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7/27/2019 Best Practices of Pre-Pregs
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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)
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