# Analysis of Building Platform Inhomogeneities in PBF-LB/M Process on Alloy 718
## 1 Introduction  
Additive manufacturing (AM) is the most advanced and notable metal-processing technology specializing in the precise fabrication of arbitrarily shaped structures [1, 2, 3, 4, 5, 6, 7, 8]. Recently, Powder Bed Fusion-Laser Beam/Metal (PBF-LB/M) has captured global attention as a cutting-edge AM technology that has matured over an extended period of research and industrial development in the past decade. PBF-LB/M compared to other metal AM techniques, enables high accuracy and lower distortions of the final part, due to low heat generation during the melting process [9, 10]. This additive manufacturing technology facilitates the production of various metal alloys, particularly nickel-based superalloys, which are challenging to manipulate using conventional subtractive methods due to their hardness and poor thermal conductivity. The maturity of this AM technology is highly evident with the wide uptake in the production of commercial products, especially to create high-value products that cannotbe technically feasible using conventional manufacturing methods. It has been shown that the PBF-LB/AM process can change the shape of metal parts, their crystallographic structure [11; 12; 13], and their related mechanical and chemical characteristics [14; 15; 16] by optimizing various process parameters. The most influential factors among the various process parameters that impact the PBF-LB/M process, either directly or indirectly, include Laser Power, Scanning Speed, Hatch Distance, and Layer Thickness [17; 18; 19; 20; 21; 22]. In particular, the formation of the Melt Pool is influenced by Laser Power and Scanning Speed. Therefore, it is crucial to identify the appropriate values for these parameters to prevent phenomena such as Keyhole [23; 24; 25], Lack of Fusion, and Balling [26; 27; 28], and to ensure that the melting regime of the powder operates in conduction mode [29; 30; 31]. During the building process, inert gases such as argon or nitrogen are generally used as shielding gases to prevent metal from oxidation and eliminate byproducts such as spatters and fumes produced in the interaction area of the laser and metal powders, which could potentially impact the quality and the microstructure of the fabricated products [2; 32; 33; 34; 35]. The fundamental variables influencing the quality and characteristics of manufactured products encompass the physical properties and flow direction of the gas. It should be mentioned that the gas flow in the PBF-LB/M process chamber is generally unidirectional, meaning that the outlet of the gas is located on the other side of the building platform from the inlet. In order to guarantee the quality of the building process, different laser scanning strategies have been proposed and implemented depending on the objectives, such as reducing residual stress, improving shape accuracy [35], and obtaining optimal microstructures [36]. On the other hand, using a low-density, high-thermal-conductivity gas such as helium in the process chamber can improve factors such as mechanical properties [37], the melt pool depth [38], and build speed [39], and suppress byproducts [37]. However, it must be noted that if the shielding inert gas flow is not well designed to assure the quality of the component, the laser windows and lenses could be contaminated with debris from the byproducts. This, in turn, leads to the attenuation and defocusing of the laser beam, generates instability in the building process, and promotes the formation of Lack of Fusion porosity in the material. In the work conducted by [PERSON] et al. [40], various levels of shielding gas flow speed were investigated to study variations in the material in terms of porosity and single-track. However, it is also important to understand the effects of shielding gas in terms of varying the exposed area to replicate the actual building conditions.