3D printing - metal powder

3D metal printing powder

Metal powder materials for 3D printing include stainless steel, die steel, nickel alloy, titanium alloy, cobalt-chromium alloy, aluminum alloy and bronze alloy.  Iron base alloy is the most important and largest metal material in engineering technology. It is widely used in the forming of complex structures and is widely used in aerospace, automobile, shipbuilding, machinery manufacturing and other industries.  

Titanium alloys have excellent strength and toughness, combined with corrosion resistance, low specific gravity and biocompatibility, making them ideal for many high-performance engineering applications in aerospace and automotive racing, as well as for the production of biomedical implants with high strength, low modulus and high fatigue resistance.  

Aluminum alloy is one of the most widely used non-ferrous metal structural materials in industry, its low density, high specific strength, close to or more than high quality steel, good plasticity.  Research shows that aluminum alloy used for 3D printing can achieve compact parts, small structure, mechanical properties comparable to casting or even better than casting molding parts, and compared with traditional process parts, the mass can be reduced by 22%, but the cost can be reduced by 30%.  

Copper alloys have excellent thermal conductivity and electrical conductivity. Copper with excellent thermal conductivity in thermal management applications can combine design degrees of freedom to produce complex internal structures and conformal cooling channels.  

The manufacturing process of 3d printer powder

1. Argon atomization method  

Argon atomization powder production is a method of pulverizing metal liquid by impinging it with fast flowing argon gas, breaking it into fine particles, and then condensing it into solid powder.  

2. Plasma rotating electrode method  

The plasma state is called the fourth state of matter, and the powder preparation process by plasma rotating electrode atomization (PREP method) can be simply described as:  The metal or alloy is made into a consumable electrode, and the consumable electrode extreme part is melted to form a liquid film under the action of coaxial plasma arc heating source. The liquid film is thrown out at high speed under the action of rotating centrifugal force to form droplets, and the molten droplets friction with the inert gas (argon or helium) in the atomization chamber, and further broken under the action of shear stress.  Then the droplets are cooled and solidified into spherical powder under the action of surface tension.  

Performance requirements of METAL powder for 3d printer powder

We have just mentioned a lot of metal powders that can be used for 3D printing, so what conditions do metal powders need to meet in order to meet the requirements of 3D printing materials?

1. Purity  

Ceramic inclusions will significantly reduce the performance of the final product, and these inclusions generally have a high melting point and are difficult to be sintered, so no ceramic inclusions must be in the powder.  

In addition, oxygen and nitrogen content also need to be strictly controlled.  At present, powder preparation technology for metal 3D printing is mainly based on atomization. Powder has a large specific surface area and is easy to be oxidized. In special application fields such as aerospace, customers have more stringent requirements on this index, such as oxygen content of superalloy powder is 0.006%-0.018%, titanium alloy powder is 0.007%-0.013%.  The oxygen content of stainless steel powder is 0.010%-0.025%.  

2. Powder fluidity and loose density  

The fluidity of powder directly affects the uniformity of powder spreading and the stability of powder feeding.  

The fluidity is related to powder morphology, particle size distribution and bulk density. The larger the powder particles are, the more regular the particle shape is, and the smaller the proportion of very fine powder in particle size composition is, the better the fluidity is.  The fluidity of powder increases with the increase of relative density and particle density.  In addition, the adsorption of water and gas on the particle surface reduces the fluidity of powder.  

3. Powder particle size distribution  

Different 3D printing equipment and forming process have different requirements for powder particle size distribution.  Currently, the commonly used particle size range for metal 3D printing is 15-53μm (fine powder) and 53-105μm (coarse powder).  

The selection of metal powder size for 3D printing is mainly divided according to metal printers with different energy sources. Printers with laser as energy source are suitable for using 15-53μm powder as consumables because of its fine focal spot and easy to melt fine powder. Powder replenisher is layer-by - layer powder.  The powder-laying printer with electron beam as energy source has a slightly coarse focal spot, which is more suitable for melting coarse powder. It is mainly suitable for using 53-105μm coarse powder.  For coaxial powder feeder printers, powder with particle size of 105-150μm can be used as consumables.  

4. Powder morphology  

The morphology of powder is closely related to the preparation method of powder.  Generally, when metal gas or molten liquid is transformed into powder, the shape of powder particles tends to be spherical, and when metal solid is transformed into powder, the powder particles are mostly irregular shape, and most of the powder prepared by aqueous solution electrolysis is dendritic.  

In general, the higher the sphericity, the better the fluidity of powder particles.  The sphericity of metal powder for 3D printing is required to be above 98%, so that it is easier to lay and feed powder during printing.