Page 32 - 3D Metal Printing Winter 2019

3D QUALITY MATTERS
Six Points to Consider for Better Powder
Powder quality greatly influences final part quality; that’s a fact. However, myriad powder vari- ables create challenges. While the chal- lenges are complex, industry users must find ways to drive control consistency and measure results. The following pro- vides a roadmap for doing just that.
Sourcing—Ask your supplier how it sources and controls its raw material (rod, wire, etc.), and how it traces back to original ingots. Suppliers often customize the handling, testing, storing and ship- ping of an order to meet any require- ments above and beyond the powder specification. For example, ordering a large lot of powder and having it drop- shipped in smaller increments to your facility may reduce traceability concerns.
Handling—Controlling how your facility handles the powder once it is received is vital. A contamination-con- trol plan helps prevent contamination and reduces the potential for accidental contamination. Personnel training can ensure a heightened awareness of the importance of powder cleanliness. Many newer machines on the market feature options for full powder-handling systems, minimizing or eliminating the potential for external contamination. While effective, these systems require access to all surfaces that the powder touches for cleaning or replacing.
Environment and storage—Temper- ature and humidity are key factors relat- ed to machine environment and powder storage. Lower humidity, especially
Caitlin Oswald is an additive manufacturing specialist with LAI International, Inc., a contract manufacturer of precision-engineered finished components and subassemblies for the aerospace, defense, energy, medical and industrial markets: coswald@laico.com; 612/300-8722; www.laico.com.
By Caitlin Oswald
30 | 3D METAL PRINTING • WINTER 2019
3DMPmag.com
when using oxygen-sensitive alloys such as titanium, minimizes the influence of water vapor in the air. However, in extremely dry environments, or with powder containing microparticles, a minimum humidity level may be neces- sary to reduce the risk of combustible dust.
Traceability—Imperative for meeting most aerospace and defense application requirements, traceability and documen- tation allow for the recall of products within a specific powder lot when unknown defects are found downstream. Most industry-standard and customer- specific audits require users to show objective evidence of traceability docu- mentation throughout the process. Numerous alloy varieties, lot numbers and specifications tracked inside of one facility can make documentation a com- plex challenge. Not only must traceabili- ty be documented digitally, it also must be traceable on the shop floor. Trace- ability here can be implemented by using specific colored labels, two-check
systems, UPC labels and other means. Reuse—Though cost-effective,
reusing powder multiple times introduces multiple issues. The reuse process, due to repeat powder handling, inherently increases the risk for contamination, disturbance of the particle-size distribu- tion, changes in chemistry due to pick- up of interstitials such as oxygen or nitrogen, and a loss of traceability when the powder is moved from container to container. Systematic and effective ways to reuse the powder include adding vir- gin powder after each build, or sending all of the powder through the machine(s) and mixing a master lot for reuse. The economies and ease of reuse depend on the alloy, as well as on the technology and machine model.
Testing—Material testing provides evidence of conformance to the powder specification. The most common required powder-property tests include particle-size distribution by sieve analy- sis or laser diffraction, chemistry com- position, tap and bulk density, and
Testing
Handling
Reuse
Storage
Sourcing
Powder Quality
Traceability