# Process Parameter Optimisation in Laser Powder Bed Fusion of Duplex Stainless Steel 2205
## 1 Introduction  
Additive manufacturing was born as a cost-effective and practical approach to prototype design. However, time has demonstrated remarkable efficiency in handling complex geometries or components that are challenging to machine through conventional techniques. Consequently, it has evolved into a key technique of contemporary industry. While its early applications primarily involved polymer families, additive manufacturing has now appeared as a powerful technique for working with metallic materials, including steels and various alloys, whose production remains very limited. This advantage in the manufacture of geometrically complex models is one of the factors that has motivated comparative studies between additive manufacturing and conventional manufacturing, such as the one by [PERSON] et al. [1]. The level of customization allowed by additive manufacturing promotes the changing of the industry to the consumer-centric business model that has gained relevance in recent years [2, 3]. Additionally, a more in-depth analysis of the energy efficiency and resource-saving advantages of this technology has been developed [4]. There are multiple additive manufacturing methods, with one of the most remarkable being Selective Laser Melting (SLM), a Powder Bed Fusion (PBF) subcategory. SLM is ideal for prototyping and small runs. Its operation is based on the fusion of a bed of powder using a concentrated laser beam with a system of mirrors [5]. The powder is heated to its melting point when it receives the laser, and after it solidifies, it remains welded to the layer immediately below, thus forming the body of the component to be printed. This process is carried out layer by layer, moving the bed vertically by a preset height and spreading a new powder surface with a roller. SLM technology allows complex three-dimensional components to be manufactured with an accuracy of 0.1 mm in 25 mm and it is capable of achieving a surface finish with a quality of 5 um to 15 um [6]. One of the main properties to be controlled is the relative density of the product, with the density offered by the base material used as a reference. Densities between 97-99% can be achieved with this method if the proper optimization parameters are used [7]. The mechanical behavior of SLM parts can be significantly different from conventionally manufactured parts because of their layered composition. Additionally, SLM components can develop some defects due to an improper choice of process parameters. On the one hand, insufficient energy input leads to pores or voids in SLM parts, producing incomplete melting and balling effects [8; 9]. The large particles and substrate are incompletely melted because of a lack of energy. An excessive laser scan speed or low laser power can lead to the spreading of melt pools or droplets. On the other hand, when the energy density of the laser beam exceeds a determinate limit, it can cause the evaporation of the metal and the formation of plasma. Metal evaporation provokes the development of a vapor cavity that enhances laser absorption. This allows the laser beam to reach deeper than usual and if a cavity collapses, it can leave gaps behind the laser trail [10; 11]. In order to optimize the properties of the printed material, it is necessary to control various parameters that influence the process, highlighting the power of the laser (P), the speed of the laser (S), the hatching of the laser beam (H), the height of each layer of powder (Th), and the wavelength. However, among these, there are three critical variables that will greatly influence the properties of the resulting product. These are the power, the scanning speed, and the separation of the laser light beam, as can be seen in the research of [PERSON] et al. [12]. There are several methodologies for optimizing the parameters of a system, which vary depending on the type of system or optimization to be analyzed. In the present research, the response surfaces methodology has been chosen.