Introduction to Micromoulding

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Introduction to Micromoulding

• Dr Ben Whiteside
• IRC in Polymer Engineering,
• Dept. Mechanical Medical Engineering,
• University of Bradford, Bradford UK

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Contents

• Micro/nanotechnology
• Micromoulding
• Challenges
• Process Technology
• Mould Manufacture
• Product Assessment

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Capsule Endoscopy
Capsule contains Camera Transmitter
Optics Battery
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Capsule Endoscopy
Full colour images for diagnosis of bowel problems
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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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Lab-on-a-Chip devices
Circuits similar to conventional silicon circuits
but using fluids rather than electricity
Allows rapid chemical and biological screening of
samples Each chamber in the illustation contains
1/1 000 000 000th of a litre!
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Current Manufacturing Techniques
Silicon wafer techniques requiring Clean-room
fabrication Expensive Illumination Processes
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Micro-Injection Moulding

• Can the injection moulding process be adapted to
  offer a cheap, high output process for the
  production of micro-scale components?

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Challenges

• Controlling the moulding machine
• Melting the polymer
• Measuring the required amount of material
• Injecting the material rapidly
• Making the moulds
• Contain very fine details
• Need to be durable
• Checking/Packaging the product
• Quality control
• Handling very small products

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Standard IM material waste

• 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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Standard IM Material Degradation
Picture of injection barrel here

• Screw/barrel typically contains 500g polymer
• Assuming a 0.5g product running every 20 seconds
  material would be at melt temperature for 5½
  hours
• Material can degrade

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Battenfeld Microsystem 50

• Purpose built micro injection process
• Servo-electric injection
• Optimum screw size 14mm
• Automatic parts handling
• Clean room filtration
• Modular

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Battenfeld Microsystem 50
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POM Micro-gear
Part weight 0,0008 g
courtesy Battenfeld
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Polycarbonate hearing aid sensor housing
courtesy Battenfeld
Weight 2,2 mg
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Micromoulding the truth?
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Making the moulds

• Moulds need to have
• Very accurate dimensions
• Good surface finish
• Good durability

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Making the moulds - Micromilling
Cutters as small as 0.1mm rotating at speeds up
to 120 000 rpm All held in special housing to
minimise vibration and changes in temperature
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Making the moulds Micro Electro Discharge
Machining
The electrode and woprkpiece are connected to a
DC power supply and are brought close together,
but never touch Sparks jump across the small gap
which heats up the workpiece metal to about
1200ºC, causing it to evaporate
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Making the moulds Laser Machining
High frequency pulsed lasers focussed on the
steel causing it to evaporate. The laser is aimed
using a computer to cut out a cavity in the
steel Problems can occur when the steel
spatters or is recast in the local area
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Making the moulds Micro-Stereolithoraphy
Object is built up of slices created by
illuminating the top surface of a bath of special
polymer with a laser When a slice is complete,
the stage holding the part drops down a fraction
of a millimeter so the next slice can be made
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Making the moulds Micro-Stereolithoraphy
T-Shaped cavity made for us by Rutherford
Appleton Labs Electroplating required to create
mould Cylinders will form holes for pins to eject
the moulded part
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Making the moulds LIGA Process

• Able to form a number of cavities simultaneously
• Excellent surface finish
• Only 2.5D structures
• Requires expensive hardware

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Product Assessment

• How is quality control implemented for such small
  components?
• Optical systems
• How do we find out how rigid and hard the product
  is?
• Need to use Atomic Force Microscopy techniques

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Machine Vision Systems
Robot
Product
CCD Camera

• Fully Automatic no user intervention required
• Able to measure dimensions/areas/geometric
  features
• Can be performed during the process

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Machine Vision Systems
Smallest product moulded at the
University Largest diameter 1mm Mass 0.34mg
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Atomic force microscopy
Can be used to study very small areas of a
component to measure- Surface finish Internal
structure Mechanical properties hardness etc
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Surface details
Ridges caused by the tools used to make the
cavity
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Structures inside the product
Indent
Rose patterns tell us about the structure of the
polymer and how strong we can expect the product
to be Indent shape also indicates how hard the
product is
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Conclusions

• Standard injection moulding machines are not well
  suited for producing microscale components
• Micromoulding offers a cheap and productive means
  for the manufacture of small components
• A number of techniques are being explored to find
  the best method for cavity production
• Testing of the moulded parts is currently only
  possible using expensive, high-tech apparatus.