Permanent Mechanical Joints - Welding

There are different methods that can be used for making permanent mechanical
joints. Permanent joining methods include: welding, soldering, brazing, riveting,
cementing, bonding, etc.
 The use of non-permanent joining elements (such as threaded fasteners, keys,
pins, retaining rings, etc.) is necessary in some cases in order to enable the
disassembly of mechanical systems for inspection and maintenance purposes.
 When the disassembly of a mechanical system is not required, the use of
permanent joining methods is preferred since it generally leads to significant
savings over non-permanent joining methods (because of the elimination of
fastening elements and holes, grooves, slots, etc.).

Wending, Soldering, and Brazing

Welding, soldering and brazing are the most widely used
techniques for joining metals. These techniques are somehow
similar in that they all involve melting and solidification of a
metal, yet, they are different from each other.
 Welding is a process in which the pieces to be joined are
melted at the joining interface (usually a filler material is
added) then allowed to solidify to become a strong joint.
 Soldering is a process in which metal parts are joined together by melting and
flowing a filler metal (solder) into the joint. The filler
metal used in soldering has a lower melting point than
the pieces to be soldered.
 Soldering is usually used for joining eclectic wires and
components (such as seen in the figure) where a low
melting point tin based solder is used.
 Brazing is a process in which a filler metal is heated above melting point and
introduced between close-fitting surfaces (the gap between surfaces is usually
less than 0.1 mm) by capillary action. Brazing usually uses higher temperatures
than soldering.
 Brazing is usually used for joining copper tubes (a
tin based solder is used) such as seen in the figure.
 Brazing can also be used for joining steel pieces
where bronze is used as a filler material.

MENG 204 - Mechanical Drawing Lecture Notes by: Dr. Ala Hijazi

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Types of Welding
Welding is a fabrication process used to join materials together and it can be used
for metals or thermoplastics. In general, during welding, the pieces to be joined (the
workpieces) are melted at the joining interface and usually a filler material is added
to form a pool of molten material (the weld pool) that solidifies to become a strong
joint.
Welded joints are usually as strong as the parent material (even stronger
sometimes), and thus it is the most widely used permanent joining method in
mechanical and structural applications.
There are many different types of welding processes and, in general, they can be
categorized as:
Arc Welding: A welding power supply is used to create and maintain an electric
arc between an electrode and the base material to melt metals at the welding
point. In such welding processes; the power supply could be AC or DC, the
electrode could be consumable or non-consumable, and a filler material may or
may not be added.
The most common types of arc welding are:
 Shielded Metal Arc Welding (SMAW): A process that uses a coated
consumable electrode to lay the weld. As the electrode melts, the flux coating
disintegrates, giving off shielding gases that protect the weld area from
atmospheric gases and provides molten slag which covers the filler metal as it
travels from the electrode to the weld pool (as shown in the figure). Once
part of the weld pool, the slag floats to the surface and protects the weld
from contamination as it solidifies. Once hardened, the slag must be chipped
away to reveal the finished weld.

 Gas Metal Arc Welding (GMAW): (also known as Metal Inert Gas "MIG"
welding) A process in which a continuous and consumable wire electrode and
shielding gas (usually an argon and carbon dioxide mixture) are fed through a
welding gun, as seen in the figure.

MENG 204 - Mechanical Drawing Lecture Notes by: Dr. Ala Hijazi

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  Gas Tungsten Arc Welding (GTAW): A process that uses a non-consumable
tungsten electrode to produce the weld. The weld area is protected from
atmospheric contamination by a shielding gas, and a filler metal that is fed
manually is usually used.
Gas Welding: In this method a focused high
temperature flame generated by gas combustion
is used to melt the workpieces (and filler)
together. The most common type of gas welding
is Oxy-fuel welding where acetylene is
combusted in oxygen (as shown in the figure).
Resistance Welding: Resistance welding involves the
generation of heat by passing a high current (1000–
100,000 Ampere) through the resistance caused by
the contact between two or more metal surfaces
where that causes pools of molten metal to be
formed at the weld area. The most common types of
resistance welding are Spot-welding (using pointed
electrodes), as shown in the figure, and Seam-welding
(using wheel-shaped electrodes).
Energy Beam Welding: In this method a focused high-
energy beam (Laser beam or electron beam) is used to melt the workpieces and
thus join them together.
Solid-State Welding: In contrast to
other welding methods, solid-state
welding processes do not involve the
melting of the materials being joined.
Common types of solid-state welding
include; ultrasonic welding, explosion
welding, electromagnetic pulse welding,
roll welding, friction welding (including
friction-stir-welding, as shown in the
figure), etc.

MENG 204 - Mechanical Drawing Lecture Notes by: Dr. Ala Hijazi

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Types of Welded Joints
The weld joint is where two or more metal parts are joined by welding. The five
basic types of welded joints are the butt, corner, tee, lap, and edge.
 Butt Joint: it is used to join two members aligned in the same
plane. This joint is frequently used in plate, sheet metal, and
pipe work.
 Corner and Tee Joints: these joints are used to join
two members located at right angles to each other.
The cross-section of the corner joint forms an L-shape
and the tee joint has the shape of the letter T.
 Lap Joint: this joint is made by lapping one piece of metal over
another. This is one of the strongest types of joints available;
however, for maximum joint efficiency, the overlap should be at
least three times the thickness of the thinnest member of the
joint.
 Edge Joint: it is used to join the edges of two or more members
lying in the same plane. In most cases, one of the members is
flanged, as seen in the figure. This type is frequently used in
sheet metal work for joining sheets that are not subjected to
heavy loads.

Types of Welds
There are many types of welds. The most common types are the bead, surfacing,
plug, slot, fillet, and groove.
 A weld Bead is a weld deposit produced by a single
pass with one of the welding processes. A weld bead
may be either narrow or wide, depending on the
amount of transverse oscillation (side-to-side
movement) used by the welder.
 Several weld beads applied side-by-side are usually
used in Surfacing, as shown in the figure. Surfacing is
usually used to apply a hard, wear-resistant layer of
metal to surfaces or edges of worn-out parts.
 A Fillet weld is triangular in shape and this weld is used to join two surfaces that
are at approximately right angles to each other in a lap, tee, or comer joint (as
seen in the figure).

MENG 204 - Mechanical Drawing Lecture Notes by: Dr. Ala Hijazi

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 Plug and Slot welds are welds made through holes or slots in one member of a
lap joint, as shown in the figure. These welds are used to join that member to
the surface of another member that has been exposed through the hole.

 Groove welds (also may be referred to as Butt welds) are simply welds made in
the groove between two members to be joined. The weld is adaptable to a
variety of butt joints, as seen in the figure.

Welded Joints Parts and Termenology

While there are many variations of joints, the parts of the joint are described by
standard terms. The figure illustrates the parts and terminology of groove and fillet
welds.
 The 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 reinforcement is a term used to describe weld metal in excess of the metal
necessary to fill a joint. The reinforcement needs to be grinded in some cases
depending on the intended use of the joint.

MENG 204 - Mechanical Drawing Lecture Notes by: Dr. Ala Hijazi

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 The root of is that portion of the welded joint where the metals are closest to
each other(the point where the back of the weld intersects the base metal
surface).
 The fusion zone is the region of the base metal that is actually melted.
 The size of a groove weld is equal to the thickness of the plate (the enforcement
is not included). If the thickness of the two butted plates is not equal, the size is
the thickness of thinnest plate.
 In a fillet weld, the leg is the portion of the weld from the toe to the root.
 In a fillet weld, 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 between the toes.
 The size of a fillet weld refers to the length of the leg of the weld. The two legs
are assumed to be equal in size unless otherwise specified.

 Also, the terms used to describe the specific requirements for a particular joint
are illustrated in the figure:
 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.
 The root opening refers to the
separation between the parts to be
joined at the root of the joint.

MENG 204 - Mechanical Drawing Lecture Notes by: Dr. Ala Hijazi

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Welding Symbols
Welding symbols are used in drawings to indicate the type and specifications of the
weld.
 There are two commonly used standards for the symbolic representation of
welded joints in drawings; the ISO welding symbols (ISO 2553) and the American
Welding Society welding symbols (AWS A2.4).
 The two standards are somewhat similar but there are some differences
between them. The ISO welding symbols will be presented here.
 The figure shows the ISO welding symbol where the most important features of
the symbol are illustrated below:

 (1) Arrow line: It points to the weld

location. It can point up or down (at any
angle but not horizontal) and it can be on
the right or left side.
 (2) Reference line (continuous): It refers to the side
of the joint where the arrow line points. The weld
information are attached to this line.
 (3) Identification line (dashed): It refers to the other
side of the joint (the side opposite to the location
where the arrow line points). The weld information
of the other side are attached to this line. The
identification line can be below the reference line
(as shown in the figure) or it can be on top of it.
 (4) Basic weld symbol: It identifies the type of weld. It can be on the reference
line (indicates that weld is on the arrow side), or on the identification line
(indicates that weld is on the other side), or on both (indicates that weld is on

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 both sides). When the weld on both sides are symmetric, the identification
line is omitted.

 (5) Weld all around: It indicates that the welding should be all around the
periphery of the member.
 (6) Size of the weld: It indicates the depth of partial penetration when used
for groove welds, and for fillet weds it indicates the leg size.

 (7) Intermittent welds specifications: When numbers are present to the right
of the basic weld symbol, this indicates that the weld is not continuous. The
specifications of intermittent wilds are given by these numbers N x L (G)
where N is number of welds, L is length of each wild, and G is the gap
between welds.

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  When intermittent welds are staggered, a Z-shaped symbol that
separates L and G is added to the welding symbol.

 (8) Tail: The tail can be added to give any further supplemental information
such as identifying the type of the welding process (e.g., SMAW, GMAW, etc.
where numeric codes are used to indicate the
different processes), or the welding position, or the
filler materials. Also, A closed tail can be used to give
specific instructions.
 (9) Field (or site) welds: When the flag symbol is present, it indicates that
welds are to be made in the field (not in a fabrication shop). It is placed at the
junction of the reference line with the arrow line. It can be placed either
above or below the reference line.

MENG 204 - Mechanical Drawing Lecture Notes by: Dr. Ala Hijazi

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