How are welding symbols represented in engineering drawings?

Short Answer:

In engineering drawings, welding symbols are used to clearly show the type of weld, its location, size, and other details needed for fabrication. These symbols follow standard formats defined by international standards such as ISO, BIS, or AWS (American Welding Society). The symbol includes an arrow line, reference line, weld symbol, and additional notes if needed.

These welding symbols make communication between the designer and welder very clear, so that welding can be done exactly as required without confusion. Using symbols saves space, avoids long descriptions, and ensures that welding is done with correct technique and position.

Detailed Explanation:

Welding Symbols in Engineering Drawings

In mechanical design and fabrication, welding is a common process used to join two metal parts permanently. But different welds are used for different needs—some are simple fillet welds, some need deep penetration, and others require finishing or inspection. To represent all these welding instructions clearly and briefly, engineers use standard welding symbols in their drawings.

These symbols allow the welder to understand what type of weld to make, where to apply it, what size it should be, and any special instructions—all through a neat and professional graphical language.

Parts of a Welding Symbol

A complete welding symbol is made up of several elements. Each part has a meaning:

  1. Arrow Line
    • Points to the location on the drawing where the weld is to be made.
  2. Reference Line (Horizontal Line)
    • Acts as the main line on which weld symbols and instructions are written.
  3. Weld Symbol
    • The graphical sign (like triangle or square) that shows the type of weld (e.g., fillet, groove, square, plug).
  4. Tail (Optional)
    • Used when extra information is needed (like process type, code, or method).
  5. Finish Symbol
    • Tells how the weld should be finished (grinding, machining, etc.).
  6. Dimensions and Angles
    • Indicates weld size, length, pitch, and angle, if needed.

Common Weld Symbols

  1. Fillet Weld:
    • Triangle shape; most common type. Used for corner and lap joints.
  2. Square Weld:
    • Straight horizontal line; used when edge faces are square.
  3. Bevel, V, U, J Welds:
    • Shaped symbols showing how the edges of the metal should be prepared.
  4. Plug and Slot Welds:
    • Circle and rectangle shapes indicating welds in holes or slots.
  5. Spot or Seam Welds:
    • Used for resistance welding, usually in sheet metal.

Each symbol gives an idea of how the metal surfaces are joined together.

Symbol Placement Rules

  • Below the Reference Line: The weld is made on the arrow side of the joint.
  • Above the Reference Line: The weld is made on the opposite side.
  • Both Sides: Same weld symbol shown on both sides of the line = weld both sides.
  • Circle on the Intersection: Means weld all around the joint.
  • Flag at Intersection: Means field weld, i.e., done at the site.
  • Filled or Open Arrow: Direction may indicate side preparation or edge type.

Additional Information Shown with Symbols

  • Weld Size: Indicated on the left side of the weld symbol (e.g., 6 mm)
  • Length of Weld: Shown on the right side (e.g., 50 mm)
  • Pitch (distance between welds): Given as number after weld length
  • Contour or Finish: Letters like “G” (grind), “M” (machine), “C” (chisel)

Example Symbol:
Arrow → Reference line with triangle (fillet) below it, size 6, length 50, G → means:
“Make a 6 mm fillet weld, 50 mm long, ground finish on the arrow side.”

Why Welding Symbols Are Important

  1. Saves Time and Space: Short symbols avoid lengthy instructions.
  2. Clear Communication: Welders get exact details without guessing.
  3. Reduces Errors: Standard format means everyone interprets it the same way.
  4. Improves Quality Control: Inspectors know what weld to check for.
  5. Legal and Documentation Use: Acts as proof of what welding was required.

Use in CAD Drawings

Modern CAD software like AutoCAD, SolidWorks, and Inventor have tools to insert standard welding symbols. They follow ISO, ANSI, and AWS standards, so that the drawings are accepted in global industries.

Conclusion

Welding symbols are a standard and essential part of mechanical engineering drawings. They use simple graphical signs along with a reference line, arrow, and notes to show type, size, and location of welds. These symbols improve communication, reduce mistakes, and ensure that welding is done exactly as per design. Every mechanical engineer should know how to read and use welding symbols properly to create professional and clear technical drawings.