Welding glossary
Cold lap (thermal signature)
In this glossary, a cold-lap thermal signature means a repeatable spatial or time-based anomaly in thermal weld data that flags conditions associated with poor fusion at a weld toe. It is a process-monitoring indication, not proof that a cold-lap imperfection exists.
Cold lap is a physical fusion problem near a weld toe. Research describing the imperfection calls it a small incomplete-fusion interface at or near that toe; the original experimental characterisation used microscopy to examine the interface. This glossary uses cold-lap thermal signature for a different thing: the pattern a monitoring system associates with the process conditions or surface response around such events. Recent multimodal welding research likewise treats cold lap as a labelled defect class inferred from process data, not as a thermal pixel value that proves the physical interface exists.
This page does not assign the signature a universal shape or unit. It might be expressed through a local thermal gradient, the width of the heated band, a cooling curve, or a combination of features. Camera band, angle, emissivity, joint geometry, process and material all change the recorded field. For that reason, the signal must be established against labelled reference welds made under the relevant setup. A generic “cold” pixel threshold is not a defensible definition.
Worked distinction: signature and imperfection
Imagine a fillet-weld monitoring rule built from a documented reference set. On one production run it flags a narrow, persistent anomaly along the lower toe while the weld pool passes. That flag is the cold-lap thermal signature. It identifies a location and time that deserve review.
If a qualified follow-up examination or section then reveals an unfused toe interface, the physical finding is cold lap, related to lack of fusion or overlap according to the observed geometry and the classification document used by the job. If follow-up finds sound fusion, the thermal flag remains a real process anomaly but is not a cold-lap defect. The signal and the imperfection therefore cannot share one pass/fail label.
This term is useful in welding data review because it keeps monitoring evidence at the correct level. Thermography can locate and trend an unusual surface response; the specified inspection and acceptance documents decide whether the joint contains a reportable imperfection and what happens next.
Where you meet this term
- Thermal weld-monitoring rules trained against labelled sound and cold-lap reference welds
- Run-to-run maps of toe temperature, heated-band width and cooling behaviour
- Process anomaly records used to select a weld for confirmatory inspection
- Root-cause reviews that align thermal data with a macrosection or another qualified examination
