An enhanced finite element modelling based on self-regulation effect in directed energy deposition of Ti–6Al–4V

Abstract

Self-regulation effect (SRE) is a unique phenomenon in laser blown powder directed energy deposition (DED), which can dynamically compensate the sloping deposition surface (within an acceptable tolerance) induced by the fluctuation of the fabricating process or part warpage. For this reason, the layer-thickness is varying in DED and strongly dependent on SRE determined by the powder standoff distance (PSD) and the inter-layer temperature (ILT), especially for cantilever structures easily deformed. However, previous numerical studies on the thermo-mechanical analyses of DED usually adopt a fixed layer-thickness, missing the reality of the printing process and impairing the credibility and prediction accuracy of simulation. In this study, an improved modelling process considering SRE in DED is proposed to enhance the high-fidelity simulation. Two single-walls were firstly fabricated by DED on the baseplates clamped as cantilevers, to quantify the relationship between the deposited layer-thickness and PSD based on in-situ measurement. Meanwhile, the relationship between ILT and the difference value of the deposited layer-thickness under different inter-layer dwell times also was investigated by combining simulations with experiments. Next, two 3D coupled thermo-mechanical finite element (FE) models with and without SRE were established to examine the proposed modelling strategy. Finally, the thermo-mechanical responses and the geometric dimension predicted by the two models were compared with experimental data. The results illustrate that, compared with the traditional model without SRE, the proposed model significantly improves the mechanical and geometric predictions of the DED parts.

Keywords

• Directed energy deposition
• Thermo-mechanical modelling
• Self-regulation effect
• Powder standoff distance
• Inter-layer temperature
• Part deformation