Resurgam Project: the major challenges for shipyards in Friction Stir Welding on steel

There are many challenges for shipyards and shipbuilders in improving the manufacture and maintenance of high-tech ships. Friction stir welding (FSW), whose performance is now proven, provides answers to these challenges.

The Resurgam project, created specifically for welding issues in the naval sector, aims to integrate high productivity friction stir welding. This project, supported by many European players, is about to revolutionise welding in the naval world, and Stirweld contributes to this revolution.

What is the Resurgam Project? Presentation, objectives and challenges of the project

Resurgam project : between Friction Stir Welding and shipyards

The Resurgam project is a European Horizon 2020 (or H2020) project. This European research and development program gathers multidisciplinary and complementary expertise to permit the use of Friction Stir Welding or FSW in large-scale applications; shipyards. The members of the Resurgam project are European players in shipbuilding and maintenance, specialised research organisations as well as SMEs specialising in the rapid development of prototype materials.

The actors involved in the Resurgam project have complementary expertise to foster the competitiveness of international markets for shipyards and small and medium-sized shipbuilders. Currently, shipyards and shipbuilders find it difficult to produce and maintain large and high-tech ships due to the lack of capacity and resources. The competitiveness of the international markets promoted by the Resurgam project makes it possible to respond to these problems. Thus, the Resurgam project opens up to all the players in the international market the advanced technologies and resources necessary for the manufacture, maintenance and renovation of high-tech ships.

The environment, a cornerstone of the Resurgam project

A key point of the project is to improve the environmental performance of shipbuilders and shipyards. By integrating the use of FSW in shipyards and shipbuilders, the environmental impact will be significantly improved on 3 major parameters:

Smoke emissions: FSW produces very little smoke. In traditional electric arc welding, hexavalent chromium is released. This does not occur with friction stir welding.

Material input: Unlike arc welding, friction stir welding does not require any additional material. These materials will not be consumed and therefore will not need to be treated as waste, thus reducing both extraction costs and reduces the environmental impact.

Energy efficiency: by using friction stir welding (FSW), the Resurgam project is also seeking to make savings in terms of CO2 emissions with the help of the European Union.

FSW in ship production and maintenance : considerable economic gains

In addition to the real environmental benefits of this new Resurgam project, there are also significant economic gains to be made.

Indeed, the assembly of ship hulls by friction stir welding could save up to 15% and reduce manufacturing times by up to 31% (source: resurgamproject.eu). This represents no less than €893 million in annual savings on production and maintenance costs in Europe.

The technical solutions provided by friction stir welding (FSW) on steel

Friction stir welding (FSW) is a high integrity welding technique, without any material fusion. The welds are made in the solid state, i.e. without reaching the melting point of the base material. Welding is achieved by mechanical deformation as the rotating tool plunges into the material and advances along the area to be welded. With this process, all the characteristics of the applications are respected, so defects are very few if the welding parameters are respected.

In the Resurgam project, new technologies are being investigated to contribute to the transformation of welding processes and the revolution in the world of shipbuilding and maintenance through friction stir welding (FSW). These new technologies can be divided into 3 areas:

Friction stir welding: from aluminium to steel

Today’s friction stir welding (FSW) solutions are ideal for welding aluminium parts. In shipyards, hulls are made of steel, a pure material that is much thicker, stronger and also much harder. While the melting point of aluminium is around 660°C, that of steel is 1300°C.

The first objective of the Resurgam project was therefore to develop new friction stir welding solutions capable of withstanding such melting points. The challenge was also to determine which hybrid materials would resist wear and abrasion in steel applications.

Maintenance of ship hulls: underwater friction stir welding by robot

One of the challenges of the project was also to develop a new technology that would allow underwater maintenance to be carried out for repairs at sea or in confined spaces using friction stir welding on steel.

A prototype of an intelligent underwater ROV robot incorporating an FSW spindle has been designed to carry out maintenance on ship hulls without having to take them out of the sea. This is a revolution in the sector, which will lead to major technological advances but also to considerable economic gains. This remote-controlled robot (ROV) is also equipped with laser imaging cameras, capable of identifying potential damage and its extent. An efficient way to identify and execute necessary repairs.

Steel boat hull construction with FSW

Ship hulls are made up of flat steel panels measuring 12m by 3m. The assembly of these panels forms the hulls of the ships. Until today, the assembly of these hulls was done by electric arc welding, with certain disadvantages and defects resulting from this.

With these new technologies for FSW on steel, the assembly of the panels will be of much better quality, with better mechanical resistance and without deformation. These joints are made directly on large machining centres equipped with a friction stir welding spindle specially designed for FSW on steel.

The heavy duty FSW head, the friction stir welding (FSW) spindle specially designed for steel, made by Stirweld

A new special Resurgam design for the high-load FSW spindle

After the Stirweld V3 and V4 friction stir welding heads, the high-load FSW spindle is now available. In practice, the head concepts are the same: a rotating shaft driven by an NC spindle.

The major change is the shape of the head and the cooling systems. The first heads were square, the new FSW head is cylindrical, which is important for the cooling system. Also, we have to mention its new proportions, as the new heavy duty head is 2.5 times bigger than its predecessors.

A new cooling system for FSW on steel

As mentioned before, welding steel is more complex than welding aluminium due to the welding temperature and melting point of the application. To adapt to this new setting, Stirweld’s teams had to reinvent a new cooling system. The melting point of steel is 1300°C against 660°C for aluminium. The challenge was therefore to redesign the chilled water circulation system that cools the friction stir welding (FSW) process.

The V3 and V4 friction stir welding heads developed by Stirweld are currently equipped with a cooling system.

With the new welding parameters for welding steel, the speed of rotation is much higher and therefore generates higher temperatures on the head. All the cooling systems have therefore been reviewed and maximised :

At the ram: new cooling system via water channels from an external chiller that sends chilled water in a coil to cover the surface of the ram.

On the spindle shaft (rotating system): the challenge was to cool this part. Being a rotating system, our Stirweld engineers designed a cooling system consisting of sealed chambers all around the spindle. As the chambers are closed by seals, chilled water floods these chambers along a circuit and cools the system.

Air cooling system: third and final cooling system. Like the previous versions, air is blown around the periphery of the tool at the friction between the part and the application, thus avoiding some of the known defects in FSW.

New technical developments to support new FSW settings

In addition to new cooling systems, the new high-load FSW spindle had to be adapted in various technical aspects to accommodate several new factors, such as load capacities.

Indeed, steel being heavier than aluminium, the load capacities of the FSW head for friction stir welding on steel were too limited. A new ball bearing slide system was introduced, compared to a rail system on the other versions. On the FSW V3 or V4 heads, the forging force capacity was 18,000 newtons and 25,000 newtons respectively for aluminium. For steel, the new FSW head and its ball bearing slide system for steel are capable of 50,000 newtons, or 5,000 kg load forces.

A European project bringing together many actors

The Resurgam project is a European Horizon 2020 (H2020) project. It has also received funding from the European Commission’s Research and Innovation Program under grant agreement n°101007005.

In this project, many actors and partners with complementary specialties allow the development and innovation of these new technologies:

A project that keeps going and innovating with these players who will, in the very near future, revolutionize friction stir welding (FSW) on steel in many other industrial fields.

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