Engineers from KNITU-KAI have patented a method for manufacturing thick-walled and volume-reinforced composite products with an adjustable gap in the technological tooling. First, a technological gap is created between the forming surfaces, ensuring the penetration of the binder through the thickness of the reinforcing material and the removal of air. Then, the tooling is closed, compacting the reinforcing package and forming the specified part thickness.
The idea is not to compress the reinforcing package to its final thickness during impregnation. The mold elements first close with a technological gap, through which the binder penetrates through the thickness of the reinforcing material, and air is removed from the preform.
After impregnation is complete, the gap is reduced until the tooling is fully closed: the resulting pressure compacts the fibrous package and forms the required part thickness.
The process involves vacuuming to a residual pressure of 0.01–0.2 bar, impregnation by transfer method under pressure of 1–20 bar, and subsequent curing at 120–250 °C. After the mold is fully closed, the tooling with the product is held at the set temperature for 30 to 500 minutes, then it is cooled at a rate of 0.2–10 °C per minute to 20–75 °C.
In one of the examples given in the patent, for a double-curvature part made of three-dimensionally woven reinforcing material, a gap of 0.5 mm was used, vacuuming to 0.1 bar, impregnation at a pressure of 1.5 bar and a temperature of 115 °C, after which the mold was fully closed and curing was carried out at 160 °C for 180 minutes.
Another example describes a thick-walled product made of carbon fiber fabric. For this, the initial gap was 1 mm, impregnation took place at a pressure of 2 bar and a temperature of 130 °C until the preform volume was completely filled. Then, after holding at 140 °C for 25 minutes, the mold was fully closed and curing continued at 180 °C for 300 minutes.
The patent claims that gap control ensures more uniform binder distribution through the thickness, reduced porosity, and shorter impregnation time.
For aviation, the problem is directly relevant: “Pervyy Tekhnicheskiy” has already written about the composite “black” wing of the MS-21, for which, as for other composite structures, the properties of the reinforcing material, binder, and the quality of composite formation are important. As the thickness of the composite part increases, the task becomes more complex – the binder must fill the volume of the reinforcing material without forming air inclusions.
The new KAI patent proposes to address this problem not only with pressure and vacuum, but also with the geometry of the forming tooling itself.
It was previously reported that designers Vladimir Galayko and Veronika Oleynikova received a patent for a method for manufacturing a composite stringer for an aircraft, in which glass roving is combined with basalt powder. The basis of the structure is glass roving impregnated with epoxy resin.
Read more on the topic:
- "Black Wing" of MC-21 to Get More Accurate Service Life Calculation: MAI Creates New Methodology for Composites
- Aircraft will fly longer: a new technology for composite diagnostics invented at SPbGU GA
- Geopolymer Foam Instability Eliminated - KAI Scientists Present Solution for Aircraft Construction