Today, speaking of 3D printing, we have already introduced many applications of 3D printing, such as printing houses, Bridges, and so on. Today, we will talk about a relevant material used in 3D printing -- metal powder.
Titanium alloy, aluminum alloy, stainless steel, can be used for 3D printing
Metal powder materials printing consumables widely used in 3D printing mainly include four types in the form: liquid photosensitive resin materials, thin materials, low melting point silk materials, and powder materials. In terms of composition, it almost covers all kinds of stuff in current production and life, including polymer materials such as plastic, resin, wax, metal and alloy materials, ceramic materials, and so on. Among them, cutting edge and the most potential is the metal powder 3 d printing, according to consultancy SmarTech predicts that by 2024 the world used in metal powder material made in increasing the size of the market will reach $11 billion.
Currently, 3d-printed metal powder materials include stainless steel, die steel, nickel alloy, titanium alloy, cobalt-chromium alloy, aluminum alloy and bronze alloy.
Iron base alloy is one of the most important. The dosage of the most significant engineering metal materials, for the formation of a more complex structure, such as 3 d printing stainless steel, compared with the traditional casting forging technology, it has high strength, excellent resistance to high temperature, wear resistance, corrosion resistance, and other physical, chemical and mechanical properties, and has high dimensional precision and material utilization. In the aerospace, automotive, shipbuilding, machinery manufacturing, and other industries are widely used.
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. They are also used in the production of biomedical implants with high strength, low modulus, and high fatigue resistance.
Cobalt-chromium alloys are commonly used in surgical implants such as alloying artificial joints, knees, and hips, as well as in engine components, wind turbines, and many other industrial components due to their high wear resistance, excellent biocompatibility and nickel-free (nickel content <0.1%).
Aluminum alloy is one of the most widely used nonferrous metal structural materials in the industry. The research shows that the aluminum alloy used in 3D printing can make the parts compact and small in structure, and its mechanical properties are comparable to or even better than casting parts. Its quality can be reduced by 22% compared with traditional process parts, 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 flexible cooling channels.
How is the metal powder for 3D printing made?
The preparation methods of metal powder can be divided into a reduction method, electrolysis method, grinding method, atomization method, etc. At present, argon atomization and rotating plasma electrode are the two most advanced powder making processes in China.
1. Argon atomization
Argon atomization powder is a powder making method that the metal liquid is crushed into fine particles by the rapid flow of argon gas and then condensed into solid powder.
2. Plasma rotating electrode method
The fourth state plasma is known as the material and plasma rotating electrode atomization method (PREP) milling process can be described as follows: the metal or droplet atomized indoor inert gas (argon or helium) friction, further broken under the alloy consumable electrode, the power consumption of extreme in coaxial plasma arc heat source melt formed under the action of liquid membrane, liquid membrane under the effect of rotating centrifugal force formed by high-speed throw droplets, molten action of a shear stress, then drop under the effect of surface tension, fast cooling solidification into spherical powder.
The metal powder produced by the plasma rotating electrode method has the following advantages:
(1) High sphericity, smooth surface, good fluidity, steep loose packing density, so
(2) Powder size is small, particle size distribution is narrow, the oxygen content
is low, printing less/no spherification and agglomeration phenomenon, melting effect
is good, product surface finish is high, and the consistency and uniformity of printing can be fully guaranteed;
(3) There are no hollow powders and satellite powders, and there are no air gap, trainability, and exhalation porosity, cracks, and other defects caused by hollow spheres in the printing process.
What are the requirements of 3D printing on the properties of
We've just mentioned several metal powders that can be used in 3D printing, so what does a metal powder need to satisfy to meet the material requirements of 3D printing?
Ceramic inclusions will significantly reduce the performance of the final product, and these inclusions generally have a high melting point, it is difficult to sintering, so there must be no ceramic inclusions in the powder.
Besides, oxygen and nitrogen content also need to be strictly controlled.
Currently used in metal powder preparation technology of 3 d printing mainly atomization method, powder has a large specific surface area, natural oxidation, in particular applications, such as aerospace customer index requirements more stringent, such as oxygen levels in the high-temperature alloy powder is 0.006% - 0.018%, oxygen content of titanium alloy powder was 0.007% - 0.013%, stainless steel powder oxygen content of 0.010% to 0.025%.
2. Distribution of powder size
Different 3D printing equipment and forming process have different requirements on powder size distribution. At present, the commonly used powder size range of metal 3D printing is 15-53 cm (fine powder) and 53-105 cm (coarse powder), which can be extended to 105-150 cm (coarse powder) in some cases.
The selection of metal powder particle size for 3D printing is mainly divided according to the metal printers with different energy sources. The printer with laser as the energy source is suitable for using 15-53 m powder as the consumable material because of its beautiful focusing spot and easy melting of fine powder. With electron beam as the energy source, the duster printer has a slightly thick focusing place,which is more suitable for melting duster and is mainly suitable for using duster of 53-105 m. For coaxial powder feeder printers, powder with a particle size of 105-150 m can be used as consumables.
3. Morphology of powder
The morphology of the powder is closely related to the preparation method of the dust. Generally, when the metal gas or molten liquid is transformed into the earth, the shape of powder particles tends to be spherical. When the solid is converted into the soil, the powder particles are mostly of irregular shape, while the powder prepared by aqueous solution electrolysis is mostly dendritic.
In general, the higher the sphericity, the better the fluidity of the powder particles. The sphericity of 3D printed metal powder is required to be more than 98%, which makes it easier to lay and send powder for printing.
The table above shows the morphology of metal powders corresponding to different powder preparation methods. It can be seen that, except for aerosol and rotating electrode methods, the morphology of powders prepared by other means is non-spherical. Therefore, aerosol and rotating electrode methods are the primary preparation methods of high-quality 3D printing metal powders.
4. Powder fluidity and loose packing density
The powder fluidity directly affects the uniformity of powder spreading and the stability of powder feeding in the printing process.
The fluidity is related to the powder morphology, particle size distribution, and loose packing density. The larger the powder particle is, the more regular the particle shape is, and the smaller the proportion of fine powder in the particle size composition is, the better the fluidity is. The particle density remained unchanged, the relative density increased, and the powder fluidity increased. Besides, the adsorption of water and gas on the surface of particles will reduce the fluidity of the powder.
Apparent density powder sample is naturally full of container, unit volume of powder quality, in general, the more coarse powder particle size, the larger the apparent density, thickness of collocation powder can obtain higher apparent density, visible density effects on metal printing density of the final product is uncertain, but apparent density increased, can improve the liquidity of powder.
For the past few years, China has actively explored 3 d printing metal powder preparation technology and has many advanced milling equipment applications. But, in general, there is still a gap between pulverizing technology at home and abroad. The current high-end alloy powder and the manufacturing equipment is still mainly relied on imports, in promoting the local 3 d printing with metal powder preparation technology on the development of China is still a long way to go.