The deep drawing process is a
widely used sheet metal forming process. It is frequently
used in the automotive industry to manufacture products
with complicated shapes and curvatures. An initially flat
or pre-shaped sheet material, the blank, is clamped between
a die and a blankholder. The blankholder is loaded by a
blankholder force, which is necessary to prevent wrinkling
and to control the material flow into the die cavity. Then
the punch is pushed into the die cavity, simultaneously
transferring the specific shape of the punch and the die to
the blank.
An incorrect design of
the tools, the blank shape or an incorrect choice of
material, lubrication and process parameters can yield a
product with a deviating shape or with failures. A
deviating shape is caused by elastic springback after
forming and retracting the tools. The most frequent types
of failure are wrinkling, necking (and subsequently
tearing), scratching and orange peel. Wrinkling may occur
in areas with high compressive strains, necking may occur
in areas with high tensile strains, scratching is caused by
defects of the tool surface and orange peel may occur after
excessive deformations, depending on the grain size of the
material.
Without extensive
knowledge of the influences of all these variables on the
deep drawing process, it is hardly possible to design the
tools adequately and make a proper choice of blank material
and lubricant to manufacture a product with the desired
shape and performance. As a result, after the first design
of the tools and choice of blank material and lubricant, an
extensive and time consuming trial and error process is
started to determine the proper tool design and all other
variables, leading to the desired product. This trial and
error process can yield an unnecessary number of deep
drawing strokes, or may even require redesigning the
expensive tools. To reduce this waste of time and cost,
process modelling for computer simulation can be used to
replace the experimental trial and error process by a
virtual trial and error process.
The finite element
method is used worldwide to simulate the deep drawing
process. For an accurate simulation of a real-life deep
drawing process an accurate numerical description of the
tools is necessary, as well as an accurate description of
material behaviour, contact behaviour and other process
variables. One of the main problems for deep drawn products
is springback. Even when the process is set up carefully,
the product will spring back when the tools are released.
In industrial practice, deformations due to springback are
compensated manually, by doing extensive measurements on
prototype parts, and altering the tool geometry by hand.
This is a time consuming and costly operation. The FE
method is a powerful tool to show springback deformations
before prototypes are made. The results of a simulation can
be used to modify the tools automatically, using the
results of a FE simulation. In other words, the original
tools are compensated for the springback. With an effective
and reliable tool, the die redesign-process can be
significantly faster. But, the tool can also be used
earlier in the process, integrating structural and
geometrical design right from the start. The application of
‘design for manufacturing’
opens up new possibilities for creating
parts with high performance materials and complex shapes.
Currently, the accuracy and reliability of numerical
simulations of sheet metal forming processes do not always
satisfy the industrial requirements. Therefore extensive
research in the field of sheet metal forming is and will be
necessary to decrease the existing gap between the
real-life deepdrawing process and the predictions obtained
from deep drawing simulations.
When the quality of the
deep drawing simulations is good enough, simulations can be
used as a tool to check the manufacturability (robustness)
and geometry of the desired part. To be able to achieve an
optimal process, several geometric and parameter variations
must be investigated.
Therefore, many
simulations must be carried out with different process
parameters and with different tool geometries. Currently,
this requires a lot of expensive and time-consuming manual
work, based on experience. Due to the use of new materials
and production processes, it becomes more and more
difficult to find the optimum process settings.
Therefore there is a strong need for an algorithm which is
able to find the optimum settings for sheet forming
processes. Nowadays, research on this topic is in full
swing.
Anthology of finished graduate projects:
Industrial partners: