Out-of-autoclave (OOA) manufacturing has generated significant buzz in the composites industry in recent years. Lower tooling costs, greater capabilities for large, highly integrated composite components and the ability to avoid the autoclave bottleneck makes OOA manufacturing a great option for many composite manufacturers. SAMPE Fellow Gary Bond, an associate technical fellow at Boeing, covered how OOA thermoset prepregs have grown and where Boeing hopes to see the market go in his CAMX educational session, “Taking the Pressure Off: Out-of-Autoclave Composite Prepregs, Past, Present, and Future.”
First-generation OOA thermoset prepregs, initially used in the 1990s, enabled low-cost tooling for manufacturers and could be cured at low temperatures. However, these prepregs also had high porosity, untoughened resins and only a few days of out-time. Boeing and the DARPA Defense Science Office co-funded efforts from 2007 to 2012 to improve OOA manufacturing technology by developing OOA prepreg epoxy composites for primary structures that demonstrate autoclave-equivalent properties with 93 C cure with vacuum pressure only and free-standing post-cure at 177 C, among other qualities.
The efforts eventually yielded what is now commercially available as Cycom®5320-1. Now, state-of-the-art OOA prepregs have better properties overall than their first-generation counterparts with 30 days of out-time, toughened resins and less than 1 percent porosity, but must be cured at higher temperatures.
Bond hopes composites manufacturers work together to enhance the future of OOA prepregs, allowing for:
- Increased strength and increased modulus fibers. Currently, these properties tend to be mutually exclusive.
- More robust processing. Bond said a simpler manufacturing process that allows good parts to be created even when things go awry would be beneficial.
- Longer out-time for larger parts.
- Reduced costs.
- Increased automation.
- Increased lay down rates to put down more pounds per hour.
- Shorter total cycle for layup, bag and cure.
- Fabrication of very large and/or thick parts.