LIBRARY ı6ıul 0) - Cranfield University

The addition of these rules improved the controller behaviour in respect to
oscillations, but the spatter generation in the low end of the wire feed speed range was
still excessive. From the analysis of the optimum values of PR for different settings of
wire feed speed in the dip mode of metal transfer, it was observed that an almost
linear relationship existed between both variables in the range of wire feed speeds
fixed for this transfer mode (from 4.0 m/min to 10.0 m/min). Taking this into account,
a further reduced range of variation for PR was introduced: the lower limit of the
range would be a function of the wire feed speed, according to the equation (4.4) and
the higher limit would be equal to the lower limit added to the allowable range of
variation, as shown in equation (4.6).
where
minWFS
maxWFS
a
minPRdip =
4maxgFS-niinWTS)
WFS- n inW S
PRLOWDIP+
(4.4)
A= PRHIQ IDIP - PRLOWDIP - PRrange (4.5)
maxPRdip = minPRdip + PRrange (4.6)
is the minimum wire feed speed allowed in dip mode of metal transfer
(4.0 m/min)
is the maximum wire feed speed allowed in dip mode of metal transfer
(10.0 m/min)
is a constant greater or equal to 1 (most suitable value found to be
1.05)
PRrange is the allowable range of variation of PR between minPRdip and
maxPRdip. (Value used: PRrange = 0.02)
By using the rules of Table 4.4 with rules 2 to 4 substituted by the ones from
Table 4.7 and equations 4.3 to 4.6, the resulting controller was able to achieve
optimum process stability for the whole range of wire feed speeds studied in the dip
mode of metal transfer as well as in the spray mode. However, the speed of response
of the controller was not very fast for situations in which an excessive voltage was
found. In order to improve that, the negative voltage correction values in rules 4,5,
6,7. a, and 11 were multiplied by 1.5. The final algorithm is shown in Table 4.8 and in
equations (4.1) and (4.3) to (4.6).
107