Additive manufacturing experts from the University of Sheffield AMRC North West are exploring an innovative technique to produce hydrogen storage tanks for aerospace applications. Dr. Evren Yasa, head of additive manufacturing for the AMRC, led a team of researchers that focused on a project using Wire Arc Additive Manufacturing (WAAM).

WAAM is used in many industrial sectors, including energy, defense, automotive, construction, and aerospace, to produce large and complex structural components – reducing the need for assembly and joining technologies, as well as waste material. WAAM has been deployed for repair and remanufacturing purposes in aerospace – saving time and costs. In addition to this, it has the advantage of greater supply chain flexibility – enabling on-demand production in small quantities.

“This project was initiated to utilize our in-house WAAM capability to construct a demonstrator storage tank for liquid hydrogen using an aluminum alloy for use in the aerospace sector – and showcase the complete value chain for producing finished AM parts,” said Evren Yasa.

Hydrogen is a highly sustainable energy carrier and is considered a key to achieving climate neutrality in the EU by 2050. However, challenges around how to store hydrogen limit its full potential. “The main challenges of storing hydrogen for use as a fuel source in aerospace, are the additional storage requirements, along with the complicated geometry needed for integral tanks as well as operation at cryogenic temperatures when it is stored in liquid form,” she said. “These challenges make AM technologies one of the promising manufacturing routes for hydrogen storage tank demands, which is also supported by the Cryogenic Hydrogen Fuel System and Storage Roadmap Report published by the UK’s Aerospace Technology Institute in 2022.”

Currently, sheet metal forming, machining, and welding are used for metallic tank production. However, these conventional techniques do not offer the design freedom to make novel shapes. WAAM provides this design freedom, which resulted in the AMRC team being able to make an array of more complex shapes, compared with the standard cylindrical/spherical shape  – opening up the opportunity, particularly in aerospace, to have the potential to store hydrogen in more compact areas.

Dr. Yasa’s team wanted to explore the feasibility of using WAAM for metallic storage tanks by identifying the process parameters, as well as the deposition strategies, for good mechanical properties. Furthermore, the aim was to investigate and counteract the residual stresses occurring due to the high heat input generated during the WAAM process.

Dr. Muhammad Shamir, technical lead within the AM team at the University of Sheffield AMRC North West, explained how different types of heat sources can be employed in WAAM, for example, an electric arc or a plasma arc to melt the wire feedstock material. “For our research, we focused on an electric arc process using a special technique to minimize heat input,” said Dr. Shamir. “The material was also difficult to work with as aluminum alloys are susceptible to oxygen and hydrogen pick-up. If the material is left in ambient air for too long, it begins to pick up moisture, leading to excessive porosity during processing  – deteriorating the mechanical properties.”

Other challenges that surfaced during the project included the narrow process window giving a limited range of suitable process parameters, and five-axis programming for complex geometries. However, overall, Dr. Yasa said the research work was beneficial as it enabled the team to explore these challenges of WAAM processing aluminum alloys.

The seven-month project was funded through the High-Value Manufacturing (HVM) Catapult, of which the AMRC is a member alongside six other national research centers. Dr. Yasa and her team now want to push the research to a second phase and are awaiting the result of a further funding bid to explore the effect of AM on the cryogenic mechanical properties, as well as hydrogen permeability to ensure that it is a feasible route for liquid hydrogen applications.

“We have applied for funding to carry out more work on the process optimization, as well as having the opportunity to test WAAM materials at cryogenic temperatures in a collaboration with the University of Southampton,” said Dr. Evren Yasa. “Moreover, AM for hydrogen storage tanks in aerospace presents challenges, including regulatory approval, standardization, cost, and industry acceptance… Our future projects will focus on overcoming these challenges by collaborating with industry stakeholders, ensuring compliance with standards and regulations, establishing additive manufacturing guidelines, conducting cost-benefit analyses, and fostering acceptance through engagement and knowledge-sharing with the aerospace industry… The goal is to showcase the economic viability and competitiveness of this solution.”