshaping conditions on the geometry of the cross section, peripheral distribution
of curvature, occurrence of defects, corner radius, peripheral shrinkage rate,
increasing rate of wall-thickness, corner bending moment and load per unit
length are investigated.
Key words : pipe/tube, reshaping process, plane strain analysis, cold roll forming, roll design, process design