Technical Insight: Welding and Joining

- OASIS: Laser Welding of a New Aircraft Cargo Door Design

In 2021, our experts worked alongside Saab AB, University West (Trollhättan, Sweden), VZLU A.S., Romaero S.A. and Queen’s University (Belfast, U.K.) on the EU Clean Sky2 project, OASIS to develop a robotic laser beam welding technique for a new aircraft cargo door design (figure 1). This involved a series of detailed design reviews for the door as well as the identification of suitable laser welding process variants, aluminium alloys and joint configurations. Representative coupon trials were then carried out by TWI to devise the welding parameters to minimise heat input and distortion, whilst maximising the quality and performance of the welded joints. Autogenous laser welding was chosen as the preferred process and suitable alloy combinations were picked alongside welding parameters to avoid cracking, with the project work leading to the creation of a full door, demonstrating that this new production method can offer opportunities to not only reduce door weight, but also manufacturing time and costs.

Weight reduction is important for industries such as aerospace and automotive, where the move towards electric vehicles (EVs) has also created welding challenges…

- Meeting EV Battery Challenges for BMW

We were approached by BMW to help solve a series of challenges related to the production of battery modules for electric vehicles (EVs) (figure 2). Drawing upon past experience with similar problems, our experts found solutions for the fixturing and manufacture of high voltage modules, including structural welds in the module’s frame, which contained the cells, and welding of the cell control system (CCS) to the individual cell terminals. Working directly for BMW as a TWI Industrial Member, we provided tooling design and manufacture, the development of laser welding procedure specifications (WPSs) for CCS to terminal and module frame joints, validation on live assemblies, series prototype production (involving both assembly and welding) and logistics (component receipt, storage, packaging and dispatch). With EV batteries requiring hundreds of welds, additional work was done to confirm incoming cell status and a number of in-line process checks and procedures to ensure finished quality.

Our work on EV batteries has led us to become experts in this field, whereby we joined an Innovate UK-funded consortium to develop electron beam welding for the fabrication of battery packs for use in the automotive sector…

- TWI Joins Faraday Battery Challenge Partnership

The Eb-Bat project, investigated the use of electron beam (EB) welding to produce battery packs at a reduced cost, using less energy, creating less scrap, in smaller factory areas and with welding fume control (figures 3 and 4). EB welding was chosen for its many benefits over other processes, such as increased welding speeds and lack of reflectivity from copper and aluminium, providing more reliable and consistent welds.

This work came under the umbrella of the Faraday challenge - a partnership between Innovate UK, the UK Battery Industrialisation Centre, and The Faraday Institution - to support research and development of innovative, and sustainable battery technologies for the propulsion of electric vehicles in the automotive sector.

While EVs have generated a great deal of interest across industry in recent years, liquid hydrogen from renewable energy sources is now being recognised as a promising source of zero carbon fuel. As part of our wider core research for the benefit of industry, TWI conducted a project to investigate the use of friction stir welding (itself invented at TWI) as a process for joining hydrogen fuel storage tanks…

- Development of Friction Stir Welding for Hydrogen Fuel Storage Tanks

Due to its low ambient temperature density, liquid hydrogen (LH2) is typically stored in large metallic pressure vessels under high pressure conditions. However, to support the decarbonisation of the transport sector, LH2 needs a portable and lightweight pressure vessel storage solution. Currently the most suitable and safest vessel type is a ‘type 3’ or composite overwrapped pressure vessel with a metallic liner. The solution was to create a carbon fibre reinforced polymer (CFRP) outer layer to provide structure around a thin-walled aluminium liner that would provide an impermeable barrier to contain the LH2. The aim was to make the liner wall as thin as possible to aid light-weighting. This liner would typically be joined using tungsten inert gas (TIG) welding, however this could lead to porosity, distortion and a reduction in joint strength. In order to provide an alternative, TWI investigated the use of both micro friction stir welding (µFSW) and stationary shoulder micro friction stir welding (SS-µFSW) for the aluminium liner (figure 5). Process parameter combinations for µFSW and SS-µFSW were iteratively explored on flat sheet specimens of 0.8mm thickness AA2024-T3, and metallographic characterisation was performed along with mechanical testing to assess the weld quality and strength, respectively. To eliminate the exit hole feature, an intrinsic characteristic of the µFSW and SS-µFSW, the use of refill FSSW as well as welds performed using retractable probe technology were explored in this project. The design of bespoke fixtures for the welding of curved sheets was also performed to validate the weld process and to produce technology demonstrators. The novel SS-µFSW process developed during this project has the potential to reduce costs and improve quality compared with other joining processes.

 

TWI’s history of welding and joining innovation spans many decades, but continues into the present with the creation of new techniques across a range of industries and materials…

- TWI Develops Wood Welding Process

We developed a method using linear friction welding to join pieces of wood in less than ten seconds. This fast bonding, wood welding process eliminates the need for mechanical joining methods like screws or nails while also avoiding the use of adhesives (figure 6). These factors offer potential benefits for the environment, making recycling a safer and easier, environmentally-friendly process. Interested parties contacted us following this innovation in order to explore its use for a range of potential applications such as the high volume manufacturing of items like furniture, barrels or even food containers.

This innovation continued through a partnership with Zero Glue Bamboo for a series of trials to weld bamboo without adhesives or fasteners…

- Welding Bamboo: The Future is Zero Glue

Taking our experience from earlier wood welding trials, we undertook trials to bond strips of bamboo using linear friction welding (LFW), creating a faster, cleaner and more sustainable bonding method and eliminating the need for toxic, fossil-fuel-based glues that currently dominate the industry. The trials successfully showed that bamboo could be joined using LFW in under two seconds, with a weld strength comparable to the bamboo itself and with a full bond across the entire interface (as confirmed with microscopic analysis). With a range of potential applications, this innovation provides a more competitive and genuinely sustainable alternative to conventional engineered bamboo and wood products (figure 7).

Other innovations include the granting of a diffusion bonding patent in 2023 for the diffusion bonding of aluminium…

- TWI Granted Diffusion Bonding Patent

We were pleased to receive a United States patent for the new diffusion bonding technique with a surface coating material that can be used for compact heat exchangers, heat sinks, cooling loops, process intensification units, and more. This proprietary technique allows for the successful diffusion bonding of aluminium with achievable joint strengths comparable to the heat-treated parent material. Invented at TWI, the technique produces an autogenous joint without the requirement of interlayers or melting point suppressants, with tests showing that the technique may demonstrate a viable route for the manufacture of compact features and other devices containing complicated internal pathways.

Of course, our work does not only include the creation of new solutions for industry, but also the development of existing welding and joining techniques into new realms…

- Handheld Laser Welding for Industry

A new joint industry project (JIP) has been launched allowing interested parties to get involved and gain exclusive access to research around the industrial adoption of handheld laser welding technology (figure 8). Handheld laser welding looks set to promise faster, more versatile, cost-effective and consistent results than conventional, manual arc welding processes such as MIG/MAG or TIG welding. However, there is still a lack of standardised assessment methodology and supporting data to validate the claims of the technology, making industry hesitant to adopt the process. This project is focussed on the ability to make sound welds, health and safety, environmental impacts, and the tolerance of the process in relation to weld quality and mechanical properties. This includes an independent validation of the technology’s performance, robustness, safe operation and capabilities, as benchmarked against conventional manual arc welding approaches (including MIG/MAG and TIG welding processes), to provide an industry-ready comparison.

One area where we have seen development in recent years is the use of welding for space applications, with TWI expertise being used for a number of new innovations and breakthroughs…

- TWI Helps Achieve World’s First Autonomous In-Space Weld

ThinkOrbital Inc. called TWI ahead of a test mission to perform the first-ever autonomous weld in space. Our experts have years of experience in building bespoke electron beam welding solutions for industry, making us the perfect partners for this history-making event. An electron beam gun, which was designed and created at TWI, was loaded aboard the Falcon 9 and performed the world’s first autonomous in-space weld on 6 May, 2024. The electron beam welding samples were returned to Earth for analysis by NASA and the European Space Agency. A real milestone in the journey towards mature technologies being used for the autonomous assembly of space stations in a single launch, this innovation also opens up the potential for advances in satellite servicing, space debris processing, in-space manufacturing, on-orbit storage and refuelling, space tourism, and scientific research.

But it isn’t just electron beam welding that has been developed for space use at TWI, as a new project looks set to deliver the UK’s first in-space robotic welding capability – using arc welding as the solution…

- Developing A Robot-Mounted, In-Space Arc Welding System

The recently-launched ISPARK project aims to develop a robot-mounted arc welding system for in-space repair, joining and future orbital manufacturing. Welding in space faces a number of significant challenges, including the vacuum environment, microgravity, and thermal instability, as well as the inherent danger and intense physical demands placed on astronauts. These challenges have meant that performing welds in space is a rare and technologically challenging undertaking. The ISPARK project aims to overcome these challenges through the creation of a new, space-qualified robotic welding capability that enables autonomous, in-orbit repair and manufacturing. Our experts are working on the project alongside those from the University of Leicester. Bringing together industry and academia, ISPARK will include vacuum environment trials to check the performance of the welding system, and digital twin modelling simulations for additional data to help validate key technologies before eventual use in the complex thermal, radiative and dynamic conditions of real spaceflight.

These are just some examples of the welding and joining solutions being pioneered by TWI for the benefit of industry, to find out more about the welding and joining expertise that we provide to industry and how we can help you, please see here:

https://www.twi-global.com/what-we-do/research-and-technology/technologies/welding-joining-and-cutting