Welding Sheet Metal.

(1) For welding purposes, the term "sheet metal" is restricted to
thicknesses of metals up to and including 1/8 in. (3.2 mm).

(2) Welds in sheet metal up to 1/16 in. (1.6 mm) thick can be made
satisfactorily by flanging the edges at the joint. The flanges must be at
least equal to the thickness of the metal. The edges should be aligned
with the flanges and then tack welded every 5 or 6 in.
(127.0 to 152.4 mm). Heavy angles or bars should be clamped on each side
of the joint to prevent distortion or buckling. The raised edges are
equally melted by the welding flare. This produces a weld nearly flush
with the sheet metal surface. By controlling the welding speed and the
flame motion, good fusion to the underside of the sheet can he obtained
without burning through. A plain square butt joint can also be made on
sheet metal up to 1/16 in. (1.6 mm) thick by using a rust-resisting,
copper-coated low carbon filler rod 1/16 in. (1.6 mm) in diameter.
The method of aligning the joint and tacking the edges is the same as
that used for welding flanged edge joints.

(3) Where it is necessary to make an inside edge or corner weld, there is
danger of burning through the sheet unless special care is taken to
control the welding heat. Such welds can be made satisfactorily in sheet
metal up to 1/16 in. (1.6 mm) thick by following the procedures below:

(a) Heat the end of a 1/8 in. (3.2 mm) low carbon welding rod until
approximately 1/2 in. (12.7 mm) of the rod is molten.

(b) Hold the rod so that the molten end is above the joint to be welded.

(c) By sweeping the flame across the molten end of the rod, the metal can
be removed and deposited on the seam. The quantity of molten weld metal
is relatively large as compared with the light gauge sheet. Its heat is
sufficient to preheat the sheet metal. By passing the flame quickly back
and forth, the filler metal is distributed along the joint. The
additional heat supplied by the flame will produce complete fusion. This
method of welding can be used for making difficult repairs on automobile
bodies, metal containers, and similar applications. Consideration should
be given to expansion and contraction of sheet metal before welding is
stated.

(4) For sheet metal 1/16 to 1/8 in. (1.6 to 3.2 mm) thick, a butt joint,
with a space of approximately 1/8 in. (3.2 mm) between the edges, should
be prepared. A 1/8 in. (3.2 mm) diameter copper-coated low carbon filler
rod should be used. Sheet metal welding with a filler rod on butt joints
should be done by the forehand method of welding.

Welding Steel.

(1) General. The term "steel" may be applied to many ferrous metals which
differ greatly in both chemical and physical properties. In general, they
may be divided into plain carbon and alloy groups. By following the
proper procedures, most steels can be successfully welded. However, parts
fabricated by welding generally contain less than 0.30 percent carbon.
Heat increases the carbon combining power of steel. Care must be taken
during all welding processes to avoid carbon pickup.

(2) Welding process. Steel heated with an oxyacetylene flame becomes
fluid between 2450 and 2750°F (1343 and 1510°C), depending on its
composition. It passes through a soft range between the solid and liquid
states. This soft range enables the operator to control the weld.
To produce a weld with good fusion, the welding rod should be placed in
the molten puddle. The rod and base metal should be melted together so
that they will solidify to form a solid joint. Care should be taken to
avoid heating a large portion of the joint. This will dissipate the heat
and may cause some of the weld metal to adhere to but not fuse with the
sides of the welded joint. The flare should be directed against the sides
and bottom of the welded joint. This will allow penetration of the lower
section of the joint. Weld metal should be added in sufficient quantities
to fill the joint without leaving any undercut or overlap.
Do not overheat.
Overheating will burn the weld metal and weaken the finished joint.

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