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Stronger 3D prints

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3D printing is a manufacturing process used for both consumer and industrial applications in the aeronautics, automotive, rail and medical industries. The Shoryuken project being developed at IMT Nord Europe aims to improve the mechanical performance of the objects printed using plastic and composite materials. To accomplish this, it combines 3D printing with laser welding technology.

In the industrial world, certain parts of cars, trains, airplanes, prostheses and orthoses are now manufactured using 3D printing. This manufacturing method enables the small-scale production of customized, geometrically complex parts using 3D digital models, without requiring expensive, specifically designed molds. This procedure saves time and materials when producing prototypes and products to be marketed. However, 3D printing has its limits, especially in relation to structural composite materials, which are plastic materials reinforced with fibers with a high level of resistance and rigidity.

3D printing processes that use composites with yarn containing cut reinforcing fibers generally produce materials with relatively weak mechanical properties. In order to improve the mechanical performance of the printed parts, manufacturing processes using yarns reinforced with continuous fibers are now in high demand in the industry. These yarns are made of thermoplastics, heat-sensitive materials, and continuous carbon or glass yarns. During the printing process, the yarns are melted in order to add the materials they contain layer by layer. The carbon fibers contained in the thermoplastic yarns do not melt and provide the object with solidity and resistance.  

However, the required level of resistance and rigidity can only be obtained in the direction of the fibers, since they are all positioned on a single printing plane. “The current composite 3D printing technology does not allow for the production of parts containing continuous fibrous reinforcements oriented in all the directions desired in space. This is a disadvantage when there are mechanical constraints in three dimensions,” says André Chateau Akue Asseko, researcher in Materials Science at IMT Nord Europe and winner of the Young Researchers call for projects by the French National Research Agency (ANR).

Hybridization of innovative technologies

This is precisely the technological barrier that the new Shoryuken* project seeks to overcome. To accomplish this, the initiative is studying the pairing of 3D printing with laser welding. This combination makes it possible to print two or more components for the same composite part in different printing directions and then use laser welding to assemble them.

“The difficulty stems from the presence of fibers or porosity, which disrupt the laser beam path due to the heterogeneity, which introduces thermal and optical diffusion phenomena,” the scientist explains. This assembly process therefore requires that the small areas filled with thermoplastics be treated differently during 3D printing. The laser radiation melts the thermoplastic polymer in a targeted manner with the composite material surrounding it. Once they are welded together, the two components become inseparable. This makes it possible to produce objects containing reinforcing fibers positioned in ways that allow them to resist mechanical loads in different directions.

Virtual engineering to optimize production

Modeling and simulation tools integrating multiphysics coupling are being developed to optimize these innovative design and production processes. These tools therefore contain information on the interaction between the laser and materials and their thermal and mechanical behavior. “Virtual engineering makes it possible to define the optimal assembly conditions that will ensure the quality of the welding interface,” says André Chateau Akue Asseko. The software, populated with information on the materials of interest, such as melting points, is used to simulate the behavior of two materials that are welded together in order to prevent spending too much time and materials on 3D printing tests.

The user can therefore adjust the laser parameters in order to conduct an optimal weld right away. “These simulations allows us to identify the optimal temperature and speed ranges for welding,” the researcher explains. The development of this type of tool would allow companies to reduce their development and industrialization costs before production by avoiding potential assembly problems. This would ensure the mechanical performance of the manufactured goods.

Read more on I’MTech: 3D printing, a revolution for the construction industry?

Multisectoral applications

 “For this project, we chose to focus on the health sector by producing a prosthetic arm as a demonstrator,” says the scientist, who is currently in contact with companies specialized in prosthesis design. André Chateau Akue Asseko explains that he initially chose to prioritize this sector for pragmatic reasons. “There is strong demand in this field for customized items, adapted to the users’ morphology. The parts are reasonably sized and compatible with the capabilities of our experimental equipment,” the researcher says.

The Shoryuken project will end in 2026. By that time, the future process and digital tool could convince other industries, such as the rail and automotive sectors, of the benefits of customizing parts and tailoring their functionalization for small and medium-scale production runs. For transportation companies, the significantly lighter weights of the parts designed and produced help to cut down on fuel consumption and thereby reduce carbon emissions, which are a key concern in the current global environmental context.

Rémy Fauvel

* The ANR JCJC SHORYUKEN project on the “Assembly of Hybrid Thermoplastic and Thermosetting Carbon Composite: Customization of Complex Structures” is funded by the French National Research Agency (ANR) as part of the 2021 Generic Call for Proposals (AAPG 2021 – CE10) on “Industry and Factories of the Future: People, Organization, Technology.”

composites

Technology for improving the recycling of plastics and composites

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Plastics and composites aren’t recycled as often as we might wish, as a result of a lack of facilities, the right technologies not yet existing or not being profitable, or hazardous waste deposits. IMT Nord Europe have been working in partnership with manufacturers to develop and improve the available technologies.

Plastics and composites get a lot of bad press, but it is hard to do without them for many objects we use every day, including our cars. In order to minimise their polluting effect, they must be recycled, but this is complicated from both a technological and an economic perspective. Two researchers from IMT Nord Europe are seeking to improve processes with a view towards industrialisation.

In order to recycle plastic, outlets have to be found for these recycled materials. One of the main stumbling blocks is the presence of pollutants, including volatile organic compounds (VOCs), which can produce unpleasant and even toxic odours. There are also very strict standards governing the emission of VOCs and odours in vehicle passenger compartments. Marie-France Lacrampe, a researcher at IMT Nord Europe, is working on a solution which is striking in its simplicity: water-assisted extrusion.

Eliminating odours

Extrusion is a process traditionally used to manufacture objects made from plastic, involving pushing a doughy material through a die of the desired cross-section. Water is injected into the extruder and the steam washes the plastic, extracting the majority of any VOCs. “A few changes need to be made to the extruder”, explains Marie-France Lacrampe. Professor Lacrampe is working alongside three industrial partners and another laboratory, with the industrial pilot expected to be operational within two years.

In order to further improve this process, the researcher intends to combine water with supercritical CO2 – pressurised CO2 which becomes a highly effective solvent. The advantage is that it removes different molecules from those removed using water.

Process organisation and eco-design

Efficient recycling normally starts with designing materials which are easy to recycle. This is particularly true when it comes to food packaging, which is often made using several different materials (cartons, thermoformed tubs or re-heatable pouches, for example). “The ideal solution is to mix compatible polymers which can then be integrated into existing recycling processes”, explains Marie-France Lacrampe.

When it comes to recycling, it’s not just a question of the technology used, but how the whole process is organised. Waste must be used as locally as possible in order to cut transport and logistics costs, requiring intelligent analysis and handling of flows.

“If we want to boost recycling rates then we have to tackle what we don’t know how to do. This is particularly true for small quantities (hazardous waste deposits) and materials which we are unable to recycle or aren’t very good at recycling such as opaque PET (the plastic used to make milk bottles, for example). We are working on recycling small quantities through additive manufacturing, the industrial version of 3D printing, extruding them again with additives so that they be reused.” 

Composites – rarely recycled

If recycling plastics isn’t always easy, just imagine what it must be like for composites, materials which are generally comprised of glass or carbon fibre and a polymer matrix. A modern aircraft such as the Airbus A350 is half-made of composites, which are used in whole sectors of industry, from transport (not just aircraft, but also cars, boats and bikes) to electronics, leisure and wind power.

Once they have reached the end of their life, composites are primarily burned in order to produce energy, which isn’t ideal from either an environmental or an economic point of view. “Solutions are being developed in the aeronautics sector to recover carbon fibres”, points out Mylène Lagardère, who is also a researcher at IMT Nord Europe. “It is mostly carbon-based composites which are used in aeronautics, which are more “noble”, making them easier to recycle.” Technology for recycling fibreglass composite does exist, but it is not yet profitable.

Developing more affordable methods

There are two possible processes for recovering fibres: a chemical process in which the matrix is dissolved in a solvent (allowing the matrix to be reused) and a thermal process in which the matrix is damaged. Matrices themselves are either thermoplastic, meaning they can be melted, or thermosetting, meaning they are damaged when heated. As a result, as Mylène Lagardère explains, “each fibre-matrix combination is processed differently,  with a different process for each product.” This is what makes recycling composites so complicated. The purer the material, the easier it is to recycle.

As we can see, improving recycling is essential, and research into this subject is rightly being prioritised. “Our aim is to develop methods which are both simple and affordable”, explains Mylène Lagardère. “Our basis is the industrial problem: if we have a deposit of materials with certain properties, then we can recover a recycled material with such properties.” The issue is that, during recycling, the properties of the material always deteriorate, as the fibres are shortened.

The recycling of composites is still very much in its infancy, but a few processes are starting to emerge,  whether in water sports, where the association APER – funded by an eco-tax on new crafts – dismantles abandoned boats, or in the wind power industry. The automobile industry is also having to adapt, with legislation requiring recycled materials to be used in the production of new vehicles.

Cécile Michaut

Large quantities of composites for recycling on the horizon?

10 million tonnes of composites are produced each year worldwide, and the market is continuing to grow at a rate of 5% year on year. But recycling is set to really accelerate: composites whihe arrived on the market 20 to 30 years ago are now reaching the end of their lives. 50,000 tonnes of wind turbine rotors will need to be recycled between 2021 and 2022. In 2023, 25,000 boats, three-quarters made from composites, are to be dismantled. 4,000 railway carriages are also awaiting dismantling. Although resources remain limited (15,000 tonnes of production waste and 7,000 tonnes of materials at end of life in 2017), significant growth is anticipated. Processes mut develop and organise in order to become sustainable.

Also read on I’MTech

“We must work now to recycle composites”
Recycling carbon fibre composites: a difficult task