Thermosensograms of Stainless Steel Tubes Butt Welding by  CO2 Laser TL5M (Russia)

Defects diagnostic criteria bind the following ordinate’s thresholds of  upper thermosensogram  to laser welding process parameters. For overheating (not considered in a given laser welding as defect one) it is an equality or excess of signal to 30%. For burn-through – an equality or excess of signal to 60%. For poor penetration – an equality or the decrease of signal lower than 17 %. For time axis defect criterion (mainly for gas protection fault) - 2% of a time scale in seconds.

Separate poor-quality  seams parts were fixed at laser welding of a pipe ( a butt joint, welding speed was 3,5 m/min, laser power 1,5 - 2 kW, focal spot diameter - 0,2mm, for steel pipes with diameter 33mm, wall thickness 1,5mm, with a gap and flange discrepancy in limits of + 10-70 % of  welded materials thickness) in real time for the following cases:

- Dot burn-through  (at movement beginning,  at stop of details feeding – 2^nd frame, 1.2s; 3^rd frame, 4.4s) and protective gas feeding suspension (1st frame - from a beginning up to 0.93s);

- poor penetration (flange discrepancy and gap  exceed 50 - 70% of thickness - 3rd frame, since 8,1s).

Conditional overheating for the given calibration threshold in controlled laser welding  process was not considered as defect. As it is shown in 1-3 frames at welding speed of 3,5m/min in power increase at 33 % (2kW - 1st frame) and normal power 1,5kW (2 - 3-rd frames) themselves do not result in  burn-through.

Contacts:

Anatoliy Lazarenko -  laser physics  - lazarenko kpi.kharkov.ua (main contact);

Eugeniy Dyomin - welder, industry security expert, tel/fax (495) 791-17-57;

Oleg Keremzhanov - thermosensor diagnostics - keremzhanov  mail.ru