Flow-enhancing layers in the vacuum infusion process

The current trend towards increased use of vacuum infusion molding for large surface‐area parts has increased the interest in an advanced modeling of the process. Because the driving pressure is limited to 1 atmosphere, it is essential to evaluate possible ways to accelerate the impregnation. One way of doing this is to use layers of higher permeability within the reinforcing stack, i.e. flow‐enhancing layers. We present an experimental investigation of the flow front shape when using such layers. The through‐thickness flow front was observed by making a number of color marks on the glass‐mats forming the reinforcing stack, which became visible when the resin reached their position. The in‐plane flow front was derived from observations of the uppermost layer. It turned out that existing analytical models agree very well with the experiments if effective permeability data is used, that is, permeability obtained from vacuum infusions. However, the fill‐time was nearly twice as long as predicted from permeability data obtained in a stiff tool. This rather large discrepancy may be due to certain features of a flexible mold half and is therefore a topic for further research. The lead‐lag to final thickness ratio is dependent on the position of the flow front and ranges form 5 to 10 for the cases tested. Interestingly the lead‐lag has a miximum close to the inlet.