Classification of Metal Powders for Additive Manufacturing (3D Printing)

The 3D printing market is currently experiencing a period of rapid growth. An increasing number of applications in the automotive industry, aircraft manufacturing, tooling and prototype production are based on additive manufacturing processes. 3D printing technology has made it possible to produce complex shapes with defined properties. Previously, producing such parts was either impossible or only possible by joining a few components together.

The advantages are clear:

• Components are lighter (weight savings of up to 80%). • Components are smaller. • Quality can be controlled and therefore fewer defective products are produced. • Components have enhanced properties due to being single-cavity and complex shapes can be produced. • Development times are much shorter because prototypes can be produced immediately after the design phase. During the printing process currently in use, a metal powder coating of 20-100 μm thickness is applied. A laser then melts the metal powders at the points where the part is to be produced, allowing the metal particles to bond together. Another powder coating is then applied and the process is repeated. This procedure is repeated until the part is finished. Production times range from 2 to 24 hours, which means that the use of this method in mass production is still limited. Metal powders used for high-quality applications in the field of "Additive Manufacturing" (AM and 3D printing) are produced by various methods such as gas, water or plasma atomization. Unfortunately, the precise and very narrow particle size distribution required for 3D printing cannot be achieved using this process method. For this reason, after the atomization process, the raw material must be classified to provide a narrow particle distribution in order to obtain a product that meets the specific requirements of the final application.

Particle size distribution of metal powders

SEM image of metal powders - fed product (left), separated fine product (center) and desired coarse product (right)

Netzsch Solution

To ensure that a good quality product is produced, it is important that the powder used has a narrow particle size range, typically around 20-60 μm. Thus, classification technology begins to play a decisive role, and this is where the Netzsch CFS/HD-S classifier series comes in. With this machine, we can achieve a sharp cut-off point during dedusting. We can demonstrate this to our customers during testing in our laboratories. Within the framework of this project developed for a company that leads the world market in metal powder production and performs technically demanding applications, the ability to transition quickly from one product to another due to having various stainless steel powders with different compositions is also a very important point. For this reason, easy accessibility to every corner of the classifier was another important criterion. The fact that the classifier used in classification facilities operates the air in a closed-loop system is of course a distinctive new innovative design, and this means that this very fine product can be almost completely separated via a cyclone! This system is possible due to the high density of the product. Thus, no filter is needed. As a result, after the product is changed and minimal cleaning is performed, the customer can collect each type of powder separately and use it for other applications. Using the Netzsch Classifier System CFS 170 HD-S, the separation of fine particles is significantly faster and operationally more reliable, so it can replace the customer's existing screening technology. Screening machines are forced to operate at the limits of their capacity in this fineness range. We can illustrate this with low efficiency and frequent clogging of screens. Error-free dedusting operations of over 100 kg and at the same time sustainable processes can be achieved with this system design. Furthermore, higher or lower capacities are also possible with the same system design and machines of different scales. As a result, users can always respond flexibly to their customers' demands.

The CFS/HD-S high-efficiency fine classifier with its specially designed hopper provides significantly increased capacity.

  Elif Uçak Arıkan Regional Sales Manager Netzsch Makine San. ve Tic. Ltd. Şti.