LIBRARY ı6ıul 0) - Cranfield University

7.2 Tests with varying stand-off and no control applied
These tests were carried out on fillet joints with the pre-weld joint search to
ensure precise initial stand-of e. Since only one degree of freedom was implemented in
the moving table and the robot used did not have facilities for off-line programming, a
mismatch between an off-line generated program and the actual joint position was
simulated by on-line programming the robot to move the welding torch along a
sloping path which would start at the programmed stand-off and finish with a stand-
off 8 mm bigger than the starting one. Care was taken to provide alignment between
the electrode wire and the joint line. The welding parameters used were generated by
the welding parameter generator for 3.2 mm mild steel plates set in a fillet joint in the
flat position without a gap, using the initial stand-off as a reference value. Table 7.1
shows the parameters along with the required and the expected leg lengths. All the
fillet welds were 200 mm in length.
Table 7.1 - Welding parameters used in the non-controlled flat position fillet
joint welding trials
Run WFS
ril/min
V. 4
Sw
H1/mm
SO,,.,,
mm
SO.. d
mm
LeS,
ea
trim
Legpmd
Imml
M2 8.0 22.1 0.6 12 20 4.0 4.46 30.3
M3 10.0 22.4 0.4 12 20 6.0 6.41 39.5
M4 11.0 32.9 0.8 15 23 4.0 4.54 39.4
M5 13.0 33.2 0.7 15 23 5.0 5.40 53.1
M6 15.0 33.4 0.8 15 23 5.0 5.43 58.0
SO,,.,: initial stand-off
SOci, d: final stand-off after 200 mm weld length
Leggy: leg length required in the welding parameter generator
Leggy: expected average leg length predicted by the welding parameter generator
Pence: expected average penetration predicted by the welding parameter generator
Pen
10/01
Figures 7.5 to 7.14 show the bead appearances, the bead profiles and the
welding data obtained from the welds produced with the welding parameters shown in
Table 7.1. Figures 7.6,7.8,7.10,7.12 and 7.14 show the quality of the on-line standoff
estimation when applying the dip-resistance-based estimation model to the fillet
joint case. It should be noted that in these cases, the estimation model included the
off-set calculation at the start of the welding and the estimates produced were filtered
using a third order moving average filter.
Weld defects in the form of porosity (see Figure 7.9) and undercut (see
Figures 7.9,7.11 and 7.13) were observed in the spray transfer welding trials. These
were possibly caused by a combination of excessive welding voltage and travel speed.
Also, a pronounced finger-like penetration profile was observed in these spray transfer
trials.
Although changing along the weld, the levels of average penetration obtained
from these welding trials were still above the minimum required level (10% of the
minimum plate thickness), despite the severe variation imposed on the stand-off (see
Table 7.2).
1 the set-up parameters, WFS, V.. and Sw were kept constant during the whole weld.
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