To become a skilled welder,
you first need to learn the technical vocabulary (language) of welding. The sections
in this chapter introduce you to some of the basic terms of the welding language. Once you
understand the language of welding, you will be prepared to interpret and communicate
welding information accurately.
When welding two pieces of
metal together, you often have to leave a space between the joint. The material that you
add to fill this space during the welding process is known as the filler metal, or
material. Two types of filler metals commonly used in welding are welding rods and welding
The term welding rod refers
to a form of filler metal that does not conduct an electric current during the welding
process. The only purpose of a welding rod is to supply filler metal to the joint. This
type of filler metal is often used for gas welding.
In electric-arc welding, the
term electrode refers to the component that conducts the current from the electrode
holder to the metal being welded. Electrodes are classified into two groups: consumable
and nonconsumable. Consumable electrodes not only provide a path for the current but they
also supply fuller metal to the joint. An example is the electrode used in shielded
metal-arc welding. Nonconsumable electrodes are only used as a conductor for the
electrical current, such as in gas tungsten arc welding. The filler metal for gas
tung-sten arc welding is a hand fed consumable welding rod.
Before performing any welding
process, you must ensure the base metal is clean. No matter how much the base metal is
physically cleaned, it still contains impurities. These impurities, called oxides, result
from oxy-gen combining with the metal and other contaminants in the base metal. Unless
these oxides are removed by using a proper flux, a faulty weld may result. The term flux
refers to a material used to dissolve oxides and release trapped gases and slag
(impurities) from the base metal; thus the flux can be thought of as a cleaning agent. In
performing this function, the flux allows the filler metal and the base metal to be fused.
Different types of fluxes are
used with different types of metals; therefore, you should choose a flux formulated for a
specific base metal. Beyond that, you can select a flux based on the expected soldering,
braz-ing, or welding temperature; for example, when brazing, you should select a flux that
becomes liquid at the correct brazing temperature. When it melts, you will know it is time
to add the filler metal. The ideal flux has the right fluidity at the welding temperature
and thus blankets the molten metal from oxidation.
Fluxes are available in many
different forms. There are fluxes for oxyfuel gas applications, such as brazing and
soldering. These fluxes usually come in the form of a paste, powder, or liquid. Powders
can be sprinkled on the base metal, or the fuller rod can be heated and dipped into the
powder. Liquid and paste fluxes can be applied to the filler rod and to the base metal
with a brush. For shielded metal arc welding, the flux is on the electrode. In this case,
the flux combines with impurities in the base metal, floating them away in the form of a
heavy slag which shields the weld from the atmosphere.
You should realize that no
single flux is satisfactory for universal use; however, there are a lot of good
general-purpose fluxes for use with common metals. In general, a good flux has the
following characteristics: It is fluid and active at the melting point of the fuller
- It remains stable and does not change to a vapor
rapidly within the temperature range of the weld-ing procedure.
- It dissolves all oxides and removes them from
the joint surfaces.
- It adheres to the metal surfaces while they are
being heated and does not ball up or blow away.
- It does not cause a glare that makes it
difficult to see the progress of welding or brazing.
- It is easy to remove after the joint is welded.
- It is available in an easily applied form.
Nearly all fluxes give
off fumes that may be toxic. Use ONLY in well-ventilated spaces. It is also good to
remember that ALL welding operations require adequate ventilation whether a flux is
used or not.
The weld joint is
where two or more metal parts are joined by welding. The five basic types of weld joints
are the butt, corner, tee, lap, and edge, as shown in figure 3-6.
joint is used to join two members aligned in the same plane (fig. 3-6, view A). This
joint is frequently used in plate, sheet metal, and pipe work. A joint of this type may be
either square or grooved. Some of the variations of this joint are discussed later in this
Corner and tee joints
are used to join two members located at right angles to each other (fig. 3-6, views B and
C). In cross section, the corner joint forms an L-shape, and the tee joint has the shape
of the letter T. Various joint designs of both types have uses in many types of
A lap joint, as the
name implies, is made by lapping one piece of metal over another (fig. 3-6, view D). This
is one of the strongest types of joints available; however, for maximum joint efficiency,
you should overlap the metals a minimum of three times the thickness of the thinnest
member you are joining. Lap joints are com-monly used with torch brazing and spot welding
An edge joint is used
to join the edges of two or more members lying in the same plane. Inmost cases, one of the
members is flanged, as shown in figure 3-6, view E. While this type of joint has some
applications in platework, it is more fixquently used in sheet metal work An edge joint
should only be used for joining metals 1/4 inch or less in thickness that are not
subjected to heavy loads.
The above paragraphs
discussed only the five basic types of joints; however, there are many possible
variations. Later in this lesson, we discuss some of these variations.
PARTS OF JOINTS
|While there are many
variations of joints, the parts of the joint are described by standard terms. The root of
a joint is that portion of the joint where the metals are closest to each other. As shown
in figure 3-7, the root may be a point, a line, or an area, when viewed in cross section.
A groove (figure 3-8) is an opening or space provided between the edges of the
metal parts to be welded. The groove face is that surface of a metal part included
in the groove, as shown in figure 3-8, view A. A given joint may have a root face or a
root edge. The root face, also shown in view A, is the portion of the prepared edge
of a part to be joined by a groove weld that has not been grooved. As you can see, the
root face has relatively small dimensions. The root edge is basi-cally a root face
of zero width, as shown in view B. As you can see in views C and D of the illustration,
the groove face and the root face are the same metal surfaces in some joints.
requirements for a particular joint are expressed in such terms as bevel angle, groove
angle, groove radius, and root opening. A brief description of each term is
shown in figure 3-9.
The bevel angle is the angle formed between the
prepared edge of a member and a plane perpendicular to the surface of the member.
The groove angle is
the total angle of the groove between the parts to be joined. For example, if the edge of
each of two plates were beveled to an angle of 30 degrees, the groove angle would be 60
degrees. This is often referred to as the included angle between the parts to
be joined by agroove weld.
The groove radius is
the radius used to form the shape of a J- or U-groove weld joint. It is used only for
special groove joint designs.
The root opening refers
to the separation between the parts to be joined at the root of the joint. It is sometimes
called the root gap.
To determine the bevel angle,
groove angle, and root opening for a joint, you must consider the thickness of the weld
material, the type of joint to be made, and the welding process to be used. As a general
rule, gas welding requires a larger groove angle than manual metal-arc welding.
|The root opening is usually
governed by the diameter of the thickness filler material. This, in turn, depends on the
of the base metal and the welding position. Having an adequate root opening is essential
for root penetration. Root penetration and joint penetration of welds are shown in figure
Root penetration refers to
the depth that a weld extends into the root of the joint. Root penetration is measured on
the center line of the root cross section. Joint penetration refers to the minimum
depth that a groove (or a flange) weld extends from its face into a joint, exclusive of
weld reinforcement. As you can see in the figure, the terms, root penetration and joint
penetration, often refer to the same dimension. This is the case in views A, C, and E
of the illustration. View B, however, shows the difference between root penetration and
joint penetration. View D shows joint penetration only. Weld reinforcement is a
term used to describe weld metal in excess of the metal necessary to fill a joint. (See
TYPES OF WELDS
There are many types of
welds. Some of the common types you will work with are the bead, groove, fillet,
surfacing, tack, plug, slot, and resistance.
|As a beginner, the first type of
weld that you learn to produce is called a weld bead (referred to simply as a
bead). A weld bead is a weld deposit produced by a single pass with one of the welding
processes. An ex-ample of a weld bead is shown in figure 3-12. A weld bead may be either
narrow or wide, depending on the amount of transverse oscillation (side-to-side move-ment)
used by the welder. When there is a great deal of oscillation, the bead is wide; when
there is little or no oscillation, the bead is narrow. A weld bead made with-out much
weaving motion is often referred to as a stringer bead. On the other hand, a weld
bead made with side-to-side oscillation is called a weave bead.
|Groove welds are
simply welds made in the groove between two members to be joined. The weld is adapt-able
to a variety of butt joints, as shown in figure 3-13. Groove welds may be joined with one
or more weld beads, depending on the thickness of the metal. If two or more beads are
deposited in the groove, the weld is made with multiple-pass layers, as shown in
figure 3-14. As a rule, a multiple-pass layer is made with stringer beads in manual
operations. As a steekworker, you will use groove welds frequently in your work
Another term you should be familiar with, when making a
multiple-pass weld, is the buildup sequence, as shown in figure 3-15. Buildup
sequence refers to the order in which the beads of a multiple-pass weld are deposited in
welding instructions specify an interpass temperature. The interpass
temperature refers to the temperature below which the previously
deposited weld metal must be before the next pass may be started.
After the effects of heat on
metal are discussed, later in the chapter, you will understand the significance of the
buildup sequence and the importance of controlling the interpass temperature.
Across-sectional view of a fillet
weld (fig. 3-16) is triangular in shape. This weld is used to join two sur-faces that
are at approximately right angles to each other in a lap, tee, or comer joint.
Surfacing is a welding
process used to apply a hard, wear-resistant layer of metal to surfaces or edges of
worn-out parts. It is one of the most economical methods of conserving and extending the
life of machines, tools, and construction equipment. As you can see in figure 3-17, a
surfacing weld is composed of one or more stringer or weave beads. Surfacing, sometimes
known as hardfacing or wearfacing, is often used to build up worn shafts,
gears, or cutting edges. You will learn more about this type of welding in chapter 6 of
this training manual.
A tack weld is a weld
made to hold parts of an assembly in proper alignment temporarily until the final welds
are made. Although the sizes of tack welds are not specified, they are normally between
1/2 inch to 3/4 inch in length, but never more than 1 inch in length. In determining the
size and number of tack welds for a specific job, you should consider thicknesses of the
metals being joined and the complexity of the object being assembled.
Plug and slot welds
(fig. 3-18) are welds made through holes or slots in one member of a lap joint. These
welds are used to join that member to the surface of another member that has been exposed
through the hole. The hole may or may not be completely filled with weld metal. These
types of welds are often used to join face-hardened plates from the backer soft side, to
install liner metals inside tanks, or to fill up holes in a plate.
Resistance welding is
a metal fabricating process in which the fusing temperature is generated at the joint by
the resistance to the flow of an electrical current. This is accomplished by clamping two
or more sheets of metal between copper electrodes and then passing an electrical current
through them. When the metals are heated to a melting temperature, forging pressure is
applied through either a manual or automatic means to weld the pieces together. Spot and
seam welding (fig. 3-19) are two common types of resistance welding processes.
Spot welding is
probably the most commonly used type of resistance welding. The material to be joined is
placed between two electrodes and pressure is applied. Next, a charge of electricity is
sent from one electrode through the material to the other electrode. Spot welding is
especially useful in fabricating sheet metal parts.
Seam welding is like
spot welding except that the spots overlap each other, making a continuous weld seam. In
this process, the metal pieces pass between roller type of electrodes. As the electrodes
revolve, the current is automatically turned on and off at the speed at which the parts
are set to move. Seam welding is almost exclusively used in industrial manufacturing.
PARTS OF WELDS
|For you to produce
welds that meet the job requirements, it is important that you become familiar with
the terms used to describe a weld. Figure 3-20 shows a groove weld and a fillet
weld. he face is the exposed surface of a weld on the side from which the weld was
made. The toe is the junction between the face of the weld and the base metal. The root
of a weld includes the points at which the back of the weld intersects the base metal
surfaces. When we look at a triangular cross section of a fillet weld, as shown in view B,
the leg is the portion of the weld from the toe to the root. The throat is
the distance from the root to a point on the face of the weld along a line perpendicular
to the face of the weld. Theoretically, the face forms a straight line be-tween the toes.
terms leg and throat apply only to fillet welds.
In determining the size of a
groove weld (fig. 3-20, view A), such factors as the depth of the groove, root opening,
and groove angle must be taken into consideration. The size of a fillet weld (view B)
refers to the length of the legs of the weld. The two legs are assumed to be equal in size
unless otherwise specified.
A gauge used for determining
the size of a weld is known as a welding micrometer. Figure 3-21 shows how the welding micrometer is used to determine the
various dimensions of a weld.
Some other terms you should
be familiar with are used to describe areas or zones of welds. As we dis-cussed earlier in
the chapter, fusion is the melting to-gether of base and/or fuller metal. The fusion
zone, as shown in figure 3-22, is the region of the base metal that is actually
melted. The depth of fusion is the distance that fusion extends into the base metal or
previous welding pass.
Another zone of interest to
the welder is the heat-affected zone, as shown in figure 3-22. This zone in-cludes
that portion of the base metal that has not been melted; however, the structural or
mechanical properties of the metal have been altered by the welding heat.
Because the mechanical
properties of the base metal are affected by the welding heat, it is important that you
learn techniques to control the heat input. One technique often used to minimize heat
input is the intermittent weld. We discuss this and other techniques as we pro-gress
through this chapter; but, first we will discuss some of the considerations that affect
the welded joint design.