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

从粉末床熔化激光(PBF-LB)，例如金属，是一种可用于制造高分辨率结构的添加剂制造工艺。通过聚焦连续波(CW)激光器，可以产生小的光束直径，从而产生高分辨率的结构。然而，PBF-LB对于加工容易破裂的材料(如玻璃)非常有限，因为该工艺引起的高温度梯度会导致材料内部的应力，从而促进裂缝的形成。利用超短脉冲(UKP)激光对这类材料进行无裂纹加工是一种很有前途的方法。尽管在PBF-LB工艺中，材料与UKP激光的相互作用不可避免地导致材料的去除，但较小的热影响区(HAZ)导致：引入的大部分热被直接散失在被去除的材料中。通过选择合适的UKP激光器的脉冲重复频率，可以将这种最小化的HAZ成形为所需的熔池几何形状。虽然材料中的温度梯度高于连续激光，但由于热影响区明显较小，热致机械应力低于脆性材料的强度极限。因此，UKP激光器原则上能够实现无裂纹添加制造，即使是对易开裂的材料也是如此。因此，在这个项目中，应用了一种PBF-LB系统(用于金属、陶瓷和硅酸盐)，该系统与连续波激光器和UKP激光器同时工作。通过同一光束偏转单元的两个激光器的共线引导使得在添加制造过程中叠加两个系统成为可能。其目的是评估使用所申请的机器将两个激光束源组合用于PBF-LB的可能性。通过将连续激光与UKP激光叠加，可以实现PBF-LB的各种优点。例如，CW激光器可以用作预热和后置热源，而UKP激光器只提供熔化所需的热量。这意味着，即使在较高的零件层中，也可以可靠地加工难以焊接的材料。同时，UKP激光器能够控制PBF-LB的冷却速度。另一方面，如果连续波激光用于熔化粉末材料，则UKP激光可用于从该熔体中局部蒸发材料。这允许通过减少熔浴体积来定制冷却条件。除了同时使用两种激光之外，该系统还提供了更多的优点，因为每一层零件都可以在交替的过程中进行处理，只使用“冷消融”状态下的UKP激光。这为调整内部和外部零部件特性打开了一系列以前不可用的选项。

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.