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1 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Numerical simulation of heat sealing process of multilayer packaging films
Presented by:
Benjamin StephanFraunhofer-Institut für Verfahrenstechnik und Verpackung IVV
Institutsteil VerarbeitungstechnikDresden, Germany
16TH TAPPI EUROPEAN PLACE CONFERENCE
In collaboration with
2 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Introduction
Simulation model setup
Material characterization
Experimental validation
Results
Conclusions
Structure
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3 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Introduction
Simulation model setup
Material characterization
Experimental validation
Results
Conclusions
Structure
4 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Seal failures are costly
Introduction
Implications:
• Food waste
• Retail penalties
• Impact consumer preference
• Slowdown of packaging speed
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5 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Simulation of heat sealing process
Goal is the modeling of caulkability or polymer flow during sealing to close leaker channels to achieve hermetic pouches
State of the art: Flow model based simulation
Too simplified
Complicated to extend for multilayer films
Our approach: Numerical simulation
Introduction
6 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Introduction
Simulation model setup
Material characterization
Experimental validation
Results
Conclusions
Structure
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7 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Simulation model setup
What do we want to predict?
Polymer flow based on tool design, film configuration and process parameters
What do we need?
Geometry model
Boundary conditions and loads
Numerical method
Material model
8 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Simulation model setup - geometry
Flat tools Dimension reduction
“Quasi-2D” simulation with one element row
One support layer, three co-extruded seal layers
Meshing with tetrahedral elements
At least two elements across height of each layer
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9 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Simulation model setup - boundary conditions and loads
Layers tied to each other
Self-contact of some layers
Temperatures, movements:
A lot more: Heat transfer coefficients, …
10 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Simulation model setup - numerical method
Main challenges
High deformation Mesh distortion
Phase transition Large drop in stiffness
Calculation time Small elements, “long” process
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11 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Simulation model setup - numerical method
Simulation method: Element-Free-Galerkin formulation
Mesh-free method
Features remeshingat high distortion
Usually used formetal forming process
Implicit calculation Calculation time
12 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Introduction
Simulation model setup
Material characterization
Experimental validation
Results
Conclusions
Structure
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13 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
As close as possible to process – tensile tests?
Compression tests!
Data analysis via semi-automated process
Material characterization
14 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Material card for elastic-plastic material model
Result: Temperature dependent stress-strain curves
No strain rate effects considered
Material characterization
increasingtemperature
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15 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Characterization of each material
In total four materials characterized
Easy change of film configuration
Further included:
Temperature dependent specific heat capacity
Constant thermal expansion & heat conductivity
Material characterization
16 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Introduction
Simulation model setup
Material characterization
Experimental validation
Results
Conclusions
Structure
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17 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Qualitative comparison to experiments
Sealing tests with different process parameters
T= 120 … 160 °C, F= 250, 1000 N, t=700 ms
Fixed tool geometry
Experimental validation
18 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Cuts by Optical Coherent Tomography
Non-destructive „cuts“ through semi-transparent material
Fast alternative to microtome cuts
Experimental validation
Cross section @ layer step of seal @ T=140°C, f=1000N
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19 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Introduction
Simulation model setup
Material characterization
Experimental validation
Results
Conclusions
Structure
20 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Results
Example of deformation
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21 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Results
Example of temperature distribution
Example of plastic strain
22 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Results – capturing of some phenomena
Unsealed area
Tendency of wrinkles
140°C, 250 N
130°C, 250 N
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23 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Results – influence of process parameters
Minimum needed time for tight seal decreases with temperature
Melt flow limited to „cut out section“melt cannot escape simulation boundaries
Minimum needed sealing time
450 ms
400 ms
252 ms
130 °C
140 °C
150 °C
All @ 1000 N
24 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Results – some drawbacks
Extreme wrinkles lead to unstable solution
197 ms
238 ms
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25 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
True 3D-model, e.g. serrated sealing tools high computational cost
Improve stability Simulation tools constantly improve
Include strain rate effects Already possible with
material model
1E+0
1E+1
1E+2
1E+3
1E+4
1E+5
0.01 0.1 1 10 100
Shear rate in 1/s
Viscosity in Pa*s
Outlook
26 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Conclusions
Simulation of melt flow is possible with special numerical methods
Model is able to capture some phenomena like wrinkles, gaps, ….
Estimation on minimum seal time for tight seal can be given
Temperature distribution, stresses, strain, … can be visualized
Large nonlinearities, like wrinkles cannot be simulated currently.
The choice of sealant material and the coextruded film composition influence caulkability
The model is now being used in Dow R&D
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27 Benjamin Stephan, Fraunhofer IVV Dresden – Numerical Seal Simulation - 17th TAPPI European PLACE Conference 2019 Porto – Session 7 - Paper 4
Presented by: Benjamin StephanFraunhofer IVV Dresden, [email protected]
Peter SandkuehlerGlobal Application Technology Leader Packaging and Specialty Plastics
Dowemail: [email protected]
“Thank You” for sticking with my
presentation
