Slot Welding Symbol Explained

Slot welding is a popular technique used in a wide range of industries, from aerospace to construction. However, understanding the various slot welding symbols can be challenging for those who are not trained in the …

Slot-weld-symbol

Slot welding is a popular technique used in a wide range of industries, from aerospace to construction. However, understanding the various slot welding symbols can be challenging for those who are not trained in the field.

In this article, we will decode the welding symbols for slot welding, providing a comprehensive guide to understanding their meanings and how they are used in welding applications.

What is Slot Welding?

Before we dive into the welding symbols for slot welding, let’s first define what slot welding is. Slot welding is a type of welding technique where a slot is cut into one of the materials being welded, and the other material is welded to the bottom of the slot. This creates a strong and durable connection between the two materials.

Slot Welding Symbols

The welding symbol for slot welds is identical to that used for plug welds, except for the absence of a diameter symbol before the size. Instead, the width of the slot is used to indicate the size of the weld, which is displayed to the left of the symbol, as is the case with plug welds.

To the right of the symbol, the length of the slot weld will be indicated, which may also include the pitch or center-to-center spacing of the welds. If a pitch is present, the number of slot welds will be shown in parentheses either below the symbol on the arrow side or above the symbol on the opposite side weld.

To avoid confusion regarding the direction along the part, the drawing must clearly indicate the orientation of the slot welds.

Elements of Slot Weld Symbol

  • Slot welds can consist of various elements similar to those of plug welds, which have been described earlier. These elements may include:
    • Type of joint (arrow or other side)
    • Width of the slot
    • Length of the slot
    • Center-to-center spacing of slot welds (pitch)
    • Depth of the weld fill
    • Number of required welds
    • Weld contour
    • Surface finish
  • It is crucial to avoid confusion between the fill of plug and slot welds. In some cases, there may be a fillet weld inside a hole instead of filling the hole, as is the case with plug welds. This mistake can also occur in slot welds.
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AWS and ISO Slot Welding Symbol

Below are examples of AWS Slot Welding Symbol (left side) and ISO Slot Welding Symbol (right side).

The symbol depicts the various slot welding symbol elements placements as per AWS A2.4 and ISO 2553 standards for arrow side and other side welding symbol placement for easy reference.

Slot Welds – Summary of Guidelines

General:

  • Arrow-Side Slots: To specify slots in the arrow-side member for slot welding, place the slot weld symbol below the reference line.
  • Other-Side Slots: To specify slots in the other-side member for slot welding, place the slot weld symbol above the reference line.
  • Dimensions: Specify slot weld dimensions on the same side of the reference line as the weld symbol.
  • Fillet Welds in Slots: Do not use the slot weld symbol to specify fillet welds in slots.

Slot Weld Width:

  • Specify the width of a slot weld to the left of the weld symbol. The width is the dimension of the slot measured in the direction of the minor axis at the faying surface.
Slot Weld width example

Slot Weld Length:

  • Specify the length of a slot weld to the right of the weld symbol. The length is the dimension of the slot measured in the direction of the major axis at the faying surface.
Slot Weld Length

Countersink Angle:

  • When a countersink angle is required, specify the angle dimension on the same side of the reference line as the weld symbol. The countersink included angle of slot welds should be specified above or below the slot weld symbol as appropriate.
Countersink Angle

Depth of Filling:

  • Specify the depth of filling inside the slot weld symbol. A depth of filling less than complete should be indicated. Omitting the depth dimension signifies complete filling.
Depth of Filling

Slot Weld Spacing:

  • Specify the pitch (center-to-center distance) of slot welds in a straight line to the right of the length dimension, following a hyphen.
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Number of Slot Welds:

  • If a specific number of slot welds is desired in a joint, specify the number in parentheses on the same side of the reference line as the weld symbol. The number should be placed above or below the weld symbol as appropriate.
  • If the countersink angle is included in the welding symbol, place the number of slot welds above (for other side) or below (for arrow side) the countersink angle.

Slot Weld Location and Orientation:

  • Specify the location and orientation of slot welds on the drawing.

Slot Weld Contour and Finish:

  • Ensure that slot welds to be contoured flush or convex adhere to the requirements outlined here.

Types of Slot Welds

There are several welding symbols used to indicate slot welding in technical drawings. Here are some of the most common symbols and what they mean:

  • Square Slot: The square slot welding symbol consists of a square with lines extending from opposite corners. This symbol indicates that a square slot is to be cut into the base material, and the other material is to be welded to the bottom of the slot.
  • Rectangular Slot: The rectangular slot welding symbol is similar to the square slot symbol but with lines extending from opposite sides of a rectangle. This symbol indicates that a rectangular slot is to be cut into the base material, and the other material is to be welded to the bottom of the slot.
  • Half-Through Slot: The half-through slot welding symbol consists of a square or rectangular slot with a diagonal line through the center. This symbol indicates that the slot is to be cut halfway through the base material, and the other material is to be welded to the bottom of the slot.
  • Plug Slot: The plug slot welding symbol consists of a circle with a horizontal line through the center. This symbol indicates that a circular hole is to be drilled into the base material, and the other material is to be welded to the bottom of the hole.
  • Slot for Seal Weld: The slot for seal weld symbol consists of a square or rectangular slot with an “S” inside. This symbol indicates that the slot is to be filled with weld metal to create a seal between the two materials being welded.
See also  Edge weld joint symbol

Applications of Slot Welding

Slot welding is used in a wide range of applications, including:

  • Aerospace: Slot welding is commonly used in the aerospace industry to join structural components.
  • Construction: Slot welding is used in construction to join steel beams and other structural components.
  • Automotive: Slot welding is used in the automotive industry to join body panels and other components.
  • Manufacturing: Slot welding is used in manufacturing to join various components in machinery and equipment.

Conclusion

Understanding the welding symbols for slot welding is essential for anyone involved in welding applications. By knowing these symbols and their meanings, welders can ensure that the desired weld joint is achieved, leading to stronger, more durable, and safer connections between materials.


Sandeep Kumar is a highly experienced welding professional and author known for his expertise in welding symbols. With certifications including IWE, AWS-CWI, and ASNT NDT Level III.