The increasing application of hybrid structures in component design and fabrication allows to constantly enhance the realization of lightweight potentials. Laser-based joining of metals to polymers can obtaina local bonding with high load bearing capability. During the process, the polymer gets molten by the energy input of the laser beam and penetrates into the structure of the metal surface by means of a defined joining pressure. Macroscopic structures on the metal surface, produced by cutting or laser processing, are possible surface treatmentsfor achieving thepolymer-metal joints. The optimal geometry and other key parameters for the macroscopic surface structures are only partially known at present, e.g. a rising structure density causes a higher load capacity. Based on grooves and drilled holes, as referencegeometries, the depth (0.1-0.9mm), width (0.3-1.1mm), alignment angle, diameter (1.0mm- 1.5mm), structure density and penetration depth of the molten polymer were correlated to the separation force. The results allow an essential insight into the main effects ofmacroscopic structures on the mechanical joint properties and the material performance of the polymer during the process

Cracking during Laser Additive Manufacturing is a problem for many higher-strength aluminium alloys, including AA6061. Here, we used a pulsed laser with ramp-down power modulation to improve the cracking resistance by about 50% compared to the use of a rectangular pulsed laser. Using synchrotron in situ X-ray imaging at 100,000 images s⁻¹, ground truth data was obtained about changes in melt pool geometry, solidification rate, and thermal gradients were calculated. An analytical hot cracking model was developed to show that these changes lead to a decreased hot tear susceptibility. Therefore, laser pulse modulation can be an effective tool to reduce crack susceptibility of alloys. More fundamentally, the results demonstrate that modifying thermal conditions provides a pathway to crack elimination in LAM and the model established in our study sets the foundation for further complex laser manipulation in modifying the printability and resulting mechanical properties of hard-to-process alloys in Laser Additive Manufacturing.

Spatter formation is a major issue in deep penetration welding with solid-state lasers at high welding speeds above 8 m/min. In order to limit spatter formation, the use of local gas flows represents a technically feasible solution. By using the gas flow, the pressure balance inside the keyhole, and therefore the keyhole stability, is affected. Existing investigations demonstrate a reduction in spatter and pore formation for partial penetration welding up to a welding speed of 5 m/min. However, the effect of the gas flow is not yet clarified for full penetration welding at welding speeds above 8 m/min. By using a precisely adjustable shielding gas supply, the effect of a local gas flow of argon was characterized by welding stainless steel AISI304 (1.4301/X5CrNi18-10). The influence of the gas flow on the melt pool dynamics and spatter formation was recorded by means of high-speed videography and subsequently analyzed by image processing. Schlieren videography was used to visualize the forming flow flied. By the use of the gas, a change in melt pool dynamics and gas flow conditions was observed, correlating to a reduction in loss of mass up to 70%. Based on the investigations, a model of the acting effect mechanism was given.