By Bjorn Fehrm
September 4, 2026, ©. Leeham News: Last week, we looked at why the preferred method to produce composite would be dry fiber infusion if you want to avoid slow and expensive autoclave curing and replace it with an oven cure (Figure 1). The laid-down dry fiber does not have blocking epoxy resin like a prepreg, which reduces the risk of air being trapped in the layup. An oven cure with a bagged layup kept under a 1 bar vacuum produced a composite with less than 1% voids.
While the cure method is clear, the way to get a dry fiber layup to keep an advanced 3D shape during resin infusion and to be automated has several possible solutions.
With dry fiber infusion, we have a pre-stage before curing that fits an out-of-autoclave (OOA) curing process. The challenge in dry fiber infusion and OOA curing has been developing an effective automated dry-fiber layup process for parts more complex than a flat laminate. The industry calls these more complex layups preforms; they have the form of the final cured composite but have not been infused with epoxy resin or cured yet.
The manual fabric layup for flat parts we described in Part 13 is a method that can be further automated. The cutting of the fabric sheets for the A220 wingbox covers is automated using NC cutters, but the picking and placement is manual (Figure 2).
The cut fabric plies can be picked up using a suction method and placed on the wing cover mould, but the logistics become more complicated as the current roll-up-and-store system for later fetching and roll-out of the ply gets shortcut.
The process chain of cutting the fabric and placing it on the layup becomes a real-time coupled process that changes the production flow. NC cutting now becomes a bottleneck, as placing cut fabric on the mould layup is much faster. This likely means investing in multiple NC cutting systems along with a wide-area pick-and-place system.
The pick-and-place system could store the cut fabric as in the system in Figure 3, but this would require very large storage stacks or dividing the plies into several fabric parts.
The technology to handle cut fabric layers and to place them on the mould is often found in the textile industry. Once the fabric layers are placed on the mould layup, these can be either mechanically clamped to fix them, or a layup stitching technique can be used.
NASA and Boeing did a joint project called PRSEUS, which combined dry fiber fabrics and stitching to produce complex structures that could be infused and cured in a one-shot procedure (Figure 4). The stitches can use either carbon fibers or a thermoplastic thread that dissolves into the epoxy resin during the layup cure.
For smaller parts, like the CFM LEAP fan blades, a preform can be assembled using textile forming techniques, placed in a closed mold, and then infused. The mold is electrically heated to cure the epoxy resin (Figure 5).
The alternative way to create dry fiber preforms before infusion is by using tape, where dry fibers are covered in a binder thermoplastic that melts at laydown and tacks the tape runs together. We will cover this in the next edition of Bjorn’s Corner.
question re “Fan blades”
are these solid or hollow?