Common causes, in order of likelihood:
1. Wire is too hot. Heat work-hardens the wire over time; combined with thermal cycling it eventually fatigues. Drop temperature 5-10% and see if the cut still completes.
2. Wire is too thin for the part. A 0.2mm nichrome bridging a 500mm gap and trying to cut dense foam stretches under drag — adjacent cycles work-harden it. Try 0.3mm or 0.4mm.
3. PSU is dropping voltage as it heats. Cheap PSUs sag at 30-60 min. Confirm with a multimeter or just use a beefier supply.
4. The wire is nicked. Inspect — a microscopic nick from clamping becomes a stress concentrator.
1. Wire is too hot. Heat work-hardens the wire over time; combined with thermal cycling it eventually fatigues. Drop temperature 5-10% and see if the cut still completes.
2. Wire is too thin for the part. A 0.2mm nichrome bridging a 500mm gap and trying to cut dense foam stretches under drag — adjacent cycles work-harden it. Try 0.3mm or 0.4mm.
3. PSU is dropping voltage as it heats. Cheap PSUs sag at 30-60 min. Confirm with a multimeter or just use a beefier supply.
4. The wire is nicked. Inspect — a microscopic nick from clamping becomes a stress concentrator.