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Poor surface quality represents one of the most critical drawbacks of metal parts produced by powder bed-based Additive Manufacturing (AM) technologies, such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM). Among the several post-process surface finishing treatments, Fluidised Bed Machining (FBM) could represent an intriguing and cost effective option for the treatment of complex AM metal parts. This work illustrates the results of the preliminary tests carried out by means of the FBM technology in which an external contribution of rotational speed of the samples was introduced. Rotation of the samples was considered in order to increase the relative speed and energy dissipation between the parts and the fluidised abrasive particles, with the aim to increase the process efficiency in terms of surface roughness reduction. For the experiments, AlSi10Mg alloy square flat samples were built in vertical direction by means of SLM technology and dipped into an abrasive fluidized bed of silica sand. The preliminary tests were carried out by adopting a minimum fluidization regime of the abrasives and establishing, through the rotation of the samples, two values of mean superficial tangential speed of 1 m/s and 2 m/s. The effect of the latter was investigated in combination with different impact angles, considering a process time of 30 min. The surfaces were characterized quantitatively by means of confocal microscopy and weight loss measurements, while SEM images were acquired in order to observe the real morphology evolution after the treatment. The experimental results suggested a slight surface modification and roughness reduction for the investigated FBM process conditions, due to a low energy transfer from the abrasives to the surfaces. On the other hand, the results shown also that a greater surface smoothing effect was achieved when increasing the tangential speed and adopting low impact angles.

Metal spinning is one of the oldest sheet metal forming processes, which involves a simple tooling and a spinning lathe, whatever manual or computer numerical controlled. However, for its high flexibility and the possibility to produce thin wall sectioned near net shape parts in a very cheap way, sometimes with high complexity geometries, could be revived as an interesting alternative in many applications fields such as automotive and aerospace, whereas other sheet forming processes like deep drawing does not match costs requirements for little dimension production batches. In this work, the production of a flame tube head sector prototype using an AISI 304L stainless steel is proposed, in order to evaluate the process feasibility for the required part geometry. The prototype production was carried out using a two-stage semiautomatic spinning process, starting from a 1mm thick sheet. No preheating of the sheet was adopted to enhance its ductility. The process effects in terms of wall thickness reduction, and hence in cold working, were investigated. Using optical microscopy and Scanning Electron Microscopy (SEM) techniques, the microstructural behavior of the metal subjected to the forming process was investigated, while for an evaluation of the hardness variation Vickers micro-indentation tests were performed. The main result of the process, as observed from all the investigation techniques adopted, is the formation of strain induced martensite, due to the severe plastic deformation and cold reduction of the material, ranging in this case from 30% to 50%. In some areas of the part section, some rips indicating an excessive tensile stress were also detected.