A Luleå Study Explains Why Powder Color Matters in Metal 3D Printing

Professor Alexander Kaplan at Luleå University of Technology has spent more than 20 years studying how lasers interact with metal. His latest paper, co-authored with former doctoral student Aylin Khajepour, looks at something most slicer profiles ignore: the actual absorbance of the powder itself.

The missing variable in energy calculations

In laser powder-bed fusion, operators calculate energy density from laser power, scan speed, hatch spacing, and layer thickness. Those numbers matter, but they assume the powder bed absorbs a fixed amount of energy. That assumption is wrong.

Kaplan's team measured absorbance across 39 powder samples from 16 materials, including steels, titanium, aluminum alloys, Inconel 718, brass, copper, and a high-entropy alloy. They tested new and used powder, different particle sizes, oxidized stock, and mixtures. The results show absorbance shifting enough that two machines running the same parameters on different powders can deliver very different energy to the melt pool.

Why this matters for production

Kaplan estimates that 30 to 70 percent of laser power can be lost to reflection in poorly matched conditions. That is a huge range. If your powder sits at the wrong end of it, you are either under-melting or overheating the part, both of which hurt density and surface finish.

The study also shows that recycled powder does not behave like virgin powder. Oxide layers, satellite particles, and changed particle size distributions all shift absorbance. Machines that automatically adjust parameters for reused powder could see real yield improvements.

What comes next

The paper does not offer a plug-and-play absorbance table for slicers yet, but it gives material scientists a clearer map of where to look. The next step is building those numbers into process monitoring so the machine can compensate in real time instead of relying on static profiles.

For now, the lesson is simple: energy density is only half the story. The other half is what the powder actually does with that energy.