Machine for laser beam melting using continuous and ultra short pulsed laser irradiation

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Laser beam melting from the powder bed (PBF-LB), of e.g. metals, is an additive manufacturing process that can be used to create high-resolution structures. By focusing a continuous wave (CW) laser, small beam diameters and thus high-resolution structures can be generated. However, PBF-LB is very limited for processing materials that are susceptible to cracking, such as glass, because the high thermal gradients caused by the process lead to stresses inside the material and thus promote the formation of cracks. A promising approach for crack-free processing of such materials lies in the use of ultra-short pulsed (UKP) lasers. Although material interaction with a UKP laser in PBF-LB processes inevitably leads to material removal, smaller heat-affected zones (HAZ) result: a large part of the introduced heat is dissipated directly in the removed material. Such a minimised HAZ can be shaped into a desired melt pool geometry by selecting a suitable pulse repetition rate of the UKP laser. Although the thermal gradients in the material are higher than with CW lasers, the thermally induced mechanical stresses are below the strength limit of the brittle material due to the significantly smaller HAZ. As a result, the UKP laser in principle enables crack-free additive manufacturing even for materials that are susceptible to cracking. In this project, a PBF-LB system (for metals, ceramics, and silicates) is therefore applied for, which is operated simultaneously with a CW laser and a UKP laser. The collinear guidance of both lasers via the same beam deflection unit makes it possible to superimpose both systems during the additive manufacturing process. The aim is to evaluate the potential of combining both laser beam sources for the PBF-LB using the machine applied for. By superimposing the CW laser with the UKP laser, various advantages can be realised for the PBF-LB. For example, the CW laser can be used as a preheating and postheating source, while the UKP laser only contributes the amount of heat required for melting. This means that hard-to-weld materials can be processed reliably even in higher part layers. At the same time, the UKP laser enables the control of the cooling rates in PBF-LB. If, on the other hand, the CW laser is used for melting the powder material, the UKP laser can be used for local evaporation of material from this melt. This allows the cooling conditions to be tailored by reducing the melt bath volume. In addition to the aspect of simultaneous use of both lasers, the system offers further advantages, as each part layer can be processed in an alternating process using only the UKP laser in the "cold ablation" regime. This opens up a wide range of previously unavailable options for adjusting the internal and external component properties.