Datapoint Testing Services 1

Understanding the Role of

Material Properties in

Simulations- Part 2

Hubert Lobo

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Introduction -

Virtual Manufacturing (CAE)

The computer as a virtual process

laboratory

– understand the process

– create and test scenarios

– make improvements at design stage

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Introduction- Material Properties

Plastics in simulation

– Each plastic has a unique property profile

– The importance of proper representation

=

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Scheme of presentation

Define property requirements

Identify evaluation parameters

Follow the injection molding process

Identify the role of material properties at

each stage of the process

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Modes of analysis- mold filling

mold filling

mold cooling

post filling simulations

shrink/warp

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Data requirements- mold filling

viscosity v/s shear rate, temperature

thermal conductivity v/s temperature

specific heat v/s temperature

melt density

no flow temperature M

eject temperature M

transition temperature C

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Viscosity

P

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Thermal Conductivity

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 50 100 150 200

Temperature °C

Th

erm

al C

ond

uct

ivit

y W

/m·K

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Specific Heat

0

1000

2000

3000

4000

5000

6000

0 100 200 300 400

Temperature °C

Spe

cific

Hea

t J/

kg·°

C

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Melt Density

High-pressure flow rate measurements

Instrument-capillary rheometer

P

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No Flow Temperature

Moldflow requirement:

Temperature at which flow

ceases under a particular applied

load. (133 Bar)

Instrument-capillary rheometer P

V

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DSC Transitions

0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

0 1 0 0 2 0 0 3 0 0 4 0 0

Te m p e r a t u r e °C

Sp

ecif

ic H

ea

t J

/kg

·°C

Eject Temperature

Transition Temperature

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Additional Data - post filling

pvT

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pvT

A: High pressure dilatometry

B: Piston-cylinder method

– Temperature ranges

» Process to ambient

– Pressure Range

» 0-200 MPa

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Additional Data - Moldflow

shrink/warp

Shrinkage/Warpage coefficients

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Shrinkage coefficients

Injection molding of grid-marked tags

Different thicknesses

Several process conditions

Bidirectional measurement of shrinkage

Correlate using Moldflow

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Evaluation Parameters

material property based parameters

evaluate effects seen in the process

understand and interpret simulation results

compare materials

develop criteria for selection based on

desired processability

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Properties of Evaluation

Parameters

Easily calculated

Estimates of actual parameters

Must be considered along with other

relevant parameters

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Viscosity V

isco

sity

Pa

·s

10.0

100.0

1000.0

10000.0

10 100 1000 10000

Shear Rate 1/s

300 °C

320 °C

340 °C

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Evaluation Parameters-Viscosity

Nature of the 2nd order matrix

– Temperatures

» Tmelt

» Tmelt+20

» Tmelt-20

– Shear rates

» 100

» 1000

» 10000

T

Tmelt-20 1000

Tmelt 100

Tmelt 1000

Tmelt 10000

Tmelt+20 100 Tmelt+20 1000

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Evaluation Parameters -Viscosity

Temperature sensitivity of viscosity

– TVL= ( ln- ln ) / 20

– TVH = ( ln- ln ) / 20

T

Tmelt-20 1000

Tmelt 100

Tmelt 1000

Tmelt 10000

Tmelt+20 100 Tmelt+20 1000

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Evaluation Parameters -Viscosity

Rules

– if TV is large, material is highly sensitive

– TVL > TVH

– Semi-crystalline

» TVL == TVH

– Amorphous

» TVL >> TVH PP

ABS

PS

PC

PPA

0 10 20 30 40 50 60

TV* 1E+03

PP

ABS

PS

PC

PPA

Resin

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Evaluation Parameters -Viscosity

Shear sensitivity of viscosity

– Defining a limited power-law index.

» SHB= ( ln- ln ) / 2.303 T

Tmelt-20 1000

Tmelt 100

Tmelt 1000

Tmelt 10000

Tmelt+20 100 Tmelt+20 1000

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Evaluation Parameters -Viscosity

Rules

– 0<SHB < 1

– Large SHB = shear sensitive

– Important exception:

» broad newtonian

(eg. PC)

Vis

cosi

ty P

a·s

10.0

100.0

1000.0

10000.0

10 100 1000 10000

Shear Rate 1/s

300 °C

320 °C

340 °C

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Thermal mass

– TMASS=(rho*Cp)

– units = J/m3.K

– True measure of heat capacity

Rules

– Large TMASS = cools slowly

– Large TMASS = more heat to remove

Evaluation Parameters- Thermal

Steel

TMASS=3.6e6

Cp=460

Plastic

TMASS=1.9e6

Cp=1700

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Evaluation Parameters- Thermal

Thermal diffusivity

– a = (k / TMASS)

– units = m2/s

– Measure of heat transfer rate

Rules

– Large a = cools quickly

PP/Talc

a = 8.7e-8

k = 0.21

PP

a = 7.7e-8

k = 0.17

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Evaluation Parameters- Thermal

No-flow temperature

– NOFLO

– maps closely with crystallization temp

– 20-30C higher than Tg (amorphous materials)

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Evaluation Parameters- Thermal

Eject Temperature

– EJECT

Rules

– High (EJECT - TMOLD) = lower cycle time

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Evaluation Parameters- PVT

0.80

0.85

0.90

0.95

1.00

1.05

1.10

0 50 100 150 200 250

Temperature °C

Sp

ecif

ic V

olu

me

m /

kg

x 1

00

0

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Evaluation Parameters-PVT

Nature of the PVT matrix

– Temperatures

» TS1 - TS7

» TB1-TB2

» TM1-TM4

– Pressures

» 0 MPa

» 160 MPa

T P V

TS1 0 VS1

TS2 0 VS2

TS3 0 VS3

TS4 0 VS4

TS5 160 VS5

TS6 160 VS6

TS7 160 VS7

TB1 0 VB1

TB2 160 VB2

TM1 0 VM1

TM2 0 VM2

TM3 160 VM3

TM4 160 VM4

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Evaluation Parameters- PVT

Volumetric expansion coefficient (VEC)

– VEC=dV/dT

– VECS=(VS1-VS2) / (TS1-TS2)

– VECM=(VM1-VM2) / (TM1-TM2)

T P V

TS1 0 VS1

TS2 0 VS2

TS3 0 VS3

TS4 0 VS4

TS5 160 VS5

TS6 160 VS6

TS7 160 VS7

TB1 0 VB1

TB2 160 VB2

TM1 0 VM1

TM2 0 VM2

TM3 160 VM3

TM4 160 VM4

0 MPa

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Evaluation Parameters- PVT

Compressibility (COM)

– COM = dV/dP

– COMS = (VS1-VS5) / 160

– COMM = (VM1-VM3) / 160

0

160

T P V

TS1 0 VS1

TS2 0 VS2

TS3 0 VS3

TS4 0 VS4

TS5 160 VS5

TS6 160 VS6

TS7 160 VS7

TB1 0 VB1

TB2 160 VB2

TM1 0 VM1

TM2 0 VM2

TM3 160 VM3

TM4 160 VM4

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In the runner..

very hot resin (TVH)

high shear rate (SHB)

viscous heating (TMASS, TVH)

flow around corners (e) dPc

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At the gate

extensional flow (e)

very high shear rates (SHB)

viscous heating (TMASS, TVH)

dPg

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Within the part

Frozen layer formation

– a

– NOFLO

– CRY

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Within the part

Flow around corners

– additional pressure loss (e)

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Within the part

Thick and thin sections

– additional pressure loss (e)

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Weld lines...

melt front temperature

– a

available pressure

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End of fill

2E+1

1E+3

250 260

275

290

1.E+1

1.E+2

1.E+3

1.E+4

Vis

co

sit

y

low shear rates (TVL)

low temperature

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Packing it in..

0

249

219

189

159

129

99

69

40

50 100

150 200

1.0000

Vo

lum

e

Semi-crystalline polymer

– Factors:

» COMM

» TVL

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Cooling off

cooling polymer

– a

– CRY, VEC

freeze off

– NOFLO

– TVL-TVH

249

219

189

159

129

99

69

40

50 100

150 200

1.0000

Vo

lum

e

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Conclusion

Evaluation parameters are:

– tools to examine simulation results

– aid in understanding resin behavior in the mold

– aid in selection of resin based on desired

processability

– easy to calculate and use every day

Questions, call us; 1-888-DATA-4-CAE

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Future considerations

extensional flow situations

accumulation of residual stresses

stress relaxation

warpage

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Effect of viscosity

shear thinning behavior reduces pressure

penalty +

high temperature sensitivity of viscosity -

high pressure raises viscosity -

high shear rate induces viscous heating +

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Effect of thermal conductivity

high solid conductivity reduces cycle time +

high conductivity tightens process window -

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Effect of PVT

shows how plastic will solidify

shows shrinkage level