| Electron-beam additive manufacturing(EBAM),as an advanced additive manufacturing technology,has received more and more attention in recent years.It can not only prepare complex parts,but also has the characteristics of production efficiency,high energy utilization,and vacuum processing.During EBAM,high temperature gradients created by rapid heating and cooling and then lead to stress and strain,which has a serious impact on the accuracy and performance of the parts.The temperature and stress evolutions of complex porous structures are more complicated.Therefore,in order to improve the performance of the parts,it is essential for studying the evolution of the temperature field and stress field during manufacturing porous materials by EBAM.In this paper,the temperature and stress fields of porous Ti-6Al-4V meshes were studied by the finite element analysis software ABAQUS.Firstly,the effects of interlayer cooling and powder preheating temperature on the temperature field and stress field are studied.The results show that in the finite element analysis of the additive manufacturing process,the temperature and stress changes with the interlayer cooling time of 1s and the actual interlayer cooling time(7s)are basically the same.Therefore,the cooling time between layers can be reduced from 7s to 1s,thus saving a lot of computing resources.The effect of the preheating temperature on the residual stress of the porous mesh is similar to the bulk material.When the preheating temperature is within the range of 650 °C to 800 °C,the residual stress of the porous mesh material decreases about 20% for every 50 °C increase in the preheating temperature.The influence of scanning strategy on the variation law of stress and temperature in rhombic dodecahedron Ti-6Al-4V alloy fabricated by EBAM includes different printing paths,different scanning layers in the same printing path,different forming positions and prisms in different positions.The temperature and stress changes corresponding to different printing paths on the same prism are different,and the stress change process can be divided into three stages.The temperature changes of different scanning layers in the same printing path are basically the same.When the interlayer cooling is not considered,the stress changes under the same scanning strategy are not the same due to the continuous accumulation of heat in the scanned position.In different forming regions,when considering interlayer cooling,the residual stress at point B1 where the post-scan layer is the intersection of four prisms is the smallest.When interlayer cooling is not considered,the effect of heat accumulation on residual stress is more obvious than stress release.Along the path of the prism,the residual stress does not gradually decrease with the increase of powder layers,but fluctuates continuously.The equivalent stress distribution of the whole rhombic dodecahedron porous material is relatively uniform,and the outer edge stress of the prism is higher.The fatigue analysis of Ti-6Al-4V porous samples with different roughness prepared by EBAM was studied by ABAQUS and Fe-safe.The error between the calculation and the experiment of fatigue life octahedral porous Ti-6Al-4V samples with different roughness is small,and the same calculation method can be used to calculate the fatigue life of rhombic dodecahedral porous material.Roughness will significantly affect the fatigue life of porous materials.After chemical polishing,the roughness and prism size of octahedral porous samples will be significantly reduced,but the impact of prism size is more obvious,resulting in a decrease in the fatigue life of octahedral porous materials after chemical polishing.The rhombic dodecahedral porous material is just the opposite of the octahedral porous material,the roughness of the rhombic dodecahedron porous structure has a greater effect on the fatigue life than the prism size,and the fatigue life is significantly increased after chemical polishing. |
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