Microcellular Injection moulding
MuCell® Technology
Ing. Andrea Romeo
Consorzio Proplast
Laboratorio di Progettazione Avanzata
Summer School, New trends in plastics engineering - Bellignat, 9-07-2013
The MuCell®-Process-Technology
1. MuCell Basics and Function
2. Strategic Advantages
3. MuCell Design Rules
4. General MuCell Examples
MuCell® Basics and Function
 Function and technical equipment
Two Main Characteristics describe the
MuCell® Process
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)
The MuCell® Process
Creating a single phase solution – injecting the SCF
(super critical fluid) into the thermoplastic melt during
screw recovering
Creating a single
phase solution
Injecting
SCF
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
Inject SCF
+
Diffusion Complete
SCF
Polymer
The MuCell® Process
Foaming occurs during injection into the mold
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Time
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Time
 Low pressure in the mold cause SCF to form cells
 Cells grow until the material freezes or the mold cavity is full
MuCell® Moulding Technology
Scanning Electron Microscope (SEM) microstructure
Source:
Material: Nylon 66 with 35% glass fibers
MuCell® Moulding Technology
Compact skin –
Foamed core –
Compact skin
MuCell® Moulding Technology
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)
Trexel Confidential
10
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!
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
Trexel Confidential
15
Strategic Benefit Capacity Use
(Reduced cycle time)
Opening/Eject./ Injection
Closing
Pack&Hold
Cooling
Solid
Δ
T
MuCell®
ΔT depends on
material type,
part design and
mould cooling
Hold time (nearly)
eliminated
Reduced cooling time
More exchange
Less temperature
Delete parameter hold
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)
Example:
Connector Housing
with PBT GF 30
 Decoupling of part dimensions
and part weight
Trexel Confidential
Strategic Benefit Machine Size
(reduction of hydraulic pressure)
MuCell®
Solid
Peak pc = 1045 bar
Peak pc = 448 bar
Screw
position
Data Com Connector,
PBT with 30 % glass
 57 % reduction in peak cavity pressure
 Due to viscosity reduction, less resin volume, no pack &
hold pressure
 Longer tool life Trexel Confidential
18
Microcellular Foam Properties
 Without foam
 10% physical foam
DSC - Curve: PBT GF 30 with
mould temp. 80°C
Source: Ticona
DSC - Curve: PBT GF30 with
mould temp. 30°C
Source: Ticona
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
Crystallinity Level is identical
Trexel Confidential
19
Strategic Benefit Quality
(faster product release)
95.9
200
Gate
1
Width- Open side
Overall Width- Rectangular Box
96,200
96,100
96,000
95,900
95,800
95,700
95,600
95,500
1
2
3
Cav1- Solid
4
2
3
Position
(Gate at # 4)
Cav1- MuCell
4
Cav2- Solid
5
Cav2MuCell
5
More consistent & predictable MuCell® dimensions simplify
mould design & reduce the number of costly iterations
Trexel Confidential
20
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
Trexel Confidential
MuCell® design rules




Designing for function
Differences in Wall Thicknesses
Shrinkage
Mechanical properties
Designing for MuCell
• If parts are designed for the
MuCell Process at the outset,
parts weight can be reduced
>20 %
Trexel Confidential
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
27
Differences in Wall Thicknesses
 Filling from “thin to thick“
Recommended
injection with MuCell®
Injection in solid
(with MuCell® still possible)
 Wall to rib ratio 1:1 possible
MuCell® design
Conventional design
Trexel Confidential
28
Shrinkage
in [mm]
599
599
600
599
599
599
598
599
Solid dimensions
MuCell dimensions
Shrinkage is a little bit higher but much more uniform
(in flow and in X-flow direction)
Mechanical Properties
Influence for mechanical properties of gate location on
test specimens and on real parts
Specimens Mould:
End of flow
3D Part Mould:
Thickness = 4 mm
Strength on test specimens
Thickness = 2 mm
End of flow
Injection point
Near the gate
Designing for Function
Example: 15% weight reduction through wall
thickness optimization and 4 % with density
reduction
1.11 mm at
tip of ribs
1.75 mm at
top of front
wall
1.55 mm at
base of
front wall
1.31 mm
1.22 mm
1.49 mm
at base
1.12 mm
1.12 mm
Gate Location
Trexel Confidential
1.2 mm
36
Part Design – Wall Thickness
• 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
40
Weight reduction [%]
35
% Wt. Reduction envelop
as a function of flow factor
Low viscous (PA) top
High viscous (PC gf30 fr) low
30
25
20
15
10
5
0
50
75
100
125
150
175
200
Flow Factor
Trexel Confidential
37
225
250
General MuCell® examples
 Glass fibers and flatness
 Appearance Applications
Performance measurement of flatness
3.2 mm test plaques
Less warpage
more uniform mechanical performance
PP 40 % LGF Solid
PP 40 % LGF Solid
PP 40 % LGF MuCell
PP 40 % LGF MuCell
Trexel Confidential
39
MuCell® Appearance Applications
 Modified materials
(PA 6, PA 6/6 & PBT)
 Mould based solutions
 Appearance parts in
mass production with
IMD Technology
Trexel Confidential
40
MuCell® Applications
Automotive
OfficeEquipment
Industry
&
Electric/
Electronic
Semi
conductors
Packaging
Trexel Confidential
41
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 %
Trexel Confidential
42
Circular Saw (Base Plate)
Replacement of aluminium die-cast part by MuCell base plate
of PA 6.6 GF55
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
44
MuCell® Electronic Housing
MuCell® Benefits
 Smaller injection moulding machine
 Shorter cycle time
 Improved flatness, reduced warpage, accurately fitting
 Improved breaking behaviour at destructive
testing
MuCell® Car Key
MuCell® Benefits
• 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
Valeo - Interior Bezel
General Motors - Opel Corsa
Quality Improvement
2002 SPE Automotive Innovation
Award Winner
• Eliminated sink marks
Category: Process / Enabling
Technologies
• Improved dimensional
stability
Process Improvement
• Clamping force reduced
from 250-tons to 75-tons
• 10% Weight savings
Cycolac CRT 3370 ABS - glass filled
•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
47
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
Trexel Confidential
48
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
49
MuCell Fan Shrouds
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
Typical materials:
PA 66 GF 30
PP GF 30
PA 6 G+M 43
Chrysler
50 RS Dual fan shroud
MuCell® Cam cover
MuCell® advantages
 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
Trexel Confidential
51
MuCell® Sun Roof Frame
MuCell® Benefits
 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)
Daimler W212 Door Trim
Winner 2009 in category
Interiors
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)
Conclusion
MuCell process allows significant savings
Very short Pay back
Valuable benefits:
•Weight reduction
-Due to the microcellular expansion,
-Via pre-design/optimization
of the part (wall thickness reduction)
usually 8-10%
up to 35%
up to 50%
40 to 60%
up to 60%
•Cycle time reduction
•Injection pressure reduction
•Machine size reduction
•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 installation
At Proplast’s site (Tortona, Italy)
IMM: Engel 180 tons, screw: 55 mm
Shot weight: 100-500 g
Mucell unit - Co2 or Nitrogen
Goals
Support 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 ongoing
Aestethical 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 Proplast
Advanced Design Lab
andrea.romeo@proplast.it
+39 01311859743
www.proplast.it
Summer School, New trends in plastics engineering - Bellignat, 9-07-2013