Fill-front and Cure Progress Monitoring for Vartm with Auto-calibrating Dielectric Sensors

Fill-front and cure progress monitoring is critical for vacuum-assisted resin transfer molding (VARTM) manufacturing processes. The experimental multi-channel system presented in this paper includes sensors, signal conditioning, data acquisition software, and signal post-processing components. The sensors are mechanically flexible and optically transparent fringing electric field electrode systems. The emphasis of the reported stage of research is on auto-calibration methods. Specifically, measurement accuracy of the system is increased by using complex sensor geometries. Effects of dielectric permittivity and temperature variations in the resin during filling and curing are also mitigated with an auto-calibration algorithm. The algorithm uses non-linear portions of the sensor to determine accurately how far the resin has progressed during filling. These sensor segments act as checkpoints and are detected by calculating first and second derivatives of the signal over time and smoothing of these curves to eliminate noise effects. Furthermore, the inclusion of additional sensors to estimate dielectric permittivity before entering the mold may provide further improvements in the monitoring algorithm. Once the resin has completely filled the mold, dielectric spectroscopy is performed to monitor cure progression using the same sensors. The transparent sensors are chosen to enable visual monitoring of the fill-front during the VARTM process.