RD&D-Programme 2004 - SKB

Figure 6-7. Macrospecimen from weld TB 122. Welding test with oscillating beam.
Figure 6-8. Radiograph of weld TB 122. If welding is interrupted, the cavity (key hole) in the
material that constantly surrounds the beam during welding is retained. This provides an image
of the shape of the beam. The round shape is important for avoiding root defects.
9 percent for surface treatment. Trials with an oscillating beam have been carried out in two
lid welds (L028 and L029). Lid weld L028 was welded both with and without an oscillating
beam at welding speeds of 250, 275, 300 and 325 millimetres per minute, see Figure 6-9 and
Figure 6-10. The surface of the weld is smooth in the oscillated area. However, it is rough in the
area welded without oscillation. A smaller quantity of near-surface incomplete penetration flaws
were also formed when the welding speed was 325 millimetres per minute. The internal quality
of the weld is good as a whole, although there are a few discontinuities in the area with rotation
speeds of 250 and 275 millimetres per minute. The other lid weld (L029) was welded with a
welding speed of 300 millimetres per minute. Both the homogeneity of the weld and the weld
surface are excellent on the whole, see Figure 6-11.
The results of these tests show that it is now possible to achieve welds of very high quality with
homogeneous weld metal and a good weld surface. The occasional flaws that occur are mostly
due to mechanical faults.
All weld specimens in copper lids were examined by means of nondestructive testing. The typical
discontinuities that were found were root defects, internal cavities, cavities associated with
the surface and near-surface pores. After the introduction of the new cathode and oscillating
beam welding at a high welding speed, the weld metal is now very homogeneous. An example
of good homogeneity can be seen in Figure 6-8, where the weld metal is completely free of
discontinuities. The shape of the electron beam can also be studied by means of radiography.
If welding is interrupted, the cavity in the material that constantly surrounds the beam during
welding is retained, which is a useful technique for understanding the relationship between
beam shape and weld quality.
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