BOC Smootharc Multi 180 - Page 57

Convex Fillet Weld
A llet weld in which the contour of the weld metal lies outside a
straight line joining the toes of the weld. A convex llet weld of
specied leg length has a throat thickness in excess of the e󹟽ective
measurement.
Concave Fillet Weld
A llet in which the contour of the weld is below a straight line joining
the toes of the weld. It should be noted that a concave llet weld of
a specied leg length has a throat thickness less than the e󹟽ective
throat thickness for that size llet. This means that when a concave llet
weld is used, the throat thickness must not be less than thee󹟽ective
measurement. This entails an increase in leg length beyond the
speciedmeasurement.
The size of a llet weld is a󹟽ected by the electrode size, welding speed
or run length, welding current and electrode angle. Welding speed and
run length have an important e󹟽ect on the size and shape of the llet,
and on the tendency to undercut.
Insu󹟾cient speed causes the molten metal to pile up behind the arc
and eventually to collapse. Conversely, excessive speed will produce
a narrow irregular run having poor penetration, and where larger
electrodes and high currents are used, undercut is
likely to occur.
Fillet Weld Data
Nominal
Fillet Size (mm)
Minimum Throat
Thickness (mm)
Plate Thickness
(mm)
Electrode Size
(mm)
5.0 3.5 5.0–6.3 3.2
6.3 4.5 6.3–12 4.0
8.0 5.5 8.0–12 & over 4.0
10.0 7.0 10 & over 4.0
Selection of welding current is important. If it is too high the weld
surface will be attened, and undercut accompanied by excessive
spatter is likely to occur. Alternatively, a current which is too low will
produce a rounded narrow bead with poor penetration at the root.
The rst run in the corner of a joint requires a suitably high current
to achieve maximum penetration at the root. A short arc length is
recommended for llet welding. The maximum size llet which should
be attempted with one pass of a large electrode is 8.0 mm. E󹟽orts to
obtain larger leg lengths usually result in collapse of the metal at the
vertical plate and serious undercutting. For large leg lengths multiple
run llets are necessary. These are built up as shown below. The
angleof the electrode for various runs in a downhand llet weld is
shown below.
57BOC Smootharc Multi 180/200 Operating manual