CompositesWorld
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CompositesWorld.com 15 OUT OF AUTOCLAVE SUPPLEMENT ยป Much is at stake with regard to out-of-autoclave processing. Although OOA methods use less energy, energy consumption is actually a small portion of total composite part cost, and if a company changes how a part is manufactured, re-qualifcation costs must be considered in the cost equation. But, if volumes are high enough, OOA is worth pursuing because it can shorten cycle times and signifcantly cut capital and tooling investments, which ultimately will make composite parts more cost efective. But much work remains to be done to improve processing and address issues that include surface porosity and pitting, debulk time and void entrap- ment. Dr. Lessa Grunenfelder, a member of the teaching faculty at the University of Southern Cali- fornia (USC) Viterbi School of Engineering (Los Angeles, CA, US), together with Professor Steve Nutt, the director of the M.C. Gill Composites Center in USC's Department of Chemical Engineering and Materials Science, has presented research on better ways to evacuate entrapped air and moisture from vacuum bag only (VBO) prepregs. "Breathable edge dams," says Grunenfelder of a popular current solution, "are great for simple parts, but what about complex parts with ply drops? We must have some degree of in-plane and through- thickness permeability." USC has actually developed a woven fabric prepreg product, called USCpreg, a vacuum-bag only (VBO) semi-preg system made in a roll-coating process. Resin impregnation of the USCpreg is uneven and irregular, which leaves dry areas that create pathways for air escape without the need for complex edge-breathing bagging setups, and eliminates long vacuum hold times. "Tis system will make larger, more complex parts possible with OOA prepregs," she says. However, VBO prepreg's greater VBO prepreg: air evacuation This scanning electron microscope (SEM) image shows an unconsoli- dated and uncured VBO prepreg, with air channels along the plane of the fbers, as well as trapped air pockets between plies, clearly visible. Source | USC/Lessa Grunenfelder By Sara Black / Technical Editor Air channel along fber plane Trapped air pockets Research on OOA processing continues Much work has been done to make OOA processing practical for aerospace applications, but much work still remains if it is to become the compelling option.