Abstract
Deep-penetration laser beam welding is highly dynamic and affected by many parameters. Several investigations using differently sized laser spots, spot-in-spot laser systems, and multi-focus optics show that the intensity distribution is one of the most influential parameters; however, the targeted lateral and axial intensity design remains a major challenge. Therefore, a laser processing optic has been developed that coaxially combines two separate laser sources/beams with different beam characteristics and a measuring beam for optical coherence tomography (OCT). In comparison to current commercial spot-in-spot laser systems, this setup not only makes it possible to independently vary the powers of the two laser beams but also their focal planes, thus facilitating the investigation into the influence of specific energy densities along the beam axis. First investigations show that the weld penetration depth increases with increasing intensities in deeper focal positions until the reduced intensity at the sample surface, due to the deep focal position, is no longer sufficient to form a stable keyhole, causing the penetration depth to drop sharply.
Highlights
The influence of the intensity distribution on the laser beam welding process is a widely investigated topic that, due to its complexity, still has open research questions
It can be seen that the intensity distribution within the measured plane changes when changing the power distribution and the focal distance
When comparing the changes in the intensity distribution due to the variation of the power distribution, it can be seen that the intensities of each separate laser beam add up when combined
Summary
The influence of the intensity distribution on the laser beam welding process is a widely investigated topic that, due to its complexity, still has open research questions. Weberpals and Dausinger analyzed the influence of the laser beam focusability [1], the inclination of the laser beam, and the variation of the focal plane on the keyhole angle and spatter formation [2] Their results showed that laser beam welding with higher intensities facilitates a higher welding depth if the beam divergence angle is small enough. Punzel et al investigated the influence of different intensity distributions on weld seam properties like penetration depth, seam width, and porosity and were able to achieve a reduction in porosity at certain intensity distributions [5] They assumed that the reason for the reduced porosity is a reduced vapor velocity due to an increased keyhole opening [5]. These systems have limitations because the power distribution between the inner core and the outer ring can be set independently, they share the same focal plane
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