WELD SYMBOLS USED IN DESIGN
WELDING SYMBOLS AND ITS MEANING USED IN DESIGN
It’s a very usual
aspect to use weld symbols in most of the mechanical drawings. Nowadays, it has
become very important to have knowledge concerned with the welding symbols. There
is a basic format given for showing the weld types used with its
specifications. The welding standards have been varying in different areas.
These standards had been updated from time to time by various non-profit
organizations like AISC (American Institute of Steel Construction), API
(American Petroleum Institute), AWS (American Welding Society) in USA and many
other countries. In India, the welding standards are summarized by BIS (Bureau
of Indian Standards) in which they are having certain IS (Indian standards)
numbers or codes which are followed by most of the Indian companies.
The above fig. shows the
format used for annotation of weld symbols. The definition of symbols used in
the format has been described in the fig. There are many terms involved in the
fig. which won’t be understood at a glance. This page describes about the terms
used in the weld, basic types of weld and joints, types of weld symbols used
for different joints in the drawings etc.
TYPES
OF WELD:-
To start with, we
need to know what is welding. Welding is an efficient method of making
permanent joints between two or more metal parts.
Basically, there are five types of weld
involved in welding, which are as follows:-
1. Groove
Weld:-
A
weld placed in an opening between two parts. There are eight groove weld
symbols that represent different groove weld shapes.
2. Fillet
Weld:-
A
type of weld that is triangular in shape and joins two surfaces at right angles
to each other in a lap joint T-joint or corner joint. Fillet welds are the most
common types of welds.
3. Plug
or Slot Weld:-
A type
of weld made by joining one metal part with a circular hole or slot to another
metal part positioned directly beneath it.
4. Spot
Weld:-
A
type of weld made between or upon overlapping metal parts. Multiple spot welds
are generally required to join parts.
5. Seam Weld:-
A
type of continuous weld made between or upon overlapping metal parts.
TYPES
OF JOINTS:-
Among
the types of weld described above, groove weld and fillet weld are existing in
different forms. All other types of weld exist in the single form each. So,
while referring to the symbols for fillet, spot, seam, plug or slot weld, there
will be no variations in the weld symbols. But, there are different types of
grooves applied for groove weld, due to which weld symbols vary as per the
shape of the groove.
However, there are five basic types of joints
which are classified on the basis of the places, where the weld has been
applied. These joints exist in different forms.
Apart from these joints, its important to know the terms involved in
welding. These terms are the most significant factors required for applying
weld symbols. The terms involved in welding is described in the following
link:- http://mechanisttimes.blogspot.in/p/basic-terms-in-welding.html.The joints are as follows:-
1. Corner
Joint:-
A type of joint between two metal parts at
right angles to one another. Corner joints require large amounts of weld
metal.
2. Edge
Joint:-
A type of joint in which the surface
of the two metal parts to be joined is parallel to one another and the weld is
made at their common edges.
3. Tee
Joint:-
A type of joint produced when two
metal parts are perpendicular to each other, forming the shape of the letter
“T”.
4. Butt
Joint:-
A type of joint between two metal
parts that lie in the same plane. A butt joint is the most common joint type.
5. Lap
Joint:-
A type of joint between two
overlapping metal parts in parallel planes.
ELEMENTARY AND SUPPLEMENTARY WELDING SYMBOLS:-
As
discussed above, there are several types of welding and for some types of
welding like groove weld or fillet weld, there exists several types of joints.
These joints also exist in different forms. Here is a list of elementary
welding symbols that are used in the drawings to denote the type of weld
applied.
The above list
shows the all types of weld involved in drawings. The format for applying these
symbols and weld specifications has already been shown in fig. 1. But its
important to know the position of the weld symbol in the format.
The above fig. shows the position of weld
symbol applied in the format. The example has been shown for fillet weld.
Before analyzing the fig., its important to know about arrow side and other
side. The arrow side is for the side where the arrow has been referred and the
other side is for the side opposite to the arrow side concerned with the joint.
These sides can better be understood from the fig. showing the T-joint and
cruciform joint. The format shown above to joints represents the format for
symmetrical welds and weld for one of the side (arrow or other side). The
dashed line shown in format is called Dual reference line.
Apart
from the elementary welding symbols, there are certain supplementary welding
symbols, which are sometimes used as combination along with former to mention
the type of finish etc. The below fig. shows the supplementary weld symbols and
its combination.
The
supplementary weld symbols show the shape and finish of the weld. Here is an
example of formats which are applied along with elementary and supplementary
welding symbols.
In
the above fig, the
first two formats are showing the places to be welded. The weld all round
format denotes that the joint should be made by welding throughout. The site
weld format shows that the welder should perform the weld on job site, not in
the welding shop. Flush (flat), Convex and Concave contours are already shown
in the previous fig of supplementary welding symbols. The example of format for
grinding finish denotes that the flat finish should be prepared by grinding.
Machining finish format shows that convex contour should be prepared by machining.
Chipping finish format shows that the flat finish should be given by chipping
after performing the fillet weld.
EXAMPLES OF COMBINATION OF ELEMENTARY WELDING SYMBOLS:-
Here is a list of examples of
combination of elementary welding symbols applied in the drawings along with
the formats. Dual reference lines are used to show the arrow side when
different types of weld are applied on both sides. Nowadays, dual reference
lines are avoided even to show the arrow side or other side.
RULES TO BE
OBSERVED WHILE APPLYING SYMBOLS:-
1. Symbols for fillet and similar welds be shown such
that the vertical position of the symbol are indicated on the left hand side of
the symbol, irrespective of the orientation of the weld metal.
2. If the welds are to be made on the arrow side of the
joint, the corresponding symbol should be placed either above or below the continuous
or dual reference line.
3. If the welds are to be made on the other side of a joint,
the corresponding symbol should be placed above or below the dashed reference
line.
4. If the welds are to be made on both sides of the
joint, the corresponding symbols should be placed on both sides of the
reference line and the dashed line is not shown.
5. The arrow of the symbol must point towards the joint
which required welding.
6. When only one member is to be edge prepared to make
the joint, the arrow should point at the plate.
7. Dimensions of size are indicated in mm without
writing the unit mm.
8. If unequal legs of fillet are to be used, they
should also be given on the left hand side.
9. If a welding is required to be made on the site or
during erection or assembly, it is dark circled as shown in format for site
weld.
10. If a weld is to be made all around a joint, a circle
should also be placed at the elbow, connecting the arrow and the reference
line.
11. If a weld is to have a flush or flat finish, a
straight line should be added above the symbol.
12. The welding process is indicated, if required, at
the end of the arrow.
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