Entering The Field Of Thermoplastic Composite Manufacturing Technology

 

Leonardo Aerostructures, a leader in composite materials for the production of the monolithic fuselage barrel for the Boeing 787, is working with CETMA to develop new production technologies, including continuous compression molding (CCM) and equally qualified resin transfer molding (SQRTM) (bottom).

 

This article is a report on an interview with Stefano Corvaglia, materials engineer, head of R&D and IP manager at Leonardo, and Dr. Silvio Pappadà, research engineer and project leader at CETMA.

 

 

Leonardo (Rome, Italy) is one of the world’s major players in the aerospace, defense and security sectors, with €13.8 billion in revenue and more than 40,000 employees worldwide. The company offers comprehensive solutions for air, land, sea, space, cyber & security, and unmanned systems worldwide.

 

Leonardo invests approximately €1.5 billion (11% of revenue in 2019) in research in the aerospace and defense sectors, ranking second in Europe and fourth in the world. Leonardo produces the one-piece composite fuselage barrels for the Boeing 787 Dreamliner fuselage sections 44 and 46.

 

Leonardo Produces Composite Horizontal Tail Fins For The Boeing 787 Dreamliner.

 

Leonardo, through its Aerostructures division, manufactures and assembles large structural components in composite and conventional materials, including fuselages and empennages, for the world’s major civil aircraft programs. In composites, the 44-section and 46-section “monolithic barrel” for the Boeing 787 mid-fuselage are manufactured at its Grottaglie plant, and the horizontal stabilizer is produced at its Foggia plant, totaling approximately 14% of the 787 fuselage. Other composite structure production includes the manufacture and assembly of empennages for the ATR and Airbus A220 commercial aircraft at its Foggia plant.

 

Foggia also produces composite parts for the Boeing 767 and military programs, including the Joint Strike Fighter F-35, the Eurofighter Typhoon, the C-27J military transport and the Falco Xplorer, the latest member of the Falco family of unmanned aircraft produced by Leonardo.

 

Collaboration with CETMA

 

“We have many ongoing activities with CETMA, for example, in thermoplastic composites and resin transfer molding (RTM),” says Stefano Corvaglia. “Our goal is to get R&D activities ready for production in the shortest possible time. In our departments (R&D and IP management), we also want to get disruptive technologies with lower TRL (Technology Readiness Level, i.e. lower TRL is more elementary and further from production), but we want to be more competitive and help customers worldwide.” Silvio Pappadà adds: “From the beginning of our collaboration, we have been working on reducing costs and environmental impact.

 

We found that thermoplastic composites (TPC- thermoplastic composites) can reduce costs and environmental impact compared to thermosets.” Corvaglia points out that “we have developed these technologies together with Silvio’s team and built some prototypes of automated workstations to evaluate them in production.”

 

Continuous Compression Molding (CCM)

 

“CCM is a great example of our collaboration,” said Padda. “Leonardo identified some parts to be made from thermoset composites, and together we explored technologies to deliver these parts in TPC, looking at places in the aircraft where there are a large number of parts, such as stitching structures and corner pieces with simple geometries.”

 

 

Parts made using CETMA’s continuous compression molding line. “We needed a new production technology with low cost and high productivity,” he continues. In the past, he points out, individual TPC components were manufactured with a lot of waste.

 

“So we produced the webs based on non-isothermal compression molding, but also made some innovations (patents pending) to reduce waste. We designed a fully automated station for this, which was then built for us by an Italian company.” This station, says Pada, is capable of producing the components designed by Leonardo “at a rate of one every five minutes, 24 hours a day.”

 

However, his team then had to figure out the production of preforms. “In the beginning, we needed a flat lamination process, because that was the bottleneck at the time,” he explains. “So our process starts with a blank (flat laminate), which is heated in infrared (IR) and then put into a press for forming.

 

Flat laminates are usually produced using large presses with a cycle time of 4-5 hours. We decided to investigate a new method that would allow us to produce flat laminates in a faster way. So, with the support of Leonardo engineers, we developed a high-productivity CCM line at CETMA.

 

We reduced the cycle time to 15 minutes for a 1m by 1m part. Importantly, this is a continuous process, so we can produce products of unlimited length.”

 

 

Infrared thermography (IRT) on the SPARE progressive roll forming line helps CETMA understand temperature distribution during production and generate 3D analyses to validate its computer models during CCM development. But what is this new product compared to the CCMs that Xperion (now XELIS, Markdorf, Germany) has been using for more than a decade? “We developed analytical and numerical models that can predict defects such as porosity,” says Padda.

 

“We did this work in collaboration with Leonardo and the University of Salento (Lecce, Italy) to understand the parameters and their impact on quality. We used these models to develop this new CCM, in which we can have very large thicknesses but also high quality. Thanks to these models, we can optimize the temperature and pressure, but also how to apply them.

 

There are many technical aspects that can be developed to achieve a homogeneous distribution of temperature and pressure; however, we need to understand the impact of these factors on the mechanical properties and defect growth of the composite structure.” “Our technology is more flexible,” continues Pada. In addition, the CCM was developed 20 years ago, but there was no information about it because the few companies that used it did not share knowledge and know-how.

 

Therefore, we had to start from scratch, with only our knowledge of composite materials and processing.” “We are now looking for parts for these new technologies, both through internal programs and with our customers,” says Kovallia. “These parts may need to be redesigned and requalified before we can start production.” Why? “Our goal is to make the aircraft as light as possible, but also competitively priced.

 

So we also have to optimize thickness. But we might find that a part can be lighter, or identify multiple parts with similar shapes, which can result in significant cost savings.” He reiterates that until now, this technology has been in the hands of a few. “But we have developed alternative technologies to make these processes more automated by adding more advanced stamping and forming.

 

We put in a flat laminate and take out a part, ready to go. We are in the phase of redesigning parts and developing flat and formed CCMs.” “We now have a very flexible CCM line in CETMA,” Padda says. “We can achieve complex shapes with different pressures as needed. The line we will develop with Leonardo will be more focused on components that meet their specific needs.

 

We think we can have different CCM lines for flat and L-shaped profiles compared to more complex shapes. This way, we can reduce equipment costs compared to the large presses currently used to produce complex shapes.”

 

 

CETMA uses CCM to produce stringers and plates from carbon fiber/PEKK unidirectional tapes, and then joins them together using induction welding in the KEELBEMAN project of Clean Sky 2, managed by EURECAT.

 

Induction Welding For in-situ Consolidation

 

“Induction welding is very interesting for composites because it allows very good regulation and control of temperature, rapid heating and precise control,” Padda points out. “In cooperation with Leonardo, we developed induction welding to join TPC components. But now we are considering TPC tapes for in-situ consolidation (ISC) using induction welding.

 

For this purpose, we have developed a new carbon fiber tape that can be quickly heated by induction welding using a dedicated machine. The tape uses the same matrix material as the commercial tapes, but has a different structure that allows for improved electromagnetic heating. We are optimizing the mechanical properties, but we are also considering the process, trying to meet different needs, such as how to achieve cost-effective processing through automation.”

 

He points out that it is difficult to achieve ISC with good productivity using TPC tapes. “To use it for industrial production, you have to heat and cool faster and apply pressure in a very controlled way. So we decided to use induction welding to heat a small area, heating only the area where we are consolidating the material, but keeping the rest of the laminate cool.” Padda says the induction welding used for assembly has a higher TRL.

 

“It seems very challenging to use induction heating for in-situ consolidation—no other OEM or grading supplier is doing it publicly at the moment.” “Yes, this could be a disruptive technology,” Kovalia says. “We have patented the machine and the material. Our goal is to develop a material that can compete with thermoset composites.”

 

Many people have tried AFP (automated filament placement) with TPC, but you have to do a second step of consolidation. This is a big limitation in terms of geometry, cost, cycle time and part size. We really could change the way aerospace parts are produced.” ” In addition to thermoplastics, Leonardo continues to focus on RTM technology.

 

This is another area where we have collaborated with CETMA and patented new developments based on older technologies, in this case SQRTM. Same qualified resin transfer molding (SQRTM) was originally developed by Radius Engineering (Salt Lake City, UT, USA). ” Adopting an out-of-autoclave (OOA) approach allows us to use already qualified materials, which is important,” Kovalia said.

 

“It also allows us to use prepregs with well-known properties and quality. We have designed, demonstrated and patented aircraft window frames using this technology. ”

 

Despite Covid-19, CETMA continues to work on the Leonardo project, with the picture showing the production of aircraft window structures using SQRTM to achieve defect-free parts and faster preforming compared to conventional RTM technology.

 

As a result, Leonardo has gained the ability to replace complex metal parts with net-shaped composite parts, without further processing “This is also an older technology, but if you go online, you will not find information about this technology,” Padda points out. “It is important that we once again use analytical models to predict and optimize the process parameters.

 

With this technology, we can obtain a good resin distribution, without dry areas or resin accumulation, and a void content close to zero. We can produce high structural properties because we can control the fiber content, and this technology can be used to produce complex shapes. The same materials are also suitable for autoclave curing, but with an OOA method, but you can also decide to use fast-curing resins, reducing the cycle time to a few minutes. ”

 

“Even with the current prepregs, we have reduced the curing time,” Kovalia points out. “. “For example, for parts like window frames, we can achieve 3-4 hours using SQRTM (Same qualified resin transfer molding) compared to a normal autoclave cycle of 8-10 hours.

 

The heat and pressure are applied directly to the part, with less mass to heat. Also, heating liquid resin faster in an autoclave compared to air gives superior part quality, which is an advantage, especially for complex shapes. No rework, zero voids and superior surface quality because the tool is controlling it, not the vacuum bag. ”

 

A Forward-looking, Technology-based Future

 

Leonardo is innovating across a rich and diverse range of technologies. Due to the rapid pace of technological development, it considers investment in high-risk R&D (low TRL) essential to develop new technologies needed for future products, beyond the incremental (short-term) development it already maintains in current products.

 

This combination of short-term and long-term strategies is combined in Leonardo’s 2030 R&D Master Plan, a unifying vision for a sustainable and competitive company.

 

As part of this plan, it will launch Leonardo Labs, an international network of corporate R&D laboratories dedicated to advanced research and technological innovation.

 

In 2020, the company will open the first six Leonardo Labs in Milan, Turin, Genoa, Rome, Naples and Taranto, and is recruiting 68 researchers (Leonardo Fellows) with skills in the following areas: 36 positions in Artificial Intelligence and Autonomous Intelligent Systems, 15 positions in Big Data Analytics, 6 positions in High Performance Computing, 4 positions in Electrification of Aeronautical Platforms, 5 positions in Materials and Structures, and 2 positions in Quantum Technologies.

 

Leonardo Labs will play the role of an innovation outpost and creator of Leonardo’s future technologies. It is worth noting that the technologies Leonardo commercializes in aircraft may also have applications in its land and sea sectors.