Decreasing pore formation in multiple-sheet laser joining with interfacial polymeric contaminations

Abstract

Deep-penetration laser welding is an efficient joining technology for overlap joints nowadays. However, contaminations usually having a lower vaporization temperature can cause seam defects like pores and melt ejections during the process. Many approaches have been investigated, e.g., for the industrially interesting case of welding zinc-coated steel sheets. Suitable techniques for sufficient reduction or avoidance of porosity require additional process steps or timeconsuming preparations. In this paper, three-sheet joints having polymeric interlayers as exemplary extensive contaminations are investigated. Seams feature extreme porosity after standard single-pass welding. The porosity can be decreased significantly when repeating the welding process (double-pass welding). This effect on formation of porosity is modified in this paper. Instead of two processes, longitudinal beam oscillation is applied. The center porosity in longitudinal sections, used as indicator for the porosity of seams, can be reduced significantly from more than 50 to 20 % by using the beam oscillation technique. As the main reason, the increased degassing time due to the lengthening of the melt pool depending on oscillation parameters is identified. Simultaneously, the results indicate that the seam width must not increase similarly to avoid that further evaporation of contamination material cancels out the achieved benefit by lengthening.

Advances in macro-scale laser processing

“…The use of such longitudinal beam oscillation can significantly decrease pore formation in deep-penetration laser welding of multiple-sheet specimens having extensive polymeric contaminations, see Figure 13. The welding speed was maintained at 3 m/min [280].…”

“…Figure13. Amount of center porosity after welding of severely contaminated high alloyed steel layers as a function of the longitudinal oscillation width[280] …”

Laser edge forming to increase the bending radius in hemming

“…A laser beam melts the rod end during the process to produce preforms with a drop-like shape and increased diameter due to the surface tension of the molten material. Woizeschke et al transferred the process approach to sheet edges and demonstrated the fundamental feasibility of producing cylindrical forms along sheet or foil edges by laser melting processes [9]. In principle, different laser beam irradiation strategies are applicable [9].…”

“…Woizeschke et al transferred the process approach to sheet edges and demonstrated the fundamental feasibility of producing cylindrical forms along sheet or foil edges by laser melting processes [9]. In principle, different laser beam irradiation strategies are applicable [9]. Figure 2 demonstrates the laser edge forming by using a defocused laser spot which is guided on the sheet surface and moved along the sheet edge [9].…”

“…In principle, different laser beam irradiation strategies are applicable [9]. Figure 2 demonstrates the laser edge forming by using a defocused laser spot which is guided on the sheet surface and moved along the sheet edge [9]. Fig.…”