33
Component Identification and Explanation
resulting in poor tie in. One issue created with a weaving technique even
if the metal deposited is the correct thickness is that it can slow the for-
ward progress down. If weaving is too wide, one side of the puddle will
cool and oxidize before the torch is brought back across to that side. This
is a point where porosity can be introduced.
What Are the Different Kinds of Welds?
Besides a butt joint (Flat edge to flat edge) and lap joint (overlapping
edges) which are often used for thinner metal gauges, consider using
one of these groove joints for best welding results. When grinding or
cutting the bevels, especially with a single V
-
groove, it may be beneficial
to leave a small land with a gap between the joint to achieve full penetra-
tion. In this case a temporary backer plate can be used to support the
bottom of the weld to create the root pass. The root weld will weld the
backer to the main plate. This backer can later be ground or cut off.
However, in many cases a plain open root can be used as a backer plate
adds to the time and labor involved. A knife edge is also acceptable so
long as the joint is fully penetrated when the weld is completed. Open
root gaps without a backer can range from
1/16”
to
1/8”
depending upon
wire diameter and application.
When Do I Use Multi
-
Pass Welds?
When welding material
1/4”
and over be careful about trying to put too
much metal down in a single pass. Use multiple passes to complete the
weld along with any necessary joint preparation especially with wires of
smaller diameter. As metal thickness goes up so does the number of
required passes. Depending upon the wire diameter and power settings
used, a
1/4”
joint may only require 1 or 2 passes, but a
3/8”
joint in
plate metal or pipe will require not only beveling but 4 to 6 overlapping
weld passes including a cap and root pass. See Example below.
Joint Preparation
DOUBLE J
-
GROOVE
V
-
GROOVE (60
-
80°)
DOUBLE V
-
GROOVE
DOUBLE U
-
GROOVE
U
-
GROOVE
BEVEL GROOVE
DOUBLE BEVEL GROOVE
J
-
GROOVE
≥
1/4”
Fillet
≥
1/4”
Fillet
s
≥
1/4”
V
≥
1/4”
Butt
Weld Pass Examples
Explanation of MIG Functions and Terms
