According to Boeing's "Commercial Market Outlook for 2020-2039" (commercial Market Outlook for 2020-2039), by 2039, there will be 48,400 commercial aircraft flying worldwide, 22,500 more than in 2019. At the same time, airlines are speeding up the replacement cycle of older aircraft to improve the efficiency and sustainability of their fleet. Thermoplastic composites can help aerospace manufacturers meet this rapidly growing demand.

Thermoplastics provide many advantages for this industry. Lightweight carbon fiber reinforced thermoplastic (CFRTP) components provide excellent strength and stiffness; corrosion resistance, chemical resistance, fatigue resistance and durability. They usually perform better than equivalent metal parts.

They are also a sustainable material. Thermoplastic components are lighter in weight than corresponding metal components, enabling airlines to reduce fuel and carbon emissions. In addition, thermoplastic composites are recyclable, so manufacturers can melt and reuse materials from production waste and scrapped parts.

Production speed is one of the obstacles to wider adoption of thermoplastic aircraft components. In the past ten years or so, the layout, consolidation, and part molding process of thermoplastics are similar to those of thermosets. Including autoclave treatment, the production process may take several hours.

The development of materials and manufacturing has opened the way for speeding up production. By using automated equipment and non-autoclave processing, manufacturers have proven that they can produce higher-quality thermoplastic parts at a faster rate, making it a cost-effective option for aircraft production.

Designers are becoming more and more accustomed to using thermoplastics. Especially in Europe, predictive modeling and software have strengthened engineers' confidence in this material. "People are always full of misgivings about new materials and do not know how to design and implement thermoplastics in production projects. Once the engineering teams of OEMs and Tier 1 suppliers understand how to design and use it, and have confidence in the manufacturing process , We can really overcome this psychological barrier." Qarbon Aerospace's engineering research director Evan Young said.

01 Progress in materials

The upgrade of unidirectional tape (UDT) is an example of a change in the materials used in the manufacture of thermoplastics. David Leach, Director of Business Development of ATC Manufacturing Company, said: "In terms of fiber consistency, polymer distribution, and elimination of voids in the prepreg, the quality of the material has been improved." Material consistency is essential for rapid, large-scale production. And automation is essential.

Progress has also been made in fiber reinforcement. Aerospace designers mainly use continuous fiber thermoplastics to achieve the strength and performance predictability required for aircraft parts. However, continuous fiber materials have some disadvantages when manufacturing complex parts. "Usually these parts are formed very fast, and it is a challenge to move the fibers and plies in a very short period of time (usually a few seconds)." Leach said, "If a discontinuous form is used, it can actually be manufactured. More complex parts, because this allows some movement in the fiber direction.” But part designers have concerns about the performance of discontinuous fiber materials.

LMPAEK was developed to find a balance between the processability and applicability of these high-performance polymer composites and automated production systems. These materials require less total energy and help significantly increase processing speed.

Low melting point PAEK has similar properties to PAEK series polymers in terms of mechanical strength, chemical resistance and other characteristics, but its melting point is about 40 degrees Celsius lower than PAEK series polymers. Gilles Larroque, Victrex's global strategic marketing manager, said that although this may not seem important, it can make huge differences in production processes such as stamping, injection molding, and automatic fiber placement (AFP).

Victrex recently collaborated with aerospace tool and automation manufacturer Electroimpact on the LMPAEK demonstration project. "Using LMPAEK and an automated fiber placement process, we have been able to reach a layup speed of 100 meters per minute. This is almost four times that of a PAEK UDT," Larroque said.

In October 2020, Victrex and French aircraft manufacturer and equipment supplier Daher announced that they have used AFP and LMPAEK UDT to produce 176-layer, 1.2-inch-thick thermoplastic structural aircraft panels. According to Victrex, this thickness was previously unavailable. The company stated that the 47 x 23-inch panel meets aviation industry standards in terms of porosity, crystallinity, consolidation and adhesion.

"What we see here is the unique UDT performance contribution to the fast AFP process, which was developed and demonstrated by our partners Coriolis Composites and Electroimpact. This manufacturing speed allows thermoplastic composites to replace on the far-reaching scale of aircraft design. Metal becomes possible." Victrex Aerospace Director Tim Herr commented.

Parts made by AFP and LMPAEK can be used for large main structures. This material is also suitable for secondary structural parts that carry high loads, such as brackets and system accessories.

LMPAEK resin and parts made from it must be certified by the aviation industry before it can be used in mass production.

02Reduce production time

Thermoplastic composites companies are using new equipment to reduce production time and steps. For example, continuous compression molding (CCM) enables manufacturers to produce large numbers of laminates at very low cost. Traditional presses have limitations on the size of the parts produced. Leach said: "As laminates become larger and larger, the pressure, temperature, size, and equipment costs required have all increased exponentially."

An alternative method for large parts is vacuum machining. "The AFP process is reaching a fairly high level of consolidation, where you may only need a final vacuum process to fully consolidate the part." Leach said.

In order to achieve the cost reduction and speed required for the production of larger parts and variable thickness parts, manufacturers need to turn to automatic layup. It is impractical to manually stack and pack these layers. Some companies are using pick and place robotic systems that can lay fabric forms (dry or prepreg) and increase or decrease the number of layers in certain areas. This makes it easier for manufacturers to tailor parts based on weight, stiffness, and strength.

Over-injection molding is used to reinforce aircraft components and add stiffeners or accessories to the parts. "If you want to use continuous fibers, the geometry will be limited, and injection molding can provide you with more complex geometries." Leach said. In mass production, this can be a very cost-effective way to create complex shapes.

03 induction welding

Thermoplastic materials can be melted and modified, which allows parts to be welded together to create larger and more complex parts. Welding reduces the need for fasteners, thereby saving production time, reducing the weight of parts, and eliminating the need to punch holes in the laminate.

"Any composite material designer or stress engineer will tell you that the main limiting factor for composite materials is fasteners." Young said.

The induction welding of carbon fiber reinforced plastics (CFRTP) has attracted widespread attention in the industry. The process uses a robot equipped with induction coils that generates a magnetic field that interacts with the electromagnetic properties of carbon fibers to induce heating. When the two carbon fiber laminates touch and the robot moves the induction coil over the area where heat is needed, a weld is formed.

04Urban Air Traffic

It is not just traditional aircraft manufacturers that are interested in thermoplastic composite parts. Companies that produce electric vertical take-off and landing vehicles (eVTOL) also understand their benefits. These urban air vehicles will be used to transport people and packages within approximately 60 miles, requiring the advantages provided by thermoplastic components.

Compared with standard aircraft or even rotorcraft, the weight requirements of urban air traffic will be more critical. They are trying to become a reusable aircraft, and they operate at a very fast pace. eVTOL will be powered by batteries, so if the aircraft is to reach the expected range, weight reduction is essential.

Source: Ringier Industrial Plastics

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