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Introduction to Micromoulding

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Presentation on theme: "Introduction to Micromoulding"— Presentation transcript:

1 Introduction to Micromoulding
Dr Ben Whiteside IRC in Polymer Engineering, Dept. Mechanical & Medical Engineering, University of Bradford, Bradford UK

2 Contents Micro/nanotechnology Micromoulding Challenges
Process Technology Mould Manufacture Product Assessment

3 Capsule Endoscopy Capsule contains: Camera Transmitter Optics Battery

4 Capsule Endoscopy Full colour images for diagnosis of bowel problems

5 Digital Micro mirror Device (DMD)
Texas Instruments 16 mm x 16 mm pixel geometry

6 Micro-assembly: Laser-fibre alignment- packaging?

7 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/ th of a litre!

8 Current Manufacturing Techniques
Silicon wafer techniques requiring: Clean-room fabrication Expensive Illumination Processes

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

10 Challenges Controlling the moulding machine Making the moulds
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

11 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. Conventional moulding technology is inefficient – injecting a lot of polymer that ends up as being waste or needs recycling courtesy: Battenfeld

12 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

13 Battenfeld Microsystem 50
Purpose built micro injection process Servo-electric injection Optimum screw size – 14mm Automatic parts handling Clean room filtration Modular A purpose designed machine – started with a blank piece of paper in terms of specking the machine – has several features

14 Battenfeld Microsystem 50

15 POM Micro-gear courtesy: Battenfeld Part weight 0,0008 g
Mass typically < 1mg – one producer says he can fit 3 months units a day into a box 1cuft. Part weight 0,0008 g courtesy: Battenfeld

16 Polycarbonate hearing aid sensor housing
Demonstrates scale – parts a generally a lot smaller than granules courtesy: Battenfeld Weight 2,2 mg

17 Micromoulding – the truth?

18 Making the moulds Moulds need to have: Very accurate dimensions
Good surface finish Good durability

19 Making the moulds - Micromilling
Cutters as small as 0.1mm rotating at speeds up to rpm All held in special housing to minimise vibration and changes in temperature

20 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

21 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

22 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

23 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

24 Making the moulds – LIGA Process
Able to form a number of cavities simultaneously Excellent surface finish Only 2.5D structures Requires expensive hardware

25 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

26 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

27 Machine Vision Systems
Smallest product moulded at the University Largest diameter 1mm Mass 0.34mg

28 Atomic force microscopy
Can be used to study very small areas of a component to measure:- Surface finish Internal structure Mechanical properties – hardness etc

29 Surface details ‘Ridges’ caused by the tools used to make the cavity

30 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

31 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.

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