In April 2020, Jonathan Wright recently submitted a paper to the Department of Materials Science and Engineering at the University of Sheffield, discussing the problem of 3D printing with rare metal tungsten. In "Additive Manufacturing of Tungsten by Selective Laser Melting and Electron Beam Melting", Wright detailed the additive manufacturing of pure tungsten powder bed (ALM) using selective laser melting (SLM) and electron beam melting (EBM) )potential.
Tungsten is derived from tungsten iron ore ((Fe, Mn) WO4) and scheelite (CaWO4), which not only has the lowest vapor pressure of all elements, but also has a high melting point and the ability to "pull into filaments". Today, it is used in filaments and many other applications. It can be used in high temperature or high density scenes, such as X-ray shielding.
Wright also explained that due to the thermal characteristics of tungsten, "low sputtering yield and short activation decay time", it is also suitable for nuclear fusion experiments.
"Although it is possible to machine tungsten (drilling, turning, milling, etc.), it is difficult, requires specialized knowledge, and strict conditions must be strictly observed," Wright said. "It is possible to form more complex structures by overcoming some difficult electrical discharge machining (EDM)."
Because the chemical, physical, and mechanical composition of tungsten poses challenges and limitations, alloying needs to be considered. However, Wright pointed out that although a large number of alloys have been tested, there is still much room for it. To date, tungsten-alloys are considered to have the greatest potential for improving ductility.
In the experimental phase of Wright ’s research, he used Renishaw SLM 125 to manufacture sample parts and Renishaw AM 400 to manufacture other parts.
For the EBM process, the Arcam S12 system is used
Wright found it difficult to produce defect-free tungsten parts, and beam power was one of the biggest causes of voids. All samples showed high levels at 200W and lowest levels at 400W.
"As the porosity in the tungsten samples produced by SLM decreases, the number of cracks is found to increase, so this is also a factor of beam power," Wright explained.
In order to produce crack-free parts, further work is required on tungsten SLM. This may include investigating the addition of external heat sources. The heated environment may reduce residual stress and make the material higher than DBTT. "
When trying to make EBM samples, Wright was able to find suitable parameters for low-defect tungsten samples. He believes that speed, current and hatch spacing play an important role in porosity.
"This is the first report of EBM printing tungsten. Specifically, EBM can produce parts with low porosity and no cracks. Due to the combination of vacuum environment, high build temperature and high beam power, EBM seems to be the preferred manufacturing process." Wright concluded.
"However, before ALM can be used to manufacture tungsten for structural applications, mechanical properties and geometric accuracy need to be further improved. For applications where mechanical properties are not critical and require complex geometries (such as X-ray collimation), the outlined here ALM technology can provide a viable processing route. "
As researchers around the world continue to improve 3D printing and additive manufacturing processes, people are studying the performance and applications of tungsten, from testing the performance of tungsten to manufacturing cutting tools and large non-alloy parts.