Ultrasound sensors for micromoulding M. Kobayashi*, C.-K. Jen, C. Corbeil, Y. Ono, H. Hébert and A. Derdouri Industrial Materials Institute, National Research Council, Quebec Canada B. Whiteside, M.T Martyn,E. Brown, P.D. Coates IRC in polymer engineering, University of Bradford.

Ultrasound basics Ultrasound pulses ~ MHz (for polymers) Evaluation of Transit time Amplitude Transmitter Detector Polymer

Equipment T & P inputs to ultrasonic transducers Computer controlled data acquisition Ultrasound input 1GHz sampling frequency Commercial pulser-receiver Digital oscilloscope (free standing or 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 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 filling Can be useful for detection of jetting effects Polymer presence is indicated by a rapid variation of amplitude

Shrinkage detection Polymer Air Polymer Transducer

Shrinkage Detection 100mm/s 75mm/s 50mm/s 10mm/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 solution Piezo films are deposited on external surface Thickness up to 100µm – determines the resonant frequency Films are poled Silver 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 Microsystem50 Allows 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