Recycling of metal powder (sieving & blending)
How closed powder circuits and screening machines save the profitability of AM centers.
1. Introduction: The hidden gold in the machine
A Laser Powder Bed Fusion (PBF-LB) printer builds a component layer by layer. But at the end of printing, often only 5 to 20% of the powder volume used consists of the finished component. The rest of the construction space is filled with "unburned", loose powder.
In view of prices between 50 and over 500 euros per kilogram (e.g. for Inconel or Scalmalloy), throwing away the remaining powder is economically unencological madness. The safe and quality-preserving recycling of the powder (sieving & blending) is therefore one of the most important disciplines in additive manufacturing.
Why can't you just pour the powder back into the funnel?
During printing, tiny splashes fly through the chamber. These solidify in the air to form extremely hard, often oxidized and misshapen particles. If these splashes fall back into the remaining powder, they contaminate it. If you were to use them again in the next printing job, they would block the squeegee, cause pores or massively impair the material strength.
2. The sieving process
The first step in recycling is mechanical cleaning.
- Vibration and ultrasonic sieves: The loose powder is sieved (often under a strict protective gas atmosphere to keep oxygen and moisture away) through fine mesh nets (e.g. 63 µm for titanium). Oversized particles, spatters and clumped agglomerates get stuck in the sieve and are disposed of.
- Safety (HSE): Titanium and aluminum powders are highly flammable. In modern systems, the entire powder handling chain from the printer to the screen to the storage container is completely closed (closed loop) and kept under argon so that employees have no contact with the powder.
3. The aging of the powder
Even if spatters have been sieved out, the powder ages with each printing process (reuse cycles).
- Oxygen absorption: Every time they are heated and sieved, the surface of the powder grains absorbs minimal amounts of oxygen. With titanium, too much oxygen makes the printed component extremely brittle (embritment). Above a certain PPM value, the powder may no longer be used for flight-critical components.
- Morphology change: Due to the heat in the chamber, the perfectly round powder grains can "bake" together (satellite formation). This causes the powder to lose its flowability and makes it harder to squeegee.
4. Blending: The perfect mix
In order to keep the powder quality stable over the years, industrial companies use huge mixers.
The sifted "used powder" is mixed with a defined amount of fresh "virgin powder" (new powder). This mix refreshes the particle size distribution and chemical composition. In addition, the hours of “tumbling” in the blender ensure that each batch behaves 100% homogeneously. Before use, a sample is taken and certified in the laboratory.
5. Conclusion: circular economy as a cost driver
The profitability of a 3D printing center depends on the quality of its powder management. Anyone who has mastered the screening and mixing process can reuse their expensive titanium or Inconel powder dozens of times (recycling rates of over 95%) without compromising on the mechanical strength of the printed high-end components.