August 21, 2026, ©. Leeham News: Last week we looked at thermoset prepreg tape layup, which is subsequently cured in an autoclave. It’s the method used for the composite structural parts for the Boeing 787 and the Airbus A350.
We presented it with laydown examples using large gantry-type fiber placement systems. We will now delve deeper into the different machine types, the tapes these use, and the techniques used for simple flat parts and parts with complex geometries.
The market differs between Automated Tape Laying (ATL) and Automated Fiber Placement (AFP) systems. The core difference is the material width and format used during layup, which defines their suitable application geometries and production speeds.
ATL uses wide unidirectional prepreg tape, typically 3 to 12 inches / 75 mm to 300 mm wide, whereas AFP uses multiple narrow slit tapes, often called tows, typically 1/8 to 1/2 inch / 3.35 mm to 12.7 mm wide. These tapes are fed side by side in the application head as in Figure 1.
The capabilities can be summarized as:
The ATL type was used whenever the geometry allowed in the early days of automated prepreg laydown. Figure 2 shows an early ATL used in Airbus’ A350 fuselage shell production.
As AFPs grew more capable, laying down eight or more tapes simultaneously, the deposition-speed advantage of broad-tape ATL declined.
Today, AFP-based systems dominate, as they offer advantages at the beginning and end of the run, where individual tapes can be started and cut to leave the minimum composite part overhang that later has to be machined away.
AFP systems range from small systems consisting of an industrial robot equipped with an application head (Figure 3) to enormous flat-bed systems, such as the systems in Boeing’s new wing center in Everett.
Figure 4 shows the laying down of the prepreg for the 777-9 wingbox spar. Note the operator watching the process halfway down the spar on the left-hand side. It gives a good idea of the size of the tape layer.
Another specialized AFP system is used to produce the Boeing 787 fuselage barrels, Figure 5. The configuration leads to very large systems with the mould, now called a mandrel, spinning while the head moves laterally and axially to follow the section contour.
The picture shows two operators checking the laid-up ply for faults, with the tape head tower moved left to allow room for the inspectors.
The mandrel design for the 787 barrel production was very complex. It had to have grooves where the stringers could be placed so they would co-cure with the section’s skin in the autoclave. After curing, the mandrel had to collapse so it could be extracted from the cured composite. The laid-down section was also dressed with so-called caul plates on the outside before entering the autoclave to give the layup a correct external shape.
We showed that actual laydown of prepreg tape was only a fraction of the time for an ATL/AFP system, Figure 6. In the early days, maintenance of the system head took a long time. Thermoset prepreg head tape runs get fouled because the tacky prepreg deposits epoxy on the feed mechanisms. It therefore needed periodic cleaning before laydown could restart.
More capable, production-oriented systems therefore got dual, detachable heads: one head is on the robot or gantry arm laying down tape, while the second head is at the re-loading and maintenance station.
Certain configurations also have alternative heads, such as an ATL for flat applications and a measurement probe head for dimensional control of the layup.
Another operation that slowed production was inspecting the laid-down ply after each tape run. Today, large system suppliers offer integrated imaging inspection downstream of the head, so missed tow stops/starts or tape breaks can be identified. The system must then stop, and the faulty area must be repaired; otherwise, the composite has a local weakness.
An important parameter for ATL/AFP systems is how much prepreg tape they can lay down per hour. Productivity is measured as applied lb or kg tape per hour.
In the early days of the Boeing 787 program, it was projected that a system could lay down around 50kg tape per hour. In reality, it was one-fifth of that rate because tape broke or residue built up in the tape-layer heads. The unfavorable shape of the time use chart in Figure 6 was not understood.
Single-head systems quickly evolved into systems with changeable heads, and the tape feeds got resin scrapers and better tape control. Today, a large production-oriented system can achieve 100kg/hour, and very large, fast systems lay down over 200kg/hour.
Nice article, you can descripe the sonic knife that cuts the prepreg.
I guess you will contine with machining, form tolerance, assembly of different carbon fiber parts in final baking and the danger of carbon fiber dust in grinding.
That mandrel for the 787 nose section is an impressive sight!