Injection Moulding Simulation

of Engineering Rubber Components

Modelling of Elastomeric Materials and Products14 Oct 2010 - London, UK

G.Ramorino

S. Agnelli , A.Franceschini , F.Baldi, T.Riccò

1University of Brescia (Italy) – Department of Mechanical and Industrial Engineering

2CF Gomma, Brescia (Italy)

- INJECTION MOULDED RUBBER COMPONENTS

� ANTIVIBRATION RUBBER COMPONENTS

CF GOMMA Spa (Brescia, Italy)

rubber compound

• ENGINE MOUNTS

• BUSHES FOR THE SUSPENSIONS

metal

rubber compound

► OPTIMIZE THE PERFORMANCE OF NEW PRODUCTS ◄

� COMPUTER AIDED ENGINEERING SOFTWARE

DESIGN TECHNOLOGY

PREVENT MOULDING PROBLEMS

Incomplete mould filling / air traps

► QUICKLY ANALISIS OF COMPONENT/MOULD

► AVOID SEVERAL ERRORS

(early phase of product development)

- NUMERICAL SIMULATION

► SAVE COST AND TIME ON MOULD TRYOUTS

� CORRECT EVALUATION OF THE CURING TIME

optimize the time cycle of the vulcanization phase of the component

► USEFUL FOR COST SAVING IN THE PRODUCT PROCESS ◄

► OPTIMIZE PART DESIGN

► SAVE COST AND TIME ON MOULD TRYOUTS

► REDUCE TIME TO MARKET

- COMMERCIAL SOFTWARE

� extensive materials property database

► THERMOPLASTIC – THERMOSET MATERIALS

� developed in close cooperation with the plastics industry

MOLDFLOW ���� LEADING CAE SOFTWARE OF INJECTION MOULDING

� measurements of curing rate - material viscosity are needed

► RUBBER COMPOUNDS

� database is out of material property

► PROPER CURING REACTION AND VISCOSITY MODELS

� MOLDFLOW SIMULATIONS

VERIFY THE CAPABILITY OF THE MOLDFLOW SOFTWARE TO PERFORM FLOW SIMULATIONS OF

RUBBER INJECTION MOULDING PARTS

- AIM OF THE PRESENT WORK

1. MOULD CAVITY FILLING STAGE

2. STATE OF CURE IN THE

POST-FILLING PROCESS

� EXPERIMENTAL TESTS

POST-FILLING PROCESS

► COMPARISON ◄

► ANTIVIBRATION ENGINE MOUNT

� thickness: 1.5 mm to 20 mm

� two metal inserts

200 mm

� overall dimensions: 170x80x45 mm

- RUBBER COMPONENT

METAL INSERT

80 m

m

TYPICAL INDUSTRIAL FORMULATION

NATURAL RUBBER COMPOUND (carbon black-silica-oil-zinc oxide curing system)

� composition of the rubber compound

� test temperature

� method employed to characterize the material

� vulcanization of NR compounds is conducted in a DSC

DSC (Heat Flux from TA Instruments)

- MATERIAL CHARACTERIZATION

(Dynamic Scanning Calorimeter)

CURE KINETIKS

DSC (Heat Flux from TA Instruments)

� isothermal and non-isothermal conditions

� INDUCTION PERIOD

� RATE OF CURE

1. SPECIFIC HEAT OF REACTION H (J/G)

2. CONSTANTS OF THE MODELS - “CLAXTON-LISKA” - “KAMAL-SOUROUR”

11

11.5

12

12.5

Heat

Flo

w (

mW

)A

non-isothermal DSC test

� SPECIFIC HEAT OF REACTION ���� H (J/g)

- MATERIAL CHARACTERIZATION

9.5

10

10.5

12 13 14 15 16 17

Time (min)

Heat

Flo

w (

mW

)

� heating rate of 10°C/min

� mass of the sample m = 10 mg

H (J/g) =A (mJ)

m (mg)� temperature range 70-220°C.

exothermic reaction peak

� MODEL TO CHARACTERIZE THE INDUCTION PERIOD

T (°C) 170 175 180 183

t (s) 133 79 46 34

)/exp( TBAt ⋅=

� CLAXON - LISKA MODEL

A, B = constants

4.2

4.4

Isothermal DSC testsT(°C)

Arrenhius type expression

T = temperature

- MATERIAL CHARACTERIZATION

INDUCTION TIME

3

3.2

3.4

3.6

3.8

4

4.2

0 100 200 300 400

Time (s)

He

at

Flo

w (

mW

)

Isothermal DSC testsT(°C)

� INDUCTION TIME ���� t (s)

T (°C) 170 175 180 183

t (s) 133 79 46 34

4.2

4.4

Heat

Flo

w (

mW

)

)/exp( TBAt ⋅=

� CLAXON - LISKA MODEL

Isothermal DSC data

A, B = constants

T = temperature

∆∆∆∆Ht1

- MATERIAL CHARACTERIZATION

INDUCTION TIME

(data of ti obtained at each isothermal DSC tests)

INDUCTION PERIOD OF THE NR

COMPOUND

3

3.2

3.4

3.6

3.8

4

0 50 100 150 200 250 300 350 400

Time (s)

Heat

Flo

w (

mW

)

temperature = 183°C

t

∆∆∆∆Htot

∆∆∆∆Htot

cure degree αt1 = ∆∆∆∆Ht1

t1

exothermic reaction

0.4

0.6

0.8

1

Cu

re d

eg

ree

, α

T

� CURE KINETICS CURVES

� MODEL TO CHARACTERIZE THE CURE KINETICS

- MATERIAL CHARACTERIZATION

(from the isothermal DSC data)

(100% cure)

0

0.2

0 100 200 300 400

Time (s)

Cu

re d

eg

ree

,

nmKK

dt

d)1()( 21 αα

α−⋅⋅+=

rate of cure m, n = constants K1 (T) , K2 (T)

� KAMA-SOUROUR MODEL *

A. Arrillaga et al. European Polymer Journal,43: 4783–4799, 2007.

*

temperature T (170,175,180,183 °C)

(0% cure)

� CURE KINETICS CURVES

0.008

0.012

0.016

0.02

0.024

Rate

of

cu

re,

dα

/dt

temperature T (170,175,180,183°C)

T

- MATERIAL CHARACTERIZATION

(data used to obtain the

constants of the

Kama-Sorour Model )

0

0.004

0.008

0 0.2 0.4 0.6 0.8 1

Cure degree, α

Rate

of

cu

re

Isothermal tests

nmKK

dt

d)1()( 21 αα

α−⋅⋅+=

rate of cure

� KAMA-SOUROUR MODEL *

m, n = constants K1 (T) , K2 (T)

A. Arrillaga et al. European Polymer Journal,43: 4783–4799, 2007.

*

0.004

0.008

0.012

0.016

0.02

0.024

Ra

te o

f c

ure

dα

/dt

temperature T (170,175,180,183°C)

T

GOOD AGREEMENT

- MATERIAL CHARACTERIZATION

0

0.004

0 0.2 0.4 0.6 0.8 1Cure degree, α

Ra

te o

f c

ure

d

Isothermal tests

nmKK

dt

d)1()( 21 αα

α−⋅⋅+=

rate of cure

A. Arrillaga et al. European Polymer Journal,43: 4783–4799, 2007.

*

m, n = constants K1 (T) , K2 (T)

� KAMA-SOUROUR MODEL * (open symbols)

experimentalmodel

� capillary rheometer (CEAST)

� flow curves at different temperatures

RHEOLOGICAL PROPERTIES

- MATERIAL CHARACTERIZATION

(data used to obtain the

constants of the

Reactive Viscosity Model )

3.8

4.2temperature T (120, 130, 140, 150 °C)

2.2

2.6

3.0

3.4

3.8

1.0 1.5 2.0 2.5 3.0 3.5

Log γγγγ (1/s)

Lo

g η

η

η

η

(P

a·s

)

T

� REACTIVE VISCOSITY MODEL

( )α+

−

α−α

α

τ

γη+

η=γαη

21 CC

g

g

n1

0

0

)T(1

)T(),T,(

&

&

5.0

6.0

Reactive viscosity model (120°C)

η0(T) = viscosity at shear rate � 0;

T = temperature;

n = shear rate sensitivity;

τ = shear stress;

α = cure degree;

C1, C2, αg = constants.

- MATERIAL CHARACTERIZATION

1.0

2.0

3.0

4.0

5.0

0.0 1.0 2.0 3.0 4.0 5.0

Log γγγγ (1/s)

Lo

g η

(P

a·s

)

120°C

150°C

Reactive viscosity model (150°C)

Experimental data

GOOD AGREEMENT

- MOLDFLOW MODELLING

0.016

0.02

0.024

Ra

te o

f c

ure

dα

/dt

temperature T (170,175,180,183°C)

T

3

3.2

3.4

3.6

3.8

4

4.2

4.4

0 100 200 300 400

Time (s)

He

at

Flo

w (

mW

)

- MOLDFLOW DATA INPUT

MODEL PARAMETERS

INPUT TO MOLDFLOW

0

0.004

0.008

0.012

0 0.2 0.4 0.6 0.8 1Cure degree, α

Ra

te o

f c

ure

d

1.0

2.0

3.0

4.0

5.0

6.0

0.0 1.0 2.0 3.0 4.0 5.0

Log γγγγ (1/s)

Lo

g η

(P

a·s

)

120°C

150°C

Reactive viscosity model (150°C)

Reactive viscosity model (120°C)

Experimental data

“REACTIVE MOULDING” MODULE

� PROCESS PARAMETERS

Injection machine: Mod. V/MP 70/800

Injection time (s): 20

Injection temperature (°C): 65

Mold temperature (°C): 165

Cure times (s): 380, 420, 475, 520

INPUT TO MOLDFLOW

- MOLDFLOW DATA INPUT

INPUT TO MOLDFLOW

- 3D MOLDFLOW MODELLING – CAVITY FILLING

METAL

FEED SYSTEM

METAL INSERT

POSITION OF THE FLOW FRONT AS THE CAVITY FILLS vs INTERRUPTED FILLING EXPERIMENTS

FILL TIME RESULT

METAL INSERT

CAVITY

MOULD

6 gate system

- 3D MOLDFLOW MODELLING – CAVITY FILLING

“comparison between the pictures of the incomplete

molded parts and the corresponding filling patterns

predicted by computer simulation”

- FILL TIME RESULT

THE PREDICTIONS ARE REPRESENTATIVE OF THE FLOW

DURING THE FILLING STAGE

REMARKABLE AGREEMENT

- MATERIAL CURING

ACTUAL MATERIAL CONVERSION (CURE) AT A NODE, CALCULATED OVER THE ENTIRE MOLDING PROCESS

CONVERSION AT NODE RESULT

N1

N1: located near the

cavity surface

N2

sectionsimulations are

performed in a part of

variable thickness

N2: located in the centre of the higher thickness

cure profile evolution

- MATERIAL CURING

CONVERSION AT NODE RESULT: XY PLOT – cure profile evolution

MO

LD

FL

OW

PR

ED

ICT

ION

S N2

N1

~ 0.75

~ 0.95

scorchC

ure

deg

ree

MO

LD

FL

OW

PR

ED

ICT

ION

S

FILLING (20 s) + CURING PHASES

N1: located near the

cavity surface (↑ T)

N2: located in the centre

of the higher thickness

slower heat transfer

scorch

Total cycle

Cu

re d

eg

ree

slower rate of cure

- MECHANICAL COMPRESSION TEST

TO EVALUATE WHICH CURING TIME PROVIDES THE

HIGHER STIFFNESS OF THE PART, SO INDICATING THE BEST CURING TIME

components obtained at different cure times (380, 420, 475, 520 s)

- COMPARISON

150

155

160

Sti

ffn

ess (

N/m

)

Experimental data

GOOD AGREEMENT

THE SOFTWARE PREDICTS 400-430 s THAT IS IN GOOD AGREEMENT WITH THE 440 s

FOUND THROUGH COMPRESSION TESTS

140

145

350 400 450 500 550 600

total cycle time (s)

Sti

ffn

ess (

N/m

)

MOLDFLOW PREDICTIONS

FILLING (20 s) + CURING PHASES

- CONCLUSIONS

� This study shows that it is possible to model very accurately the filling and cure

stages of rubber injection molding process.

� The computations are found in good agreement with the experimental results,

indicating that reliable information on material viscosity and curing kinetic play a

key role for well-founded predictions.key role for well-founded predictions.

ACKNOWLEDGEMENT

The authors want to acknowledge CF Gomma Spa (Brescia, Italy) and Fondazione

Cariplo for the financial supports.