ClassNK Issues Approval for Friction Stir Welding Method

Tokyo - ClassNK announced that it had issued an approval to IHI Corporation for a friction stir welding (FSW) method using a floating bobbin tool. The approval certifies that this new method complies with ClassNK’s Guidelines on Friction Stir Welding.

IHI is considering applying this welding method to the aluminum sections of LNG carriers and/or FLNGs cargo tanks, such as the IHI-SPB tank, which had been independently developed by IHI group at its Aichi Works.

Key advantages of FSW are that it does not produce arc and fume at the time of welding and provides relative control over welding deformation. Its application is now limited to low melting point materials, such as aluminum alloy or magnesium alloy because of the friction heat generated in the welding process. However, it is expected to be widely used in shipbuilding in relation to the construction of aluminum alloy structures.

Furthermore, this welding method is equipped with a solution to one of the common defects in FSW. Generally, a rod-like tool with a projection called a “pin” is used in FSW, but it can result in a lack-of-penetration defect called a “kissing bond,” which occasionally occurs on the underside of the contacting surfaces, depending on welding conditions. This welding method, however, provides a solution to this problem with a special tool called floating bobbin. This tool is expected to effectively avoid the occurrence of kissing bonds by enabling double-sided welding.