Laser Powder Bed Fusion of 17-4PH stainless steel components; an approach to increase the production rate

Laser Powder Bed Fusion (LPBF) is an Additive Manufacturing (AM) process, capable to manufacture parts by melting the material’s powder locally layer-by-layer. This technology allows the production of very complex geometries with properties comparable to components obtained by traditional manufacturing processes. Selective Laser Melting (SLM), and the other LPBF processes, found their application in a large range of utilization, from the aerospace field to the agricultural one. Over the past decades, several studies have been needed to improve and optimize the process and the quality of the built parts as well. Among the several advantages, low productivity is the factor that limits large-scale usage since low productivity leads to high production time and, consequently, high production costs. This study explores the correlation between process parameters involved in SLM technology and the productivity of 17-4PH stainless steel, a precipitation-hardened steel that found application in different fields. The purpose is to demonstrate how different combinations of process parameters influence productivity and mechanical properties and find the best tradeoff between them. This thesis is divided into five chapters. Chapter one, “Introduction”, presents a general overview of AM, LPBF and other technologies. Chapter two, “State of art”, collects the main findings during the research activities done in the past years. Describes all the parameters involved during the process and how each of them can influence the final product's mechanical properties and productivity. Investigate, also, the cost model suitable for this study and the method to select the optimized process parameters. Chapter three, “Material and method”, deals with the experimental part of the thesis. In the beginning, 16 cube samples were printed with different combinations of process parameters, then they were analysed and characterized in order to identify a correlation between porosity and VED. Once find the two best promising sets of parameters, six specimens were printed and tensile strength tested. Chapter 4, “Results and discussion”, presents and analyses the results obtained in the previous chapter focusing on the influence of parameters on density, surface roughness and quality, tensile strength and build cost of 17-4PH components. In addition, the final part of this chapter explores a cost case of a mechanical component describing how productivity and cost change with the two different sets of parameters selected before. The last chapter, summarized the conclusion of the whole project, clearly highlighting that it is possible to improve the building rate without declining the mechanical properties just by optimising the SLM process parameters.