05-03-2013, 03:31 PM
STAMPING SIMULATION STUDY ON AL-6061 ALLOY USING FEA APPROACH
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ABSTRACT
Roof header made of Al-6061 alloys an important component in a passenger car. It is the
roof headers profile that plays an important role in giving the befitting elegance to an
automotive vehicle. The key features of the roof header are built in using the stamping
operations of a sheet metal of light alloys like Al. 6000 series. During the stamping process
it’s of utmost importance to ensure all the key features in the roof header die gets impressed
to the closest tolerance. It is equally important to ensure good surface finish during the
stamping operation. All the above factors discussed in this section are mainly controlled by
the stamping process parameters. Ram velocity, clamp holding pressure, the uniformity in
the thickness of the sheet metal, the design of the die and the punches are some of the
important parameters to control in order to ensure high quality roof header. Optimizing the
stamping process for the metals in producing high quality roof headers is time consuming
and very expensive because of much Iteration involving several combinations of the designs
of the die and the punch and the work piece materials. In the light of the above: researchers
are currently adopting FEA based software’s to overcome the challenges associated with the
stamping process. With the advent of high computing technologies, complex shaped sheet
metal profiles for automotive applications can be modeled with ease and can be imported to
FEA solvers for design optimization studies of die and tooling’s .
INTRODUCTION
Stamping is very important in aspect for manufacturing of any sheet metal components. In
the past decades it has been found that stamping simulation can save lot of metal and also
can be cost effective, will make the manufacturing cheaper and with better quality product. In the present study a portion of the roof header is considered of an automotive convertible roof
system and it’s made up of alloy-Al 6061. An attempt has been made to reduce the metal for
a quality product and comparison study for different thickness of the work piece and with
various Ram velocities is presented to understand the forming / stamping urge in the current
scenario of the competitive market.
Formability plot shows the cracks and other important aspects for the metal thinning after it is
formed. The strain and von-Mises stress plays a major role in the forming process. Many
times it’s possible to get the risk of cracks in the locations near the transition from concave
and convex geometry. A comparative study based on three different parameters and we
along with results based on the combination of the parameters tabulated. Following are the
parameters considered for the forming / stamping.
FE MODEL SET UP
FE modelling for the simulation is done using ANSA (Beta-CAE-Systems). For setting up the
simulation deck the CAD models are derived from the CAD software. Basically we ha ve 3
parts Punch, Holder and Blank for the simulation. Initially the CAD data of Punch or Die is
considered then suitable modifications are made to fit in to other parts like blank die. As in
the stamping / forming process of any sheet metal features are the important ones. The
features like fillets, bosses, beads, grooves are very vital from the modeling perspective as
these are the regions where the forming is very different from normal flat regions. These are
the areas where there will be maximum material flow and maximum stress builds up so these
regions needs to be dealt with more care. So typically flat regions are modeled with an
average element size of 8-10 mm where as the critical features are modeled with extremely
finer element size like 2-3 mm. Hence forth the features on die are modelled in detail as
shown in Figure 1.
LOADING AND BOUNDARY CONDITIONS
BOUNDARY CONDITIONS
For any Finite element analysis to get a good result its quite essential to define proper
constraints and bounda ry conditions. A proper boundary condition definition ensures that we
get a proper result. Basically while defining the boundary condition we try to simulate the FE
analysis in a way, which resembles the actual physical process. So in a way resembling
actual process we try to replicate the same in the FE model by constraining or arresting
some Degrees of Freedom.
In the present case we are constraining all the nodes of die along all 6 degrees of freedom
by following this step we are making the die a perfectly rigid. We are also ensuring that the
Punch is free to move in all direction so as the blank.
LOADING CONDITIONS
INITIAL VELOCITY OR PUNCH VELOCITY
Here we will be applying the loads to the model set up in 2 ways. The first is the initial
velocity or the punch velocity. In this load condition we will be applying the velocity on all the
nodes present on the punch along z-axis. Based on specific requirement we will be turning
on the velocity and acceleration displacement card. We will be describing the Load CASE ID
(LCID) in order to specify the motion value v/s time. We also will be defining a load scale
factor.
HOLDER FORCE
The second loading condition which we are going to apply on this model is the clamping
holding force or simply know as holding pressure. This we will be applying on the holder,
which encircles the blank, which is getting formed. Here also we will be applying a load curve
to pre describe the motion pattern in terms of time steps.
CONCLUSIONS
The Thickness of the material which is getting formed has a major impact on the
stresses (Both von -mises as well shear stress). Normally stress will decrease with
increase in the thickness of the material but due to the spring back effect and due to
high bending stress in high thickness of the blank the thickness of the material the
stresses may increase even with if we increase the thickness of the material