Fillet Welds - Linde BOC Smootharc Advance MIG 425R Operating Manual

48 BOC Smootharc Advance III MIG 425R & 555R Operating manual
Convex Fillet Weld
Actual Throat Actual Throat
Convexity
Effective Throat Effective Throat

12.6 Fillet Welds

A fillet weld is approximately triangular in section, joining two surfaces not in
the same plane and forming a lap joint, tee joint or corner joint. Joints made
with fillet welds do not require extensive edge preparation, as is the case
with butt welded joints, since the weld does not necessarily penetrate the
full thickness of either member. It is important that the parts to be joined be
clean, close fitting, and that all the edges on which welding is to be carried
out are square. On sheared plate it is advisable to entirely remove any 'false
cut' on the edges prior to welding. Fillet welds are used in the following
types of joints:
'T' Joints
A fillet weld may be placed either on one or both sides,
depending on the requirements of the work. The weld metal
should fuse into or penetrate the corner formed between the
two members. Where possible the joint should be placed in
such a position as to form a "Natural 'V' fillet" since this is the
easiest and fastest method of fillet welding.
Lap Joints
In this case, a fillet weld may be placed either on one or
both sides of the joint, depending on accessibility and the
requirements of the joint. However, lap joints, where only
one weld is accessible, should be avoided where possible and
must never constitute the joints of tanks or other fabrications
where corrosion is likely to occur behind the lapped plates.
In applying fillet welds to lapped joints it is important that
the amount of overlap of the plates be not less than five
times the thickness of the thinner part. Where it is required to
preserve the outside face or contour of a structure, one plate
may be joggled.
Corner Joints
Actual Throat
& Effective Throat
Convexity
Leg
Lengh
Theoretical Throat Theoretical Throat
Concave Fillet Weld
Actual Throat
& Effective Throat
Concavity
Leg
Size
Leg
Lengh
Theoretical Throat
The following terms and definitions are important in specifying and
describing fillet welds.
Leg Length
A fusion face of a fillet weld, as shown above. All specifications for fillet weld
sizes are based on leg length.
Throat Thickness
A measurement taken through the centre of a weld from the root to the face,
along the line that bisects the angle formed by the members to be joined.
Effective throat thickness is a measurement on which the strength of a weld
is calculated. The effective throat thickness is based on a mitre fillet (concave
Fillet Weld), which has a throat thickness equal to 70% of the leg length. For
example, in the case of a 20 mm fillet, the effective throat thickness will be
14 mm.
Convex Fillet Weld
A fillet weld in which the contour of the weld metal lies outside a straight
line joining the toes of the weld. A convex fillet weld of specified leg length
has a throat thickness in excess of the effective measurement.
Concavity
Leg
Size
Size Leg Size Leg
Theoretical Throat
The members are fitted as shown, leaving a 'V'-shaped
groove in which a fillet weld is deposited. Fusion should be
complete for the full thickness of the metal. In practice it
is generally necessary to have a gap or a slight overlap on
the corner. The use of a 1.0–2.5 mm gap has the advantage
of assisting penetration at the root, although setting up is a
problem. The provision of an overlap largely overcomes the
problem of setting up, but prevents complete penetration
at the root and should therefore be kept to a minimum,
i.e. 1.0–2.5 mm.