The 3D printing revolution that has upended modern manufacturing
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Update time : 2019-08-07 11:39:26
Compared with traditional material reduction manufacturing methods, 3D printing hardly causes waste of metal materials, and the direct forming characteristics of this material addition manufacturing make the equipment problems in the production process greatly reduced. Metal powder material is the raw material of metal 3D printing. Its basic properties have a great relationship with the final product quality. The requirements of metal 3D printing for powder are mainly in chemical composition, particle shape, particle size, particle size distribution, fluidity, recycling and so on. chemical composition
The main chemical components of raw materials include metal elements and impurities. The main metal elements commonly used are Fe, Ti, N, A, Cu, Co, Cr and precious metals Ag, Au, etc. Impurities include Si, Mn, C, S, P, O in reduced iron, other impurities mixed from raw materials and powder production, water and other gases adsorbed on the surface of powder, etc.
During the forming process, impurities may react with the matrix, change the properties of the matrix, and bring negative effects on product quality. The existence of dopants can also make the powders melt unevenly and easily cause internal defects of the products. When the oxygen content of powders is high, metal powders are not only easy to oxidize and form oxide film, but also cause spheroidization, which affects the density and quality of products.
Therefore, it is necessary to strictly control the impurities and doping of raw material powders to ensure the quality of products. Therefore, metal powders for 3D printing need to use metal powders with high purity. Particle Shape, Particle Size and Particle Size Distribution
1.Shape requirements. The common shapes of particles are spherical, subspherical, flaky, needle and other irregular shapes. Irregular particles have larger surface area, which is conducive to increasing sintering drive. But the powder with high sphericity has good fluidity and uniform powder feeding, which is conducive to improving the density and uniformity of the product. Therefore, powder particles for 3D printing are generally required to be spherical or near-spherical.
2.Particle size and particle size distribution of powders. The results show that the powders are melted and sintered by directly absorbing the energy of laser or electron East scanning. The smaller the particle size, the larger the surface area, the more the energy is absorbed directly, and the higher the temperature is, the more conducive to sintering. In addition, the powder size is small, the gap between particles is small, the loose density is high, and the density of parts after forming is high, which is conducive to improving the strength and surface quality of products. However, when the particle size is too small, the powder tends to adhere and agglomerate, which leads to the decrease of powder fluidity and affects the transportation and uniformity of powder.
Therefore, fine powder and coarse powder should be mixed in a certain proportion, and appropriate particle size and particle size distribution should be selected to achieve the desired forming effect. Processing Performance Requirements of Powder
The technological properties of powders include bulk density, compacting density, fluidity and recycling performance.
1. Loose packing density is the density of powder when it is naturally accumulated. Vibrating density is the density after vibration. The powder with good sphericity and wide particle size distribution has high bulk density and low porosity, and the parts after forming have high density and good forming quality.
2. Liquidity. The fluidity of powder directly affects the uniformity of powder spreading or the stability of powder feeding. The poor fluidity of powder easily results in the uneven thickness of powder layer and the uneven melting amount of metal in the scanning area, which results in the uneven internal structure of products and affects the forming quality. The powder with high fluidity is easy to fluidize, deposit uniformly, and the powder utilization rate is high, which is conducive to improving the dimensional accuracy and surface uniformity and compactness of 3D printing parts.
3. Cyclic performance. After the 3D printing process, the unmelted powder remained in the powder bed can be recovered through screening and still be used. However, under long-term high temperature environment, the powder in the powder bed will have certain performance changes.
