Ultrasound based monitoring of the injection moulding process - Methods, applications and limitations

Ultrasound Sensors for Process Monitoring in Injection Moulding

“…In 1964, Thurston [ 20 ] proposed an equation for ultrasound velocity of longitudinal wave based on bulk moduli ( K ), shear moduli ( G ), and the density of a polymer media: Since the shear moduli in polymers is negligible, the sound velocity can be expressed as: k is the adiabatic compressibility, which can be calculated as [ 21 ]: where v is the specific volume and is the specific heat capacity at constant pressure P . The specific volume, at temperature T and pressure P can be obtained from the Tait equation [ 22 ], is zero-pressure isotherms, is a function of temperature, which is independent of pressure and C is a universal constant: …”

“…Hence, by combining ( 2 )–( 4 ), the longitudinal velocity of ultrasound in the polymer can be derived as a function of pressure and temperature. Praher et al in 2014 [ 22 ] simulated the contour of sound velocity based on temperature and pressure for polypropylene, presented in Figure 2 . It should be noted that extracting temperature and pressure information from ultrasound echoes is an indirect measurement, which requires a model specific to the material being investigated.…”

“…The application of ultrasonic probes in monitoring the melting and conveying processes in the screw of the injection moulding process has also been investigated. Praher et al [ 22 ] proposed a fan-shaped ultrasonic transmitter and receiver array along the barrel for measuring the two-dimensional temperature in the screw antechamber, shown in Figure 5 a. The temperature of each ring segment in Figure 5 a was calculated through numerical simulation using the fact that the transit time of ultrasound echoes in each ring segment is related to the temperature and pressure.…”

Intelligent Injection Molding on Sensing, Optimization, and Control

“…Praher and Steinbichler [41] measured the clearance between screw and barrel in the plasticization unit of an injection molding machine, where the wear status of the tribomechanical screw-barrel system and unsuitable process conditions could be detected. Moreover, besides the melt content and melt condition in the plasticizing process being detected by ultrasound, a noninvasive ultrasound tomography system was also proposed by Praher et al [42,43]. An ultrasound transmitter and five ultrasound receivers were employed, and five individual sound paths through the polymer melt were achieved (cf.…”

“…Figure 4: (a) Positions of the ultrasound transducers and resulting sound paths through the concentric ring segments used in ultrasound tomography [43]. (b) A cross-sectional view of an in-mold detection system [44].…”