{"id":54450,"date":"2026-06-15T11:51:47","date_gmt":"2026-06-15T09:51:47","guid":{"rendered":"https:\/\/composites-united.com\/?p=54450"},"modified":"2026-06-15T11:57:49","modified_gmt":"2026-06-15T09:57:49","slug":"surface-pre-treatment-barrier-layer-automated-machining-and-assembly-of-cryogenic-cfrp-hydrogen-tanks","status":"publish","type":"post","link":"https:\/\/composites-united.com\/en\/surface-pre-treatment-barrier-layer-automated-machining-and-assembly-of-cryogenic-cfrp-hydrogen-tanks\/","title":{"rendered":"Surface pre-treatment, barrier layer, automated machining and assembly of cryogenic CFRP hydrogen tanks"},"content":{"rendered":"\t\t
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At ILA 2026, Fraunhofer IFAM presented \u201cHYTANK\u201d project results on the efficient production of lightweight hydrogen tanks for zero-emission aviation<\/h2>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Researchers from Plasma Technology and Surfaces, Paint\/Lacquer Technology as well as Automation and Production Technology at Fraunhofer IFAM, in collaboration with \u201cHYTANK\u201d project partners, developed groundbreaking, resource-efficient manufacturing and joining technologies for the production of large-format, double-walled hydrogen tanks made of carbon fiber-reinforced plastic (CFRP) \u2013 ranging from suitable surface pre-treatments and functional barrier layer up to automated production on a 1:1 scale, including machining and adhesive bonding assembly. The goal was to lay the groundwork for the future efficient production of lighter, leak-tight and \u2013 under cryogenic conditions \u2013 more reliable tank structures, e.g., for the aerospace industry.<\/b><\/p>\t\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Liquid hydrogen (LH\u2082) is considered a promising option for the aircraft engines of the future. However, the tanks required for this purpose have to meet extreme requirements: despite their minimal weight, they must remain permanently leak-tight and structurally sound at temperatures as low as -253 \u00b0C, while also withstanding mechanical and thermal stresses. CFRP structures generally offer favorable conditions for this, but place high demands on design, manufacturing and joining technology. In particular, cryogenic temperatures, pressure loads and the combination of different materials require tailored design and process concepts.<\/p>

In the \u201cHYTANK\u201d project (\u201cDevelopment of coating, joining, and assembly processes for the manufacture of a CFRP LH\u2082 tank for emission-free flight\u201d; funding code: 20W2214D), Fraunhofer IFAM addressed these challenges with an integrated approach covering key process steps \u2013 from the preparatory functionalization of surfaces to the development of barrier layer for increased leak tightness and vacuum stability, right through to the automated machining and assembly of the tank structures.<\/p>

At ILA 2026 in Berlin, the scientists presented a true-to-scale model of the automated machining and assembly plant as well as a 1:1-scale original tank structure segment that has undergone surface pre-treatment and barrier layer.<\/p>\t\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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\u00bbHYTANK\u00ab \u2013 Contactless atmospheric-pressure plasma pre-treatment of a CFRP surface. (\u00a9 Fraunhofer IFAM)<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t
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\u00bbHYTANK\u00ab \u2013 Automated application of the barrier layer using a painting robot and a conventional automatic spray gun. (\u00a9 Fraunhofer IFAM)<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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Surface pre-treatment: Improving adhesion in a targeted manner<\/h4>

To ensure that subsequent coating systems function reliably on CFRP structures, a consistently high level of adhesion to the substrate is required. A main focus of the R&D work within the \u201cHYTANK\u201d project was therefore on the appropriate pre-treatment of surfaces. The goal was a combined pre-treatment and coating process that improves the barrier properties of the CFRP structure, thereby permanently stabilizing the insulating vacuum between the inner and outer shells of a double-walled cryogenic tank. The focus is on enhancing the barrier effect against moisture penetrating from the outside as well as against outgassing products from the CFRP. For the barrier layer to function reliably, in addition to the actual barrier effect, excellent adhesion to the CFRP substrate is required. The challenge: Due to the manufacturing process, the CFRP surface has release agent residues that are critical for adhesion; these must be removed or specifically modified without damaging the matrix or exposing the fibers.<\/p>

The project involved a comparative study of various pre-treatment methods, including vacuum suction blasting, atmospheric pressure plasma treatment, VUV irradiation and laser treatment. Three of these process variants proved to be fundamentally suitable. However, which solution is best suited in each individual case depends heavily on the specific application \u2013 for example, on component geometry, accessibility, available processing time, the CFRP material used as well as the type and amount of release agents applied.<\/p>

Dry, non-contact or material-friendly processes show particular promise. Thus,\u00a0atmospheric pressure plasma treatment<\/b>\u00a0increases wettability and adhesion without subjecting the surface to significant thermal or mechanical stress.\u00a0Vacuum ultraviolet (VUV) light irradiation<\/b>\u00a0activates the surface by inserting polar functional groups, while\u00a0laser treatments<\/b>\u00a0enable precise cleaning and activation.<\/p>

The studies clearly showed that surface pre-treatment is a decisive factor in ensuring the reliable function of subsequent coatings on large-scale CFRP structures.<\/p>\t\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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\u00bbHYTANK\u00ab \u2013 A milestone toward the future serial production of lightweight CFRP hydrogen tanks for aviation \u2013 a flexible, modular, automated assembly line (FFT Produktionssysteme GmbH & Co. KG). (\u00a9 Fraunhofer IFAM)<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Barrier layer: Increasing leak tightness and stabilizing the vacuum<\/b><\/h4>

A second research priority of the project focused on coating solutions for cryogenic hydrogen tanks made of lightweight materials. Fraunhofer IFAM developed barrier layers that can reduce gas permeability in polymer-based tank systems. They are designed to minimize hydrogen leakage while also limiting the ingress of atmospheric gases \u2013 such as oxygen \u2013 or moisture. In this way, they could make a twofold contribution: on the one hand, by increasing the operational safety of the tank system and on the other hand, by supporting the maintenance of the heat-insulating vacuum in double-walled tank structures.<\/p>

The coating systems developed are based on polymeric binders with integrated barrier pigments. By specifically designing the layer structure, the diffusion path for gas molecules is lengthened, thereby reducing permeation. A key advantage of these approaches is that they can generally be applied to complex geometries using established coating processes, making their transferability to industrial processes plausible.<\/p>

Here, Fraunhofer IFAM contributed its expertise in application technology and coating development. This included, among other things, the transfer of layer systems to real tank geometries, process\u00a0<\/a>stability and behavior under cryogenic conditions. To evaluate performance, methods such as permeation measurements, cryocycling and SEM analyses were used.<\/p>

The results highlight the potential of barrier layer to increase the use of lightweight materials in hydrogen tanks, thereby reducing weight and energy consumption \u2013 not only in aviation, but prospectively also in other applications related to mobility and hydrogen infrastructure.<\/p>

Manufacturing: Automated machining and assembly of large-scale tank structures on a 1:1 scale<\/b><\/h4>

Finally, the \u201cHYTANK\u201d R&D activities relating to process-reliable manufacturing and assembly of large-volume CFRP hydrogen tanks complete the research project. For this purpose, Fraunhofer IFAM developed technologies for the mechanical machining of functional areas, for the precise positioning of the joining partners and for automated adhesive application. The goal was the controlled joining of the subcomponents to form a closed inner tank. The developed processes were tested on large-scale components at a 1:1 scale.<\/p>

A comprehensive assembly concept was developed for a double-walled tank approximately six meters long, featuring an inner and outer tank, an integrated internal structure and insulation. Due to the large component dimensions, non-rigid CFRP cylinders, tight tolerance requirements, and long curing times, a precisely aligned and scalable assembly concept was required. For this reason, a\u00a0modular assembly system on linear axes<\/b>\u00a0with parallel handling and joining processes was selected, as it enables precise, robust, prospectively scalable handling of the sensitive CFRP tank structures.<\/p>

In addition, a\u00a0validation platform<\/b>\u00a0featuring linearly movable mounting systems was developed and metrologically qualified. This platform allowed for the investigation of key factors influencing the joining process \u2013 such as the stability of the structural adhesive, the adjustment of overlap and gap ratios as well as the squeezing behavior of the joining partners \u2013 under controlled conditions. At the same time, the significant influence of form and positional tolerances on process stability became apparent.<\/p>

A customized system was also developed for\u00a0adhesive bonding<\/b>, which required special automated process control. A custom-developed robot-guided end-effector with roller guidance and a spring mechanism ensured a constant nozzle distance on curved joining surfaces, thereby supporting reproducible adhesive application. After application, the joining partners were automatically positioned relative to one another and joined via a rail system on the assembly line. Heating mats then accelerated the curing of the adhesive.<\/p>

The results show that automated machining, positioning and adhesive bonding processes for large-format CFRP LH\u2082 tank structures are fundamentally feasible. For industrial implementation, robust strategies for tolerance management, reproducible gap adjustment and reliable adhesive application must be further developed.<\/p>



Conclusion l Perspective<\/h4>

As part of the \u201cHYTANK\u201d R&D project, Fraunhofer IFAM developed key technologies for the future resource-efficient production of hydrogen tanks, e.g., for the aviation industry: tailored surface pre-treatments, functional barrier layers as well as automated machining, joining and assembly processes. Together, these approaches help make large-format, high-strength CFRP LH\u2082 tank structures lighter, more leak-tight and better manageable in industrial production \u2013 including applications in other industries, such as shipping and hydrogen infrastructure.<\/p>



Funding<\/b><\/h4>

The \u201cHYTANK\u201d project (\u201cDevelopment of coating, joining and assembly processes for the manufacture of a CFRP LH\u2082 tank for emission-free flight\u201d; funding code 20W2214D) was funded by the German Federal Ministry for Economic Affairs and Energy pursuant to a resolution of the German Bundestag as part of the LuFo VI-3 program. On behalf of all project partners, Fraunhofer IFAM would like to thank the Federal Ministry for Economic Affairs and Energy as well as the German Aerospace Center (DLR) as DLR Project Management Agency for their support.<\/p>

\u00a0<\/p>

Project partners<\/b><\/h4>