Micromoulding: Process

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Micromoulding Process Property Interaction

• Prof Phil Coates, Dr Mike Martyn
• Dr Ben Whiteside
• Profs Mike Bevis Peter Hornsby, Dr Peter
  Allan
• IRC in Polymer Engineering,
• Dept. Mechanical Medical Engineering,
• University of Bradford, Bradford UK
• Wolfson Centre for Materials Processing,
• Brunel University, Uxbridge UK

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Contents

• Micro-technology
• Micromoulding
• Process technology
• Results of studies at Bradford
• Process dynamics
• Process interaction
• Product properties

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Micromoulding at the IRC, Bradford
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Digital Micro mirror Device (DMD)
Texas Instruments
16 mm x 16 mm pixel geometry
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Micro-assembly Laser-fibre alignment- packaging?
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Micromoulding
Micro-injection moulding - a cost-effective
process employed to produce micro-dimension
moulded parts in high volumes.
Packaging and interfacing of MEMS with real
world
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POM Micro-Gear
Part weight 0,0008 g
courtesy Battenfeld
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PC Sensor housing of a hearing aid
Weight 2,2 mg
courtesy Battenfeld
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Mikrostruktur
Sensorscheibe (PC) with Microstructur
courtesy Battenfeld
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Mikrostruktur
Kugelschreiberspitze
Sensorscheibe (PC) with Microstructur
courtesy Battenfeld
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microstructure
Sensor disk material PC
courtesy Battenfeld
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microstructure
Sensor disk material PC
courtesy Battenfeld
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Micromoulding Process TechnologyChallenges

• Process Engineering
• Machine control process control
• Repeatability consistent shot size
• Controlled/ consistent mould filling
• Part handling
• Material
• Variation batch/batch, granule/granule,
  intra-granule
• Rheology - nanoscale?
• - minimum surface feature replication?

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Micromoulding Process TechnologyChallenges

• Product
• Properties process influence
• High shear shear heating
• Residence time degradation
• Material variation
• Rapid cooling structured micromorphology -
  crystallinity
• Surface properties dominate
• Mould surface replication tribology
• Mould design jetting, hesitation, orientation
  (anisotropy)
• Other issues
• Metrology testing how do we measure
  analyze properties of small moulding?

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Material efficiency

• Conventional Moulding
• 4-cav. Mould
• Part weight 4 mg
• Sprue weight 2530 mg
• Shot weight 2546 mg
• Material efficiency 0,16
• Cycle time 17 sec.

courtesy Battenfeld
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Injection moulding machine shot control
Screw stroke for 1 mg shot weight
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MicroMoulding Tooling Considerations
Multicavity is not vogue Tooling for small and
micromolded parts is an area in which customers
often need to be educated. We've pushed customers
to go to fewer cavities. Instead of running an
eight-cavity mold with half of the cavities
blocked off, we go with two four-cavity molds on
smaller machines to control dimensions better.
Duplicate mold set I always feel it's better
to have two molds than one for a part that is
running all the time, because if the mold goes
down, you at least have the other one going. On
one project, ship 35,000 parts per day from two
four-cavity molds. Having two molds also gives us
time for maintenance.
Design Proper venting at the proper location
is as essential to profitable micromolding as it
is to profitable general-purpose molding because
of the high-speed injection involved. You don't
start venting at the cavity - must get rid of the
air before it gets to the cavity.
Cost Favourable Four cavity micro mould
5,500 Four
cavity for std machine is 20,800
No preconceptions !
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MicroMoulding Tool Manufacture

• Fine EDM
• Laser machining
• Silicon reactive etching (RIE)
• LIGA ( lithography electroplating)
• Micro-milling
• Laser ablation

Rutherford Appleton Laboratory making these
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Studies at Bradford investigate process -
property interaction
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Moulding Studies Battenfeld Microsystem 50

• Purpose built micro injection process
• Servo-electric injection
• Automatic parts handling
• Clean room filtration
• Modular

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Battenfeld Microsystem 50 3-stage injection
technology
Dosing piston
Extrusion screw
Sprue
Shut off valve
Cavity
Injection piston
Heater
3-plate mould
Mold Machine
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Operation simulation
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Operation simulation
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Operation simulation
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Operation simulation
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Operation simulation
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Operation simulation
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Operation simulation
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Operation simulation
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Operation simulation
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Operation simulation
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Operation simulation
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Microsystem 50 Additional sensors for process
interrogation
Dynisco PCI 4011 Piezo load transducer ( 10kN)
Two J Type Thermcouples
Temposonics R Series Displacement Transducer
Dynisco PCI 4006 piezo load transducer (2.5kN)
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Micro- rheology issues
Constitutive equations hold? Slip at
wall? Process dynamics Reynolds number rvd/h
still low?
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MicroMoulding Process Analysis Typical shear
rates
Battenfeld Microsystem 50, 5.0 mm piston, 4
cavity mould, runners 15 x 1 x 1 mm, cavity
0.0008g
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Rheometric nozzle fitted to the Microsystem 50
MicroMoulding Machine
Capillary dies 8 x 0.5 mm, 0.25 x 0.5 mm
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In-process rheometry. Orifice die pressure trace
at piston velocity of 400 mm/s

• Even when no polymer present, pressure increases
  linearly
• Caused by friction between injection pin and
  barrel

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In-process rheometry.
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Rheological characteristics of POMC109 at high
shear rates.
Melt temperature 210C
extensional viscosity
shear viscosity
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Stepped plaque mould


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Initial Mouldings

• POM Mass of shot 0.0635 g
• Mass of cavity 0.0218 g

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Pressure profiles.Polyacetal at 210C, mould 70C,
stepped cavity, 400 vol, 500 mm/s, 180 bar back P
N
406
Injection piston force
338
271
203
cavity sensor
135
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Rectangular plaque mould cavities
25 x 2.5 x 0.25 mm
25 x 2.5 x 1.0 mm
Gates w 0.5, d 0.25 , l 0.5 mm
KERN CNC High Precision Micro Milling
Tolerance 2 4 mm 200mm milling cutter 42,000
rpm, 1m/min feed rate
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Properties of the Polyacetal rectangular plaques
1.0 mm shot weight 0.1488 g
plaque 0.0780 g
0.25 mm shot weight 0.1025 g
plaque 0.0179 g
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Injection pressure profiles POMC109 at 210C,
70C, 0.25 mm cavity, 500 mm/s, 390 vol. 100 bar
back P
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Injection pressure profiles of POMC109, 210C,
70C, 500 mm/s.
1 mm 570 vol, 0.25 mm 390 vol
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Product Quality?
But what about moulding integrity?
courtesy Battenfeld
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Property Evaluation
How?
Atomic Force Microscopy (AFM) nano-indentation
powerful tools for evaluating local differences
in micro-morphology and nanomechanical properties
structure hardness stiffness density aniso
tropy
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AFM surface topology
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AFM surface topology
POM copolymer watch gear, 0.0008g
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Polyacetal stepped plaque.Analysis at 1 mm
section
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Polyacetal stepped plaque.Analysis at 0.25 mm
section
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Properties of the rectangular plaques
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AFM surface topologyPOM109, 0.25mm Moving Half
- near Gate
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Machine marks in the bottom of the 0.25 mm cavity
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POM109, 0.25mm Moving Half - near Gate
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POM109, 0.25mm Moving Half - Centre of bar
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POM109, 0.25mm Moving Half - End
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POM109, 0.25mm Moving Half - End
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POM109, 1.0mm Fixed Half middle
Flow direction
Flow direction
SEM of the moulding surface
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Top Hat Moulding

• Disc diameter 1mm
• Cylinder diameter 0.5mm
• Volume 0.34mm2

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Properties from nano-indentation
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Modulus from Nano-indentation
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SummaryModulus (GPa) gradients in moulded POM
bars
54 change
1 mm bar
33 change
Gate end
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POM stepped samples LOT nanoindentation results
(Brunel)
High modulus from AFM and nanoindentor?
A
B
C
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Conclusions

• Constitutive equations appear to hold at high
  shear rates
• ( gt 2 million 1/s).
• High injection pressures required -
• 0.5 x 0.5 x 0.25 gate stepped plaque 1750
  bar
• Pressure profiles from Microsystem 50 show good
• repeatablility
• Machine marks on mould surface replicated -
• features of 400 nm.
• Mould filling influence surface properties
  gradients in
• moulded bars.

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Acknowledgements
The authors gratefully acknowledge the support
of EPSRC, Battenfeld, Rutherford Appleton
Laboratories Smith Nephew Rondol Middleton
Miniature Mouldings Ultratools Ltd, UK.