Jens Wipperfürth

A concept for non-invasive temperature measurement during injection moulding processes

Current models of the injection moulding process insufficiently consider the thermal interactions between melt, solidified material and the mould. A detailed description requires a deep understanding of the underlying processes and a precise observation of the temperature. Because todays measurement concepts do not allow a non-invasive analysis it is necessary to find new measurement techniques for temperature measurements during the manufacturing process. In this work we present the idea of a set up for a tomographic ultrasound measurement of the temperature field inside a plastics melt. The goal is to identify a concept that can be installed on a specialized mould for the injection moulding process. The challenges are discussed and the design of a prototype is shown. Special attention is given to the spatial arrangement of the sensors. Besides the design of a measurement set up a reconstruction strategy for the ultrasound signals is required. We present an approach in which an image processing algorithm...

Spatially resolved temperature measurement in injection moulding using ultrasound tomography

Current simulation of the injection moulding process insufficiently consider the thermal interactions between melt, solidified material and mould. To improve the prediction accuracy in terms of shrinkage and warpage these interactions cannot be neglected and requires a precise observation of the temperature field within the ongoing process. Nowadays temperature measurements at the transition of the polymer melt to the mould or near the surface of the polymer melt are applicable and do not allow either a non-invasive analysis or a determination of the temperature field. In the approach of ultrasound tomography, presented here, an ultrasound beam is emitted into the melt and the time-of-flight (TOF) is detected by a set of transducers, which are radially arranged around the melt. Subsequent the measurement is repeated from different directions. Using algebraic reconstruction techniques, a distribution of the ultrasound velocity can be calculated based on the TOF-dataset. With additional information about th...

Ultrasound Tomography for Spatially Resolved Melt TemperatureMeasurements in Injection Moulding Processes

In injection moulding processes, the measurement of the temperature distribution is very important for the validation of models used for simulative part design due to the high influence on shrinkage and warpage of the moulded part, but is also very challenging to measure. During the injection moulding process high mould pressures occur and the cavity is not easily accessible. Therefore, contact sensors cannot be used since they induce shear stress into the melt, which changes the flow behaviour of the melt and thus the temperature field. In this work, we present a method for the contactless determination of the temperature distribution of a moulded part during injection moulding using ultrasound tomography. With time-of-flight ultrasound measurements from different directions it is possible to reconstruct the distribution of ultrasound velocity in the cross-section of a moulded part. With this distribution, the temperature field can be calculated using additional material characteristic properties. Based on this concept, an injection mould was designed, that allows performing ultrasound tomography with 20 ultrasound transducers radially arranged around a cylindrical shaped cavity. This allows the temperature determination under real process conditions with a spatial resolution of 3.5 mm2. A highly parallelised measurement device allows recording of several complete datasets before no more signals can be detected due to shrinkage of the moulded part. During several injections moulding-cycles all sensor positions were able to detect noticeable signals. Due to internal signal processing of the measurement device, it is not yet possible to calculate arrival times of the ultrasound signal but amplitude-scans show the general feasibility of ultrasound tomography during injection moulding..