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Ultrasound sensors for micromoulding
M. Kobayashi*, C.-K. Jen, C. Corbeil, Y. Ono, H. Hébert and A. DerdouriIndustrial Materials Institute, National Research Council, Quebec CanadaB. Whiteside, M.T Martyn ,E. Brown, P.D. CoatesIRC in polymer engineering, University of Bradford.
Ultrasound basics
Ultrasound pulses ~ 3.6-30MHz (for polymers)Evaluation of
•Transit time•Amplitude
Transmitter
Detector
Polymer
Equipment
T & P T & P inputsinputs
to ultrasonic transducersto ultrasonic transducers
Computer controlled Computer controlled data acquisitiondata acquisition
Ultrasound Ultrasound inputinput
1GHz 1GHz sampling sampling frequencyfrequency
Commercial Commercial pulser-receiverpulser-receiver
Digital oscilloscope Digital oscilloscope (free standing or (free standing or internal PC card)internal PC card)
Ultrasound velocity change with elastic moduli and density
• Longitudinal velocity– Bulk Modulus– Shear Modulus– Density
• For the melt range tested, G <<K
3
41 GKCl
KCl
Sensitive to filler level, morphology, temperature, pressure
Attenuation– Scattering
• Inclusions/impurities in the material
– Absorption• Wave energy is absorbed by the material as heat.
Attenuation coefficients:-
Air:10 dB/MHz/cm Polyethylene:0.25 dB/MHz/cm Tool Steel:0.002 dB/MHz/cm
Pulse – echo mode
Transducer
Polymer
A single transducer acts as transmitter and detector
When polymer enters the cavity, the amplitude of the steel/cavity interface drops and echoes are seen from the far cavity wall
These echoes are seen to move due to the cooling and freezing of the polymer, which reduces the transit time
Flow front detection
Multiple sensors can be employed to monitor cavity fillingCan be useful for detection of ‘jetting’ effects
Polymer presence is indicated by a rapid variation of amplitude
Shrinkage detection
Polymer
PolymerPolymer
Air
Polymer
Transducer
Transducer
Transducer
Shrinkage Detection
1.04
1.06
1.08
1.10
1.12
1.14
1.16
1.18
1.20
1.22
0 2 4 6 8 10
Time (s)
Pe
ak
he
igh
t (v
)
0
1
2
3
4
5
6
7
8
9
10
Trig
ge
r (v
)
100mm/s
75mm/s50mm/s10mm/s
53.5
54.0
54.5
55.0
55.5
56.0
56.5
0 10 20 30 40 50 60Melt pressure (bar)
Transit time (s)
Temperature/Pressure dependence
180°C
200°C
220°C
Summary• Advantages
– Non-invasive technique– Sensitive to temperature, pressure,
morphology, filler level (nanocomposites)– Can be used to monitor cavity filling, cooling
and shrinkage
• Disadvantages– Difficult to isolate actual temperature and
pressure values – other sensors required
Micromoulding applications?
Sol-Gel spray application
1µm Bizmuth Titanate powder dispersed into solutionPiezo films are deposited on external surfaceThickness up to 100µm – determines the resonant frequencyFilms are poledSilver paste electrodes added to form transducer
Technique benefits
• Very small form factor – well suited for micromoulding applications
• Installation of sensors on any surface, including curved surfaces
• Transducer can operate in pulse-echo mode• Able to operate at temperatures in excess of
500C
Extrusion monitor
Sensors installed on external surface of extrusion module on Battenfeld Microsystem50Allows evaluation of material variations, screw wear
Extrusion monitor
All pulses/echoes reflected from steel/cavity interface
Centre frequency of transducer~13Mhz
Extrusion monitor
Polyethylene material
Screw speed 100rpm
Cavity sensors
Cavity data
Runner (Thickness 1mm) Cavity (Thickness 0.3mm)
Cavity data
Polyethylene material
Lower transit times for the thinner section
Can be used to study cooling of the material
Cooling monitoring
Result agree well with static tests
Conclusions
• Sol-Gel method great potential route for manufacture of ultrasound transducers suitable for micromoulding applications
• Sensors have been installed on Microsystem50 and data has been produced
• Technology allows characterisation of the entire process
• Sensor size to be scaled down further