⌣ Concave weld contour
Concave weld contour · Soldadura en plano · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “△ with concave contour” states a concave weld contour requirement.
What controls
Contour symbol requiring the weld face to be recessed relative to the line joining its toes. On fillet welds it smooths the transition into the plate, which is favorable for fatigue, but it reduces the actual throat compared with a flat-faced weld of the same leg size. That is why concavity and size must be read together: the load-bearing section is what is actually there, not what the legs suggest.
How to verify
Throat gauge, not leg gauge: it is the only way to verify that a concave weld keeps the required section. The toe transition is inspected visually for smoothness and absence of notches. When concavity is a fatigue requirement, the acceptance criteria usually cover both the profile and the absence of undercut at the toes.
Common mistakes when interpreting it
- Measuring a concave fillet with a leg gauge and accepting it: the actual throat can be considerably smaller than nominal.
- Treating any sunken bead as concave by design when it is actually underfill.
- Assuming concavity is always better: it is favorable for fatigue only if the load-bearing section is maintained.
How to get it in the workshop / if it comes out of tolerance
If the drawing calls for concavity, the throat size shown in the dimension is the one you actually have to achieve, usually with somewhat larger legs. It is obtained with slightly faster travel and the right position. Be careful not to confuse a concave weld with an underfilled weld: the latter does not meet the throat and is not acceptable.
Concave weld with short throat: increase filler or reduce travel speed while keeping the shape; if the position prevents it, rethink the sequence. In horizontal welding on a T-joint, an overly fluid puddle sags and produces unintended concavity: adjust the parameters or change to a more favorable position. Never compensate for a short throat by grinding the surrounding plate so it looks like more weld.
Related symbols
Other symbols in Flat welding
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