RD&D-Programme 2004 - SKB

Conclusions in RD&D 2001 and its review
SKB stated in RD&D 2001 that trial fabrication with the methods in question will continue.
Important aspects of the continued work are optimizing grain size, improving material yield and
developing inspection methods. In parallel with development and trial fabrication at different
suppliers, research projects will be conducted at trade research institutes, institutes of technology
and universities. The purpose is, by means of computer simulation and laboratory-scale
trials, as well as material testing, to obtain greater knowledge that can contribute to the optimization
of technical specifications and fabrication technology.
SKI comments that SKB, by simulation, calculations, etc, must show that an adequate degree
of working is obtained in the entire tube and straight through the copper thickness, regardless of
fabrication method.
Newfound knowledge since RD&D 2001
Computer simulations have been carried out in a doctoral thesis project at the Royal Institute of
Technology in Stockholm /5-11/. These simulations have primarily involved extrusion of copper
tubes and forging of blanks for lids and bottoms. The results have yielded greater knowledge
concerning how the material is deformed by different forming methods and what conditions
must be met to obtain a microstructure with acceptable grain size. For forging of lids and
bottoms, the results have been used to optimize the forging dies. A number of forgings done
with the improved technique have shown that blanks for lids and bottoms can now be produced
with very satisfactory results.
Simulation of pierce and draw processing for the purpose of fabricating copper tubes with
integral bottoms has been carried out by Posiva Oy and Vallourec & Mannesmann Tubes. The
results have been used to design the hot-forming tools. Fabrication trials with pierce and draw
processing have so far indicated that a sufficiently fine-grained microstructure can be obtained
in the integral bottom. Continued optimization of forging dies and process parameters will be
able to further improve the results.
Trial fabrication of copper tubes by forging at Scana Steel Björneborg AB has shown that the
method gives an acceptable grain size. This method needs to be further developed by optimization
of tool design and process parameters.
Figure 5-9. Forged and machined copper lid.
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