LIBRARY ı6ıul 0) - Cranfield University

Note that the calibration model shown in equation (6.3) also includes
correction for the differences in weld penetration caused by the distinct cooling rate
which results from different jigging systems used in the experimental trials carried out
with the BDH320 and the BDH550.
The new model coefficients shown in Table 6.3 and the calibration models
shown in equations (6.2) and (6.3) were used to make the necessary adjustments in
the algorithm shown in section 3.3.2.1.
A new set of bead on plate welding trials was carried out with welding
parameters generated by the adjusted algorithm. Good and stable conditions were
obtained, although the process was somewhat spattery for low wire feed dip transfer.
This behaviour was compensated for by reducing the high limit of PR for the dip
mode of metal transfer in the Step 17 of the algorithm shown in section 3.3.2.1. The
value of 0.37 was found to reduce the welding voltage to levels that produced
acceptable spatter levels in all the range of wire feed speeds in dip transfer.
In order to check the validity of the calibration models, a flat position fillet
welding trial was carried out with parameters generated for producing a fillet weld
with an average leg length of 4.5 mm and adequate level of penetration (between 10%
and 60% of minimum plate thickness) in 3.2 mm thick plates, using a stand-off of 15
mm and no gap. Figure 6.6 shows the resulting bead geometry and Table 6.5 shows
the comparison between predicted and measured values.
Table 6.5 - Bead geometry obtained from welding parameters generated with
adjusted models
Predicted values Measured values Prediction error'
Imea [amps] 228.9 222.0 -3.01 %
Vme.
" [volts] 21.0 20.86 -0.67 %
11 Le nun 4.51 4.7 4.2%
Pence, [% Turin
25.6% 20.3% -20.7
The large error in the penetration model was still acceptable since the actual
penetration was within the requirement range. The imprecision of the penetration
model has also been highlighted by Ogunbiyi [ref. 51].
Z Prediction error
=
measured - Value Value
predicted
x 1001/0
Value
predicted
132