In a study recently published by a research group, using X-ray microcomputer tomography (CT), the porosity produced by Ti6Al4V powder bed melting-electron beam melting (PBF-EB) additive manufacturing was carried out a series of 30 times. Characterization of the build cycle (including approximately 480 hours of cumulative build time). Studies have shown that additively manufactured powders can be reused up to 30 times without a significant increase in porosity.
In the pursuit of the industrialization of metal additive manufacturing (AM), powder reuse has become a core issue. In addition, porosity is a key issue for the reliability of metal parts and the damage tolerance of metals. However, the contribution of powder reuse to metal porosity has received little attention.
The pores are derived from the pores of the gas atomized powder and the pores caused by the incomplete fusion of the molten pool. Although the pore size distribution decreases slightly with the repeated use of the powder, the overall average volume porosity is 0.10±0.02%, and with the increase in repeated use, the porosity does not change significantly.
In addition, the study also found that there is an inverse relationship between the aperture and the sphericity, and the large aperture constitutes a greater effective stress concentration. The largest pore density is located at the transition between the contour line and the melt beam. For parts near the surface of about 0.5-1.0mm, the largest pore density is located in the inner hatch area.
Therefore, although the particles gradually deform and the degree of oxidation increases, in the PBF-EB additive manufacturing of Ti6Al4V, with the repeated use of the powder, the metal porosity does not change significantly. Although the specific requirements for powder quality and porosity vary greatly according to specific applications, medical and aerospace applications often implement very strict regulations, but in fact, there are still not so many documents on the quality of powder after repeated use. , And generally believe that it cannot be remelted and reused many times, sometimes it seems very dogmatic, rather than based on proven facts.
As the additive manufacturing industry transitions to large-scale production, the repeated use of additive manufacturing powders, especially the high spherical powders required by the PBF process, will be one of the key factors in reducing the overall cost of parts.
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