LIBRARY ı6ıul 0) - Cranfield University

Table 6.6 - Welding parameters used in the stand-off slope trials and measured
proportionality constants
Run
s15
WFS Sw Vt V
q
SOr
,,, caic
2001 5.0 0.6 21.3 19.4 20 _
-0.3243 -0.6975
s15 2002 6.0 0.7 21.5 19.6 20
-0.3590 -0.4668
s15 2003
S15
7.0 0.8 21.8 19.9 20
-0.3696 -0.3521
2004 8.0 0.9 22.1 20.2 20
-0.3276 "0.2826
s15 2005 9.0 0.5 22.5 20.5 20
-0.3030 -0.2366
s15 2006 9.5 0.5 22.7 20.7 20
-0.2857 -0.2188
s15 2007
s15 2008
s15 2009
11.0
12.5
13.5
0.6
0.7
0.7
33.1
33.8
34.3
30.5
31.1
31.5
20
20
20
-0.1519
-0.1474
-0.1443
-0.2182
-0.1784
-0.1592
s15 2010 14.5 0.7 34.8 32.0 20
-0.1296 -0.1437
s15 1001 5.0 0.6 21.3 19.4 10
-0.3158 -0.6975
s15 1002 6.0 0.7 21.5 19.6 10
-0.2414 -0.4671
S15 1003 7.0 0.8 21.8 19.9 10
-0.2179 -0.3521
S15 1004 8.0 0.9 22.1 20.2 10
-0.2184 -0.2826
S15 1005
s15 1006
9.0
9.5
0.5
0.5
22.5
22.7
20.5
20.7
10
10
-0.2174
-0.2174
-0.2366
-0.2188
s15 1007 11.0 0.6 33.1 30.5 10
-0.1481 -0.2182
s15 1008 12.5 0.7 33.8 31.1 10
-0.1061 -0.1784
s15 1009
S15 1010
13.5
14.5
0.7
0.7
34.3
34.8
31.5
32.0
10
10
-0.0986
-0.1022
-0.1592
-0.1437
WFS :, wire feed speed Im/min] Sw : travel speed Im/min]
V, d : set-up welding voltage [V] V eq : required mean voltage [V]
SO1: stand-off at end of slope path [mm)
4.: measured constant by applying equation (6.6) to the welding data collected for these trials (see
Appendix J)
Figure 6.9 shows a plot of 4mß and 0.1. versus the wire feed speed. The
plotted values of 0m.. correspond to the average of the values measured for positive
and negative stand-off slopes (SOf = 20 mm and SOf = 10 mm, respectively), with the
same wire feed speed. Note the difference between 4,,,, and which grows with
,
decreasing wire feed speed. For most of the wire feed speeds, is smaller than 0.,,.
(bigger absolute value). This results in over prediction of the stand-off, might cause
over correction in the table controller, hence leading to instability in the control loop.
In addition, the amount by which the absolute values of 4t are bigger than their
counterparts is not constant, thus introducing a further prediction error.
Another difficulty in applying the model of equation 2.22 is the determination
of when to start estimating the stand-off, that is, which level of current should be
considered as corresponding to a stable process after first striking the welding arc.
This is a very difficult task since the welding current signal is generally corrupted by
random noise.
The problems outlined above led the author to search for a more robust way
of estimating the stand-off using primarily the welding voltage and current transient
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