During laser powder bed fusion (PBF), the complex thermal cycles and intensive heat accumulation may lead to serious residual stress and deformation, which have a great impact on the forming accuracy of parts. For parts with characteristic structures such as thin-walled structures and cantilever beams, various scanning strategies can cause different residual stresses and deformations. Thus, it is important to study the influence of printing parameters on the characteristic structures to improve forming accuracy. Numerical simulation can be used to well predict the residual stress and deformation of characteristic structures in order to enhance the data integrity and further avoid the deficiencies of experimental measurements. However, it is difficult to simulate the residual stress and deformation of large-scale structures by using the thermal-elastic-plastic model due to the high computational cost. In this work, the inherent strain method is adopted to achieve a fast and accurate prediction of residual stress and deformation, which is based on the improved intrinsic strain theory for different characteristic structures under four scanning strategies.

In order to achieve an efficient and accurate prediction of residual stress and deformation of characteristic structures, the modified inherent strain method is used for simulation. The thermal-elastic-plastic model is first established using the ABAQUS software to simulate the temperature and stress fields during the two-layer laser PBF of Ti-6Al-4V for the 0° line scanning strategy. Subsequently, the elastic and plastic strain vectors of multiple points along the scanning path are extracted. The inherent strain vector of each point and the averaged inherent strain vector for the 0° line scanning strategy are finally calculated. The inherent strain vector for the scanning strategy along the 0° direction without rotation between layers is obtained via averaging the inherent strain vector of each point. Moreover, the inherent strain vector for the 90° rotation scanning strategy is obtained via averaging the inherent strain vectors in the x and y directions. The finite element model for the characteristic structures is established using the approach of equivalent layer containing several individual layers. The direction of the inherent strain vector is updated to realize the simulations along different scanning directions via changing the allocation of material properties. The simulation of residual stress and deformation for the whole structure is completed via taking the inherent strain as the thermal expansion coefficient and sequentially activating the equivalent layer with the increase of temperature.

The modified inherent strain model is successfully used to predict the residual stress and deformation of characteristic structures during laser PBF. It is found that the crossed thin wall has concave shrinkage along the length direction (Fig. 8), and the deformation is asymmetrical along the height direction (Fig. 11) due to the asymmetric constraint during printing. The unsupported cantilever beam has serious warpage deformation and the deformation rate approaches 50% during the printing process (Fig. 13). The warpage deformation rate of the supported cantilever beam after cutting is reduced to 6.7% (Fig. 15). For the suspended circular hole structure, the vertical tensile stress on the outside of the structure increases with the increase of printing height (Fig. 19). After cutting from the substrate, the tensile stress along the z-direction on the outside of the free edge is obviously reduced and the warpage deformation occurs at the free edge (Fig. 20). The minimum deformation occurs in the scanning direction along the short side, which results from the corresponding shortest scanning vector length and deformation.

The finite element model based on the inherent strain method is developed for the fast and accurate prediction of residual stress and deformation of characteristic structures under typical scanning strategies for laser PBF of Ti-6Al-4V. The crossed thin wall has shrinkage deformation along the length direction, and the deformation first increases and then decreases along the height direction as the consequence of asymmetric constraints during the printing process. The warpage deformation of the overhanging part is reduced after cutting from the substrate compared with that of the cantilever beam without support. For the suspended circular hole structure, the vertical tensile stress occurs on the outside of the structure due to the restraint of the substrate. After one side from the substrate is cut, the free edge shows the warping deformation. The reason is that the residual stress along the z-direction on the outside of the suspended circular hole structure is released and the warpage deformation of the free edge occurs. It is found that the thin-walled structure, cantilever beam, and suspended circular hole structure show the same deformation trend for different scanning strategies. The results obtained from this research can provide valuable support for the printing of low stress and high precision additive manufacturing parts.