RD&D-Programme 2004 - SKB

Conclusions in RD&D 2001 and its review
It is stated in RD&D 2001 that it is possible to join 50 millimetres thick copper with FSW and
that the process can probably be developed into an alternative production method for welding
of copper canisters. The work, which was performed on a development machine developed at
TWI, was focused on continued development of tool and process parameters. Welding tests were
planned in both 50 and 30 millimetres thick copper tubes. At this time there was no solution for
how to handle the exit hole left by the tool at the end of the weld. There were plans to build a
completely new FSW machine specially designed for the purpose at the Canister Laboratory.
Investigations of the strength properties of the FSW material were under way.
Newfound knowledge since RD&D 2001
It was shown in 2001 that friction stir welding is a promising technique for sealing copper canisters
in serial production as well. The technique had been presented to SKI, which gave its support
to continued development. A decision was made to transfer the FSW technology to the Canister
Laboratory for further development. The information that was gathered from the welding of rings
at TWI was used to formulate operating specifications for a new FSW machine. The new machine
was developed and built by Esab during 2002. The welding machine has been in operation at
the Canister Laboratory since April 2003. It has performed outstandingly, and the transfer of the
technology from the experimental machine to a production-adapted machine has gone well.
The FSW machine has a unique design with respect to strength and stiffness which makes it
suitable for production welding. The welding machine, which is shown in Figure 6-17, has a
spindle power of 110 kW, making it one of the most powerful welding machines in the world.
Only 35 kW is used in operation, since the heat input must be limited.
Programme
The FSW machine’s potential as a production machine will be demonstrated in a test series of
about 20 welds under operation-like conditions. The work entails:
• Development and improvement of software for controlling and monitoring the process.
• Improvements of the system for process monitoring.
• Improvement to enable the constant welding angle to be adapted to the welding direction.
Figure 6-17. The FSW machine in the Canister Laboratory.
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