Civil Engineering Reference
In-Depth Information
FIGURE 5.2
First forging operation of an aeronautical rotor, beginning and end.
Nowadays, the numerical simulation provides much faster results as the toolings are only virtually
designed. Moreover, these results are more accurate and more varied, such as the flow at different times
of the process, the velocity field, the strain, the strain rates, the stresses, the temperature, the tool wear,
and the tool deformation. Several softwares have been marketed, such as the well spread FORGE2
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[9],
[40] and DEFORM2D
[65] (initially called ALPID), [47] for axisymmetrical and plane strain problems.
They are actual tools for designers and their industrial use is ever increasing. Indeed, they make it easy
to quickly find the main shortcomings of the studied design, and then to test several modifications to
improve it. For expensive safety parts, or for very large single parts, they also provide a quality insurance
as they give an estimation of the mechanical characteristics of the part which should otherwise be
obtained by destructive testing. Regarding the true three-dimensional problems, automatic remeshing
difficulties, as well as computational time and memory requirements, have long hindered the industrial
use of these softwares. Nowadays, both the software and hardware progresses have made these compu-
tations possible. They are used in forging companies, for instance to understand the development of a
fold and test whether a new preform design can remove it [22]. The tool shape discretization required
for the numerical simulation, often a finite element mesh of the tool surface by triangles, can almost
directly be obtained from the CAD design. It reduces to rather insignificant times the specific numerical
design required by the finite element simulation. FORGE3
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[13], [15] and DEFORM3D
©
[66] are such
available softwares.
The following example shows how the numerical simulation can be used to design a forging sequence.
It has been carried out using the FORGE2
software. The problem is the forging of an axisymmetrical
aeronautical rotor in three steps, starting from a cylinder. The preliminary upsetting (
Fig. 5.7
)
only
provides the correct high/radius ratio, so it does not require a specific study. The first actual forging step,
the preforming operation (
Fig. 5.2
) h
as to be optimized. In fact, during the second and finishing operation
(
Fig. 5.3
),
as in the actual process, a piping defect is observed (
Fig. 5.4
)
under the inside rib. The study
of the velocity field (
Fig. 5.5
)
helps to understand the defect formation, due to the conjunction of two
flows to fill the rib. After several trials and errors, a better preform shape is proposed to prevent this kind
of flow.
Figure 5.6
shows the modified upper tool of the preforming operation, and the resulting flow
during the finishing operation. It can be noticed that the conjunction of flows has been removed. Starting
from this new preform, the final shape is well obtained, without noticeable defects. The process is then
more precisely studied, with a special focus on the material deformation. Marks are made on the initial
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