SAMPE Journal - September/October 2012 - (Page 40)

Feature Article Approach to Optimizing a Combined Out-of-Autoclave (OOA) Prepreg/Liquid Composite Molding (LCM) Process for Integrated Structures C. Di Fratta, M. Danzi, V. Gabathuler, M. Zogg and P. Ermanni ETH Zürich, Centre of Structure Technologies Zurich, Switzerland Abstract Hybrid processes combining characteristics of prepreg and resin infusion/injection techniques are interesting and advantageous solutions for manufacturing of highly integrated structures. The possibility, given by traditional prepreg technology, to manufacture with a good reproducibility parts having elevated mechanical performances and as well to introduce additives like flame retardants or tougheners, can be successfully combined with liquid composite molding (LCM) characteristics. This work aimed to investigate these combined processes. The present research involved furthermore out-of-autoclave (OOA) prepreg, which provide additional cost-savings and environmental advantages compared with standard autoclave techniques: OOA prepreg plies and dry fabrics are laid up together in a mold and then resin is injected (RTM-like) or infused (VARI-like) in the cavity. When the impregnation is completed the part can be cured in oven. Goal of the investigation is to analyze the performances of hybrid laminates, in respect to pure OOA prepreg- and LCM-parts and to optimize the manufacturing route, assessing the process robustness through several tests. Simple demonstrators have been also realized to prove the hybrid technique feasibility and effectiveness. Introduction Distinctive characteristics of composite materials underlie the widening of their applications’ range during the last decades: nowadays composite structures are largely employed in several fields, especially when elevated mechanical properties are required together with light weight. However, their final performances (and also the effective convenience to use them for a designed application) result from the way they are manufactured. Each fabrication technology bears specific technical or economical advantages and disadvantages as well. With a special reference to aerospace industry, two main processing techniques are used for structural applications1,2: prepreg technology and liquid composite molding (LCM). Traditional prepreg processing is chosen for high-end applications, since it can provide parts presenting excellent mechanical characteristics with good reproducibility. Moreover, the material behavior can be adjusted by additives, such as flame retardant or tougheners, in order to meet special requirements. Typical disadvantages are to be found in high production costs and quite laborious manufacturing of complex shape structures, with limited potential for automation and possibility of delamination. On the other hand, LCM processes, which involve infusion or injection of liquid resin into a dry preform prior curing, give higher freedom in the design of components’ geometries, but usually lower mechanical properties of materials. Combination of already established fabrication processes is a practicable way to improve product performances, integrate multiple functions in the same structure and reduce manufacturing costs. A classic example of combined technology is provided by Airbus Industries and named co-bonding3: this technique implies the consolidation in a single component of more parts manufactured through different processes, using a sequential hardening, therefore without a real resin systems’ cross-linking (or co-curing). A further instance is given by P. Ermanni4, which obtained a stringer-stiffened fuselage through a ‘one-shot’ curing, employing wet-filament winding to manufacture the fuselage skin and prepreg materials to produce the stiffening parts. In more recent times, actual processing that combines prepreg and LCM techniques has been investigated by different industries and research institutes: Eurocopter GmbH and DLR (German Aerospace Center) provided1,5 several evidences of combined prepreg and infusion (CPI) process by manufacturing successful demonstrators, like spars, stringer-reinforced panels and helicopter floor covers with improved fire, smoke and toxicity properties. Japan Aerospace Exploration Agency (JAXA) proposed6 a VaRTM and prepreg hybrid (VPH) process for the production of a quadrant section of fuselage, consisting in a stringer-stiffened skin with window cutouts supported by curved frames. A deeper insight into this hybrid technology is given by the research of R. Kaps2,5: he has identified clear advantages by using it in the fabrication of components that possess the deSAMPE Journal, Volume 48, No. 5, September/October 2012 40 http://www.revchem.com http://www.revchem.com

Table of Contents for the Digital Edition of SAMPE Journal - September/October 2012

SAMPE Journal - September/October 2012
Contents
President’s Message
SAMPE Journal Editorial Calender
Technical Director’s Corner
Prepreg Non-Autoclave Manufacturing Technology: Program Overview and Co-Cure Enablers for Disruptive, Pervasive Use
Welcome SAMPE’s Newest Members
Materials & Products
SAMPE Tech 2012|Charleston, SC
Perspectives
SAMPE Proceedings
Perspectives- Taking Material Science To The Next Frontier: Models Of Past Material Innovations And How They May Impact The 21st Century
Europe News & Views
SAMPE Europe’s SETEC 2012, Lucerne, Switzerland
SAMPE Europe’s SEICO 2013, Paris, France
SAMPE 2013|Long Beach Call for Papers
Industry News
Approach to Optimizing a Combined Out-of-Autoclave (OOA) Prepreg/Liquid Composite Molding (LCM) Process for Integrated Structures
SAMPE LinkedIn Communities
Corporate Partners
The SAMPE Foundation
Tech Tidbits
SAMPE Upcoming Events
Face-Sheet Quality Analysis and Thermo- Physical Property Characterization of OOA and Autoclave Panels
Advertiser’s Index
Resource Center
SAMPE Membership Application
SAMPE Books & CD’s Order Form
Industry Events Calendar
Chapter Meetings Dates and Contacts

SAMPE Journal - September/October 2012