Welding Joint Types — Butt, Fillet, Lap and Plug Welds
Introduction
A welded joint is the geometric configuration of the workpieces to be joined. The joint type defines groove preparation, welding positions, parameters and resulting mechanical strength.
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Joint Types
1. Butt Joint
Workpieces in the same plane, edge to edge. Variants: square edge (no groove), single V, double V (X), U, J, single bevel.
2. T-Joint / Fillet Joint
One piece perpendicular to another. Interior angle (T-joint) and exterior angle (corner joint).
3. Lap Joint
Workpieces partially overlapping. Fillet weld on edges.
4. Plug / Slot Weld
Weld through a hole or slot in one of the workpieces.
5. Edge Joint
Parallel workpieces with aligned edges.
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Groove Preparation
| Element | Symbol | Description |
|---|---|---|
| Groove angle | α | Total angle (typically 50-70°) |
| Bevel angle | β | Angle of each face (α/2) |
| Root gap | b | Opening between pieces at root |
| Root face | c | Unbeveled face (typically 1-2 mm) |
| Groove depth | h | Depth of preparation |
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Joint Selection Criteria
- Thickness — square edge for thin; V/X/U groove for thick
- Loading — butt for axial; fillet for shear
- Access — X or K need access from both sides
- Process — TIG allows smaller root gaps
- Economy — narrow grooves (J, U) save filler but cost more to prepare
- Position — some preparations suit difficult positions better
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*Article based on vocational training centres training materials and ISO 9692-1. Published on WeldFC Academy.*