Analysis of weld line formation in injection moulded parts using thin-film sensors to model mechanical properties

• Applicants: Professor Dr.-Ing. Christian Hopmann; Professor Dr.-Ing. Marc Christopher Wurz
• Subject Area: Microsystems ; Plastics Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564473956

Modern production technology is subject to the highest demands in terms of quality, production speed and resource conservation. To meet these requirements, sensors are used in production machines for condition monitoring and process control. This research project focuses on the injection moulding process and its process monitoring using thin-film sensors. Particular attention is paid to weld lines in injection moulded components, which occur when two flow fronts meet and weaken the mechanical properties at the joints. The strength of the weld lines depends strongly on the local process conditions, which have not been sufficiently investigated so far. In particular, conventional sensors are limited due to their size and have not been able to enable detailed process investigation.The overall objective of the proposed project is to understand the formation of the weld line, taking into account the prevailing process conditions such as local temperature and pressure, in order to also consider the influence of process fluctuations. The focus here is on temperature measurement as a crucial process variable in the injection moulding process. The approach is to use polymer-free, directly deposited thin-film sensors to monitor the condition at previously inaccessible measuring positions, which generate significantly more precise temperature measurement data with increased local resolution. The sensors are applied directly to the injection mould and have only a minimal influence on the injection moulding process due to their low height of a few micrometers. Due to their small size and the resulting high number of temperature sensors located directly on the measuring surface, these sensors can provide new insights into the formation of the weld line. By evaluating the resulting mechanical weld line strength and correlating it with the measured sensor values, this enables a more detailed understanding of the weld line formation and its optimisation for applications. In addition, the effects of process fluctuations, such as those that can arise from different material batches or residual moisture, are being investigated. Such fluctuations can already lead to challenges for injection-moulded components. However, they have an even greater effect on weld lines. Therefore, the extent to which the sensors are able to detect these fluctuations and enable appropriate countermeasures is being investigated. The overall aim of the project is to examine the formation of weld lines in more detail in order to improve mechanical stability, optimise error detection in the event of process fluctuations and enable new component designs with respect to their mechanical strength. This should ultimately help to make the production of injection-moulded components with weld lines more resource-efficient, higher quality and faster.

• DFG Programme: Research Grants