Press-processing of sheet molding compounds (SMC) is a technology for series production of lightweight structures providing elevated mechanical properties. The degree of homogeneity produced during the curing of the thermoset material poses a significant challenge to further technological advancement. This contribution presents a new monitoring method that allows spatially resolved Electrical Time Domain Reflectometry (ETDR) measurements during curing of an SMC. The results show local changes of the impedance along the sensor that can be correlated to the degree of cure (DOC). Two heating cycles are compared. While during the first cycle curing of the SMC takes place, the second cycle serves to detect the heating behavior of the cured part. By analyzing the differences between both cycles, values for the local DOC can be derived. To validate the suggested approach, differential scanning calorimetry (DSC) scans are performed. The results show that ETDR is a promising tool for in-situ process monitoring of thermoset based production technologies. It provides comprehensive data while being a cost-effective and flexible method.
Winkler et al. (Thu,) studied this question.