Visualizza wikitesto di Manufacturing and characterization of similar to foam steel components processed through selective laser melting

'''Title''': Manufacturing and characterization of similar to foam steel components processed through selective laser melting

'''Authors''': Fabrizia Caiazzo, Sabina Luisa Campanelli, Francesco Cardaropoli, Nicola Contuzzi, Vincenzo Sergi, Antonio Domenico Ludovico

'''Keywords''': Selective laser melting; Additive manufacturing; Stainless steel; Lightweight structures; Steel foam

'''Abstract''': The growing interest from the industry for lightweight metal components has driven the development of processes that would allow creating lightweight high melting point metals as steels, able to guarantee mechanical characteristics superior to existing foam (typically aluminium), without penalizing one of the characteristics that cell structures have: lightness.
Conventional manufacturing methods, such as casting, however, face difficulty in making complex periodic steel structures with designed shape and size and volume fraction. This study evaluates the manufacturability and performance of lightweight 17–4 PH steel components with spherical porosity fabricated via selective laser melting (SLM). Samples were designed and fabricated with the purpose to produce a structure similar to foam. Built samples were characterized in terms of dimensional accuracy, mechanical strength under compression and energy absorbed per unit mass. The designed structures have a designed relative density or volume
fraction ranging between 31.1 and 32.8%.

'''Purpose''': The purpose is to produce periodic cellular lattice structures that can be used to develop of structures with advanced or multifunctional performance for high value engineering products. These periodic lattice structures, however, currently face a higher manufacturing complexity and costs than the stochastic structures. 

'''Methodology''': The first choise, very important, was made on the powder to be used.The periodic porous structures were made from a 17–4 PH alloy powder, which was purchased from Electro Optical System (EOS) GmbH, Germany. A powder with a mean particle size of 20 μm has been used in this investigation, and alloy chemical composition is listed in Table 1. The powder quality is important to reduce the content of impurities (oxygen, hydrogen and nitrogen), which might negatively affect mechanical properties of laser-sintered parts with phenomena like embrittlement. Figure 1 depicts the SEM images of the 17–4 PH alloy powder at different scales. The powder has a nearly spherical shape and smooth surfaces, which lead to a good flowability. Table 2 highlights 17–4 PH stainless steel mechanical properties. The method tried to design of similar to foam structures.To characterize the porous structures there are Several superimposed pore layers of two different types (type A and type B, Fig. 2).

'''Findings''': This paper has studied the possibility of manufacturing lightweight steel structures with spherical porosity adopting SLM technology. A stainless steel powder has employed, using an EOSINT M270 titanium version laser sintering system considering optimized parameters to have minimal content of porosity in laser-sintered parts. Different samples, having an effective average porosity ranging from 70.1 to 72.5% were successfully fabricated.

'''Limitations/benefits''': SLM has the capability of producing structures of complex freeform geometry. It has been demonstrated to manufacture cellular lattice structures with fine features, showing a great potential to make advanced lightweight structures and products that are highly desired by engineering sectors such as aerospace, automotive and medical industries. However, SLM requires support structure to build an overhang section if its angle from the horizontal is less than a certain degree. This introduces design and manufacturing complications for the SLM of lightweight cellular structures and engineering components. The cellular lattice structures with a large unit cell size or low strut angles from the horizontal (usually lower than 30°) could not be built using the SLM process because overhanging struts led to the occurrence of serious deformation.

'''Link''': https://link.springer.com/article/10.1007/s00170-017-0311-4