Transcript Slide 1

Design Improvement of a U-Profile Extrusion Die
Using Inverse CFD Simulation
2005 CFD Summit
The Meeting of the Minds in Flow Modeling
June 7-9, 2005
Dearborn, Michigan
M. Kostic, Northern Illinois University
Srinivasa Rao Vaddiraju, Northern Illinois University
Louis G. Reifschneider, Illinois State University
Motivation and Objectives
To design and fabricate a U-profile die for testing
using a laboratory extruder
To assess the role of CFD simulation for extrusion die design
(1) die swell
(2) mass flow balance, and
(3) optimum die profile-shape
How the simulation results compare
to actual experimental results
To assess the role of the calibrator in shaping the final profile
of the extrudate
Cooling simulation in the calibrator using the experimental data
Polyflow Inverse Extrusion Simulation
General Assumptions :
The flow is steady
and incompressible
Body forces and Inertia effects are negligible
in comparison with viscous and pressure forces.
Specific heat at constant pressure, Cp, and
thermal conductivity, k, are assumed constant
Required Extrudate Profile
27.94 mm
25.4 mm
(2.54 mm thick)
Viscosity Model: Cross-WLF
h0 (T )
where
h (T , g &) =
,
1 n
&
 h0 (T ) g 
1+

*
 t

 A1 (T - D2 ) 
h 0(T ) = D1 exp 
 A2 + (T - D2 ) 
HIPS: DOW Styron 478 (MFI=6)
BASF 496N (MFI=2.8)
Pseudoplacticity included
Viscoelastic effects neglected.
Exploded View of Die Assembly
Extruder Die Mounting Plate
Extruder U-Profile Adapter Plate
Transition Plate
Melt Flow
direction
Simulation determines
Pre-Land & Die Land
plates
Pre-Land
Die Land
Finite Element Mesh
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MESH
16,592 hex. elem.
19,530 nodes.
Solution
Windows PC,
1 GB RAM,
@ 2.39 GHz,
Isothermal analysis
required 552 minutes
CPU.
Boundary Conditions (symmetry)
Pre-land inlet geometry fixed
No slip at die surface
Inlet: fully
developed flow
Die land: uniform passage
Free Surface:
Zero traction &
No normal velocity
Free surface exit matches target
extrudate: fixed
Symmetry
Plane
Exit: Zero normal stress &
Plug flow
Flow simulation only within the die
30
Profile of the inlet to the pre-land plate
was determined by a series of trial and
error extrusion simulations to insure a
balanced mass flow exiting the die.
25
20
Prela
Prela
Prela
Prela
Prela
Outlet 1
Prela
15
Outle
Outle
Outle
Outlet 2
Outle
Outle
Outle
Outlet 3
10
Outlet 4
Outlet 5
5
Outlet 7 Outlet 6
0
0
2
4
6
8
10
12
14
16
18
Representative Pressure and Velocity
Results
Pressure (Pa)
Velocity Magnitude (m/s)
Inverse Extrusion simulation results with Pre-land and
Die Land Contours
Extrudate Free Surface
(Target Profile)
Die Land
Pre-land Inlet
Preland Inlet
Preland Inlet
Preland Inlet
Preland Inlet
Preland Inlet
Preland Inlet
Dieland
Dieland
Dieland
Dieland
Dieland
Dieland
Outlet
Outlet
Outlet
Outlet
Outlet
Outlet
Pre-land Inlet
Symmetry
Plane
Die Land
(Target Profile)
Direct Extrusion simulation result with Styron
478 and Styron 496
30
478 direct extrusion extrudate profile
496 direct extrusion extrudate profile
25
Target extrudate profile
Outlet
20
Outlet
Outlet
As expected the free surface outlet
profile from the results of direct
extrusion with Styron 478 is very
close to the target profile we used in
inverse extrusion CFD simulation.
Outlet
Outlet
Outlet
478 iso direct
478 iso direct
478 iso direct
15
478 iso direct
478 iso direct
478 iso direct
496 iso direct
496 iso direct
496 iso direct
496 iso direct
10
496 iso direct
496 iso direct
5
0
0
2
4
6
8
10
12
14
16
18
Photograph of U-Profile Die Stack
Vacuum Calibrator Design
Vacuum Lines
Extrudate Passage
Stacked Plate Design:
Passage matches target profile, no
taper along flow direction.
Cooling Lines
Vacuum
Lines
Schematic of U-Profile Extrusion Line
with Data Acquisition
Upper Exit
IR
Cut Off
Puller
Cooling Tank
Upper
Calibrator
Lower
Calibrator
Puller
Product
Upper
T/C
Lower Exit
IR
Lower
T/C
Inlet IR
U-Profile
Die
Calibrator Set-up (opened)
Exit Top
IR
Inlet IR
Die
Cooling Tank
Exit
Bottom IR
Closed Calibrator
Calibrator
Exit
Inlet
Die
Exit
Bottom IR
Product Shrinkage at Calibrator Exit
Corner pulling away
Side wall shrinkage:
3% – 6%
Air gap =
shrinkage
Calibration rearranges mass balance
U-Profile Wall Thickness Distribution
Air cushion mass balance
% of Target Dimension (2.54 mm)
100
Calibrated mass balance
98
96
4 kg/hr
94
5 kg/hr
92
6 kg/hr
P @ 5.5 kg/hr
90
P @ 3 kg/hr
88
E
86
84
A
B
C
D
E
F
G
H
I
C
G
A
I
Measurem ent Point
P@3 kg/hr (most uniform thickness) is 6% thinner
than target: draw down and shrinkage affects.
h_upper
h_lower
Heat
Transfer
Data
Ref. [10]
Fredette
h (W/m^2/K)
10000
1000
100
Order of magnitude
difference: can testing
results be generalized?
10
0.5
1.0
1.5
Fourier Number ~ (contact time/thickness^2)
Representative U-Profile Calibrator Heat Transfer Data
Recorded temperatures for P @ 3 kg/hr (C )
Inlet IR
Upper IR Lower IR Upper T/C Lower T/C
206
71
60
30
24
Contact time with calibrator: 15 sec.
Thickness of extrudate between IR probes: 2.34 mm
Fourier number = 0.93
Estimated heat transfer coefficients (W/m^2/K)
h_upper = 175
h_lower = 225
Temperature data input
to transient 1-D
simulation to iterate for
effective heat transfer
between extrudate and
calibrator.
Boundary Conditions
for Extrudate Cooling Simulation
Tinlet = 505 K
Free Surface
L = 50 mm
h tot = h conv+ h rad
= 10 W/m2K + 15 W/m2K
T  = 295 K
Calibrator
L = 95 mm
hupper = 175 W/m 2 K, T  = 303 K
hlower = 225 W/m 2 K, T = 297 K
upper
h
h lower
V = 6.3 mm/s
Adiabatic
Evolution of Temperature Contours as Extrudate Passes
Through Calibrator
Temperature History Plot Points
Upper
Middle
Lower
150 - 200
200+
150 - 200
100 - 150
100 - 150
50 - 100
Black area
solidified
Inlet
Outline of full
profile shown
Midway
< 50
Exit
Center-line Temperature History
at Three Critical Points
Middle
Upper
Lower
Calibrator
Free Surface
Temperature (C)
250
200
150
100
50
0.00
0.05
0.10
Distance from die exit (m)
0.15
Conclusions
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Inverse extrusion simulation predicts profile
die shape
Custom tuning of profile dies still required.
Total product design requires coupled design
of the die and the calibrator, however…
Calibration design difficult due to coupled heat
transfer and product deformation
difficult to gather general empirical data,
 difficult to simulate due to contact element
boundary conditions.
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ACKNOWLEDGEMENTS
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Dr. M. Kostic and S. R. Vaddiraju thank:
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NICADD (Northern Illinois Centre for Accelerator and
Detector Development), NIU
Fermi National Accelerator Laboratory, Batavia, IL
NIU’s College of Engineering and Department of
Mechanical Engineering
Dr. L. Reifschneider thanks:
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College of Applied Science and Technology at Illinois
State University for financial support to conduct the die
design research.
QUESTIONS ?
Contact Information:
mailto: [email protected]
www.kostic.niu.edu
mailto: [email protected]
www.vaddiraju.com
mailto: [email protected]