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A 3D thermo-mechanical finite element model was developed to study the effect of the laser jump speed on the temperature distribution and thermal stress in laser powder bed fusion (LPBF) of Ti6Al4V alloy. Gradient grid and gradient time step were used to further improve solution efficiency. It was found that the temperature of the scanned region rapidly increased as the laser jump speed increased from 100 mm/s to 1000 mm/s. The temperature distribution reached a stable state when the laser jump speed was above 5000 mm/s. The pre-heat peak, the heat peak and the post-heat peak increased with the laser jump speed. The effect of the laser jump speed on the post-heat peak was greater than the pre-heat peak. Compared with the long scan track, the thermal stress distribution varies more sharply with the laser jump speed when using the short scan track. The influence of the laser jump speed on the stress perpendicular to the scan direction was greater than that along the scan direction, whether in a short scan track or in a long scan track. To reduce the residual stress, the length of the scan track should be reduced while the laser jump speed should be increased as much as possible to make the post-heat peak close to the fusion temperature of the material. The simulated results were well validated by the experimental data. The findings of this research help to reduce the thermal stress in laser powder bed fusion.

Rescanning has been introduced as a new method to improve the performance of selective laser melting (SLM) in recent years. However, many of the related works were done on the investigating of the rescanning parameters and only one rescanning cycle was used. In this work, the influences of rescanning cycle on the relative density, microstructure, residual stress and mechanical properties of SLMed Ti6Al4V alloy were investigated. The results show that as the rescanning cycles increase from 0 to 4, the relative density and residual stress of the samples increase at first and then decrease, the highest relative density and residual stress are found when the number of rescanning cycle is one. The number of rescanning cycle has little effect on the microstructure. The microstructures all consist of the martensitic α′ laths which grow inside the columnar prior β grains. The ultimate tensile strength (UTS), yield strength, micro-hardness and micro-strain of the samples all increase as the rescanning cycles increase from 0 to 3, but decrease when the samples are rescanned fourth times. This research provides an insight in the influence of rescanning cycles on characteristics of SLM process and can be used to optimize the process parameters of SLM.