Metal powder left over from additive manufacturing is safely reusable if properly stored. By analysing the powder, it is possible to determine the quality and, if necessary, take measures to improve it. Reuse of metal powder is relevant not only for the purpose of cost reduction, but also for environmental reasons.
This reports UT PhD student Laura Cordova Gonzalez in her thesis, which she defended on 30 January. Various forms of additive manufacturing are available. For metal printing, many printers use selective laser melting. In this process, a laser melts the metal powder at specific spots, causing it to harden. By repeating this process, it is possible to build up an object layer by layer.
A lot of powder goes to waste
Only a small proportion of the metal powder that goes into the printer hardens during the printing process. Users remove the remaining powder from the printer after the printing process. However, too little was known about the quality of this powder for it to be safely reused. Therefore, in practice, much of the powder goes to waste.
Reuse of metal powder has therefore been too great a risk for many companies until now. "With most critical components, such as in the aerospace industry, it is important that the metal powders, and therefore the end products, maintain their quality and exhibit a high degree of repeatability," says Cordova Gonzalez.
No impact on mechanical properties
In her thesis, the PhD student describes a method to safely reuse metal powder for selective laser melting. In her research, Cordova Gonzales looked at about four metal powders commonly used in additive manufacturing. Each powder was found to exhibit different properties after being reused several times.
The PhD student explains, "After being reused four times, parts built with reused powder show more micropores than parts made from virgin powder. However, the altered structure (see Figure 1) had no effect on the mechanical properties under static loading."
Analysing powder
Cordova Gonzales recommends a new method for reusing and storing metal powder. Thus, she recommends analysing the powder both before its first use, after prolonged storage periods and between print cycles. How often the powder is best analysed depends on the required reliability of the final product.
Does the quality not appear to be up to scratch? Then manufacturers can increase the quality of the powder by sieving the material and removing large particles from the powder. It is also possible to increase the quality by mixing used powder with new, unused powder.
Author: Wouter Hoeffnagel
