LIBRARY ı6ıul 0) - Cranfield University

data. Measurements of resistance between the contact tip and the workpiece showed
that in dip mode of metal transfer the resistance calculated during the short circuiting
phase has a strong correlation with the stand-off. This was also observed by Philpott
[ref. 21], who used the term dip resistance to designate such resistance. Based on this
observation, a method was devised to calculate the dip resistance using the
windowing technique developed by Chawla [ref. 161] together with the standard
statistical features extracted from each window of data (see section 2.6.3).
In the dip mode of metal transfer, a short circuiting phase is characterised by
the extinction of the welding arc which occurs when the electrode wire touches the
weld pool and transfers the molten droplet to the pool. During this time, the wire
forms a continuous bridge between the contact-tip and the workpiece. The short
circuiting phase can be detected by analysing the welding voltage transient waveform
and identifying the periods when the voltage falls steeply to a value close to zero (see
Figure 6.10). In this work, in order to make sure that the measured resistance would
correspond to a real short circuit, only the voltage samples with magnitude equal to or
smaller than the background voltage were considered for calculation purposes. The
dip resistance for a window of data was obtained as the average of all the resistances
calculated for voltage samples complying with VS Vbk. Equations (6.7) and (6.8)
show the method explicitly.
where
Vk
DipA 1'ý
k
[Vk E[], 2,..., N l; Vk _