Download pdf - TRAINING IN THE FIELD OF POLYMER MATERIALS / … · Source: T. Kisslinger: Einfluss der thermischen Stoffdaten auf Berechnungsergebnisse in Moldflow Plastics Insight (MPI), Studienarbeit

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Ass.Prof. Dr. Thomas Lucyshyn 24th April 2014

Influence of material data on injection moulding simulation

Application examples

TRAINING IN THE FIELD OF POLYMER MATERIALS / PLASTICS

www.kunststofftechnik.at Thomas Lucyshyn 2

Content

Introduction

Melt Flow Rate (MFR) as reference value for viscosity

Pressure dependence of viscosity

Transition temperature

Thermal conductivity and specific heat capacity

pvT-data at different cooling rates

Summary


Content

Introduction






Summary


Required material data

Viscosity as a function of

Shear rate, temperature and optionally pressure

Transition temperature Ttrans

Thermal conductivity (ideally temperature dependent)

Specific heat (ideally temperature dependent)

pvT-data

Mechanical properties

Young´s modulus, Poisson ratio, shear modulus, coefficient of linear thermal expansion

Fibre properties


Material data for injection moulding simulation

Source: Internet


Content

Introduction






Summary


Measuring method of MFR

Source according to: Waßner, E.: Rheologische Grundlagen für die Auslegung von Extrusionswerkzeugen, VDI-Praktikum: Werkzeugauslegung mit Excel, Paderborn, 2003.

Weight

Piston

Sample

Heating

Nozzle Shear rate:

Viscosity:

Shear stress: Weight (mass):

MFR: Melt mass flow rate in g/10min

MVR: Melt volume flow rate in cm³/10min

Nozzle:


MFR as reference value for viscosity?


MFR for comparing materials?

MFR of A = MFR of B Rheological behaviour of A = Rheological behaviour of B?

MFR

log

log

Material A Material B


Example: pressure calculation at same MFR

2 unfilled POM-grades of same supplier


Viscosity curves of the two POM-grades


Part for simulation

Square box 100 x 100 x 40 mm³ (1 mm wall thickness)

Hot runner with central gate at the bottom


Pressure at swich over point (filling pressure)

Hostaform s9363 Celcon M50-14

1185 bar 1476 bar

25%


Content

Introduction






Summary


Cross-WLF-equation in Moldflow



n

1

0

0

1

(8)

*TTA

*TTAexpD

2

110

pDD*T 32

pDAA ~ 322

Pressure dependence!

Approx. 8.800 thermoplastics in Moldflow 2014, of which about 100 materials with D3



CB1

A

n

1

0

0

1

(8)

0

0

*

1-n temperature

pressure


Part: thin walled bush

Wall thickness about 0,4 to 0,8 mm

Injection pressure at the injection moulding machine: 2400 bar


Measuring results of pressure dependent viscosity

1000 bar

1 bar

Vis

cosi

ty in P

a*s

Shear rate in s-1


Calucations with and without pressure dependence

Without pressure dependence With pressure dependence


Pressure at switch-over point (injection pressure)

1284 bar

Without pressure dependence

2368 bar

With pressure dependence

85%


Content

Introduction






Summary


Transition temperature (No-Flow)

Experimental determination

DSC-Measurement (Differential Scanning Calorimetry) In cooling mode at -20 K/min Determination of the „onset temperature“

Capillary rheometer (not used any more) Melt polymer turn off heating piston with constant load

squeeze out melt until strand speed = 2mm/min (equals 0,033 mm/s!)

Further (less frequent) methods: Adapted injection moulding machine Pressure measurement at capillary rheometer Cone-plate-rheometer


Transition temperature with DSC

oven chamber

DSC sample and reference

Source:

Mettler Toledo AG, CH


20 40 60 80 100 120 140 160 180 2000

10

20

30

40

50

60

70

80

H (

mW

)

T (°C) Hostacom BR 735 G

Heat flow H as a function of temperature T

PP

cooling rate -20 K/min


Cooling mode

Source: T. Lucyshyn, G. Knapp, M. Kipperer, C. Holzer: Determination of the Transition Temperature at Different Cooling Rates and Its Influence on Prediction of Shrinkage and Warpage in Injection Molding Simulation. Journal of Applied Polymer Science, 2012, 123, S.1162-1168.

Transition temp. of a semi-crystalline polymer


Transition temperature (point of inflection)

Cooling mode


Transition temp. of an amorphous polymer

ABS (cooling rate -20 K/min)


Heat flux at different cooling rates for PP

20 40 60 80 100 120 140 160 180 2000

10

20

30

40

50

60

70

80 5 K/min

10 K/min

20 K/min

40 K/min

50 K/min

H (

mW

)

T (°C) Hostacom BR 735 G



Transition temp. as a function of cooling rate for PP

b

transt

TaT

Parameter PP

Hostacom BR 735 G

a (minbK(1-b)) 415,4

b (-) -0,0148

Correlation coefficient R2

0,983 0 10 20 30 40 50 60 70 80 90 100 110

380

385

390

395

400

405

410

Ttr

ans (

K)

Hostacom BR 735 GCooling rate (K/min)

Ttrans



Box for simulation and experiments

100 x 100 x 40 mm³



Results for warpage simulation for PP

10 20 30 40 50 60 70 80 90 100 1100,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

Defo

rmation (

%)

Cooling rate (K/min) Hostacom BR 735 G 3D

L1 experiment

L2 experiment

L3 experiment

H1 experiment

H2 experiment

L1 simulation

L2 simulation

L3 simulation

H1 simulation

H2 simulation

Box:

1 mm wall thickness



Content

Introduction






Summary


Semi-crystalline thermoplastics

0

0,1

0,2

0,3

0,4

0 50 100 150 200 250 300 350Temperatur [°C]

Wä

rme

leit

fäh

igk

eit

[W

/mK

] PP

PA

POM

Amorphous thermoplastics

0

0,1

0,2

0,3

0 50 100 150 200 250 300 350Temperatur [°C]

Wä

rme

leit

fäh

igk

eit

[W

/mK

]

PS

ABS

PC

Thermal conductivity

Source: T. Kisslinger: Einfluss der thermischen Stoffdaten auf Berechnungsergebnisse in Moldflow Plastics Insight (MPI), Studienarbeit am Institut für Kunststoffverarbeitung, Montanuniversität Leoben, 2007.

Th

erm

al

co

nd

ucti

vit

y (

W/m

K)

Temperature (°C)

Th

erm

al

co

nd

ucti

vit

y (

W/m

K)

Temperature (°C)


Specific heat capacity (cp)


0

4000

8000

12000

16000

0 50 100 150 200 250 300 350Temperatur [°C]

Cp

[J

/Kg

K]

PP

PA

POM

0

500

1000

1500

2000

2500

0 50 100 150 200 250 300 350Temperatur [°C]

Cp

[J

/Kg

K]

PS

ABS

PC

Semi-crystalline thermoplastics

Amorphous thermoplastics

cp (

J/k

gK

)

cp (

J/k

gK

)

Temperature (°C) Temperature (°C)


Single values – temperature dependent values

Single value of specific heat at melt temperature (example for PP)

Single value of thermal conductivity at melt temperature (example for PP)

0

0,05

0,1

0,15

0,2

0,25

0,3

0 50 100 150 200 250 300

Temperatur [°C]

Wä

rme

leit

fäh

igk

eit

[W

/mK

]

0

4000

8000

12000

16000

0 50 100 150 200 250 300

Temperatur [°C]

Cp

[J

/Kg

K]


cp (

J/k

gK

) T

he

rma

l co

nd

ucti

vit

y (

W/m

K)

Temperature (°C)

Temperature (°C)


Influence on cycle time

Temperature of hottest region in part over time

Time to reach ejection temperature evaluated

Investigated region of part




Example PP, 3 mm wall thickness


Tim

e (

s)

Mesh variations



Example PS, 3 mm wall thickness

18,08

22,1621,65

17,28

20,4120,63

25,02

29,02

0,00

5,00

10,00

15,00

20,00

25,00

30,00

35,00

PS Fusion 3mm PS 3D 3mm

Berechnungsvarianten

Ze

it [

se

c]

λ(T) cp(T)

λ(T) cp

λ cp(T)

λ cp


Tim

e (

s)

Mesh variations


Content

Introduction






Summary


Semi-crystalline polymer

Temperature (°C)

Specific volume (cm³/g)

pvT-data

Amorphous polymer


Source according to: Kennedy, P.: Flow Analysis of Injection Molds; Carl Hanser Verlag, München, 1995.

melt

solid

melt

solid

Temperature (°C)

Specific volume (cm³/g)



Standard measurement method for pvT-data

m

rlT,pv

2

Cooling rate of approx.

0,1 K/s (6 K/min)


high cooling rate (hcr) pvT-device

Stroke transducer

Thermocouple Ejector piston

Measuring cell

Polymer sample

Cooling channels

Cooling channels

Piston

IR-sensor

Oven

IR-sensor

Pressure transducer

in hydraulic system

Cooling rates up to

15 K/s

Source: T. Lucyshyn: Messung von pvT-Daten bei prozessnahen Abkühlraten und deren Einfluss auf die Simulation von Schwindung und

Verzug mit Moldflow Plastics Insight, Dissertation an der Montanuniversität Leoben, 2009.


Results of hcr-pvT-device for ABS

0,92

0,94

0,96

0,98

1,00

1,02

1,04

1,06

0 50 100 150 200 250

Temperatur in °C

Sp

ezif

isc

he

s V

olu

me

n in

cm

³/g

200 bar hcr-pvT

400 bar hcr-pvT

600 bar hcr-pvT

800 bar hcr-pvT

200 bar MPI

400 bar MPI

600 bar MPI

800 bar MPI

ABS

Ca. 13 K/s

Ca. 0,1 K/s

2,3 mm sample



Temperature (°C)

Sp

ecif

ic v

olu

me

(cm

³/g

)


Results of hcr-pvT-device for PP

Ca. 15 K/s

Ca. 0,1 K/s

0,94

0,96

0,98

1,00

1,02

1,04

1,06

1,08

1,10

1,12

0 50 100 150 200 250

Temperatur in °C

Sp

ez. V

olu

me

n in

cm

³/g

400 bar hcr-pvT

600 bar hcr-pvT

800 bar hcr-pvT

400 bar MPI

600 bar MPI

800 bar MPI

PP

2 mm Probe



Temperature (°C)

Sp

ecif

ic v

olu

me

(cm

³/g

)


Simulation results for ABS

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

L1 L2 L3 H1 H2

Vergleichsmaße

De

form

ati

on

in

%

Standard pvT

hcr-pvT

Experiment

ABS, 3D-Model



Reference dimensions


Simulation results for PP

PP, 3D-Model

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

L1 L2 L3 H1 H2

Vergleichsmaße

De

form

ati

on

in

%

Standard pvT

hcr-pvT

Experiment



Reference dimensions


Content

Introduction






Summary


Summary 1

Complex material data required for simulation

Melt Flow Rate (MFR) as reference value for viscosity?

Good orientation for limitation of potential similar materials

Important: compare viscosity curves!

Example: pressure difference of 25% at same MFR


Viscosity increases with increasing pressure

Especially important for thin walled parts

Relevant at expected injection pressures > 1000 bar

Example: pressure difference of 85%


Summary 2


Determined with DSC measurement

Cooling rate has influence on transition temperature

Transition temperature has influence on warpage results

Temperature dependent thermal data

Significant differences between single point data and temperature dependent data

Especially cycle time differs by up to 15%

pvT-data

Cooling rate has influence on pvT-curves

Improved shrinkage simulation with pvT-data obtained at process near cooling rates


Thank you for your attention!

Contact: Ass.Prof. Dr. Thomas Lucyshyn Chair of Polymer Processing Montanuniversitaet Leoben Otto Gloeckel-Str. 2 8700 Leoben 03842 / 402 – 3510 [email protected]