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