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Researchers study melt pool dynamics using high-speed x-ray diagnostics

Researchers at the Institut für Strahlwerkzeuge (IFSW) at the University of Stuttgart are using a high-speed x-ray video facility to investigate the usage of dynamic beam laser (DBL) technology to improve keyhole stability in industrial welding applications. 

The facility will enable the researchers to view inside the melt pool during laser welding with an OPA 6 DBL from Civan Lasers, enabling them to better understand the origin of defects such as pores, spatter, and cracking.

While other in situ diagnostic technologies such as high-speed cameras and optical sensors can be used to study melt pools, they only reveal phenomena on the surface of the process, according to the scientists.

In contrast, the high-speed x-ray diagnostics system of the IFSW enables the fluid dynamics occurring within process samples to be viewed with high spatial and temporal resolution – features well below 250μm in steel can be detected at rates exceeding 10,000Hz.

‘When developing improved laser-based manufacturing techniques for processes such as ablation, drilling, joining, cutting, and additive manufacturing, comprehensive diagnostics of melt pool and keyhole dynamics are crucial for understanding the interaction between laser beams and matter,’ said Professor Rudolf Weber, head of the process development department at IFSW. ‘We are thrilled to have access to this game-changing laser tool and are eager to improve the understanding of how Civan’s dynamic beam-shaping lasers can influence control of keyhole and melt-pool dynamics and be applied to industry’s most challenging materials-processing applications such as welding thick materials, asymmetric parts, dissimilar metals, and metals with coatings.’

The DBL uses coherent beam combination to modulate beam shape as desired at speeds of up to hundreds of megahertz without any moving parts. In addition to beam shape, Civan’s DBLs also enable control of shape frequency, shape sequence, and depth of focus. The ability to control these parameters is a powerful tool for optimisation of evaporation in the capillary, the flow in the molten pool, the temperature gradients near the process and with it the solidification of the melt for any laser materials-processing application. Such control does away with pore, spatter, and crack formation while increasing feed rates and speeds in welding and additive manufacturing applications. 

'IFSW already has projects funded by the Israel Innovation Authority in collaboration with Bosch and with the Israeli Institute of Metals as part of the LAMP (Laser for Advanced Material Processing) consortium,' said Civan CEO Dr Eyal Shekel. 'The integration of our OPA 6 laser into IFSW’s x-ray facility will help researchers and industrial companies better understand the impact of laser beam shape, shape frequency, and shape sequencing on weld geometry and microstructure to tap into greater flexibility of laser processing.'

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