JEC COMPOSITES MAGAZINE - Issue #77 - December 2012 - 43

b) Dynamic mode: The pressure regulator gradually adjusts the pressure difference between the upper and lower chamber by generating a compressive action on the resin, which is forced to flow across the reinforcement. The frequency of the pulsation depends on the resin and on the elastic characteristics of the materials constituting the lower chamber, the upper chamber, and the pressure distributor. In order to provide a continuum pulsation during the infusion, a valve is added on the vacuum pump and controlled from a remote interface in the LabVIEW software.
Fig. 2: Panel produced by Pulsed Infusion

Key benefits
Before introducing the new Pulsed Infusion technology, it has been necessary to compare it with other assessed infusion processes to establish its processing benefits and determine the differences in terms of final composite properties and manufacturing cycle costs. For example, the feasibility of the Pulsed Infusion process for manufacturing long-fibre composites was assessed by comparing the tensile properties of epoxy/glass fibre composites produced by a conventional vacuum infusion process and by static and dynamic Pulsed Infusion. The experimental results showed that the laminates obtained by dynamic Pulsed Infusion have mechanical properties similar to those measured on laminates obtained by the traditional vacuum infusion process (VIP), so the processes can be considered equivalent from that point of view (see Table 1).
Tab. 1:Tensile properties

and eliminate voids and dry spots in the finished part. In the case of Pulsed Infusion, two vacuum bags are used and the resin distribution medium is eliminated. The lower vacuum bag determines a lower chamber, where the resin infusion occurs almost like in the VARTM process. The lower vacuum bag is stacked on the dry fibre reinforcement without a resin distribution medium. A suitably designed pressure distributor (Figure 1) is positioned on the lower vacuum bag and under the second upper vacuum bag, creating an upper chamber. Through application of a different vacuum pressure in the two chambers and timely control of the pressure difference between the chambers (Figure 2), the resin flow is pulsed and assisted both in the plane and through the thickness of the reinforcement. There are two ways of working: a) Static mode: Initially, a higher depression is applied in the upper chamber than in the lower chamber, causing the pressure distributor to move up. Due to its particular shape, the distributor pulls up certain parts of the bottom bag, creating a thin opening between the reinforcement and the lower bag through which the resin can flow. Once the full amount of resin required to impregnate the dry fibres has been introduced, the vacuum is released in the upper bag and increased in the lower bag, forcing the resin through the reinforcement and compacting the fibres.
Pulsed Infusion is an alternative vacuum infusion process based on the use of a double bag and a silicon membrane in place of the traditional VIP distribution medium. It can work both in static and dynamic mode (using an automation system) and provides a material cost saving of around 19%.

Technology
VIP Static Pulsed Infusion Dynamic Pulsed Infusion

Elastic Modulus, MPa
20,204 17,366 19,810

Tensile strength, MPa
475 420 450

Main features

A cost analysis was also done on VIP and Pulsed Infusion, focusing on the resin and ancillary materials used to produce a biaxial glass-fibre composite panel (1 m², 2 mm thick). Resin consumption is lower for Pulsed Infusion, due to the better distribution of the vacuum pressure and more restricted use of bleeder cloth, yielding a material cost advantage of around 19% for Pulsed Infusion, and a waste reduction due to the elimination of the distribution medium. n
Contact: vinanton@unina.it

No77 December 2012 /

jec composites magazine 43

JEC COMPOSITES MAGAZINE - Issue #77 - December 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #77 - December 2012