LIBRARY ı6ıul 0) - Cranfield University

Table 3.1 - Ogunbiyi's model coefficients
Regression Coefficients
Variable E . No a S SE R2
'mean (3.1) 61.318 24.053
-0.4611
9.98 97.22
TSI (3.2) 2.8758
-0.002549 -0.060936
0.1237 88.12
Imean (3.3) 0.363842 0.642844
-
12.2015 99.71
VbkVmean (3.4)
-0.47318
0.002481 0.044959 0.09 92.57
Vbk (3.5) -27.3364 -0.039555
2.2558 1.441019 98.62
Leg, (3.6) 1.0 0.561068
-
0.0980 99.58
Leb (3.6) 1.0 0.592637
-
0.129228 99.35
Pen, (3.7) 0.01782
-0.449818 -
0.356612 89.07
Penb (3.7) 0.019058 -0.639698 -
0.415507 82.92
Pr(und) (3.8) -0.0982
0.0044 0.0265 0.3502 65.98
Pr(arc) (3.9) 13.519345 0.97619
-
2.2976 48.61
PR (3.10) -0.9785 -7.0094E-6 0.083019
Obs: *= not available.
The algorithm used for generating welding parameters is an adaptation of the
one proposed by Ogunbiyi [ref. 51]. The algorithm searches for the combinations of
welding parameters that would satisfy a series of constraints relative to bead
geometry, joint position, presence of gap, weld penetration, metal transfer and
stability, and arranges the predicted parameters in order of growing possibility of
producing a weld with defects.
Two main types of constraints are used in the algorithm: a) geometrical
constraints and b) process constraints.
The geometrical constraints refer to the weld geometry limits such as
minimum allowable leg length, maximum allowable leg length, minimum allowable
weld penetration, maximum allowable weld penetration and maximum allowable gap
size. These constraints are normally set relative to the thinner member of the joint and
can vary according to different specifications. The constraints chosen were based on
the Inauxa specification [ref. 190] (see Figure 3.3) and the AWSD8: 8-79 specification
[ref. 107] (see Figure 3.4) and on the validity range of the models [ref. 51]. The
constraints are listed below.
a. 1) Geometrical constraints relative to models validity range (Fillet joints)
" Minimum allowable plate thickness: 1.0 mm
" Maximum allowable plate thickness: 6.0 mm
" Minimum allowable leg length: 2.5 mm
" Maximum allowable leg length: 6.0 nun
" Minimum allowable stand-off: 12 mm
" Maximum allowable stand-off: 20 mm
" Suggested stand-of 15 mm
5 From this point on, the contact tip-to-workpiece distance will be referred to as stand-off
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