Cold Spray Additive Manufacturing (CSAM) Powder Recycling and Reuse

Project Challenges

During the deposition process, not all particles adhere to the substrate—some are successfully deposited, while others miss or are deflected. Softer materials such as copper and aluminium tend to perform more efficiently because they are easier to deform, whereas harder materials like steels and nickels can see deposition rates drop to as low as 50%, or even 10%, particularly when using low-pressure air systems such as xSPEE3D*. This inefficiency becomes costly when powders can reach prices of up to £200 per kilogram, making significant losses in unused powder a major concern.

Further analysis revealed notable changes in the characteristics of waste powder compared to virgin powder. The waste stream contained a higher proportion of coarse and smooth non-spherical particles, often formed through deformation during impact without adhesion, resulting in distinctive pancake-shaped particles. Additionally, deflected particles, broken deposits, and other contaminants introduced during extraction contribute to waste powder contamination. Interestingly, an increase in hardness was observed in some particles due to work hardening effects caused by deflection, highlighting the complex interplay between material properties and deposition efficiency.

MTC's Solution

To ensure the powder met the required particle size distribution (PSD) for Cold Spray Additive Manufacturing (CSAM) on the xSPEE3D system, a sieving step was carried out using an AS200 Tap and a RETSCH 75 µm mesh. This process effectively removed large contaminants and maintained the powder within specification, with only 10 grams of waste lost during the sieving stage. As previously noted, blending techniques were employed to restore flowability in the reclaimed powder.

Initial trials using a blend of 75% waste powder and 25% “old” powder failed to achieve adequate flow. However, a 50:50 blend ratio proved successful, enabling consistent flow and allowing parts to be printed. This approach provided the opportunity to evaluate both mechanical and metallurgical properties of the printed components, demonstrating the viability of reusing waste powder through controlled blending.

The Outcome

It was demonstrated that copper deposition using a 50% waste and 50% ambient-exposed powder blend is achievable; however, the process exhibited significant inconsistencies during the build. These inconsistencies stem from the varying proportions of work-hardened copper particles, which negatively impact deposition efficiency. While the CSAM process naturally introduces some variation in build profiles, incorporating recycled waste powder amplifies this effect, making the process less predictable.

Mechanical testing revealed that builds produced with the 50% waste powder blend had substantially poorer tensile properties compared to those made with virgin powder. Specifically, ductility dropped from 19% in virgin powder builds to just 4% in the waste blend, primarily due to pervasive coarse porosity. As a result, this method is only suitable for applications where geometry is the primary concern and not for components requiring critical mechanical performance. Further research is recommended into vacuum drying or conditioning techniques to remove excess moisture from processed powders, as this could improve flowability and enhance deposition efficiency.

Benefits to Industry

Being able to reduce waste is a critical step for any industry and client and finding ways to re-use old and waste powders where mechanical properties are not as critical is an immediate cost saving and sustainability improvement step forward.