A new control parameter to predict micro-warping-induced job failure in LPBF of TI6AL4V titanium alloy

Abstract

Laser powder bed fusion (LPBF) includes a few printing techniques widely used, in recent years, concerning the additive manufacturing of Ti6Al4V alloys. These produced parts, typically utilized in sectors such as aerospace and biomedical, are characterized by very high added value. It is therefore fundamental to identify the influence of process parameters typical of LPBF technology on the occurrence of warping leading to process failure. This study deals with the characterization of single-track and “micro-scale” level warping phenomena which may lead to protrusion of material over the powder bed and process failure before normal termination. This phenomenon was investigated as a function of process parameters, referring also to the strength and ductility characteristics of the manufactured samples. With this purpose, several samples were printed using variable process parameters both in terms of line energy density (LED) values and in terms of laser power and speed combinations such as to guarantee constant LED values. For the samples that did not show significant micro-warping phenomena, in addition to the transversal and longitudinal geometric characterization of the single track, tensile tests were performed to determine both the resistance of the material and the ductility characteristics. The single tracks, for given process parameters, were printed on a homogeneous material substrate. For every single track, a microstructural and morphological transverse and longitudinal characterization has been carried out and the measured geometrical features were correlated to the process parameters. The obtained results allowed the identification of a new threshold parameter, indicating the limit operating conditions beyond which significant warping phenomena and process failure occur.

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“…Warping is a prominent issue associated with metal additive manufacturing, particularly with materials including titanium, aluminum, and kinds of stainless steel. Warping is a deformation or distorting of a printed component during the printing processes or after it is completed [126,127].…”

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“…Components produced using metal additive manufacturing methods may exhibit significant residual stresses due to large heat gradients and quick solidification of molten powders [4]. This has the potential to cause undesirable distortions [5,6]. Limited research has been conducted in recent years to investigate the process mechanics and the role of the most important process parameters through numerical simulations.…”

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