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This paper reports on a study aiming at separating the effects of side assisting gas flow from a metallic vapour jet on the transient behaviour of a molten pool and a keyhole during laser full-penetration welding. To achieve the research purpose, laser welding process was simulated under three different conditions: in the presence of both side gas flow and metallic vapour jet, in the presence of side gas flow alone and in the presence of metallic vapour jet alone. It was found that the side gas flow not only pushed the molten melt to flow towards the rear part of the molten pool but also formed, on the molten pool surface, a proper pressure distribution which helped maintain both the humping in the rear part of the molten pool and the concave around the upper exit of the keyhole. Under the condition with side gas flow, the swelling formed around the keyhole blocked the side gas flow and on the other hand the side gas flow pushed them to flow backwards to the rear part of the molten pool more effectively, thereby enlarging and stabilizing the keyhole exit. Furthermore, the peak value of the average pressure in the region composed of the molten pool and keyhole decreased step by step with the growth of the concave. Finally, the interaction between the metallic vapour and molten melt was well controlled using the side gas flow, which led to an improvement in the stability of the molten pool and a reduction in spatters and pores.

Selective laser melting (SLM) opens the possibility to produce porous structures with designed mechanical characteristics. This study focuses on the coupling effect between unit cell topology (Dode and body‐centered cubic (BCC)) and forming orientation (horizontal and vertical) with regard to the actual geometric characterization and mechanical properties of SLM produced Ti6Al4V porous structures. The results show that for the mechanical response, there is a coupling effect between forming orientation and unit cell topology. This is most pronounced for the Dode topology, where the compressive and yield strength for specimens produced in vertical orientation are increased with 14.6% and 7.5% compared with those build horizontally. However, for the BCC topology, this effect cannot be seen. The fatigue properties for specimens processed vertically are better compared with those processed horizontally, especially for the BCC topology, it shows an increase of 51.6%. This study presents initial findings on how to handle the selection of unit cell topology and forming orientation for porous structures prepared using SLM, which may be beneficial for different applications.

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