3D printing, also known as additive manufacturing, refers to the creation of new parts or products layer by layer. After the solid material is crushed into fine spherical particles, it can be used as a powder raw material for 3D printing. Therefore, the materials used in 3D printing are often called spherical powders. They are usually made of metal, alloy, ceramic, or polymer. The powder materials used in the 3D printing process determine the properties of the final product. This article will take you through these powder materials used in 3D printing.
This guest commentary was written by Julissa Green of Stanford Advanced Materials.
The Importance of 3D Printing
Powder materials make 3D printing fast and allow for rapid prototyping. Manufacturers can also modify designs more efficiently.
This approach is also cost-effective, using only the required amount of material needed to manufacture the desired part; there is less misuse of material.
This approach makes it easy to design complex machine parts by simply importing design drawings into the additive manufacturing system.
How to Use Powder Materials in 3D Printing?
Initially, 3D printers used filaments as raw materials, but later spherical powders were used more widely. The smaller particles of the powder make it easier to transfer through the 3D printer, and the resulting product has a smoother surface. At present, the particle size categories of powder materials widely used in metal 3D printing are 15-53μm (fine powder), 53-105μm (coarse powder), and in some cases, 105-150μm (custom) [2].
In the process, we need to heat the powder to the point of easy distribution, and the roller puts a thin layer of powder on the platform for stacking. Instead of cutting the pattern with a laser beam, a special print head places adhesives at different specific points, tightly bonding the layers of powder together. This process is repeated until a complete model is obtained.
How to Produce 3D Printing Powder?
Today, the mainstream method of producing powder materials is atomization, including water atomization (WA), gas atomization (GA), electrode induction melting gas atomization (EIGA) and plasma atomization (PA). The following are the details of these methods.
Water Atomization (WA)
Water atomization is also known as steam atomization. It follows the steps below:
- Melt the solid raw alloy or metal material in a furnace.
- Maintain the high temperature for a period of time to ensure that the molten liquid is evenly distributed.
- Transfer the liquid to a crucible with a flow-controlled nozzle.
- Open the nozzle of the crucible and allow the liquid to enter the spray chamber in free fall.
- Cool, atomize, and consolidate the liquid by high-speed water jets.
- Collect powder at the bottom of the chamber.
- Dry the collected powder.
This method requires very simple production equipment and technology, and has become the most industrialized metal powder production method. However, the powder produced by water atomization is usually irregular and poor for 3D printing, so it is not often used.
Gas Atomization (GA)
Figure 1 shows the schematic of water atomization process and gas atomization. They are almost the same, except for the way they atomize the liquid (step 5 in the previous paragraph). The difference between the two is actually easy to distinguish from their names, that is, gas atomization uses high-flow gas (usually inert gas); while water atomization, as mentioned earlier, uses high-speed water jets.
In contrast, the powder produced by gas atomization is more suitable for 3D printing. The reason is that the specific heat capacity of gas is smaller than that of water, so it will take more time for the liquid droplets to cool and solidify. The result is that the powder will be more spherical.
The disadvantage of gas atomization is that it is difficult to control the diameter of the powder, which can vary from 0 to 500 μm. In addition, this method is prone to contamination during the transfer of the molten liquid from the furnace to the crucible or other steps, resulting in reduced powder purity.
Electrode Induction Melting Gas Atomization (EIGA)
Electrode induction melting gas atomization (EIGA) is developed on the basis of gas atomization. The difference is that instead of melting solid raw materials in a furnace, EIGA uses rotating metal rods as raw materials, which are melted by induction heating. Under the action of gravity, the molten rod can directly fall into the atomization chamber, which reduces the pollution during the experiment and can obtain a high-purity metal powder.
EIGA can produce powders with smaller particle sizes and higher purity, and has gradually become the main method for producing active alloy powders such as Ti-6Al-4V.
Plasma Atomization (PA)
Plasma atomization (PA) uses plasma as a heat source to melt the raw material (powder or wire). Figure 2 shows the schematic of the plasma atomization process.
1) Send the wire feedstock into the atomizing furnace through the wire feeding system.
2) Use the plasma torch heating device to melt and atomize the wire.
3) Obtain metal powder and dry it.
The above processes are all carried out under an inert gas atmosphere to isolate the interference of foreign impurities, thereby producing a purer powder. Moreover, by controlling the wire feeding rate, powder with a specific particle size distribution can be obtained, which improves the quality control of the powder.
The limitation of this method is that it is only suitable for alloys or other metal materials with good ductility, that is, they can be drawn into wires.
Figure 3 is a summary of these four atomization methods for manufacturing powder materials.
Types and Requirements for 3D Printing Metal Powders
As mentioned above, water atomization is not suitable for the production of 3D printing powder, because the particle size of the powder it produces is irregular. Powder materials must meet specific requirements and standards before they can be used for 3D printing.
Metal powders for 3D printing are required to meet the following properties:
- A standard high purity
- Good flowability
- Good sphericity
- Narrow particle size distribution
- High packing density
- Very low oxygen content
Find out more at sputtertargets.net.
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