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<p>The Directed Energy Deposition (DED) technique enables the fabrication of near-net-shape metal parts with tailored geometries. However, the formability of DED-fabricated sheets, especially their behavior under complex deformation paths, remains insufficiently characterized due to microstructural anisotropy and defects induced by the layer-wise manufacturing process. The goal of this study is to evaluate the forming limit diagram (FLD) of 316&#xa0;L stainless steel sheets produced by the DED process using a combination of experimental Nakazima punch testing and theoretical prediction using the Marciniak–Kuczynski (M–K) model. Before the fabrication of the specimens, a multi-objective optimization framework was used to find appropriate process parameters (scan speed and laser power) that compromise between melt geometry and metallurgical quality. The theoretical FLD predicted by the M–K model captured the onset of localized necking across various strain paths. The model included strain compatibility and stress equilibrium assumptions between an imperfect zone and a homogeneous zone, which are governed by Swift’s hardening law and Hill’s non-quadratic yield criterion. The optimized DED parameters resulted in consistent melt geometry, enabling reliable FLD extraction from printed sheets. The predicted FLD showed the expected sensitivity to the strain path ratio and effectively delineated the forming limits under plane stress conditions. This is among the first studies combining experimental and theoretical analysis of FLD in DED-fabricated sheets using the M–K model. The incorporation of process optimization enhances the reliability of the FLD analysis and supports its application in hybrid and performance-driven manufacturing workflows.</p>

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Experimental and theoretical determination of the forming limit diagram for 316 L stainless steel sheets fabricated by directed energy deposition

  • 期刊论文

  • 发表日期：

    2026年5月13日

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  • Farnoosh turki,
  • Abdolhossein Jalali Aghchai

摘要

The Directed Energy Deposition (DED) technique enables the fabrication of near-net-shape metal parts with tailored geometries. However, the formability of DED-fabricated sheets, especially their behavior under complex deformation paths, remains insufficiently characterized due to microstructural anisotropy and defects induced by the layer-wise manufacturing process. The goal of this study is to evaluate the forming limit diagram (FLD) of 316 L stainless steel sheets produced by the DED process using a combination of experimental Nakazima punch testing and theoretical prediction using the Marciniak–Kuczynski (M–K) model. Before the fabrication of the specimens, a multi-objective optimization framework was used to find appropriate process parameters (scan speed and laser power) that compromise between melt geometry and metallurgical quality. The theoretical FLD predicted by the M–K model captured the onset of localized necking across various strain paths. The model included strain compatibility and stress equilibrium assumptions between an imperfect zone and a homogeneous zone, which are governed by Swift’s hardening law and Hill’s non-quadratic yield criterion. The optimized DED parameters resulted in consistent melt geometry, enabling reliable FLD extraction from printed sheets. The predicted FLD showed the expected sensitivity to the strain path ratio and effectively delineated the forming limits under plane stress conditions. This is among the first studies combining experimental and theoretical analysis of FLD in DED-fabricated sheets using the M–K model. The incorporation of process optimization enhances the reliability of the FLD analysis and supports its application in hybrid and performance-driven manufacturing workflows.