High fidelity thermo-mechanical model of in-situ micro-rolling in laser-directed energy deposition: multi-track multi-layer case

The International Journal of Advanced Manufacturing Technology https://doi.org/10.1007/s00170-026-18399-6 ORIGINAL ARTICLE High fidelity thermo-mechanical model of in-situ micro-rolling in laser-directed energy deposition: multi-track multi-layer case Ravi Raj1,2,3 · Louis Ngai Sum Chiu2,3 · Deepak Marla1 · Aijun Huang2,3 Received: 11 November 2025 / Accepted: 22 May 2026 © The Author(s) 2026 Abstract In-situ micro-rolling at elevated temperatures during Directed Energy Deposition (DED) improves build quality by providing plastic deformations. However, experimentally characterising the deformations and understanding mechanisms behind these improvements remains challenging and thus necessitates thermo-mechanical finite element analyses (FEA). Previous FEA studies in the literature have focused on single-track and thin-wall multi-layer cases, and a more realistic multi-track, multi-layer scenario has not yet been the subject of a comprehensive study. This study develops and validates an FEA framework for in-situ rolled DED in a representative case of three-track, three-layer Ti-6Al-4V deposition, achieving thermal predictions with 90% accuracy compared to experimental results. Unlike single-track multi-layer cases, where in-situ rolling significantly influences thermal behaviour, its impact in the multi-track scenario is found to be minor due to increased lateral heat diffusion. In-situ rolling is found to induce compressive plastic strain in the build direction across the part, substantially reducing the tensile residual stresses typically found in unrolled cases in the longitudinal direction. Additionally, the findings reveal that deposition and in-situ rolling at the top of the layers have a more pronounced influence on thermal and deformation cycles than at the side tracks. These findings provide essential guidance for optimising more practical multi-track, multi-layer scenarios and serve as a stepping stone towards controlling process–structure–properties relationships when manufacturing parts with the hybrid process. Keywords Finite Element Methods · Hybrid Metal Additive Manufacturing · Ti-6Al-4V · Computational Mechanics · Residual Stress 1 Introduction Directed Energy Deposition (DED) is a Metal Additive Manufacturing (MAM) technique in which a heat source, such as a laser, electron beam, or arc, is used to melt and deposit fed powder/wire of metal/alloys layer by layer [3]. Due to its free-form deposition capability, the technique offers immense scope, including economical printing of Ravi Raj 1 Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, Maharashtra, India 2 Department of Materials Science and Engineering, Monash University, Melbourne 3800, Victoria, Australia 3 Monash Center for Additive Manufacturing, Monash University, Melbourne 3168, Victoria, Australia near-net-shaped parts, repairs, multi-material printing, fabrication of functionally graded materials, and high-entropy alloy printing [3, 37]. However, controlling the built quality remains challenging due to the complex nature of the deposition process, particularly the dynamics of the melt pool and the involved thermal cycles. As a result, defects are observed in a build which includes porosity in parts, high tensile residual stresses and thermal cracks, and columnar grain growth [26, 38]. Columnar grains result in anisotropic mechanical properties and reduced strength. Recently, depositions have been carried out with field-assisted techniques, including rolling, to address these resulting defects [39, 41, 46]. The rolling process involves bulk deformation, resulting in plastic flow of the material. The plastic flow significantly improves material properties, such as strength, due to strain-hardening. Moreover, when conducted with thermal conditions, this strain hardening results in grain refinement, and consequently, the material exhibits isotropic properties [45]. Recent rolling hybridisations in DED have also shown The International Journal of Advanced Manufacturing Technology enhancement in the build quality due to the induced plastic flow with the inherent thermal cycle during a build [19, 29]. These rolling hybridisations have been done mainly in two ways: (i) inter-layer/post-build cold rolling after the tilldeposited part cools nearly to room temperature [4, 29] and (ii) in-situ rolling at elevated temperatures [41, 46]. Both hybridisations have shown grain refinements due to static recrystallisation of deformed material on subsequent heating during the next-layer deposition, thus providing isotropy in mechanical properties and improved strength [21, 22, 43]. Here, the cold rolling strategy is best suited for reduction in the tensile residual stresses and minimisation of the thermal distortions [14, 29], while in-situ rolling at elevated temperatures yields better microstructure due to the added potential of dynamic and metadynamic recrystallisations [22, 47]. Currently, cold rolling strategies have been applied in Wire and Arc Additive Manufacturing (WAAM) [6, 28], while insitu rolling strategies have been utilised in both laser-DED [19, 22, 41] and WAAM [16, 20, 24]. Now with the establishment of this hybrid technology, it is also finding practical applications, including the repair of a cylindrical shaft [44]. Understanding the underlying mechanisms of rolling hybridisations is crucial, especially in how induced plastic deformation impacts the quality of the build. This involves examining the thermo-mechanical responses, which include residual stresses and thermal distortions, as well as metallurgical improvements like grain refinement and enhancements in mechanical properties. All these factors are affected by the deformation and thermal history experienced by a part during deposition. So, quantifying them remains crucial. Additionally, it is crucial to determine the most effective methods for applying deformation to achieve optimal improvements. This includes selecting the appropriate rolling techniques/ ways, roller profiles, and necessary process parameters. Simultaneously quantifying temperature, deformation, and their effects during the hybrid process using experimental methods presents significant challenges due to the complexities involved, particularly with the roller’s interference [34]. To address these challenges, modelling and simulation techniques have long been employed to reveal hidden aspects of such intricate processes while remaining costeffective and supporting experimental efforts. Finite Element Analysis (FEA) has been widely used in the literature to reliably capture the thermo-mechanical behaviour in Directed Energy Deposition (DED) and rolling processes [30]. Its multi-physics framework enables a detailed representation of the coupled thermal and mechanical interactions involved in these processes, even at a part scale. [31]. Additionally, recent advancements in FEA strategy have enabled the predict (...truncated)