Abstract
Laser-based powder bed fusion (L-PBF) is an additive manufacturing (AM) technique that uses a computer-controlled laser beam as the energy source to consolidate a metal powder according to a layer-upon-layer strategy in order to manufacture a three dimensional part. This opens the way for an unprecedented freedom in geometry, but the layer-wise build-up strategy typically results in a very poor surface finish, which is affected by the staircase effect and by the presence of partially molten particles. Surface finishing treatments are therefore necessary to obtain an adequate surface finish, to improve the fatigue behavior and to meet mechanical and aesthetic needs. The present contribution systematically compares numerous surface finishing techniques, including laser shock processing, plastic media blasting, sand blasting, ceramic shot peening and metal shot peening with steel particles of different sizes (ϕ = 0.2 mm and ϕ = 0.4 mm). The results show that all the proposed methods improve the surface quality and the fatigue life of A357.0 L-PBF parts. However, the achievement of the lowest surface roughness does not necessarily correspond to the best fatigue performance, thus suggesting that multiple mechanisms may be active and that besides surface roughness also residual stresses contribute to increase the fatigue strength.
Highlights
At present, laser-based powder bed fusion (L-PBF) is the prevailing additive manufacturing (AM)technique to produce metal-based parts [1]
A wavy pattern could be detected as a consequence of the propagation of pressure waves, whereas the surface was extremely flat, without obvious marks, after plastic media blasting
The surface quality of as-built workpieces produced by L-PBF is a critical issue, since their high surface roughness may compromise fatigue resistance, aesthetic properties and correct functioning
Summary
Laser-based powder bed fusion (L-PBF) is the prevailing additive manufacturing (AM). Technique to produce metal-based parts [1]. A powder bed is selectively melted (or sintered) and solidified layer-upon-layer by a laser beam that is computer-controlled according to an assigned model, which can be either a computer-aided-design (CAD) or a tomography-based project. L-PBF paves the way for the production of extremely complicated parts, conformal channels and assemblies, with substantial advantages for high-end applications in the automotive, aeronautic and biomedical fields. L-PBF is still a recent technique and, for this reason, very few feedstock materials are currently available on the market [5]. Substantial progress has been achieved to extend the range of raw powders that may be successfully used for L-PBF. According to a recent survey [8], Metals 2019, 9, 1284; doi:10.3390/met9121284 www.mdpi.com/journal/metals
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