In most cases, you can recycle quite a bit of metal powder. How much depends on the chemical and physical properties of the powder.
In most AM powder systems, a fraction of the powder is actually used for the build. The rest remains in the build chamber and can be used in the next builds, and thus is recyclable. The main concern is how the AM equipment’s process in previous builds affects the chemistry and physical properties of the leftover powder.
One area to pay attention to is the powder near the edge of a weld pool. The powder granules can become fused together even though they are not directly a part of the build object. If used in the next build, these fused granules will affect the final part, potentially leading to internal gaps within the part. Unfused powder should go through a sieving process in the powder recycling system to remove these granules.
Vendors are testing the reusability of metal powder in their systems. So far the results indicate that, with an effective powder sieving and management system, powder can be reused. The powder does not undergo significant changes that would prevent reuse.
However, another factor to consider is the application for the part. For example, if you are building a part for the aerospace industry, then your process will need to prove the recycled powders’ traceability, predictability and repeatability.
A research paper on this topic was presented at AMUG 2016 by Lucy Grainger. For more details, view her slide share: Investigating the effects of multiple powder re-use cycles in AM.