RD&D-Programme 2004 - SKB

According to SKI, SKB should in its continued work more clearly compare the advantages
and disadvantages of different fabrication methods for producing seamless tubes, for example
heating in several stages during pierce and draw processing and the effects on tubes (and
bottoms) of pierce and draw processing with an integral bottom.
Newfound knowledge since RD&D 2001
Pierce and draw processing of tubes makes it possible to fabricate copper tubes with integral
bottoms. Three tubes have been fabricated with this objective. Computer simulation has made it
possible to study the degree of deformation in the different hot forming steps. The results have
been used to design the tools that are used so that hot working of the bottom is sufficient. The
most recently fabricated tube had a homogeneous bottom with an acceptable grain size. The
technology will probably be able to be further improved. In connection with this development,
a couple of detailed studies have been conducted of the large copper ingots that are needed.
These studies have yielded greater knowledge of the solidification structure and the occurrence
of defects such as centre cracks in the ingots. This has in turn led to measures being taken by the
copper supplier to minimize the flaws. An approved fabrication of tubes with integral bottoms
will require deliveries of sufficiently homogeneous copper ingots, optimized tool design and
tested process parameters.
Even if pierce and draw processing of tubes with an integral bottom does not turn out to be a
practical alternative, it will still be possible to use pierce and draw processing as a method for
fabrication of copper tubes open at both ends, along with extrusion and probably forging.
Three copper tubes have been fabricated by forging at Scana Steel Björneborg AB. The results
so far indicate that forging of copper tubes can probably be developed into a workable method.
The results have been gradually improved, mainly by improvements in tool design.
Figure 5-12. Fabrication of copper tube with integral bottom by pierce and draw processing.
RD&D-Programme 2004 59