The internal residual stress generated inside 316L stainless steel parts formed using selective laser melting (SLM) is one of the key factors affecting the mechanical properties of fabricated components. At present, most studies primarily focus on reducing the residual stresses on the surface layer and improving the surface quality. Thus, the internal residual stress level remains high, leading to the fabrication of components with poor mechanical properties that may not meet the specified requirements. With the goal of investigating the reduction of the mechanical properties of components caused by internal residual stresses, the effects of remelting on the residual stresses were studied. An “interlayer laser remelting” forming method was proposed for components, and the effects of interlayer remelting on the internal residual stresses of components fabricated using SLM were studied in a targeted manner. In contrast to the traditional surface laser remelting, remelting was performed at intervals inside the components to eliminate any internal residual stresses and provide references for the optimization of the laser remelting process and improvement in the quality of the fabricated components.
The interlayer laser remelting forming method was proposed based on the effects of laser remelting on the residual stresses. The non-remelted layers were formed layer-by-layer using optimized process parameters, with the same process parameters used to form the remelted layers at intervals. The laser remelting was performed after the powder layer was initially pre-melted by laser scanning. This laser remelting operation was performed at evenly spaced layers until the printing of the component was completed. First, a three-dimensional transient simulation model of the forming process was established using Abaqus to simulate the variation law of the internal residual stresses of the components during remelting at intervals of 1‒10 layers, along with those of the non-remelted components. Then, the influence of the stress field corresponding to the number of remelted intervals was analyzed, and the accuracy of the simulation model was verified by comparing the simulation results with experimental results. The interval number for the layers was selected based on the simulation results. The “interlayer laser remelting” components were prepared using the same process parameters as the simulation. Then, mechanical properties tests of the interlayer laser remelted components were carried out to study the internal residual stresses, microstructure, surface morphology, tensile strength, impact toughness, and microhardness of components subjected to remelting at intervals of 2, 5, and 10 layers, along with non-remelted components.
The interlayer laser remelting method could significantly reduce the residual stress distribution in a formed part, which significantly improved its mechanical properties (Fig.2). The simulation results showed that the minimum residual stress occurred when using an interval of 2 layers. As the remelting interval increased, the heat accumulation decreased, and the internal residual stress of the formed part showed an increasing trend (Fig.8). The experimental results showed that the internal residual stress of the formed part was the highest, and the surface morphology and mechanical properties were poor, when non-remelting was performed (Fig.9). The tempering effect generated by interlayer laser remelting inside the remelted layer and its adjacent layer is conducive to reducing the residual stress in the formed part (Fig.13).The simulated residual stress of the formed part was reduced by 70.6% compared to the non-remelted specimen when the remelting interval was 2 layers. At the same time, the tensile strength of the formed part reached 702.99 MPa, which was 6.2% greater than that of the non-remelted part. The impact absorption work reached 209.5 J, which was 11.97% greater than that of the non-remelted part. The microhardness reached 391.8 HV, which was 6.35% greater than that of the non-remelted part. These research results will be valuable for adjusting the SLM remelting process and optimizing the mechanical properties of formed parts.
The effects of remelting on residual stresses were considered to address the problem of the reduction of the mechanical properties of components caused by internal residual stresses. The interlayer laser remelting forming method for components was proposed to verify the improvement of the internal residual stresses of components by interlayer remelting. A three-dimensional transient simulation model of the forming process was established using Abaqus to simulate the variation law of the internal residual stresses of components with remelting at intervals of 1‒10 layers, as well as those of non-remelted components. Stress and mechanical property analyses of components with typical interval layers were carried out based on the simulation results. The internal residual stresses of formed parts were reduced by adjusting the layer interval for remelting. The internal residual stresses, microstructure, surface morphology, tensile strength, impact toughness and microhardness of components subjected to remelting at intervals of 2, 5, and 10 layers, as well as of non-remelted components, were studied. After analyzing the influence law of the interval used for remelting on the internal residual stresses, the remelting process parameters were adjusted to reduce the internal residual stresses of the formed parts and improve their mechanical properties.
