Jul 7, 2017 | By David

A new way to optimize the performance of metal 3D printing technology is currently being developed and tested by the National Institute of Standards and Technology (NIST). NIST has created the Additive Manufacturing Metrology Testbed, a custom-made 3D printer that gives its researchers complete control over the 3D printing process so it can be studied in depth, in real-time. This research will hopefully lead to the production of new monitoring and metrology tools for use in metal 3D printing.

The NIST is part of the U.S Department of Commerce, and the AMMT was built in a collaborative effort between two NIST laboratories- the Engineering Laboratory and the Physical Measurement Laboratory. They sought to address the growing problem of quality control in metal additive manufacturing. As 3D printing is being implemented more and more in manufacturing, with everything from automotive engine parts to bone implants now being produced with the technology, the imperfections in this relatively new process are becoming more of an issue. Metal parts can often be printed with tiny pores in some of their layers, which leads to a build-up of stresses that weaken the structure, eventually causing warping or cracking.

Addressing this issue required the NIST researchers to gather some fundamental information about the 3D printing process, including exactly how hot the melting metal gets and how stresses can be lowered. This would enable them to figure out what kind of sensors could be provided for 3D printer users to find out in detail what’s going on inside their machine. “In the additive manufacturing realm, there was already a push in industry to start incorporating sensors and monitoring systems on their machines,” says Brandon Lane, a member of the Engineering Laboratory (EL). “So we wanted to be able to have that capability, and we also wanted a platform where we could test completely new ideas.”

The testbed is set up to work like a conventional metal 3D printer, with a powder bed being melted with lasers, building up the shape of a part layer by layer. Unlike most commercial printers with their own proprietary software, the AMMT’s printing process is completely open to real-time modifications. The speed and power of the laser can be controlled at 10kHz, which is to say, every 10 microseconds. This allows for a much tighter feedback loop in terms of information about the process, giving a clear picture of what’s happening and how it can be improved.

The AMMT is set-up currently to melt 3 different common types of metal powder- titanium, cobalt chrome and a nickel alloy. Most problems with the 3D printing process occur during this melting of the powder, before it re-solidifies, so the NIST team decided they needed to get a precise measure of the temperature of the molten metal. The best way to do this is to measure properties of light reflecting off the ‘melt pool’. The color of this light varies depending on how hot the liquid metal is, and getting information about the brightness of various wavelengths is helpful for determining fluctuations in temperature while an object is being 3D printed.

According to Lane, sensors that provide relative observations of these fluctuations would probably give enough detail for most 3D printer users to optimize their process. The ultimate aim of the NIST team, however, is to get absolute measurements of temperature from these relative measurements. “Eventually we’ll want to get to a full temperature map of the surface”, he says. ''PML is essential for helping us to do that.” The PML researchers are currently using a camera with a special achromatic lens to measure brightness over some of the longer wavelengths, but different diagnostics will be needed for the highest temperatures, where the shorter wavelength, visible blue light is more relevant.

(representation of a melt pool emitting range of different wavelengths)

To this end, a new addendum sensor system known as TEMPS (Temperature and Emittance of Melts, Powders and Solids) will be developed over the next year and half. It will incorporate spectrographs and a hemispherical reflectometer. “When the TEMPS system comes in, we’re going to get three times the magnification and expanded wavelength regime,” Lane says. As this metrology technology is advanced, sensors that are capable of making similar measurements for other types of metal powder could also be developed.

Eventually, the measuring capabilities of PML and EL could be expanded even beyond the realm of 3D printing, with their research being applicable for observing any solid material undergoing extreme heat changes. The wingtips of a supersonic aircraft, for example, would be a perfect candidate. NIST’s work suggests that the adoption of 3D printing technology is continuing to not only change manufacturing, but to stimulate important and useful research across a broad range of fields.



Posted in 3D Printer



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Tomek wrote at 7/14/2017 5:23:00 PM:

Why does this have a picture of a taz with a geared extruder, and then talks about DMLS

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