Civil Engineering Reference
In-Depth Information
Decomposition of a three-dimensional forging flow into several plane strain flows which can be then
studied with a simpler two-dimensional method.
FIGURE 5.1
Some approximated models and methods have been developed, for instance by Chamouard [11], in
order to predict the filling of the forging dies and the forging force. Unfortunately, they are not easy to
use. In order to bring them within the reach of these persons, recently, the Chamouard's approach has
been incorporated into computer software [56]. However, according to the present computer perfor-
mances and the restricting hypothesis of such models, this is probably not the most efficient and modern
way to simulate the process, as we shall see.
As a matter of fact, all the proposed methods are restricted to two-dimensional (axisymmetrical or
plane strain approximation) problems. For complex three-dimensional flows, the 3D problem has first
to be decomposed into several 2D plane strain problems (see
Fig. 5.1
)
, which is both not easy and not
always possible.
Forging Simulation
According to the difficulties which have just been presented, the design problem often results in trial
and error. It is both time and money consuming, as the shapes of the dies are complex, difficult, and
expensive to produce. In order to lower these costs, several simulation strategies have been developed to
replace the actual trials. Easy to form model materials such as lead, plasticine [52], and wax [64] can be
substituted to the current metal, making it possible to reduce the forming force. These materials, and
more particularly plasticine and wax which are more widely used today, exhibit nearly the same behavior
as the metal under hot isothermal conditions. One of the main restriction of this approach is the
temperature dependency of the model materials, which is quite different from the behavior of the metal.
However, for most of the processes, the forging is so fast that the heat exchanges with the dies is small
and that the heat generated by the material deformation is not enough to significantly modify the material
flow. Thus, this technique provides an easy way to study the material flow, to predict the major defects
such as folds [42] and insufficient pressure in the die details, and to estimate the forging force. Moreover,
it is possible to study the material deformation and the fibering by mixing model materials of several
colors. With some mechanical models, the total strain can be computed out of these pieces of information
[52]. By mixing model materials with different properties, or by adding some other components, the
behavior of the model material can be slightly adjusted to the behavior of the studied metal. As often
for metal forming processes, the friction phenomenon is difficult to simulate. However, some kind of
model materials for the lubricants can be proposed.
The main shortcoming of this simulation approach is that although the dies can be produced into a
less expensive material and without heat treatment, they are as complex as the actual process, which
requires significant time and energy to produce them. Moreover, as has been mentioned earlier, the
thermal effects cannot be taken into account.
