Automated scanner for kissing bond detection in friction stir welded materials

Project Information

FrictionHarmonics

Grant agreement ID: 820531

DOI

10.3030/820531

Project closed

EC signature date 20 July 2018

Start date 1 August 2018

End date 31 May 2021

Funded under

• Horizon 2020 Framework Programme

Total cost

€ 2 691 936,13

EU contribution

€ 2 191 242,13

Coordinated by

VERMON SA
France

Periodic Reporting for period 2 - FrictionHarmonics (Automated scanner for kissing bond detection in friction stir welded materials)

Reporting period: 2019-09-01 to 2021-05-31

Summary of the context and overall objectives of the project

Friction stir welding (FSW) is a solid-state joining process that works by plunging a rotating non-consumable tool into the interface between two work pieces. As the tool is moved along the interface, the frictional heat generated causes the material to heat-up and soften. The rotating tool then mechanically mixes the softened material to produce a solid-state bond.

Friction stir welding offers many advantages over fusion-based joining processes, especially when joining aluminium alloys:

• The material remains in the solid-state, avoiding many of the defects associated with melting and solidification during fusion welding, such as pores and solidification cracks.
• The peak temperatures are lower, leading to reduced distortion and shrinkage.
• FSW is capable of joining many ‘non-weldable’ aluminium alloys, namely from the 2xxx and 7xxx series.
• It is a fully automated process, making the process highly repeatable.
• It is energy efficient.

Overall, FSW is a major breakthrough due to its substantial advantages over other techniques for welding aluminium alloys. However, despite its merits FSW use is limited due to the potential for ‘kissing bond’ defects. Kissing bonds, more commonly known in the friction stir weld community, as as unbonded joint remnants originate from an incorrectly broken and stirred fusion face, which leaves a residual layer of oxide in a plane parallel to the weld. This flaw is fully bonded and microscale in nature and still provides some mechanical strength. However, kissing bonds reduce the stress-load resilience of FSW materials and are extremely difficult to detect using conventional Non-Destructive Testing (NDT) methods.

The FrictionHarmonics project has developed the ‘KiScan’ inspection system for the detection of kissing bonds in friction stir welds, it incorporates:
• Bespoke Non-linear Ultrasonic Testing (NLUT) software, which utilises advanced signal processing algorithms.
• Specially designed ultrasonic probes, wedges and probe holders.
• A custom-built scanner for rapid automated inspection of flat and curved surfaces.

Advantages of the Kiscan system include:
• Reliable detection of kissing bonds (greater than 0.6mm in length).
• Rapid automated inspection (up to 10mm/second).
• User-friendly operation.
• Simple ‘traffic light’ interpretation of inspection results.
• More advanced inspection analysis methods for NDT specialists.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The prototype design developed in the previous FrictionHarmonics project was revised with both operational and production requirements in mind. The NLUT hardware, software and associated transducers were optimised for volume production, whilst minimising the production costs.
The scanner design was modified to accommodate more complex specimen geometries, including the convex and concave contours that are common in aerospace components. Particular care was taken to ensure that the production cost of the scanner was kept below the target cost of €12.5k.
The existing NLUT algorithms were optimised both for efficiency and for performance, thereby reducing the computational loading and enabling scanning speeds of up to 10mm/s. The software architecture was redesigned and implemented to facilitate maintainability, a key feature for industrial grade software. A user-friendly GUI was developed for both system control and inspection assessment/analysis. The software provides both a simple ‘traffic light’ system integrity assessment, as well as a more advanced view for NDT experts.
The KiScan system was validated in an operational environment (i.e. reaching Technology Readiness Level TRL7). The performance trials identified issues relating to the practical operation of the system and the need for a single unified GUI for system control and inspection analysis. These aspects were addressed following this validation exercise.

The necessary certification tasks for CE marking have been performed, demonstrating that the equipment complies with all relevant EU directives. The CE label can now be displayed on the KiScan inspection system. Certification for the North American markets was hindered severely by the coronavirus pandemic, which stalled meaningful business interactions across the Atlantic. Certification for these regions will be addressed once the KiScan product has been established within Europe.
A mix of face-to-face and Internet-based promotional activities were performed to generate interest in the FrictionHarmonics/KiScan developments. As a consequence of the coronavirus pandemic, company engagement was predominantly achieved through Internet-based actions, such as the project website, use of social media channels, news releases, product flyers, technical animations and an interactive webinar.
A commercial team has been established at Coşkunöz to execute the KiScan marketing plan developed over the course of this project. The consortium partners continue to promote the KiScan inspection system and the outcomes of the FrictionHarmonics project to potential customers in order to prepare for successful post-project commercialisation of this novel inspection technique.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Prior to the development of the KiScan inspection system, it was not possible to reliably detect
zero-volume kissing bond flaws of less than 1mm in length in friction stir welded components/structures using commercially available NDT equipment. Commercial phased array ultrasonic testing (PAUT) systems are available and claim to have the capability to detect kissing bonds but it has been identified that the test pieces used to demonstrate the technique did not contain representative kissing bond flaws. The technical developments performed as part of this project in combination with the validation trials carried out on a range of specially produced defect samples, have shown that NLUT can be utilised to detect kissing bonds of height greater than 0.6mm. This provides a substantial business opportunity for the consortium in the aerospace and automotive sectors.

FSW is particularly important in these industry sectors, as it enables the joining of aluminium alloys that are significantly lighter than their conventional counter-parts, while achieving significant reductions in manufacturing time and energy consumption. Kiscan kissing bond detection will facilitate the use of lightweight aluminium components in these industries and will have a strong financial impact, as it will lead directly to reduced fuel consumption (due to weight saving), reduced maintenance costs (due to easier testing), extended part life and simpler recycling/disposal processes.

At the project outset, manufacturing cost savings were calculated to be €1.6 billion over a 20-year period. During the same period, the weight reduction that FSW offers will allow these industries to achieve fuel savings of more than €1.9 billion, leading to a reduction of around 2 million tons of Carbon Dioxide, which represents a significant contribution to the ‘Smart, Green and Integrated Transport’ societal challenge.

In light of the restrictions introduced by the Covid-19 pandemic in early 2020, The Consortium have revised the five-year financial forecasts for FrictionHarmonics estimated project impacts. The consortium recognises that the potential market for the KiScan system has shrunk considerably and consequently estimates approximately €22 million of cumulative revenue, more than €5.5 million in operating profit and the creation of 142 new jobs.

Friction Stir Welding Process