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IBEX 2013, September 17

BEST PRACTICES: OUT OF

AUTOCLAVE PREPREGS

D. Michael Bergen, Custom Technologies LLC

David Jones, DE Jones & Associates

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ADVANTAGES: NAVY PERSPECTIVE

Current technology for naval structures is based on VARTM process Drawback to VARTM is the inability for full infusion wet-out on large scale and/or thick

parts (DDG-1000 deck house is about 700tons of carbon composite) primary focus of university funded research

Material handling on vertical surfaces & hull sides complicate the ability to scale VARTMsuccessfully

OOA prepreg eliminates the critical weaknesses of VARTM: spray tack, a proven contaminant most race tracking resin deprivation laminate vacuum lock maintains full atmosphere of vacuum under the bag (better consolidation) eliminates the need for complex flow models and monitoring systems

Incorporate complex features in initial laminate

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Basic VARTM Layout

Full vacuum

Atmospheric pressure behind front

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FLIPPING DDG 1000 DECK HOUSE

PhotoCourte

syHuntingtonIngalls

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DDG 100 DECK HOUSE NEARING

COMPLETION

PhotoCourtesyHuntingtonIngalls

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DECKHOUSE ROLL OUT

PhotoCourtes

yHuntingtonIngalls

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SPECIFIC ADVANTAGES

The OOA prepreg fabrication system also provides specific: Fiber volume fraction & resin to fiber ratio

resulting in the ability to maintain critical dimensions and strength incomplex cross-sections

Co-curing of the inner & outer skin to core no need to hot coat the core more effective structure with negligible resin migration into the

core the former provides the additional benefits of labor reduction

through process reduction More accurate laminate placement for focused structural requirements (tooling aswell as hull / superstructure) Successful cures in prepreg laminates up to 2.5 thickness

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SPECIFIC ADVANTAGES CONT.

Longer working times for lamination (measured in weeks) Include complex features that VARTM cannot due to inability to reverse

flow Ability to achieve autoclave quality with proper laminating practice Loss of vacuum do not necessarily lose the part (oven off, fix bag) Less recurring material waste Much cleaner shop environment Happy workers (get to work in A/C) No VOC No HAZMAT, resin is already polymerized (non-hazardous warehouse)

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TOOLING

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TOOLING CONT.

Advantages Matched CTE for post curing Excellent strength & stiffness

Thinner tools is less mass to heat during curing cycles

Requires less backing structure and is lighter

Lower void content Less issues at elevated temperatures Potentially less porosity relating to vacuum integrity

Dimensional stability is key element Tighter tolerances when producing multiple parts which come together

Speed of construction based on laminate design Much cleaner than wet laminate construction

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NO SPRAY TACK

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MAINTAIN CRITICAL DIMENSIONS

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CRITICAL DIMENSIONS CONT.

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CRITICAL DIMENSIONS CONT.

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INCORPORATE COMPLEX FEATURES

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DISADVANTAGES

Post curing phobias, especially in large structures need large oven for large production parts

Perception of limited resin choices Intermediate de-bulking steps Requires different skill set May be labor intensive (placement and hand consolidation) Cold storage Lead times for materials, especially recovering from errors Initial cost of material

Needs A/C work environment

control tack moisture contaminates parts (condensation or sweat)