Monitoring laser beam welding of zinc coated sheet metal to analyze the defects occurring
2009 (English)In: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Conference paper (Refereed)
During laser welding of overlapping zinc-coated steel sheets typically blowouts as a defect can occur. They can be crucial to the mechanical performance and to the optical appearance of the product. In the present research approved regions are compared to regions where the blowouts are in majority. Time-dependent radiation is captured with a commercial photodiode monitoring system in three different wavelengths ranges, 400-600 nm, 1100-1800 nm and 1064 nm, corresponding to metal vapour emissions, surface temperature emissions and reflected laser light, respectively. Accompanying high speed imaging as well as mathematical modelling of the process emissions was carried out, enabling combined analysis. Different gap widths and laser beam positions were studied. From imaging, surface elevations of the melt indicate a Zn-bubble formation that travels to the rear part of the melt pool before it breaks through, often completely separated from the keyhole. The escaping vapour ejects melt and causes a significant crater, if not flooded with melt again. Although this violent surface event is clearly visible, it was hardly found in the temperature sensor signal. The separate mechanisms that can be responsible for the lack of contribution of the dynamic blow-out formation to the emissions generating the photodiode signal are discussed, e.g. melt surface geometry changes, drops, temperature and emissivity changes, the role of the Znvapour and the detection area of the sensor. This study demonstrates that obvious defects can sometimes be hard to detect on-line.
Place, publisher, year, edition, pages
Kgs. Lyngby: ATV-SEMAPP , 2009.
Welding, Materials science - Other processing/assembly
Svetsning, Teknisk materialvetenskap - Övrig bearbetning/sammanfogning
Research subject Manufacturing Systems Engineering
IdentifiersURN: urn:nbn:se:ltu:diva-29938Local ID: 39265ea0-a1fc-11de-8293-000ea68e967bOAI: oai:DiVA.org:ltu-29938DiVA: diva2:1003165
Nordic Conference on Laser Processing of Materials : 24/08/2009 - 26/08/2009
Godkänd; 2009; Bibliografisk uppgift: CD-ROM; 20090915 (petern)2016-09-302016-09-30Bibliographically approved