7 Lab-on-a-Chip devices Circuits similar to conventional silicon circuits but using fluids rather than electricityAllows rapid chemical and biological screening of samplesEach chamber in the illustation contains 1/ th of a litre!
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 polymerMeasuring the required amount of materialInjecting the material rapidlyMaking the mouldsContain very fine detailsNeed to be durableChecking/Packaging the productQuality controlHandling very small products
11 Standard IM – material waste Conventional Moulding4-cav. MouldPart weight: 4 mgSprue weight: 2530 mgShot weight: 2546 mgMaterial 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 recyclingcourtesy: Battenfeld
12 Standard IM – Material Degradation Picture of injection barrel hereScrew/barrel typically contains 500g polymerAssuming a 0.5g product running every 20 seconds – material would be at melt temperature for 5½ hoursMaterial can degrade
13 Battenfeld Microsystem 50 Purpose built micro injection processServo-electric injectionOptimum screw size – 14mmAutomatic parts handlingClean room filtrationModularA purpose designed machine – started with a blank piece of paper in terms of specking the machine – has several features
18 Making the moulds Moulds need to have: Very accurate dimensions Good surface finishGood durability
19 Making the moulds - Micromilling Cutters as small as 0.1mm rotating at speeds up to rpmAll 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 touchSparks 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 steelProblems 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 laserWhen 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 LabsElectroplating required to create mouldCylinders will form holes for pins to eject the moulded part
24 Making the moulds – LIGA Process Able to form a number of cavities simultaneouslyExcellent surface finishOnly 2.5D structuresRequires expensive hardware
25 Product AssessmentHow is quality control implemented for such small components?Optical systemsHow do we find out how rigid and hard the product is?Need to use Atomic Force Microscopy techniques
26 Machine Vision Systems RobotProductCCDCameraFully Automatic – no user intervention requiredAble to measure dimensions/areas/geometric featuresCan be performed during the process
27 Machine Vision Systems Smallest product moulded at the UniversityLargest diameter 1mmMass 0.34mg
28 Atomic force microscopy Can be used to study very small areas of a component to measure:-Surface finishInternal structureMechanical properties – hardness etc
29 Surface details‘Ridges’ caused by the tools used to make the cavity
30 Structures inside the product IndentRose patterns tell us about the structure of the polymer and how strong we can expect the product to beIndent shape also indicates how hard the product is
31 ConclusionsStandard injection moulding machines are not well suited for producing microscale componentsMicromoulding offers a cheap and productive means for the manufacture of small componentsA number of techniques are being explored to find the best method for cavity productionTesting of the moulded parts is currently only possible using expensive, high-tech apparatus.
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