- Blow Molding
- Thermoforming
- Stamping
- Miscellaneous
POLYFLOW can simulate all phases of various blow molding
processes: Extrusion Blow Molding (EBM), Injection Blow Molding (IBM), Stretch
Blow Molding (SBM) and 3D extrusion blow molding. For EBM, this includes
the stage of the extrusion of the parison with, if desired, moving mandrels.
Similar methods are used to simulate the thermoforming process, including
pre-stretching and pressure or vacuum-forming.
Click on Image to view Animation
POLYFLOW simulations give you a window on the blow molding and thermoforming
processes, allowing you to see how they evolve with time and how potential
troubles might develop. The software is accessible in a user-friendly
environment and provides graphical feedback and detailed information
to determine the range of optimal process conditions and/or material properties
and to correct potential problems.
 Click on Image to view Animation
In particular, POLYFLOW's robust numerical algorithms account for large displacements
of the parison or sheet and predict the contact between the fluid and
the mold and other mechanical devices during the closing of the mold and
parison pinch-off and the parison inflation. Moving molds or plugs can
be considered, including the effect of slip, as well as complex geometries
(gas tanks, containers, bottles with handles) and multi-layer blow molding.
For the entire process, POLYFLOW provides information on:
- the effects of gravity on the sagging of the extruded parison
- the pinch-off and inflation process and possible blowability limitations
and the location of flashes
- the process sensitivity to operating parameters and materials properties
- the fluid temperature distribution resulting from cooling during the
shaping
- the thickness and extensions distribution, the results of which can
be transferred to structural analysis software for further analysis
- the cooling phase resulting from contact with the die including the
crystallization
In POLYFLOW, the parison is modeled as a fluid. Standard rheological
data are only required for a simulation. POLYFLOW offers the largest library
of fluid models (including viscous, generalized Newtonian and KBKZ viscoelastic)
for a realistic representation of the material properties of the melt.
Both a membrane model approach and a full three-dimensional elements approach
are available and all current capabilities are available both for single
and multilayer configurations.
The initial (extruded or injected) parison shape and mold geometry are
set-up by standard CAD tools or extracted from parison extrusion simulations.
The melt model and the operating conditions are selected interactively
and also stored for further analyses. It is then easy to modify the geometry,
the fluid properties or the process conditions to select the best process
scenario. With these data, POLYFLOW calculates the flow within a few hours
on standard PC or Unix platforms and produces a sequence of "snapshots"
of the process with detailed information about various features of interest.
These can smoothly be animated to offer additional insight in the transient
effects of the blow molding and thermoforming processes.
Blow Molding
- Process Description
- The Challenges
- Benefits Gained
- Advanced Numerical Aspects
Process Description
The extrusion blow molding or injection (stretch) blow molding process
is the method of choice to form any kind of hollow product such as bottles,
gas tanks, or car bumpers. The process has four
stages : extrusion, pinch-off, blowing and cooling. Each phase presents
numerous challenges and the success of the whole process depends upon
the success of each phase.
The final goal of the extrusion blow molding process is
a blown bottle with a uniform thickness or at least a formed container
where the blown products minimum thickness is above the minimum thickness
everywhere else. In order to meet this final objective the parison extruded
in the first phase must have the proper thickness profile.
Extrusion
A thin parison is extruded through a die whose die lip is usually, but
not always, circular. In order to adjust the thickness profile of the
parison, the inner die mandrel can move up and down according to a predefined
transient motion. This will open or close the aperture at the die lip
creating a more or less thick parison. The influence of the gravity is
quite significant in this process since as the material is extruded and
the parison grows, its weight will pull the material downward, stretching
the extruded parison and modifying its thickness profile.
For gas tanks and bottles, multi layered parisons (up to 7 layers) are
usually considered in order to gain the mechanical, chemical and
optical features. In addition to the global thickness profile, the designer
has to make sure that each layer also keeps the proper thickness.
Pinch-off
After the parison has been extruded, it is cut and placed between the
two halves of the mold. Next, the molds are moved toward each other to
close the container. Part of the parison is crushed between the two halves
of the mold, creating the scraps. This is lost material, since it will be
cut before the bottle is shipped. An objective of the designer is to reduce
the quantity of material wasted in this section.
The quality of the welding line is very important. This is usually a
weakness of the blown part.
Blowing
When the cavity is closed, air (or another gas) is injected into the
cavity in order to blow the melt parison. Typical blowing pressure of
a few bar, is applied along the inner parison. Potentially, this blowing
pressure can change as a function of time
As the parison is blown, some sections of it hit the mold. Step-by-step,
the parison takes the exact shape of the mold leading to the final blown
product.
Cooling
When the parison has been blown, heat is exchanged by both the mold
and possibly by the injection of cold air. The thin parison is quickly
cooled down to room temperature. This often induces some phase change
and crystallization.
The Challenges
The goal of the blow molding process is to obtain a blown product
whose parison is neither too thin (otherwise, the container would break
at the thinnest section as soon as it is under constraint) nor too thick.
A too thick section is
a waste of material and money. Also, a well defined thickness
profile must be obtained at the end of the process.
Numerous difficulties prevent the mold designer from reaching this objective
in the first trial.
Phase change and crystallization will induce additional deformation and
residual stresses. This weakens the final bottle and modifies its thickness
profile.
During the blowing phase, the parison is blown like a balloon, generating
a lot of stretching. Viscoelastic effects such
as strain hardening sometimes prevent a too-large decrease of the
parison thickness during the blowing phase. However, the more the parison
is blown, the thinner the final thickness. Also, the sections first in
contact with the mold will not deform much whereas the sections of the
parison where the fly will be the longest could see their thickness reduced
a lot. These problems make it very difficult to guess a priori what the
final thickness will be considering the initial thickness of the parison.
The pinch-off is definitely a critical phase of the process. The quality
of the welding line must be maintained.
The difficulty is even greater for multilayer blow molding processes.
It is then important to make sure that each layer is still present along
the welding line despite some different rheological behavior and sometimes
very different viscosities.
Finally, the extrusion step is perhaps the most critical, since it
determines the initial thickness distribution of the parison. The difficulties
include the swelling and sagging of the parison, together with heat exchange
with the environment air and the moving inner mandrel. The motion of the
mandrel provides a degree of freedom for the designer in adjusting
the initial thickness of the parison. Trial-and-error is usually necessary
in order to find the relevant transient motion.
Benefits Gained
POLYFLOW is able to simulate the different phases of both the extrusion
blow molding and the injection (stretch) blow molding processes. It allows
you to understand the influence of each parameter independently.
All the challenges described above can be analyzed and solved using
POLYFLOW.
2D axisymmetric simulation of the (co)extrusion phase can be carried
out taking into account the swelling, the sagging, the heat exchange and
the moving mandrel. As a result of the die geometry, the flowing material
and their operating conditions, it is possible to determine what the thickness
profile of the initial parison would be.
Next, you start from this initial thickness distribution to blow
the product and calculate the final thickness profile. Most of the time
this final thickness is far from meeting the target requested by the product
designer. Also, the thickness profile of the initial parison, hence the
motion of the inner mandrel of the mold, has to be modified. Step-by-step
you are able to improve the quality of the final product, making
sure that the thickness is above the minimum value everywhere.
Certainly, most of the key parameters of the simulation such as the inflation
pressure and the speed of the mold are time-dependent, possibly with very
complex functions of time. These dependencies can be simulated either
by using the typical functions already predefined in the code, or by specifying
arbitrary time functions.
Temperature profiles across the parison are another key point that POLYFLOW
simulates. As soon as the parison is blown or during the blowing process
itself, the heat exchange between the polymer and the mold is calculated.
The parison is cooled down while the mold is slightly heated in the vicinity
of its inner cavity. Simulating the cooling process is especially important
since this is usually a long part of the the whole process (a few seconds).
Also, the cooling stage must be long enough to allow for the completion
of the cooling while remaining as short as possible in order to keep the
cycle time low. In addition, change of phase, i.e. the crystallization
of the material during the cooling may be calculated during the simulation.
It is then possible to get another evaluation of the quality of the final
product.
The blow molding process is a typical example where biaxial and possibly
uniaxial (stretch blow molding) extensional behaviors are important. Also,
the strain hardening phenomenon, i.e. the increasing resistance of the
resin to the extension as the deformations increase, can not be neglected.
Otherwise, inaccurate results would be calculated. Polyflow has
implemented differential viscoelastic models in 2D and KBKZ viscoelastic
models in 3D in order to take this behavior into account.
Most of the time a membrane approximation for the parison is considered.
This strongly reduces the computational time required to solve a simulation
while barely affecting the quality of the results. Indeed, the thickness
dimension (~1 mm) is very very small compared to typical dimensions of
the blown product (from a few cm up to 1 m). Here, the parison is modeled
as a surface deforming in a 3D environment. However, in some specific
situations where the temperature, velocity or thermal gradient across
the thickness can not be neglected, a full 3D simulation including
volume elements across the parison can also be simulated.
Advanced Numerical Aspects
One of the greatest challenges of blow molding simulation lies in the
fact that there is a parison flying in open room until it comes into contact
with a mold whose geometry can be quite complex. We have developed an
intelligent contact algorithm that detects whether the parison is still
flying or whether it has already reached the mold, whatever its shape.
Furthermore, the boundary conditions switch from a free surface without
heat exchange (or limited heat exchange with the surrounding air) toward
an adherence or partial slip condition and an intense heat exchange with
the mold.
Due to the very large deformation undergone by the parison, very specific
and powerful remeshing rules have been implemented. One of the them, the
Lagrangian remeshing technique, tracks each material point so that it is
possible to understand where each point is coming from in the initial parison.
Thermoforming
- Process Description
- The Challenges
- Benefits Gained
- Advanced Numerical Aspects
Process Description
Thermoforming is the method of choice to form any kind of
large flat product such as a car door panel, a truck wind deflector, or a
yogurt container. The process has
three stages : extrusion, blowing and cooling. Each phase presents numerous
challenges and the success of the whole process depends on the success
of each phase.
The final goal of the thermoforming process is to have a blown product
with either a uniform thickness or at least a formed container where the
minimum blown product thickness is above the minimum thickness everywhere
else. In order to meet this final objective, the parison extruded in the
first phase must have the proper thickness profile.
Extrusion
A thin sheet is extruded through a coat hanger die. The thickness of
the extruded product should be as uniform as possible. Only the edge of
the sheet where border effects are observed will be cut.
Often, multi layered sheets (up to 7 layers) are considered in order
to gain from the mechanical, chemical and optical features of each resin.
In addition to the global thickness profile, the designer has to make
sure that each layer keeps the proper thickness.
Blowing
The initial sheet is pre heated. Usually a non-uniform map of temperature
is considered in order to locally modify the resistance of the material
to the deformations. Next, air (or another gas) is blown onto the sheet
in order to deform the melt sheet. Typical blowing pressure of a few bars
is applied along the inner parison. Potentially, this blowing pressure
can change as a function of time. As the parison is being blown, some
sections of it hit the mold. Step-by-step, the parison takes the exact
shape of the mold, leading the the final blown product.
Another technique consists of creating a vacuum between the sheet and
the male mold, so the melt sheet is attracted toward the mold, quickly
acquiring the shape of it.
Cooling
When all the parison has been blown, heat is exchanged by both the mold
and possibly by the injection of cold air. The thin parison is quickly
cooled down to room temperature. This often induces some phase change
and crystallization.
The Challenges
The final goal of the thermoforming process is to obtain a product
neither too thin (otherwise, the container would break at
the thinnest section as soon as it is under constraint) nor too thick.
A too thick section is a waste of material and money. Also, a well defined thickness
profile must be obtained at the end of the process.
Numerous difficulties prevent the mold designer from reaching this objective
in the first trial.
During the cooling of the parison, due to the density variation on the
temperature, residual flow of the polymer or glass is observed. Furthermore,
phase change and crystallization will induce additional deformation and
residual stress. This weakens the final bottle and modifies its thickness
profile.
During the blowing phase, the sheet is blown like a balloon generating
a lot of stretching across the parison. Viscoelastic effects such
as strain hardening can sometimes prevent a too large decrease of the
parison thickness during the blowing phase. However, the more the sheet
is blown, the thinner the final thickness. Also, the sections first in
contact with the mold will not deform much whereas the sections of the
sheet where the fly will be the longest could see their thickness reduced
a lot. These problems make it very difficult to guess a priori what the
final thickness will be, considering an initial thickness of the parison.
Benefits Gained with POLYFLOW
POLYFLOW is able to simulate the different phases of the thermoforming
process, including the sheet (co)extrusion stage. It allows the user to
understand the influence of each parameter independently. All the challenges
described above can be analyzed and solved using POLYFLOW.
Full 3D simulation of the extrusion or coextrusion of the sheet process
is simulated. This provides valuable information, such as the thickness
profile of the extruded sheet as well as the position of the interface(s).
It also tells you the width of the sheet with a constant
thickness. This is usually what is used for further thermoforming applications.
If you are buying your plastic sheets from an external company,
these sheets usually come with a constant thickness. You start from
this initial thickness distribution, but usually specify a non uniform
temperature map in order to adjust the final thickness distribution of
the formed product. Due to the temperature dependence of the viscosity,
the resistance of the material to the deformations will change a lot if
the material is cold or warm. By adjusting the initial temperature map,
you fine tune the local behavior of the sheet during the forming
process.
Most of the time this final thickness is far from your final target.
Also, the temperature map of the initial
sheet, hence the preheating process, has to be modified. Step-by-step,
you are able to improve the quality of the final product making sure
that the thickness is above the minimum value everywhere.
Certainly, most of the key parameters of the simulation, such as the inflation
pressure and the speed of the mold, are time dependent, possibly with very
complex functions of time. These dependences can be simulated either by
using the typical functions already predefined in the code or by specifying
arbitrary time functions.
The temperature profile across the sheet evolves during the process.
As soon as the sheet is blown, or during the blowing process itself, the
heat exchange between the polymer and the mold is calculated. The sheet
is cooled down while the mold is slightly heated in the vicinity of its
inner cavity. Simulating the cooling process is especially important since
this is usually a long part of the whole process (a few seconds). Also,
the cooling stage must be long enough to allow for the completion of the
part cooling while remaining as short as possible in order to keep the
cycle time low. In addition, change of phase, i.e. the crystallization
of the material during the cooling may be calculated during the simulation.
It is then possible to get another evaluation of the quality of the final
product.
The thermoforming process is a typical example where biaxial extensional
behaviors are important. Also, the strain hardening phenomenon, i.e. the
increasing resistance of the resin to the extension as the deformations
increase, can not be neglected. Otherwise, inaccurate results
would be calculated. POLYFLOW has implemented differential viscoelastic
models in 2D and KBKZ viscoelastic models in 3D in order to take this
behavior into account.
Most of the time, a membrane approximation for the sheet is considered.
This strongly reduces the computational time required to solve a simulation
while the quality of the results is barely affected by this approximation.
Indeed, the thickness dimension (~1 mm) is very very small compared to
typical dimensions of the blown product (from a few cm up to 1 m). In
this case, the sheet is modeled as a surface, deforming in a 3D environment.
However, in some specific situations where the temperature, velocity or
thermal gradient across the thickness can not be neglected, a
full 3D simulation, including volume elements across the sheet, can be
simulated.
Advanced Numerical Aspects
One of the greatest challenges of the thermoforming simulation lies in
the fact that there is a sheet flying in the open room until it comes
into contact with a mold, which may be of complex shape. We have
developed an intelligent contact algorithm that detects whether the sheet
is still flying or whether it has already reached the mold, whatever
the shape of it.
Furthermore, the boundary conditions switch from a free surface without
heat exchange (or limited heat exchange with the surrounding air) toward
an adherence or partial slip condition and an intense heat exchange with
the mold).
Due to the very large deformation undergone by the sheet, very specific
and powerful remeshing rules have been implemented. One of the them, the
Lagrangian remeshing technique, tracks each material point so that it is
possible to understand where each point is coming from in the initial sheet.
Stamping
- Process Description
- The Challenges
- Benefits Gained
- Advanced Numerical Aspects
Process Description
The stamping process is very similar to the thermorforming process used
for large flat plastic products and practically identical to the stamping
process used in the metal industry. The process has
three stages : extrusion, blowing and cooling. Each phase presents numerous
challenges, yet the success of the whole process depends on the success
of each phase. The major difference between it and the thermoforming
process is the presence of additional moving parts that will either
speed up the process by pushing the sheet of plastic or avoid some undesired
crease.
The final goal of the stamping process is a blown product
of either uniform thickness or at least a formed container where the minimum
blown product thickness is above the minimum thickness everywhere else.
In order to meet this final objective the parison extruded in the first
phase must have the proper thickness profile.
Extrusion
A thin sheet of plastic is extruded through a coat hanger die. The thickness
of the extruded product should be as uniform as possible. Only the edge
of the sheet where border effects are often observed will be cut.
Often, multi layered sheets (up to 7 layers) are considered in order
to gain from the mechanical, chemical and optical features of each resin.
In addition to the global thickness profile, the designer has to make
sure that each layer keeps the proper thickness as well.
Blowing
The initial sheet is pre heated. Usually a non-uniform map of temperature
is considered in order to locally modify the resistance of the material
to the deformations. Next, a male mold starts moving, pushing and deforming
the sheet towards the female mold. This stamp motion allows the process
to go faster than simply blowing the sheet. However, this process can
lead to a local tearing of the sheet, completely ruining the product.
Also, a modification of the process could be to first blow the sheet of
plastic while the stamp starts moving a round, blown shape of the blown
sheet usually prevents any residual tearing while keeping the benefit
of a faster process.
During the blowing phase, air (or another gas) is blown onto the sheet
in order to deform the melt sheet. Typical blowing pressures of a few
bars are applied along the inner parison. Potentially, this blowing pressure
can change as a function of time. As the sheet is deforming, some sections
of it hit the mold. Step-by-step, the sheet takes the exact shape of
the mold, leading to the final blown product.
Another technique consists of creating a vacuum between the sheet and
the male mold, so that the melted sheet is attracted towards the mold,
quickly acquiring the shape of it.
Cooling
As soon as the sheet is in contact with the mold, heat is exchanged by
both the mold and possibly by the injection of cold air. The thin parison
is quickly cooled down to room temperature. This often induces some phase
change and crystallization.
The Challenges
The final goal of the stamping process is to obtain a product whose thickness
is neither too thin (otherwise, the container would break at the thinnest
sections as soon as it's under pressure) nor too thick. A too thick section
is a waste of material
and money. So, a well defined thickness profile must be obtained at the
end of the process.
Numerous difficulties prevent the mold designer from reaching this objective
in the first trial.
During the cooling of the product, due to the density variation of the
temperature, residual flow of the polymer or glass is observed. Furthermore,
phase change and crystallization will induce additional deformation and
residual stress. This weakens the final container and modifies its thickness
profile.
During the blowing phase, the sheet is blown like a balloon, generating
a lot of stretching across the thin sheet. Viscoelastic effects, such
as strain hardening, could sometimes prevent a too large decrease of the
plastic sheet thickness during the blowing phase. However, the more the
sheet is blown, the thinner the final thickness. Also, the sections first
in contact with the mold will not deform much whereas the sections of
the sheet where the fly will be the longest could see their thickness
reduced a lot. These problems make it very difficult to guess a priori
what the final thickness will be considering the initial thickness of
the parison.
Benefits Gained with POLYFLOW
POLYFLOW is able to simulate the different phases of the stamping process
including the sheet (co)extrusion stage. It allows you to understand
the influence of each parameter independently. All the challenges described
above can be analyzed and solved using POLYFLOW.
Full 3D simulation of the extrusion or coextrusion of the sheet process
can be done. This provides valuable information such as the thickness
profile of the extruded sheet as well as the position of the interface(s).
It also tells you the width of the sheet with a constant
thickness. This is usually the part that is used for further stamping
applications.
If you buy your plastic sheets from an external company, these
sheets usually come with a constant thickness. You starts from this
initial thickness distribution but usually specify a non uniform temperature
map in order to adjust the final thickness distribution of the formed
product. Due to the temperature dependence of the viscosity, the resistance
of the material to the deformations will change a lot if the material
is cold or warm. By adjusting the initial temperature map, you fine
tune the local behavior of the sheet during the forming process.
Most of the time this final thickness is far from your product design target.
Also, the temperature map of the initial
sheet, hence the preheating process, has to be modified. Step-by-step,
you improve the quality of the final product, making sure
that the thickness is above the minimum required value everywhere.
Certainly, most of the key parameters of the simulation such as the inflation
pressure and the speed of the mold are time-dependent, possibly with very
complex functions of time. These dependencies can be simulated either
by using the typical functions already predefined in the code or by specifying
arbitrary time functions.
The temperature profile across the sheet evolves during the process.
As soon as the sheet is blown, or during the blowing process itself, the
heat exchange between the polymer and the mold is calculated. The sheet
is cooled down while the mold is slightly heated in the vicinity of its
inner cavity. Simulating the cooling process is especially important since
this is usually a long part of the the overall process (a few seconds
at least compared to the longer inflation time). Also, the cooling stage
must be long enough to allow for the completion of the cooling part while
remaining as short as possible in order to keep the cycle time low. In
addition, change of phase, i.e. the crystallization of the material during
the cooling may be calculated during the simulation. It is then possible
to get another evaluation of the quality of the final product.
The stamping process is a typical example where biaxial extensional behaviors
are important. Also, the strain hardening phenomenon, i.e. the increasing
resistance of the resin to the extension as the deformations increase,
can not be neglected. Otherwise, unaccurate results would be calculated.
Polyflow has implemented differential viscoelastic models in 2D and KBKZ
viscoelastic models in 3D in order to take these behaviors into account.
Most of the time a membrane approximation for the sheet is considered.
This strongly reduces the computational time required to solve a simulation
while the quality of the results is barely affected by this approximation.
Indeed, the thickness dimension (~1 mm) is very, very small compared to
typical dimensions of the blown product (from a few cm up to 1 m). Here,
the sheet is modeled as a surface deforming in a 3D environment. However,
in some specific situations where the temperature, velocity or thermal
gradients across the thickness can not be neglected, a full 3D
simulation including volume elements across the sheet can also be simulated
by POLYFLOW.
Advanced Numerical Aspects
The stamping process is typically a transient process. However, the use
of an implicit transient scheme in order to solve the equation allows for
the use of a large time step. An algorithm monitors the size of each time
step and adjusts them according to the convergence criteria and the difference
between the predictor and corrector models used in POLYFLOW.
One of the greatest challenges of the stamping simulation lies in the
fact that there is a sheet flying in open room until it comes in contact
with one or several mold(s) whose geometry can be quite complex. Also,
we have developed an intelligent contact algorithm that detects whether
the sheet is still flying or whether it has already reached the mold, whatever
the shape may be.
Furthermore, the boundary conditions switch from a free surface without
heat exchange (or limited heat exchange with the surrounding air) towards
an adherence or partial slip condition and an intense heat exchange with
the mold).
Due to the very large deformations undergone by the sheet, very specific
and powerful remeshing rules have been implemented. One of the them, the
Lagrangian remeshing technique tracks each material point so that it is
possible to understand where in the initial sheet each point is coming
from.
Miscellaneous
- Dish Shaping
- Tube Coating
- Glass Pressing
- Compression Molding
- Roll Coating
There are many other applications where the contact capabilities of POLYFLOW
are very useful. Every day, our users come up with
new ideas that make use of these specific contact features. Here are a few of these ideas.
Dish Shaping
The dish shaping process is an interesting process
where a sample of material (glass, clay, polymer) is dropped on a rotating
mold. Due to the high rotational speed, the material tends to move toward
the rim of the rotating dish. This action causes the gob to deform strongly.
The initial free surface moves away. During this deformation, the
free surface falls onto the rotating mold. Using the contact detection
features of POLYFLOW, we are able not only to predict the deformation of
the free surface but also where and when it will enter into contact with
the mold.
Thanks to powerful remeshing techniques available in our code, very large
deformations have been calculated, completing the whole process. Information
such as the local velocity, the temperature map, the local shear rate,
stresses, etc can also be calculated.
Tube Coating
For specific materials that can not undergo high shear rates (fluoropolymers
such as FEP), the pressure coating process, where the material is quickly
stretched as it touches the moving cable, can not be applied. In order
to avoid the polymer deterioration, a smoother contact between the FEP
and the wire is created after the polymer has left the die. The contact
between the moving cable and the flowing polymer occurs after the die
lip. There is a vacuum created in order to push the resin towards the
cable. The material comes into contact with the cable at a position that
can vary depending on the operating conditions.
Glass Pressing
Glass pressing is a widely used process to form glasses. In this process,
a gob of glass at high temperature falls into a cylindrical cavity. Next,
the stamp comes down and presses the melt glass. The material climbs up
along the narrow channel left between the moving down stamp and the mold.
It can easily be understood that very large deformation of the initial
mesh is encountered. Despite the powerful remeshing techniques available
in POLYFLOW, the mesh deformation can be so large that a new mesh needs
to be defined. Then, an interpolation between the two meshes allows us
to proceed with the simulation while restarting with the previous results
of temperature, velocity, stresses. Heat exchange with the mold is particularly
important in this process.
Compression Molding
The compression molding process is similar to glass pressing, but
the material is not the same (polymers are more widely used for
compression molding) and the shape of the male mold is usually more complex.
For the compression molding process, POLYFLOW simulates the
stamp coming down into the layer of polymer. The contact between the moving
mold and the polymer is detected by the code so that the free surface
deforms accordingly. The material is possibly pushed away from its initial
position.
Roll Coating
A thin layer of polymer leaves the die. After some distance in the open
air, the polymer is squeezed between two rotating rolls. Sometimes, the
thin layer is simply pulled by a single rotating roll. Many parameters
can influence this process and move the position of the contact point
between the rotating roll(s) and the polymer. Also, the contact detection
technique available in POLYFLOW allows us to easily determine the position
of the contact as well as its evolution as a function of time or due to
any perturbation introduced into the flow.
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