Sample metal heat exchanger, additively manufactured (AM) by laser-sintering produced by Stratasys Direct Manufacturing services on an EOS DMLS system. Image courtesy Stratasys Direct Manufacturing.

Whether you’re new or experienced in powder-bed laser sintering of metals, you know that a basic operational mode for this form of 3D printing (additive manufacturing/AM) is to reuse most of the powder for the next build. But every time you 3D print with anything but 100% new material, in the back of your mind (or front), you’re wondering about the effects of building parts from a mix of new and used powder. What, if anything, changes from build to build, and how does this affect part performance?

To get real data (based on one material and one additive manufacturing system, for starters), engineers at Stratasys Direct Manufacturing did an in-depth, eight-month study that measured and evaluated a number of part properties. The results are really interesting and could pave the way to analyzing powder reuse for other materials and equipment.

All-New Powders Vs. Mixed New and Old Powders

Andrew Carter, process and manufacturing engineer at Stratasys Direct Manufacturing, Austin TX, says that educated users know AM processes generally involve reuse and blending of metal powders. “This is an efficient process if adopted,” explains Carter, “but users can be uncomfortable with how it’s done and how to be sure of results.” For example, he notes if 10% of the raw material is consumed by laser sintering a given part, what are the effects, if any, on the next part if it is built from a mix of 90% original (once-used powder) plus 10% new, replacement powder?

Looking at a different aspect of powder reuse, some people in the industry believe that raw powder simply degrades over time on its own. They will therefore stipulate an arbitrary age limit: for example, that you can’t build any parts with powder that is more than 90 days old. This begs a number of questions, says Carter. “When do you start counting? On the day the powder was made? The day you opened the container? The day you loaded it? Or the day you started using it?”

This situation can mean the difference between continuing a production run on an AM machine or throwing away $10,000 worth of unused material. Defining the parameters for an effective expiration date is becoming a critical need both for achieving process repeatability and avoiding unnecessary waste.