Abstract
Part warpage and residual stress are two of the main challenges for metal additive manufacturing (AM) as they result in lower geometric precision and poor mechanical properties of the products. This work investigates the effect of the building strategy on the heat transfer process and the evolution of the thermally induced mechanical variables in laser directed energy deposition (L-DED) in order to minimize residual stresses and deformations. A 3D finite element (FE) thermo-mechanical model is firstly calibrated through in-situ experiments of rectangular workpieces fabricated by L-DED technology, and, secondly, the coupled thermo-mechanical responses for different process parameters and scanning patterns are discussed in detail. On the calibration stage, the remarkable agreement is achieved between predicted results and experimental data. Regarding the modeling stage, the numerical results indicate that minimization of the part warpage is achieved by reducing the back speed and shortening the scanning lines during the building process. Both residual stress and deformation can be further reduced if preheating the baseplate is added before L-DED.
Highlights
Laser directed energy deposition (L-DED), one of the advanced additive manufacturing (AM)technologies, has been extensively applied in different industrial fields due to its high deposition efficiency and near-net-shape fabrication [1,2]
Lindgren et al [8] developed a thermo-mechanical finite element (FE) model based on computational welding mechanics (CWM) able to predict thermal stresses and distortions during AM
Wang et al [11] used compression experiments at 600 ◦ C and 700 ◦ C with in-situ neutron diffraction to study the stress relaxation of Ti-6Al-4V fabricated through conventional processing and AM
Summary
Laser directed energy deposition (L-DED), one of the advanced additive manufacturing (AM). Denlinger et al [9] simulated the thermo-mechanical responses of Ti-6Al-4V and Inconel® 625 during the L-DED process and found that compared with Inconel® 625, an allotropic phase transformation (PT) in Ti-6Al-4V triggers both significant stress relaxation and distortion mitigation They achieved the best match between the calculated result and in-situ measurement with a PT temperature of 690 ◦ C. The influence of the building strategy on the mechanical behavior of AM built is not yet fully understood, especially for complex structures This given, the goal of this paper is to explore the influence of the building strategy (process parameters and scanning path) on the stress relief and warpage development entailed by the L-DED process as complex rectangular Ti-6Al-4V workpieces are deposited.
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