Page 22 - 3D Metal Printing magazine Fall 2022

3D
FEATURE
Powder Uniformity
—Essential
to Quality
Part Builds
BY LOUIS A. KREN, SENIOR EDITOR
Get a glimpse into the importance of maintaining powder uniformity during builds, and how one powder producer is expanding to meet growing need for uniform powders.
“You don’t get pink Legos by mixing red and white Legos.” In discussing powder mixing for additive manufacturing (AM) appli- cations, Eric Bono, vice president of sales, powders at 6K, starts with that quote, which he borrowed from AM executive John Barnes. The Lego analogy has pow- erful resonance when considering how powders are formulated and, specifically, how compositions are mixed to bring bulk
chemistry back into spec.
In a recent video tutorial from 6K Addi-
tive, a division of 6K, Bono describes a common practice in 3D printing where companies employ a top-off strategy— filling the hopper with virgin powder as the existing powder routes to print. In the video, he cites use of a titanium alloy that must maintain less than 1300 ppm of oxy-
Remote monitoring allows safe and full control of microwave plasma powder production at 6K Additive, and forms part of the company’s full-automation push.
20 | 3D METAL PRINTING • FALL 2022
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gen. Titanium commonly accumulates unwanted oxygen during printing, Bono notes, leading to an out-of-spec condition after a few prints—“white Legos,” he terms the out-of-spec alloy containing, say, 1600 ppm of oxygen. Many users, Bono offers, will mix new fresh powder, the “red Legos” with 900 ppm of oxygen, for example, with the 1600-ppm-oxygen white Legos and then claim a blended oxygen level of 1100- ppm-oxygen Ti alloy, or the “pink Legos.”
The problem? Printed parts produced via this batch may contain pockets of very high or very low oxygen, with none of the batch measuring the claimed 1100 ppm of oxygen. The result: part failure and other adverse conditions.
To explore the video topic further, 3D Metal Printing dove into the details with Bono.
“Such mixing may occur before print- ing even begins, at the powder manufac- turer,” Bono explains, “with mixing of, say, 1600-ppm-oxygen and 800-ppm-oxy- gen powder batches to arrive at what the customer wants. But, controls and specs outlined beforehand can prohibit such mixing procedures.”
The challenge accelerates as heating during printing introduces more oxygen, while hopper refilling of pink Lego powder further upsets oxygen levels. Out-of-spec
parts result. One sometimes-employed attempt to correct: adding very-low-ppm oxygen to bring down oxygen levels. Here, the entire process becomes an unstable play-it-by-ear balancing act.
“With nonuniform distribution of high- oxygen-ppm Ti powder, certain part fea- tures with that high oxygen content will fail prematurely,” Bono explains.
Defining specs for powder delivery from the material producer will help, but diligence must be maintained within the AM facility. In some cases, to ensure that powder maintains needed specs, AM oper- ations only will use a single batch until it falls out of spec.
6K Expansion Underway
To gain more insight into powder mix- ing and the importance of uniformity, 3DMP recently attended a tour in Bur- gettstown, PA, where 6K Additive unveiled plans to double its powder-manufacturing capacity, including a facility-size increase of 35,000 sq. ft. and the adding of as many as 35 employees. 6K Additive offers what it describes as sustainable production of engineered materials for AM and lithium- ion batteries via its UniMelt plasma tech- nology, which employs plasma to produce uniformly spherical powders in needed formulations.