Page 13 - 3D Metal Printing Winter 2019
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 bulk powder such as powder-size distri- bution, packing density, etc. However, no standard practices are identified for this method. Each service provider uses experience to develop best practices, which typically vary based on material used and type of build geometry.
Another plausible reconditioning technique: using an induction-plasma process, which consists of in-flight heat- ing and melting of feedstock, followed by solidification under controlled condi- tions. This method can improve powder characteristics such as flow and packing density by producing spherical particles (Fig. 2; decreasing porosity by remelting and resolidifying the powder particles; increasing powder density; and improv- ing powder purity through the selective/ reactive vaporization of impurities by increasing the plasma melting tempera- ture and modifying the shielded gas.
EWI has performed some early studies using this method but further testing must be performed to evaluate viability for bulk-powder reconditioning.
Develop Guidelines
Third challenge: Develop industry guidelines for improved traceability.
A lot of work remains when it comes to powder-reconditioning techniques. For example, while powder blending reduces the overall oxygen content of the bulk-powder lot, the powder batch still can contain particles with high oxy- gen content. If these particles end up in the final part, catastrophic part failure may occur. Several studies have shown that in Ti-6Al-4V powders, higher oxy- gen content leads to reduction in the ultimate tensile strength of the final components.
Currently, companies tend to use vir-
gin powders for critical AM builds to maintain consistency in manufactured- part properties and minimize risk. This practice has produced thousands of pounds of out-of-spec powder, either stored or wasted. As AM production and powder consumption increase, so, too, will concern about powder traceability. This will result in higher costs and larger energy footprints associated with AM processes.
To keep AM materials affordable as the technology expands, the need to develop qualified methods to not only recondition powders, but also to requal- ify and bring them back into produc- tion, is paramount. EWI is working toward development of some of these guidelines through its Additive Manu- facturing Consortium as well as through the ASTM AM Center of Excellence. Stay tuned. 3DMP
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