Tue, 20 February, 2024
Residual magnetism is a major problem in electron beam (EB) welding, particularly in thick section EB welding where deviation of a few degrees from the joint plane can cause miss-joint defects to occur.
Demagnetisation techniques exist, but their effectiveness very much depends upon the materials type and component geometry.
As an output of the Open Architecture Additive Manufacturing (OAAM) project, which was supported by Innovate UK (ref:113164), TWI has established new capability with a new degauss unit. The OAAM programme developed directed energy deposition (DED) additive manufacturing (AM) technologies that can be scaled up to accept multi-metre component sizes for the benefit of UK aerospace. These new platforms have enabled aerospace manufacturers and their supply chains to develop advanced AM manufacturing concepts.
The ZM150 degauss controller from Diverse is capable of measuring and neutralising magnetic fields which may be present in the weld preparation region of steel components. Experiments on thick section (200 mm x 300 mm x 1200 mm) S275 steel blocks suggested the down cycling process to reduce the magnetism from over 100 Gauss to less than 5 Gauss typically takes less than 10 minutes.
Figure 1. Graph showing the demagnetisation cycle, showing nested BH loops as the material is demagnetised
The electron beam department at TWI has significant experience in the field of demagnetisation of ferritic components. We can provide both face-to-face or remote training and consultation on demagnetisation strategies to support our Members. We have access to specialist finite element analysis software, such as the Opera simulation software, to optimise the joint design by performing simulations of electromagnetic and electromechanical in 2D and 3D.