Microcellular Injection moulding

MuCell® Technology

Summer School, New trends in plastics engineering - Bellignat, 9-07-2013

Ing. Andrea Romeo

Consorzio ProplastLaboratorio di Progettazione Avanzata

1. MuCell Basics and Function

2. Strategic Advantages

3. MuCell Design Rules

4. General MuCell Examples

The MuCell®-Process-Technology

MuCell® Basics and Function

Function and technical equipment

1. Lowering of the viscosity of thermoplastic resins

by controlled feeding of gas (either N2

or CO2)

into the melt

2. Creation of a microcellular Structure in the part

core by gas expansion in the cavity (Injection

Moulding) or after the die (Extrusion)

Two Main Characteristics describe the

MuCell®

Process

Creating a single phase solution – injecting the SCF

(super critical fluid) into the thermoplastic melt during

screw recovering

Injecting

SCF

Creating a single

phase solution

The MuCell®

Process

Dissolving SCF into the melt

Screw flights break-up SCF stream

Mixing flights cause SCF to divide

into smaller bubbles

and then dissolve

Diffusion Complete

Inject SCF

+

SCF Polymer

The MuCell®

Process

Foaming occurs during injection into the mold

Time

Low pressure in the mold cause SCF to form cells

Cells grow until the material freezes or the mold cavity is full

Time

..

.

..

.. . .

.. ..

. ..

.

. ...

.

..

.

. .

.

.

The MuCell®

Process

MuCell®

Moulding Technology

Source:

Material: Nylon 66 with 35% glass fibers

Scanning Electron Microscope (SEM) microstructure

Compact skin –

Foamed core –

Compact skin

MuCell®

Moulding Technology

Trexel Confidential 10

Control of Foaming

Controlling cell size and the number of cells

– Correct SCF level: Higher SCF creates more cells (Always a limit to how much SCF)

– Rate of pressure drop (controlled primarily by injection speed)

MuCell®

Moulding Technology

MuCell® Strategic Advantages

MuCell Design Rules

Limitations of Solid Molding

Influence on part quality

Saving potentials

MuCell Design Rules

Limitations of Solid Molding

Solid molding is constrained by:

Need to push plastic from gate to end of fill without freezing off

Need to pack the part along the entire flow length…

To obtain uniform shrinkage for dimensional stability

To eliminate sink marks and vacuum voids

These processing limitations impose design restrictions

that affect the ability to reduce wall thickness

The MuCell Process removes these restrictions!

Trexel Confidential 15

MuCell versus Solid Molding

• Reduced viscosity (10% to 15% for a 30% glass fiber)– Increased flow length

– Lower fill pressures

• Cell growth replaces the pack/hold phase, resulting in lower and more uniform cavity pressure– Pack pressure does not need to go from gate to end of flow

• Pack takes place locally

– Lower pack and hold pressures

– Shorter pack and hold times

– Reduced cavity pressures

– Lower clamp forces

• Less molded-in stress = Reduced warpage

• Reduced cooling required

Reduced cooling time

More exchange

Less temperature

Hold time (nearly)

eliminated

Δ

T

Solid

MuCell®

Pack&Hold CoolingInjectionOpening/Eject./

Closing

ΔT depends on

material type,

part design and

mould cooling

Strategic Benefit Capacity Use

(Reduced cycle time)

Trexel Confidential

The parameters hold pressure pH and hold time tH

are deleted by the MuCell® Foaming Process.

Part formation by cell growth, independently of part weight

Counteraction against shrinkage not by additional packed mass

Equal pressure distribution in the cavity (significant less difference

in pressure levels near injection point and far injection point)

Decoupling of part dimensions

and part weight

Delete parameter hold

Example:

Connector Housing

with PBT GF 30

Trexel Confidential 18

57 % reduction in peak cavity pressure

Due to viscosity reduction, less resin volume, no pack &

hold pressure

Longer tool life

Strategic Benefit Machine Size

(reduction of hydraulic pressure)

Peak pc

= 448 bar

Peak pc

= 1045 bar

Screw

position

Solid MuCell®

Data Com Connector,PBT with 30 % glass

Trexel Confidential 19

DSC - Curve: PBT GF 30 with

mould temp. 80°C

DSC - Curve: PBT GF30 with

mould temp. 30°C

Melting temperature : 225,4°C

Heat of Fusion (H): 40,67 J/g

Melting temperature: 225,0°C

Heat of Fusion (H): 41,93 J/g

Without foam 10% physical foam

Crystallinity Level is identical

Source: TiconaSource: Ticona

Microcellular Foam Properties

Trexel Confidential 20

Overall Width- Rectangular Box

95,500

95,600

95,700

95,800

95,900

96,000

96,100

96,200

1 2 3 4 5

Position

(Gate at # 4)

Wid

th-

Op

en

sid

e

Cav1- Solid Cav1- MuCell Cav2- Solid Cav2MuCell

1

2

3

4

5

Gate

95.9

200

More consistent & predictable MuCell®

dimensions simplify

mould design & reduce the number of costly iterations

Strategic Benefit Quality

(faster product release)

Trexel Confidential

Maximizing MuCell Advantages

• Phase I: existing mold - Learning and Validation

– Current designs at Pre-production stage or earlier

– Establish comparisons with solid parts

• Phase II: Using New Design Rules

– Design for MuCell with thinner walls, wall thickness variations, and different rib structures

MuCell® design rules

Designing for function

Differences in Wall Thicknesses

Shrinkage

Mechanical properties

Trexel Confidential

Designing for MuCell

• If parts are designed for the

MuCell Process at the outset,

parts weight can be reduced

>20 %

Trexel Confidential 27

MuCell Vs Solid Molding

• Foam expands more into thick sections -less in thin sections

– Foam expands until the flow front freezes

• Freeze happens more quickly in thin sections– Necessary to push the plastic further into thin sections to

have complete fill

– Gate into thin sections, flow into thick sections

• Expansion will eliminate sink marks

Trexel Confidential 28

Filling from “thin to thick“

Wall to rib ratio 1:1 possible

Differences in Wall Thicknesses

Conventional design MuCell® design

Recommended

injection with MuCell®Injection in solid

(with MuCell® still possible)

600599 598599 Solid dimensions

in [mm]

599599 599599 MuCell dimensions

Shrinkage is a little bit higher but much more uniform

(in flow and in X-flow direction)

Shrinkage

Influence for mechanical properties of gate location on

test specimens and on real parts

Mechanical Properties

Injection point

Strength on test specimens

Specimens Mould:

End of flow

3D Part Mould:

End of flow

Near the gate

Thickness = 4 mm

Thickness = 2 mm

Trexel Confidential 36

1.75 mm at

top of front

wall

1.55 mm at

base of

front wall

1.2 mm

1.11 mm at

tip of ribs

1.31 mm

1.12 mm

1.49 mm

at base1.12 mm

1.22 mm

Gate Location

Designing for Function

Example: 15% weight reduction through wall

thickness optimization and 4 % with density

reduction

Trexel Confidential 37

• Weight reduction is highly dependent on flow factor- Ratio of Flow Length to Part Thickness

• Weight reduction also dependent on- Part Thickness

- Material

- Gate Location

Part Design – Wall Thickness

0

5

10

15

20

25

30

35

40

50 75 100 125 150 175 200 225 250

Flow Factor

Wei

gh

t re

du

ctio

n [

%]

% Wt. Reduction envelop

as a function of flow factor

Low viscous (PA) top

High viscous (PC gf30 fr) low

General MuCell® examples

Glass fibers and flatness

Appearance Applications

Trexel Confidential 39

PP 40 % LGF Solid PP 40 % LGF Solid

PP 40 % LGF MuCell PP 40 % LGF MuCell

Performance measurement of flatness

3.2 mm test plaques

Less warpage

more uniform mechanical performance

Trexel Confidential 40

MuCell®

Appearance Applications

Modified materials

(PA 6, PA 6/6 & PBT)

Mould based solutions

Appearance parts in

mass production with

IMD Technology

Trexel Confidential 41

Office-

Equipment

Automotive

Industry

&

Electric/

Electronic

Semi

conductors

MuCell®

Applications

Packaging

Trexel Confidential 42

Packaging – Super Light Injection Molding

MuCell®

Benefits:

• Reduce clamp tonnage (smaller machines)

4+4 cavities on 350 t instead of 500 t Higher cavitation

• Reduced injection pressure

Design reduced wall thickness, -15 % Improved performance with IML Technology Use thinner labels (lower material viscosity)

• Weight reduction = 5,5 %

Replacement of aluminium die-cast part by MuCell base plate

of PA 6.6 GF55

Circular Saw (Base Plate)

44

Wire Harness

Key MuCell Objectives:

• Dimensional stability

• Flatness of parts and ease of assembly

Key MuCell Results:

• Weight reduction = 8 %

• Cycle time reduction = 10 %

• Dramatically improved dimensional stability

and warpage reduction

MuCell®

Electronic Housing

Smaller injection moulding machine

Shorter cycle time

Improved flatness, reduced warpage, accurately fitting

Improved breaking behaviour at destructive

testing

MuCell®

Benefits

MuCell®

Car Key

• Equal shrinkage with different wall thicknesses on the

part (reduced warpage)

• Elimination of sink marks

• Achieve „Class-A“ surface for application of high

gloss scratch resistant clear lacquer

MuCell®

Benefits

Trexel Confidential 47

Quality Improvement

• Eliminated sink marks

• Improved dimensional

stability

Valeo - Interior Bezel

General Motors - Opel Corsa

Cycolac CRT 3370 ABS - glass filled

2002 SPE Automotive Innovation

Award Winner

Category: Process / Enabling

Technologies

Process Improvement

• Clamping force reduced

from 250-tons to 75-tons

• 10% Weight savings

•Not necessary to preform the IM

label (label is thinner, because of

less wash-out effect)

MuCell is generally targeted to non-aesthetic parts unless the

part is covered, in-mold decorated, in-mold labeled or painted

Trexel Confidential 48

MuCell®

Torso Airbag Cover

Key MuCell®

Objectives:

• Elimination of different shrink

(elimination of “sink marks” caused by different cross sections)

• Design freedom

• Painted

Key MuCell®

Results:

• No deviation in shape (no “sink marks”)

• Improved dimensional stability

• Improved function of the living hinge

• Smaller machine requirement

(300 t instead of 500 t in solid)

• Successful painting

49

MuCell HVAC Systems

Key MuCell Objectives•Avoidance of warpage

•Machine size reduction

•Weight savings

Key MuCell Results•9-12% weight reduction

•Machine size reduction

from 1000 tons to 600 tons

•Cycle times savings of 10-15%

•Improved product assembly

•Fewer mold corrections

20% Talc Filled PP

50

MuCell Fan Shrouds

Typical materials:

PA 66 GF 30

PP GF 30

PA 6 G+M 43

Key MuCell Objectives•Cycle time savings

•Machine size reduction

•Weight savings

•Warpage reduction

Key MuCell Results•Typical weight reduction 7-10%

•Machine size reduction

from 1000 tons to 500 tons

•Cycle time savings of 25-40%

•200% improvement in fatigue

resistance

Chrysler RS Dual fan shroud

Trexel Confidential 51

MuCell®

Cam cover

30 % reduced machine size (350 instead of 500 t for

conventional molding)

Improved cycle times, which allow for simultaneous

production and assembly process

Lighter part

Improved flatness

MuCell®

advantages

MuCell®Sun Roof Frame

Reduced amount of components, tools and assembling

processes

Dramatically reduced warpage in spite of a complex

geometry

Only one optimization loop required after tool

construction (shorter project time)

MuCell®

Benefits

Daimler W212 Door Trim

MuCell®

parts (abs):

Carrier:

Thinner wall thickness by lower

viscosity

10 % density reduction by MuCell

Tandem-Mould Technology plus

MuCell (with > 50 % cycle time red.)

Wall thickness to rib ratio = 1:1

Map Case:

Wall thickness to rib ratio = 1:1

Deletion of one tool and an

additional assembling process (by

MuCell Design)

Advantages with IML Technology

(lower pressure levels)

Winner 2009 in category

Interiors

Conclusion

MuCell process allows significant savings

Very short Pay back

Valuable benefits:

•Weight reduction-Due to the microcellular expansion, usually 8-10%-Via pre-design/optimization

of the part (wall thickness reduction) up to 35%

•Cycle time reduction up to 50%

•Injection pressure reduction 40 to 60%

•Machine size reduction up to 60%

•Warpage/deformation reduction

•Avoidance of sink marks

•Uniform directional dimensional shrinkage

•Time to market reduction (fewer mould modifications to dimensional conformity)

•Lower energy consumption/Environmental impact

PROPLAST, Trexel, ENGEL partnership

To promote and disseminate the Mucell technology

Demo installationAt Proplast’s site (Tortona, Italy)

IMM: Engel 180 tons, screw: 55 mm

Shot weight: 100-500 g

Mucell unit - Co2 or Nitrogen

GoalsSupport customers at every stage of the technology implementationa and application

•Part design for Mucell (optimization, moldflow Mucell simulation etc)

•Support to mould design

•Mucell moulding trials / mould piloting

R&D projects ongoingAestethical aspect optimization (class A surface, material design and optimization)

Combination with H&C technologies (pressurised water, induction)

Thank you for your attention

Ing. Andrea Romeo

Consorzio ProplastAdvanced Design Lab

andrea.romeo@proplast.it+39 01311859743www.proplast.it

Summer School, New trends in plastics engineering - Bellignat, 9-07-2013