Influence of the metal vapour on the beam properties and the capillary during laser beam welding by investigations at ambient pressure and in vacuum

在激光深熔焊接中，焊接过程受工艺气氛和环境压力的影响很大。这在毛细管的形成和焊接深度上尤为明显。气体毛细管及其稳定性是激光深熔焊接过程中的一个关键因素，毛细管的形成对焊接过程中发生的过程以及产生的焊缝有着重要的影响。毛细管的形成由环境压力和入射光强分布共同决定，而入射强度分布又受射束路径中过程排放的影响。根据环境压力和过程区内的氧含量，产生的金属蒸气部分凝结和凝固成不同尺寸的金属颗粒，或与可用的氧气发生反应形成金属氧化物。根据发射的大小和类型，会出现吸收、散射、热散焦和光束偏转的混合机制。到目前为止，还没有对单个效应对所产生的光束轮廓和焊接过程、毛细形成以及最后的焊缝的影响进行量化。工艺排放的影响和纯环境压力对毛细管几何形状的影响也没有相互分离。因此，拟议项目的目标是通过调整环境大气和环境压力对工艺排放的定向影响来分离单个相互作用机制对激光的影响，并量化它们对强度分布和毛细形成的影响。要实现这一点，第一步是定量和定性地确定常规焊接条件下工艺排放的组成以及受控气氛的环境压力降低对工艺排放的影响。此外，还将研究不同成分的工艺发射对束流特性的影响。为此，测试激光束的光束测量与光线跟踪相结合，以便分离工艺发射对光束特性的影响因素。此外，还研究了纯环境压力对毛细几何形状形成的影响，以及受工艺发射影响的束流性质对毛细几何形状形成的影响。最后，这应该允许分离和量化不同影响因素对束流、毛细形成和焊接结果的影响。

In deep penetration laser welding, the welding process is strongly influenced by the process atmosphere and the ambient pressure. This is particularly evident in the formation of the capillary and the welding depth. The vapor capillary and its stability is a key element in the deep penetration laser welding process and the formation of the capillary has a significant influence on the occurring processes during the welding process as well as on the resulting weld seam. The formation of the capillary is determined by both the ambient pressure and the incident intensity distribution, which in turn is influenced by the process emissions in the beam path.Depending on the ambient pressure and oxygen content in the process zone, the generated metal vapour partly condensates and solidifies into metallic particles of different sizes or reacts with the available supply of oxygen to form metal oxides. Depending on the size and type of the emissions, a mixture of the mechanisms absorption, scattering, thermal defocusing and beam deflection occurs. A quantification of the influence of the individual effects on the resulting beam profile and the welding process, the capillary formation, and finally the weld seam has not been performed so far. Nor have the effects of process emissions and the purely ambient pressure-dependent effects on the capillary geometry been separated from each other.The aim of the proposed project is therefore to separate the influence of the individual interaction mechanisms on the laser beam by the targeted influencing of the process emissions by adjusting the ambient atmosphere and the ambient pressure and to quantify their effect on the intensity distribution and the capillary formation.To achieve this, the first step is to quantitatively and qualitatively determine the composition of the process emissions under regular welding conditions and the influence of the reduction of the ambient pressure of a controlled atmosphere on the process emissions. Furthermore, the effect of process emissions with different compositions on the beam properties will be investigated. For this purpose, beam measurements of a test laser beam, which propagates coaxially to the working laser beam through the process emissions, are combined with ray-tracing in order to separate the influencing factors of the process emissions on the beam properties. Furthermore, the purely ambient pressure-dependent effects on the formation of the capillary geometry are investigated, as well as the effects of the beam properties, influenced by the process emissions, on the formation of the capillary geometry. Finally, this should allow to separate and quantify the effects of the different influencing factors on the beam, the capillary formation and the welding result.