The MC-21 wing is one of the most notable technological distinctions of the Russian medium-haul aircraft. Large composite power elements of the wing are manufactured using vacuum infusion without autoclave curing.
For the main composite power structures of the Boeing 787 and Airbus A350, automated prepreg layup with subsequent autoclave curing is used. “Pervy Tekhnichesky” compared two completely different technologies across five key parameters.
Production Cost
In vacuum infusion, dry carbon fiber is first laid out, forming the blank for the future part. Then it is placed in a sealed vacuum bag, air is removed, and liquid resin is supplied, which impregnates the reinforcing material. After this, the structure is cured in a thermal oven.
This process allows for the elimination of an autoclave at the stage of manufacturing the corresponding large elements — a massive sealed unit in which composites are cured at elevated temperature and pressure.
Dry fiber and liquid resin can also be cheaper than ready-made prepreg — material pre-impregnated with a binder. However, part of the savings is offset by the high cost of precision tooling required for manufacturing large-sized parts. We award a point in favor of the domestic approach.
Weight and Strength
Both technologies allow for the creation of lightweight and strong carbon fiber structures. Their characteristics are determined not only by the molding method but also by the type of fiber, binder, layer orientation, impregnation quality, and part design.
Vacuum infusion on the MC-21 allows for the manufacture of large integral wing elements. In this case, the uniformity of impregnation is of particular importance: if the resin is distributed incorrectly, unimpregnated areas or pores may remain inside the part, reducing mechanical characteristics.
Autoclave molding for the Boeing 787 and Airbus A350 also provides high quality indicators. Pressure and temperature help to compact the prepreg layers and control the curing process.
Therefore, it is incorrect to declare one technology an unconditional winner in terms of strength or weight. The characteristics of a specific design and the test results are important.
Part Size and Integration
Vacuum infusion allows for the manufacture of large power elements of the wing without an autoclave. In Ulyanovsk, at the AeroKompozit enterprise, composite panels and elements of the MC-21 wing caisson are formed. Integral manufacturing reduces the number of individual parts and subsequent assembly operations.
On the Boeing 787 and Airbus A350, large composite wing panels are produced from prepreg using automated layup and autoclave curing. This method also allows for obtaining large parts with a high degree of integration, reducing the number of joints and fasteners.
Infusion technology allows not to limit the dimensions of the part by the size of the autoclave, but it does not in itself guarantee the manufacture of larger or stronger elements. This requires appropriate tooling, equipment for uniform heating and impregnation control, as well as confirmation of the characteristics of the finished structure — it is impossible to identify the best solution.
Serial Production
Automated prepreg layup and autoclave molding are widely used in the production of modern wide-body aircraft. Boeing and Airbus use these processes for the production of large composite elements, and production chains include specialized equipment, material suppliers, and established quality control.
The MC-21's vacuum infusion represents a rarer approach for large loaded aviation structures. Its implementation required the development of technological processes, tooling, and impregnation control for large-sized parts. At the same time, the technology was applied to a real aircraft, and not just in laboratory experiments.
The autoclave method wins due to its industrial maturity and accumulated experience in serial production of composite structures for wide-body liners.
Technological Complexity
Vacuum infusion eliminates the need to place a large part in an autoclave, but it places high demands on the preparation of the reinforcing material, the tightness of the vacuum bag, and the uniformity of resin supply. For large structures, it is especially important to prevent the formation of dry areas and impregnation defects.
The autoclave process uses prepreg, the quality of which is controlled at the material manufacturing stage. However, it requires strict adherence to storage temperature conditions: prepregs are usually kept in freezers to slow down premature resin curing.
According to five criteria, the comparison does not reveal an absolute winner, the score is 1:1. Vacuum infusion offers potential savings on equipment and materials, and also allows for the production of large integral elements without an autoclave.
The autoclave technology of the Boeing 787 and Airbus A350 relies on a mature production base and the widespread use of prepreg in aircraft construction.