Included angle
The included angle is the total angle between the two prepared faces of a weld joint. It determines how well the welding torch, filler material, and shielding gas reach the weld root. Too small an angle causes lack of fusion, too large an angle increases distortion and weld metal volume.
Physical-Chemical Mechanism of Action
The groove angle determines how much space remains between the flanks. The arc or flame must reach the root through this space. A large angle opens the gap wide. Heat and molten metal then flow deep into the joint and wet the flanks reliably. A small angle creates a narrow, deep gap. The arc then only heats the upper flanks, leaving the root cold and unmelted.
Metallurgical Relevance & Welding Risks
If the groove angle is too small, the root remains unwelded. This causes lack of fusion, slag inclusions, and porosity. The weld will fail at the root under load. If the groove angle is too large, the welder must deposit much more weld metal. Heat input increases, and the part distorts more. Slow cooling coarsens the grain and reduces toughness.
Workshop Practice & Action Instructions
For butt welds on plates from 3 mm to 15 mm thick, choose a groove angle of 60°. For thicker plates from 20 mm onward, reduce to 45° to 50° to save weld metal. Maintain a root gap of 2 mm to 3 mm and a root face of 1 mm to 2 mm. Check the angle with a gauge before tacking. Weld in multiple passes if the angle is large. Each pass must fully fuse the flanks.