Part-scale thermo-mechanical modelling of distortions in Laser Powder Bed Fusion – Analysis of the sequential flash heating method with experimental validation

Residual stresses and deflections are two major issues in laser-based powder bed fusion (L-PBF) parts. One of the most efficient and reliable ways for predicting residual stresses and final distortions is via a calibrated numerical model. In this work, a part-scale finite element thermo-mechanical model for Ti6Al4V is developed in the commercial software Abaqus/CAE 2018.

The flash heating (FH) method is used as the initial multi-scaling law to avoid time-consuming meso-scale simulations. The model has been verified by doing a mesh-independency analysis. To check the validity of the model, dedicated experiments involving samples with specific scanning strategies were performed.

Experimental measurements were made by optical 3D scanning with the fringe projection technique. An in-house made Python script was written for the stripe-wise and layer-wise partitioning of the numerical model, along with material and boundary condition attributions. As expected, the results show that layer-wise FH is insensitive to the scanning pattern and will lead to an isotropic stress field.

It is shown that the FH method overestimates the minimum deflection magnitude compared to the experiments by 46.2 %. Sequential FH (SFH) is then proposed to resolve this problem. Results show that by refining the stripe widths in SFH from 15 mm to 1.5 mm, the deviation between the predicted and measured deflection reduces from 35.7 % to 1.19 %.

However, the required computational time increases from 9.3 h to 65 h.