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AFRICAN FUSION
November 2015
the joint to prevent disruption of the arc. The orientation of
the torch and cooling head is shown in Figure 14, illustrating
the part being welded using the robotic LSNDwelding system
developed. The second image in this figure clearly shows that
the seal is working effectively to contain the CO
2
and to allow
through head extraction of the gas after sublimation of the CO
2
snow cooling to the hot surface of the weld bead.
Visual inspection of the trial parts after welding fromboth
the LSND process and the standard GMAW process revealed
significant differences in the distortion patterns. This exami-
nation, as shown in Figure 15, reveals that the distortion oc-
curring in the standard weld part has caused the assembly to
move relative to the pre-programmed robotic weld path, and
effectively the weld is off seam.
This effect begins to appear fromabout half way along this
weld and gradually moves further off toward the end of the
weld (the point closest to the camera). This is not the casewith
the LSND weld, which results in a stronger, more consistent
and better quality weld
It should be noted that the holding fixture did have a small
lateral clearance to allow the parts to be assembled, which
made movement possible. It was designed with some clear-
ance to ensure that any distortion would not cause the part
to become stuck in the fixture.
The differing effects of the two welding processes were
also evident in the magnitude of the heat-affected zones be-
ing displayed on the surface of the parts. It was clear to see
the material phase-change regions (HAZ) due to the effects of
the welding on the part and these were considerably smaller
on the LSND part than the standard GMAW welded part. This
can be seen in Figure 16, where the two parts are compared
next to each other. In Figure 16 the part to the top of the im-
age being a LSND part and the one in the lower half being a
conventionally welded part.
The levels of distortion seen in the part are apparent to
the naked eye, and therefore it is straightforward to do a quick
visual assessment of the parts to compare the differences in
distortion.
Bending of the part occurs along the length of the com-
ponent when moving towards the centre from the stiffer
outside sections. In addition there was some twist occurring
in the parts. It could be seen that the GMAW-welded part
exhibits a significantly higher level of bow and twist than
the LSND part. The difference in twist was hard to accurately
quantify using simple measurements; however the reduc-
tion in bowing could be estimated to be reduced by around
3.0 mm, with a peak bow on the conventional part being in
the region of 10 mm.
The majority of the distortion occurred while the part
cooled after it was removed from the fixture. It should also be
remembered that the level of distortion occurring in the con-
ventional part, before removal fromthe fixtureandduringweld-
ing, was such that some of the welds were produced off-seam.
This was not the case when welding using the LSND process.
Discussion and conclusions
A prototype robot mounted DC-LSND GMAW system with a
cooling head andwelding torchon the same side of thewelded
joint has been integrated and demonstrated successfully in an
industrial facility.
Welds have been produced with acceptable weld quality
withnosignificantmetallurgical discrepancieswhencompared
to standard samples. Distortion has been reduced by up to
40%-50%on simple components. The systemhas been shown
to successfully overcome any disruption of the welding arc
and GMAW process when the cooling is applied to the same
side of the weld joint with the cooling delivery system close
behind thewelding torch. Although further work is required to
optimise the configuration anddesign to suitmore generalised
complex 3D weld profiles.
Repeatability of the welding results on butt welds and
simple profile joints and sections has been demonstrated. The
process has been successfully applied and demonstrated on
a number of real component example geometries, although
further refinement and development of the system would
be required for full production and acceptability in a general
industrial manufacturing environment.
Acknowledgements
The author acknowledges the support of all project partners
involved in “Creating Opportunities for the Manufacture of
Lightweight Components” MALCO (TSB Project No. TP/TP/
DSM/6/1/16131); TWI; Gestamp Tallent; BOC Gases (Linde);
Isotek Electronics; Dytel Technologies; Comau Estill (UK); Bent-
ley Motors; Komatsu (UK); and the University of Strathclyde.
The author andall project partners alsogratefully acknowl-
edge the financial support and assistance in the part funding
of the MALCO project received from The Technology Strategy
Board/Innovate UK.
Copyright
©
2015 International Institute of Welding: Originally published
in the proceedings of the IIW International Conference of 2015, Helsinki,
Finland: High-Strength Materials – Challenges and Applications.
Low stress no distortion welding
Figure 15: A comparison of the effect of distortion on repeatability and weld
quality on typical LSND (top) and conventional GMAW welded (bottom) beam
parts manufactured in the trial. It can be seen that the induced distortion in
the conventionally welded part causes the weld path to drift off the seam.
Figure 16: A comparison of the visible HAZ on typical LSND (top) and
conventional MAG welded (bottom) beam parts manufactured in the trial.