3D printing performance requirements for metal powders
1. Purity
Ceramic inclusions will significantly reduce the performance of the final part, and these inclusions generally have a high melting point and are difficult to sinter, so there must be no ceramic inclusions in the powder. In addition, the oxygen and nitrogen content also needs to be strictly controlled .At present, the powder preparation technology for metal 3D printing is mainly based on the atomization method. The powder has a large specific surface area and is easy to oxidize. In special application fields such as aerospace, customers have stricter requirements for this index, such as superalloys. The oxygen content of powder is 0.006%-0.018%, the oxygen content of titanium alloy powder is 0.007%-0.013%, and the oxygen content of stainless steel powder is 0.010%-0.025%.
2. Powder fluidity and bulk density
Powder fluidity directly affects the uniformity of powder spreading during the printing process and the stability of the powder feeding process. The fluidity is related to the powder morphology, particle size distribution and bulk density. The smaller the proportion of fine powder, the better its fluidity; the particle density remains unchanged, the relative density increases, and the powder fluidity increases. In addition, the adsorption of water, gas, etc. on the particle surface will reduce the powder fluidity.
3. Powder particle size distribution
Different 3D printing equipment and forming processes have different requirements for powder particle size distribution. At present, the powder particle size range commonly used in metal 3D printing is 15-53μm (fine powder), 53-105μm (coarse powder). The choice of metal powder particle size for 3D printing is mainly According to the metal printers with different energy sources, the printers using laser as the energy source are suitable for using 15-53μm powder as consumables because of their fine focusing spot and easy to melt fine powder, and the powder supply method is layer-by-layer powder coating; For powder-spreading printers with electron beams as the energy source, the focusing spot is slightly thicker, which is more suitable for melting coarse powder, and it is suitable to use coarse powder of 53-105μm; for coaxial powder-feeding printers, the particle size of 105-150μm can be used powder as consumables.
4. Powder morphology
The powder morphology is closely related to the preparation method of the powder. Generally, when the metal gaseous or molten liquid is transformed into powder, the shape of the powder particles tends to be spherical. Most of the powders prepared by the method are dendritic. Generally speaking, the higher the sphericity, the better the fluidity of the powder particles. The 3D printing metal powder requires a sphericity of more than 98%, so that it is easier to spread and feed the powder during printing. .
