Thermoforming the question that why we use this


A/C Taimoor, A/C Salman, A/C

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Theoretical Background:

of all, thermoforming is a process in which a sheet is first heated and then
molded into a required mold shape. Here we will see what is the background
process, means that how certain inputs are varying and how are they changing,
because in software (Ansys) we are just giving the inputs not the formulas or
the relations by which they are varying.

polydata there is geometry as well as meshing, but these donot involve any

polydata we create some tasks as well as their sub tasks and we have to create
mold as well

Velocity or Force Driven:       

            In polyflow, when we define a
contact we do it with the help of penalty technique. In this way we define the
fluid velocity and wall velocity are related by the condition (in normal
direction) which involves the penalty co-efficient k, i-e,


            Similarly, we can use this equation
for the tangential direction but we have to take the slip co-efficient into
account, i-e


We have
seen how the contact force is applied, now here we have some selection of
whether we want our problem to be velocity imposed or force driven. If our
problem is velocity imposed we can use the above mentioned equations but if it
is force driven then we have to solve the corresponding momentum equation,

                                                            Fm+Ff =Ma

= force applied on mold

Ff  = resistance from the fluid

a = acceleration of the mold

of the moving part

Now here
is the question that why we use this equation? It is because we want to define
a limit for the maximum displacement, because when the deformation increases
shear force and hence the motion of the mold is decreased. So if displacement
tends to increase beyond its limit its motion is stopped. That’s why maximum
displacement is calculated.


Isothermal or non-isothermal:

            If our simulation is isothermal then
the conditions (thermal boundary conditions) are same before and after the
contact but if our simulation is non-isothermal then the flow conditions are
not the same before and after the contact,i-e


                                    where ‘a’ is convective co-efficient


the viscosity changes with change in temperature as shown by the following


Constant viscosity and strain
dependent viscosity:

            Most of the times we take constant
viscosity for shell models but sometimes it is more desirable to take viscosity
in terms of local strain. For this case the fluid constitutive equation is
written as follows:


simple traction experiment, we, at constant stretching velocity, stretch the
sample of initial length L0 and record the tensile stress as a
function of deformation. After some manipulation we can take viscosity as a
ratio of stress to strain rate.

= V0/(L0+?L)


?0+a ?2+bexp(-((?-
?p)/ ?w)2)


 Typical Viscosity Curve Exhibiting Strain

Viscosity Curve Described with the Smooth Ramp Function


how postprocessor things are calculated.

Mass of the blown


of the parison



Permeability of the
blown product:

            Permeability is important to be calculated in the
packing of pharmaceuticals where moisture content is important.

                                                p= ? /h

is permeability co-efficient

is local thickness






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