Key Engineering Materials
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Key Engineering Materials Vols. 340-341
Paper Title Page
Abstract: A successful THF process depends largely on the loading paths for controlling the
relationship between the internal pressure, axial feeding and the counter punch. In this study, an
adaptive algorithm combined with a finite element code LS-DYNA 3D is proposed to control the
simulation of T-shape hydroforming with a counter punch. The effects of the friction coefficients at
the interface between the tube and die on the loading path and thickness distribution of the formed
product are discussed. Experiments of protrusion hydroforming are also conducted. The final shape
and thickness distribution of the formed product are compared with the simulation results to verify the
validity of this modeling.
627
Abstract: Blank holder force (BHF) plays an important role in sheet metal forming. Previous
studies demonstrated that variable blank holder forces can improve the cold formability of
steel blank, but the research on the application of variable blank holder force in warm forming
of magnesium sheet forming has not been well investigated. In this study, the mechanical
property of AZ31 magnesium alloy sheet is measured through some uniaxial tensile tests. In
order to obtain the variational rule of the BHF, a mathematical model of BHF is deduced
based on the energy theory. The variational rule of the BHF over the punch stroke is analyzed.
Finally, three profiles of the BHF curve are designed, and the numerical simulation of warm
deep drawing process of magnesium alloy sheet is also performed. A suitable variable blank
holder force scheme is obtained through comparison among three results of simulation. The
simulation indicates that the limiting drawing ratio of AZ31 magnesium alloy sheet can be
improved from 3.0 to 3.5 with the suitable blank holder force varied by an inverted V curve.
639
Abstract: This paper is concerned with the analysis of plastic deformation of bimetal co-extrusion
process. Extrusion is related to large deformation of material and leads to non-homogeneous
deformation within work-piece material. The mechanism of plastic deformation during the composite
rod extrusion is much more complicated than that in single metal extrusion. Deformation patterns of
co-extrusion of two different materials are characterized by several process parameters. In this paper,
the analysis is focused to investigate the effect of contact conditions along the interface between two
different materials. The rigid-plastic finite element method was applied to the analysis of co-extrusion
process. The selected materials are AA 1100 aluminum alloy as hard material and CDA 110 as soft
one. This type of material selection was to examine the effect of hard core and soft sleeve and vice
versa in terms of deformation pattern. The initial composite billets were prepared by inserting the core
material in tight (0.023mm) and weak (0.012mm) interference bonding, respectively. Four different
cases of co-extrusion process in terms of material combination and interference bonding were
simulated to investigate the effect of material arrangement between core and sleeve, and of bonding
on the plastic zones. It is concluded from the simulation results that the plastic zones in this
co-extrusion process are not influenced much by the selection of material arrangements or bonding
condition between construction materials. However, it was seen from the simulation results that the
extrusion ratio of each construction material, i.e. homogeneity of co-extrusion, depends much on the
material arrangement and the bonding condition.
645
Abstract: Combined extrusion processes generally have advantages of forming in terms of the
minimum deformation power since the material is pressed through two or more orifices
simultaneously. This paper is concerned with the analysis of forming load characteristics of a
forward-backward can extrusion process using thick-walled pipe as an initial billet. The combined
tube extrusion process was analyzed by using a commercial finite element code. A thick-walled pipe
was selected as an initial billet and the punch geometry has been chosen on the basis of ICFG
recommendation. Several tool and process parameters were employed in this analysis and they are
punch nose radius, backward tube thickness, punch face angle, and frictional conditions, respectively.
The main purpose of this study is to investigate the effect of process parameters on the force
requirements in combined extrusion process. The possible extrusion process to form a
forward-backward tube parts in different process sequences were also simulated to investigate the
force requirements in sequential operations, i.e. separate operations. It was easily concluded from the
simulation results that lower forming load was predicted for the combined extrusion, compared to
those for separate sequential operations. It was also revealed that the punch nose radius and the punch
face angle have little effect on the force requirements and the forming load increases significantly as
the frictional condition along tool-workpiece interface becomes severe. The simulation results in this
study suggest that the combined extrusion process has strong advantage in terms of force
requirements as long as the simultaneous material flow into multiple orifices could be closely
controlled.
649
Abstract: This paper is concerned with the pressure distribution along the die-powder interface in
long parts. The pressure exerted on the interface at various points on the moving and stationary punch,
and also on the sidewall of container was investigated by the finite element method. A plasticity
theory describing asymmetric behavior of powdered metals in tension and compression was briefly
summarized. The yield criterion applied to the sintered powdered metals had been modified for
describing this asymmetric behavior. The material properties of copper powders under compaction
were also briefly described for the completeness of the paper. The copper powders were selected as a
model material in the present study. The main purpose of this study is to investigate the pressure
distribution along the interface of tooling quantitatively by the finite element method so that the
results could be applied usefully to the design of tooling, especially container design for powdered
metal compaction. Geometrical condition for analysis was confined to the Class II components which
is very long parts without steps. It was concluded from the simulation results that the pressure exerted
on the moving punch increases sharply near the outer circumference of punch and the pressure on the
sidewall decreases at a distance from moving punch to fixed punch. It was also seen from the
simulation that the pressure on the stationary punch is not significantly built up and decreases toward
outer periphery. These trends were seen amplified with severe frictional conditions imposed on the
tooling and powder interface.
655
Abstract: Numerical simulation technology has been used widely in plastic forming area. However,
the simulation of increasingly complex forming process leads to the generation of vast quantities of
data, which implies much useful knowledge. Consequently domain knowledge is very significant to
product design and process development in metal plastic forming area. The paper presented a new
robust optimization method based on knowledge discovery from numerical simulation. Firstly, the
knowledge discovery model from numerical simulation is established. In this model, interval-based
rule presentation is adopted to describe the uncertainty of design parameters quantitatively to enhance
the design robustness. Secondly, the optimization process based on knowledge discovery and
management is presented, and genetic arithmetic is used to obtain the robust optimization parameter.
Finally, the application to robust optimization of extrusion-forging processing is analyzed to show the
scheme to be effective. The proposed method can overcome the pathologies in simulation
optimization and improve the efficiency & robustness in design optimization.
659
Abstract: This paper is concerned with hole flangeability of steel sheet, which is evaluated by
experiment and finite element analysis with respect to the hole processing condition. The hole
flangeability of a material as a forming limit needs to be verified to predict and prevent the
undesirable fracture during a flanging process. Hole expanding tests are carried out to identify the
effect of hole processing conditions on the hole expanding ratio (HER), which is an indicator of the
hole flangeability. Specimens with two different hole conditions are prepared: one is produced with
punching process; and the other is reamed after punching to get smoother hole surface. Experimental
results show that the facture mechanism and the HER are quite different with respect to the hole
conditions. Thorough investigation of those effects is carried out with tensile tests of a specimen with
notches. From the experiments, the fracture strain is obtained with different hole conditions and is
used to determine the material constants of a new proposed ductile fracture criterion which is applied
to finite element analyses of the hole flanging process for prediction of the HER. The experimental
results are confirmed and reevaluated by the finite element analysis with the ductile fracture criterion.
665
Abstract: It has long been found that the crystal orientations would induce macroscopic anisotropy
during deformation process, and then affect the deformation properties of sheet metal. So it is very
important to find the true relation between texture distribution and macroscopic anisotropy. In this
paper, the anisotropy coefficients of the yield function are fitted by Taylor factor and crystal plastic
model. Metal flow is assumed to occur by crystallographic slip on given slip systems within each
crystal. Then this simulation results are compared with those of microscopic crystal plastic method.
671