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With the help of RESURGAM partners, new and emerging technologies will be developed and come to the aid of turning this project into a revolutionary way of how ships maintenance is performed. The main technology that this project is going to rely on is Friction Stir Welding (FSW) and its underwater application (UFSW).

Friction Stir Welding is a solid-state welding process invented by TWI in 1991. It is widely used for the fabrication of structures requiring high strength, lightweight and fatigue resistant joints. FSW was quickly adopted as a fabrication technique for spacecraft, trains, shipping and automotive components, as well as electronics assemblies and costumer goods.

Conventional fusion welding processes used for repair of marine structures are essentially a casting technique. Two components are brought together and energy is applied causing the metal in the joint region to melt and coalesce. As the energy source is removed, this molten weld pool freezes and the previously separate components are now a single piece. There are some potential problems associated with this process, such as:

  • Structural distortion arising from the thermal energy input and the phase change from solid to liquid and back to solid;
  • Changes in metal properties due to the creation of a cast microstructure in what was previously typically wrought plate;
  • Changes in material properties due to the addition of a filler material, or the boiling off or segregation of the original alloying elements;
  • The potential for generating defects such as porosity, undercutting, lack of penetration and inclusions.

Using FSW, two components are placed side by side and a rotating tool is lowered and brought in contact with them at the joint line. The rotating tool generates frictional heating causing a plasticised zone to form, which means that the metal does not melt. The tool is driven into the metal and traversed along the joint line. At the end of the weld, the tool is extracted.

The benefits of FSW arise primarily from:

  • The elimination of melting in the joining process;
  • The generation of a forged rather than cast weld microstructure;
  • The elimination of human variability and skill from the welding process.

The greatest obstacle in transferring the technology of friction stir welding from light metals to steel has been that of finding a tool material with which to stir the steel. Aluminium starts to soften at 300oC and flows sufficiently well for friction stir welding at 450oC. FSW tools made of steel are able to withstand such temperatures and retain adequate strength and tend not to react with most types of aluminium. For welding higher strength grades, FSW tools are typically made of nickel cobalt superalloys

Element Six, as part of this project, are developing FSW tools for steel based upon hybrid materials technology, combining hard wearing and chemically resistant superhard ceramics with strong, tough, metallic components in order to produce a tool capable of welding industrially useful lengths of steel.

Forth Engineering is developing robotic systems for underwater repair welding and retrofit CNC welding heads manufactured by Stirweld.

Forth Engineering with the assist of University of Limerick (UL), that has an extensive knowledge in this area, will help and provide complementary technology for a remoted operated vehicle (ROV), equipped with cameras and laser imaging, being capable of identifying the location of the damage, the type and degree of the damage sustained, the accessibility and the structural design of the ship in the damage area in order to allow a repair to be planned or executed.

Robotic underwater welding repair will include different robotic systems, each one with a different aim:

Forth Engineering with the assistance of University of Limerick (UL), that has an extensive knowledge in this area, will help and provide complementary technology for a remotely operated vehicle (ROV), equipped with cameras and laser imaging. The ROV is capable of identifying the location of the damage, the type and degree of the damage sustained, the accessibility and the structural design of the ship in the damage area in order to allow a repair to be planned or executed.

Robotic underwater welding repair will include different robotic systems, each one with a different aim:

  • USFW Forth - FSW frame robot with FSW head integrated with crawler/frame. When locked onto the hull the Forth robot delivers the FSW head along the weld line with 5 axis motion control to follow the weld line.
  • UL MRE ROV – Scanning the hull with high-resolution imaging. Preparation of high-definition geometry damage of the hull section for repair patch design.
  • UL Support ROV – Provide touch down support to the USFW frame robot and welding process, and reposition the Forth FSW frame robot if repair requires multiple weld positions.

The development of underwater FSW will transform the way ships hulls are repaired. This will enable responsive, remote, at sea repair anywhere in the world, which will have major advantages in safety, time management and money.