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Demonstrating effectiveness of FSW steel for shipbuilding

TWI was among a group of eight organisations that collaborated on a project to investigate the viability of friction stir welding of steel for shipbuilding applications.

Friction stir welding (FSW) is a well-established process for joining lightweight aluminium and magnesium structures, its solid-state nature bringing a number of advantages over higher-temperature welding methods. These metals’ relatively low melting point makes them excellent candidates for the FSW technique.

Now research carried out for an EU project, HILDA (High-Integrity Low-Distortion Assembly), has shown how FSW can be used to join steel, a metal with a significantly higher softening point that makes much greater demands on the FSW tool.

Improved processes for the shipbuilding sector

This research was carried out with the shipbuilding industry in mind, so efforts focused on joining typical marine engineering steel, grade DH36. HILDA examined two aspects of the FSW technique: weld quality and its economic viability.

Efforts focused on characterising the microstructure of friction stir welds, and identifying its relationship with different weld parameters. Evaluation of the microstructure allowed a preliminary FSW parameter envelope to be identified, which was refined over the course of the project. The welding speeds attainable in typical 6mm-thick shipbuilding steel were increased from 100mm/min to 500mm/min, making the process competitive, in terms of production speed, with conventional fusion welding techniques.

Research showed that the welds produced have enhanced strength, toughness and fatigue life when compared with conventional arc or laser welds, and the process is also tolerant to defects.  A programme of classification compliance testing is currently being developed that recognises these property enhancements.

Increased performance and practicality

The case for using FSW in shipbuilding is further strengthened by its low weld-induced distortion,

excellent surface quality and potential to be carried out underwater. Results from the HILDA project, which ended in August 2015, are available on the European Commission Community Research and Development Information Service website.

For more information on our FSW expertise and how it could benefit your business, please email contactus@twi.co.uk

Friction stir welding in half-inch-thick shipbuilding steel
Friction stir welding in half-inch-thick shipbuilding steel
Avatar Stephen Cater FRIN MEI ARINA AWeldI Principal Project Leader – Friction and Forge Processes

Stephen Cater is a Principal Project Leader at TWI’s Yorkshire Technology Centre, responsible for research into the friction stir welding (FSW) of both thick section light metal alloys such as aluminium and magnesium, and high plasticisation point materials such as steel, titanium and nickel based alloys.

A metallurgist by training, and winner of the Richard Weck Award for his work on steel, Stephen led TWI’s Core Research Programme (CRP) into the development of FSW for steel, and also led the welding elements of projects looking at FSW for marine construction. These programmes were HILDA (High Integrity Low Distortion Assembly), MOSAIC (Materials Onboard: Steel Advancements and Integrated Composites) and RESURGAM ( Robotic Survey, Repair & Agile Manufacture). Stephen also developed the capability to friction stir weld steel under oil in the FSWBOT programme which is currently developing a robotic system able to conduct patch repairs of defects inside live oil pipelines.

Stephen has led a number of single client projects on the welding of thick section (>25mm) aluminium for safety critical applications and is currently leading two major projects in this area. One is a CRP project investigating new tool designs and FSW techniques for thick section aluminium and the second is a Joint Industry Project (JIP) for a group of sponsors interested in the early commercialisation of these new FSW techniques. Stephen also led a SCP for a customer in the Power sector who had a requirement for high integrity aluminium FSW in cryogenic service. Stephen also leads TWI’s FSW training programme, having developed a series of FSW courses in accordance with the requirements of the ISO FSW Standard, ISO 25239:2011.

Prior to joining TWI, Stephen served as a soldier with experience of both combat and technical attachments to DSTL (Defence Science & Technology Laboratory)

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