Temperature Field Investigation Of Selective Laser Meltigng Considering Size Edge Effect And Investigation Of Melt Pool Flow Field

Selective laser melting is widely used in aviation,aerospace,ships,medical equipment and other fields due to its characteristics of small batch,fast production,no limitation of complex structure,great precision and strength.At the same time,the defects are difficult to predict for the selective laser melting part,especially the defects crack,pore,balling effect caused by uneven temperature distribution and large temperature gradient will seriously influence the quality and mechanical properties of the printed parts.Optimizing the temperature distribution of selective laser melting scanning process according to the process parameters considering the edge effect is one of the main research orientations faced by selective laser melting technology.In this paper,Ti-6Al-4V metal is taken as the research object by means of analytical calculation,and the powder bed is regarded as a continuous entity.Firstly,the two semi-infinite laser selective melting single track scanning temperature prediction models based on the solution of continuous moving Gaussian surface heat source and instantaneous Gaussian surface heat source calculated by using Green's function method are established.Meanwhile,the instantaneous Gaussian surface heat source is used to establish the selective laser melting temperature prediction model with arbitrary path in semi-infinite large domain.The continuous moving Gaussian surface heat source is utilized to established the multiple lines scanning temperature prediction modeling.Due to the formation of edge defects,the linear multi-tracks and arbitrary path laser selective melting temperature prediction model considering edge defects was established based on the mirror method.And the relationship between the process parameters and the temperature field,the sizes of the molt pool in the laser selective melting process was researched.The sizes of the melt pool for analytical modeling are agreement with the experimental results.It can be found that the sizes of melt pool increase at the edge of the forming part when the edge effect is considered,and the temperature field near the melt pool increases as a whole,while the temperature gradient decreases.It also explains that the phenomenon of high ridge or even balling effect at the edge of the forming part is caused by the heat concentration at the edge of the forming part.In this study,in order to investigation the melt pool flow effects on the temperature distribution and melt pool sizes,the finite element simulation software COMSOL Multiphysics were used to establish the finite element model of laser selective melting temperature and flow field prediction.And the simulation results were verified by laser selective melting experiment.The results show that when the laser energy density is below 65J/mm~3,the flow of the melt pool has little effect on the size and shape of the melt pool.When the laser energy density is above 65J/mm~3,the flow of the melt pool increases the width of the melt pool,but make a little effect on the depth.At the same time,the maximum temperature in the melt pool decreases as well as the temperature gradient in the center of the melt pool.And in the multi-tracks scanning considering melt pool flow,the research indicated that melt pool width and elongated gradually with the completion of each scan.When the laser scanning closed to the edge of part,melt pool flow velocity will reduce under the influence of edge effect,and will be in a steady dynamic range because of no effect by the edge of the part.