Characterizing Powder Metal for 3D Printing: Particulate Contamination

1:08PM May 10, 2017
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This article is Part 2 of a series on Powdered Metal Manufacturing Characteristics for 3D Printing written by Stephen Kennedy, Ph.D. of RJ Lee Group.

Additive manufacturing, also known as 3D printing, is quickly becoming an industry standard for product manufacturing in a variety of applications, including medical devices, aviation and aeronautics parts, and transportation. The powdered metals (PM) used in these products have introduced a wide range of questions for experts, who must determine whether the materials are appropriate for a specific use in regards to durability and cleanliness.

There are many aspects of PM that determine its suitability for a product. For instance, the quality of powder metal is influenced by the number, size, and type of particulate contamination, which can result from the production process. The unused powder in 3D printing in each build cycle is recycled numerous times, creating the potential for environmental contamination from handling procedures, or from wear debris generated in the printer.

A full characterization of the particulate allows assessment of contaminant sources, possibly leading to prevention or remediation actions. Finally, the absolute amount of contamination that can raise quality issues with the end product may be extremely small, requiring a high degree of sensitivity of the analytical procedure.

Contamination Assessment

To assess PM quality, a combination of contaminant concentration by heavy liquid separation (HLS) followed by particle characterization by computer controlled scanning electron microscopy (CCSEM) is performed. For example, in an analysis of samples consisting of virgin powder, and recycled powder after multiple build cycles, a total of 19 contaminant particle types were identified. The AlMgO ceramic, the aluminum metal, and the carbon-rich types, which were abundant, are illustrated in Figure 1.

Figure 1 – Backscattered electron image and EDS spectra of the AlMgO ceramic (left), the Al metal (center), and the carbon-rich matrix with enclosed particulate (right).

Figure 2 shows the results of evaluating virgin powder and powder recovered after multiple build cycles for contamination. The ceramic particle content decreases through the cycles, while the aluminum metal particle content increases from zero percent, possibly resulting from printer wear. The carbon-rich particles also increase, possibly resulting from poor powder handling procedures.

Powder metal CCSEM analysis — Figure 2 – The results of CCSEM analysis show that 19 particle types were observed in the powder (insert) with three types predominating.

Table 1 shows that the AlMgO ceramic particles and to a lesser extent the carbon-rich particles have nearly constant average and maximum particle size through the cycles. The average and maximum particle size of the aluminum metal show an increase through the cycles.

Table 1 – The average and maximum diameters (μm) through the build cycles for the three major types of contaminants observed.

The experts at RJ Lee Group can work with your team to answer questions and find solutions for your powder metal manufacturing facility. Call us today at 1.800.860.1775, ext. 4, then 2, then 1, or click on the button below to learn more.