Sensor based analysis and identification of leak-prone areas in vacuum bagging for high perfor-mance composite components

Abstract

Leakage detection is an essential process step in the manufacturing of high performance composite components. During production, a composite layup is hermetically sealed against the environment by auxiliary materials creating a so-called vacuum bag. Faulty vacuum bags lead to complex repair work and can drastically impair the quality of the composite. A two-stage process for automated leakage detection was developed at the German Aerospace Center in Stade. Possible leakage locations are limited by a sensor system for subsequent in-depth examination by infrared thermography. In this work, the possibilities of volumetric flow meters as a sensor system for leakage detection are investigated. Through a series of experiments, it was proven that the existence of leakages in vacuum bags can be explicitly identified during evacuation of the vacuum bag due to the volumetric flow rate converging towards a notably elevated threshold value. The magnitude of threshold flow was directly correlated to the leakage area. A mathematical model for prediction of vacuum loss based on a measured elevated flow rate was developed and verified experimentally. For multiple vacuum lines, the volumetric flow rate caused by a leakage was observed to distribute in a regular pattern, based on the respective distance of leakage and vacuum ports. A first attempt at localization via trilateration showed promising results, but the need for further experimental investigation was identified. Based on the conducted experiments, measurement of volumetric flow rate transpired to be a favorable system for the detection of leakages in vacuum bags. Their implementation is expected to reduce both process times and effort.