Chapter 29 Shielded Metal Arc Welding 795
Copyright Goodheart-Willcox Co., Inc.
When making a fi llet weld, rock the back of the electrode slightly from
side to side in order to direct the heat of the arc uniformly into each side of
the joint. Welding vertical-up with a fast-freeze electrode requires more of a
whipping pattern than a weaving motion. The arc is rapidly moved from the
pool to the unmelted base metal and back in an effort to prevent excessive
heating. On thinner material, a stringer bead may be adequate.
Travel Speed
Travel speed is the rate of forward motion during
welding. The condition of the weld pool is the major
indicator of correct travel speed. Welding is like riding
a bike—you do not watch the bicycle, but rather focus
your attention on the road ahead. When welding,
focus on the shape and stability of the molten weld
pool. It should be calm and oval-shaped, Figure 29-29,
extending from the not-yet-welded base metal up
into the edge of the solidifying bead. Keep the arc in
the leading one-third of the weld pool. Correct travel
speed results in a smooth, consistent ripple pattern on
top of the bead. This appearance is often described as
the stacked dimes effect; however, it should actually be
smoother than a true stack of dimes. See Figure 29-30.
Traveling too slowly allows heat to be directed into
the pool, rather than into the base metal. This produces
a wide, convex bead with shallow penetration and leads
to poor fusion. The result is a “cold” weld that appears
to be simply sitting on the surface of the material.
Excessively rapid travel speed also decreases
penetration. Moving too fast creates a narrower,
possibly high-crowned bead and often results in
undercutting. Undercutting, or poor tie-in, means that
the outside edge of the welded bead is concave or
recessed. See Figure 29-31. Traveling too fast can create
a thin or undersized bead.
Anatomy of a Weld—Weld
Quality
There are a number of reasons to inspect a
completed weld. The most important reason is
to determine if its quality is suffi cient for its
intended application. Welds are examined to
check their size and to look for discontinuities.
The size of a weld often correlates directly to
strength and ultimate performance. The optimum
size of a weld is determined by the thickness of the base metal—thicker
materials require larger beads. Too much weld material, on the other hand,
Goodheart-Willcox Publisher
Figure 29-29. A calm, properly shaped weld pool.
Roman023/Shutterstock.com
Figure 29-30. A bead with proper surface character
has a uniform width and a uniform, unbroken pattern
of semicircular waves across the top.
Goodheart-Willcox Publisher
Figure 29-31. A bead exhibiting severe undercutting.