PSI - Issue 34

J. Gil et al. / Procedia Structural Integrity 34 (2021) 6–12

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J. Gil et al. / Structural Integrity Procedia 00 (2019) 000–000

Scanner mirrors

Laser

Lens

Chamber

Component

Roller

/ rake

Powder tank Supply piston

Powder bed Build Piston

Fig. 1. Schematic representation of a typical LPBF setup. Adapted from W. E. Frazier (2014)

This paper focuses on selective laser melting (SLM), also known as laser powder bed fusion (LPBF), characterised by the deposition of a thin layer of powder by a powder coater or rake in a platform named powder bed; after the material has been spread in a uniform fashion, one or several laser beams, controlled by a system of mirrors, melts the layer according to the supplied numerical code, with the solidified melt pool creating the component’s cross section of the respective layer. After a layer is complete, the powder bed is lowered, the rake spreads a new layer on top of the previously deposited material, the process is repeated, as described by W. E. Frazier (2014). Figure 1 schematically illustrates the LPBF manufacturing process. Selective laser melting, and broader metallic AM technologies, present disadvantages such as their low productivity rates - specially in the case for PBF methods, as discussed by W. E. Frazier (2014) - besides component defects, such as lack-of-fusion, entrapped gases, solidification cracks, geometrical distortions and residual stresses, as described by Zhang et al. (2018). The appearance of these defects is often related to the process parameters employed in the printing process, which creates a need to paramatrise the build, a task that proves expensive due to the necessity of tweaking the parameters and evaluating the outputs according to the specific needs. Therefore, a simulation package that predicts some of the characteristics of an additively manufactured component is alluring from a commercial standpoint, a demand that is increasingly being supplied by software companies with finite element analysis (FEA) packages. This work aims at analysing two di ff erent approaches at simulating SLM processes by comparing the simulation’s outputs with experimental results gathered from physical specimens.

Nomenclature

Thermal expansion coe ffi cient

α

el Elastic strain vector pl Plastic strain vector th Thermal strain vector t ot Total strain vector σ Stress vector σ xx Longitudinal stress σ yy Transverse stress η Absorption e ffi ciency

Density

ρ a b c

Goldak ellipsoid’s longitudinal length Goldak ellipsoid’s transverse length

Goldak ellipsoid’s pool depth