PSI - Issue 71

Ravi Prakash et al. / Procedia Structural Integrity 71 (2025) 325–332

326

1. Introduction Additive manufacturing (AM), also known as 3D-printing, is a process that creates objects by building them layer by layer, following the instructions of a digital 3D model. It enables designer to produce customized or complex models in a single process, bypassing the constraints of traditional manufacturing, such as significant material waste, challenges in fabricating intricate shapes, and the need for specialized tooling (DebRoy et al., 2018). Parts fabricated using α+β Ti -alloy play a crucial role across various industries to produce components ranging from miniature to large scale, such as turbine blades, combustion chambers, nuclear reactors, medical devices, stents, bone implants, and military and aircraft parts (Maietta et al., 2019). Because of its excellent mechanical stability, high strength-to-weight ratio, and minimal anisotropy when compared to steels in terms of microstructural-mechanical performance, the Ti6Al4V α+β -alloy is a good option (Kyvelou et al., 2020). Laser-based powder bed fusion (LPBF) is an additive manufacturing process that selectively melts powder material using an intensely focused and quick-moving laser heat source. The production process generates high-temperature gradients and localized transients, leading to the development of residual stresses and distortions in the fabricated components (Li et al., 2018). To produce parts of acceptable quality in the metal-based additive manufacturing (MAM) process, several factors must be meticulously controlled, such as laser power, energy density, scanning velocity, and powder or wire feed rate (Yadroitsava et al., 2015). Researchers have developed various approaches to accurately estimate residual stress field in build-substrate systems. (Mukherjee et al., 2017) enhanced the accuracy of residual stress and distortion predictions by integrating transient heat transfer and fluid flow behaviour with a thermo mechanical model using FE methodology. Their findings indicate that reducing layer thickness can minimize residual stress throughout the metal-based AM process, while neglecting convection effects may significantly overestimate cooling rates. (Parry et al., 2016) found that an alternate scan strategy reduces residual stress and plastic strain due to lower temperature gradients. (Wang et al., 2023) used an FE model to simulate the LPBF process for 316L stainless steel thin-walled parts, revealing that optimal residual stress and deformation occurred at a laser power of 30 W and a scan speed of 20 mm/s, with effective in situ annealing. (Kumar et al., 2024) used FE modeling to predict cooling characteristics and residual stress transformation in IN625 material during the LPBF process, found that tensile residual stress increased with wall thickness. (Walker et al., 2019) developed a thermo-mechanical model to study stress evolution in IN718 during DED, discovering that longitudinal stress had the highest magnitude, though their model was limited to single track deposition. Although numerous numerical methods have been explored in the literature to tackle the thermomechanical analysis of the additive manufacturing process, most of these studies focus on simple AM structures. Therefore, this work aims to investigate the thermo-mechanical behaviour and the growth of residual stresses brought on by the LPBF process to build the part of Ti-6Al-4V alloy, specifically when parts are fabricated using a multi-layer and multi-pass deposition system, through FE modelling. The present model simplifies the heat transfer analysis by convection caused by fluid motion by integrating linearly increased thermal conductivity. A 3D sequentially coupled thermo-mechanical model is established, utilizing the “Model change” feature to enable the acti vation of elements, while a Python-driven user interface automates the deposition process for the multi-layer and multi-track system. 2. Materials and methodology A base plate (substrate) with a thickness of 10 mm, is used, over which a build part with volumetric dimension 60 × 4 × 4.5 mm 3 consisting of five layers and each layer comprising two tracks is deposited layer by layer. The geometric configuration of the build-substrate system presented in Fig. 1 was considered to investigate thermal response and residual stress distribution. The same material α+β Ti -alloy, namely, Ti-6Al-4V, was assigned for both the build-part and the substrate. The temperature-dependent thermo-mechanical material properties used in this study are adapted from ref. (Cao et al., 2016) and chemical composition from (Kumar & Nagamani Jaya, 2023). The process parameters employed for different cases to build the part over the substrate are shown in Table 1. Four samples with different P and v combinations were made to evaluate the influence of scan speed (v) and laser power (P) on the temperature field and residual stress in LPBF of Ti-alloy components. The laser scanning pattern followed in the current study is shown in Fig. 2. The direction of laser scanning was the same for the odd-numbered layers (i.e., layers I, III, and V), while for the even-numbered layers (i.e., layers II and IV), the laser scanning direction was opposite to that of the odd numbered layers. In the cartesian coordinate system, the X, Y, and Z axes were selected as the scan, transverse, and