Symbols and conventions used in welding documentation
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- Welding is process of joining similar or dissimilar metals by the application of heat and sometimes pressure.
Welding process has become popular in recent decades for joining of metal parts with each other. Many techniques and methods have been available for general as well as specific purposes. For simplicity,it is necessary to have Symbolic Representation and conventions.
Types of joints
- Square butt joint
- Single V preparation joint
- Lap joint
- T-joint.
Types of symbols
Various categorie s of welded joint are represented by symbols which are similar to the shape of welds to be made. These symbols are categorised as:
- Elementary symbols
- Supplementary symbols
- Combination of elementary and supplementary symbols
- Combination of elementary symbols
Elementary Welding Symbols
The elementary symbols are as follows:
Supplementary Welding Symbols
These symbols are used with elementary symbols to show the finishing of the weld joint. Such as flatness, convexity, concavity etc.
Conventional Signs
- Bureau Of Indian Standards (BIS):
According to this standard the welding all around the joint is represented by
- using a hallow circle
- using a filled-in circle
at the elbow (connecting corner of the arrow and reference line).
- International Standards Organization(ISO):
This convention indicates the process of welding used.To represent this the 90°V is formed at the tail end of the arrow and the name of process is written in that.
Location of welds
The location of welds is specified by the following:
- Position of the arrow line
- position of the reference line
- position of the symbol
Position of the arrow line
The arrow line joins one end of the continuous reference line in such a way that it forms an angle with it and is completed by an arrow head. The adjoining figure shows the relation between the arrow line and the joint. 'Arrowside' and 'otherside' are the two terms which are used with respect to the continuous plate. The position of the arrow line with respect to the weld is not significant. But, in the case of edge preparation, the arrow line points towards the plate which is prepared.
Position of the reference line
The reference line should be drawn parallel to bottom edge of the drawing and if it is not possible; then it should be drawn perpendicular.
Position of the symbol
The position of the symbol is either above or beneath the reference line. If weld is on the arrow side of the joint or on the dashed line side,then symbol is placed on the continous side of the reference line.
Rules to be observed while applying symbols
- The symbols for fillet and similar welds are to be shown, such that the vertical position of the symbols are indicated on the left hand side of the symbol, irrespective of the orientation of the weld symbol.
- If the welds are to be made on the arrow side of a joint, the corresponding welding symbol should be placed either above or below the continuous reference line.
- If the welds are to be made on the other side of a joint, the corresponding welding symbol should be placed either above or below the dashed reference line.
- If the welds are to be made on both sides of a joint, the corresponding symbols should be placed on both sides of the reference line and the dashed line is not shown.
- The arrow of the symbol must point towards the joint which requires welding.
- When only one member is to be edge prepared to make the joint, the arrow should point at that plate.
- Dimensions of size are indicated in mm without writing the unit mm. The letter 'a' or 'z' is placed in front of the value of the fillet size, depending upon whether the throat or leg and length of the weld is shown on the right hand side. If no length is given, it implies that full length is to be welded.
- If unequal legs of are to be used, they should be given on the left hand side.
- If the weld is to be made all around a joint, a circle should be placed at the elbow, connecting the arrow to the reference line.
- If a weld is required to be made on the site or during assembly or erection, it is represented by a filled-in circle at the elbow, connecting the arrow and the reference line.
- If the weld is to have a flush or flat finish, a straight line should be added above the symbol.
- The welding process is indicated at the end of the arrow, if required.
Welding process designation
While,representation of welding symbol it is necessary to have some abbreviations for simplicity and to avoid lengthy notes.
- welding process designation as follows
| Designation | Welding process |
|---|---|
| CAW | Carbon arc welding |
| IB | Induction Brazing |
| CW | Cold welding |
| IRB | Infra red brazing |
| DB | Dip brazing |
| OAW | Oxy-acetylene welding |
| DFW | Diffusion welding |
| OHW | Oxy-hydrogen welding |
| EBW | Electron beam welding |
| PGW | Pressure gas welding |
| ESW | Electro-slag welding |
| RB | Resistance welding |
| EXW | Explosion welding |
| RPW | Projection welding |
| FB | Furnace welding |
| RSEW | Resistance seam welding |
| FOW | Forge welding |
| RSW | Resistance spot welding |
| FRW | Friction welding |
| RW | Resistance welding |
| FW | Flash welding |
| SAW | Submerged arc welding |
| GMAW | Gas metal arc welding |
| TB | Torch welding |
| GTAW | Gas tungsten arc welding |
| UW | Upset welding |
References
- K.L.Narayana,P.Kannaiah,K.Venkata Reddy (2008). Machine Drawing. New age International. ISBN 978-81-224-1917-7.
{{cite book}}: CS1 maint: multiple names: authors list (link) - N.D.Bhatt,V.M.Panchal (2003). Machine Drawing. Charotar Publishing House. ISBN 81-85594-19-8.