Effect of Process Parameters on the Quality of 17-4 PH Samples Produced by Directed Energy Deposition

This thesis project is the result of the collaboration between Politecnico di Torino and Prima industrie S.p.A. The Group Prima Industrie operates in the field of mechanical industry, in particular it develops, manufacture and markets laser systems, sheet metal cutting machinery, electronics, CNCs components and additive manufacturing systems. This last field is the most recent and is managed by the newly constituted Prima Additive division. It deals with both Directed Energy Deposition and Powder Bed Fusion technologies. Directed Energy Deposition is an innovative Additive Manufacturing method that represents the evolution of the cladding technology. These machines are predominantly prototypes and, for this reason, process parameters must be evaluated and optimized case by case. In the framework of a scientific support, Prima Additive assigned the analysis of single scan tracks and massive cubes samples made of 17-4 PH with different goals. The single scan tracks were produced covering a wide range of process parameters and the aim was providing a correlation between the process parameters and the meltpools’ characteristics. The massive cubes, instead, were printed using 7 sets of parameters selected by the company’s knowledge and experience with the objective of analysing their quality. In this dissertation, the state of the art of Additive Manufacturing technologies is described, focusing on the metal based ones and presenting the metal powder production. Then, 17-4 PH stainless steel is presented, providing an outline of its characteristics when used in Additive Manufacturing processes. The experimental section of the thesis describes the machine of Prima Additive, the powder feedstock used, how the samples were produced, prepared, and characterized. The feedstock powder was analysed in terms of granulometric distribution, flowability and tap density. It was observed an excellent flowability, crucial for DED applications. Then, the on-top and the cross-section evaluations were carried on the single scan tracks, defining the deposition effectiveness and the meltpools’ geometrical characteristics. Some correlations between them and process parameters were found. The massive cubes’ quality was analysed in terms of porosity, microstructure, and hardness. Generally, they had high hardness and good porosity values, even if few sets of parameters showed more defects than others. In conclusion, the single scans’ analysis allowed to exclude the most critical sets of process parameters while the overall most promising sets were found through the massive cubes’ analysis.