Beijing Institute of Technology 3D printed molybdenum ion thruster components
Researchers in Beijing are exploring better ways to identify ionic optics by making molybdenum components through additive materials. Their work was recently published in a paper called "Applications of 3D Printed Molybdenum in Ion Thruster Grids and Protective Electrodes."
The main components of ion thrusters are ion optics and protector. Optics plays an important role in the geometry of the engine. However, their erosion limits the life of the ion thrusters. The purpose of the protector is to protect the hollow cathode from "ion bombardment", causing the cathode to discharge open. Metal and carbon materials are usually used to make the necessary electrodes. Molybdenum is a metal material commonly used in ionic optics and conservation manufacturing.
In the construction chamber of the SLM equipment, the piston (left) and the powder delivery piston (right) are assembled, on which the metal powder has been sprinkled. The printing process begins when all the powder is required to be loaded onto the powder conveying piston, whose surface is flat and aligned on the construction plate of the manufacturing piston.
The researchers say
Among carbon-based materials with near zero coefficient of thermal expansion (CTE) and lower sputtering yields than molybdenum, graphite is the conventional choice due to its low cost and high understanding of its manufacturing methods, although graphite and carbon-carbon composites have been used several times in ionic optical systems mounted on important propellers. In order to simplify the manufacture of ionic optical systems, the Beijing Institute of Technology has carried out a study focusing on the 3D printing of molybdenum components for electric thrusters. It is successful and is still in the development stage, and several healthy electrode sets have been produced so far. The researchers chose selective laser Melting (SLM) for the project primarily because of its capabilities in metal printing, but also, of course, because of the level of precision it can offer, especially in aerospace. Commonly used metal materials are titanium, aluminum and stainless steel.
The Beijing Institute of Technology research project has created several 3D-printed ionic optical elements previously used in titanium to further study the concept of ionic optics in additive manufacturing. Another study measured energy density and involved:
· Laser power
· Laser scanning speed
· Layer thickness
The molybdenum components were printed using SLM, and as the research progressed, they decided to use ionic optical materials mounted on a laboratory ion source for testing.
"Several sets of screens and accelerator grids were printed on different manufacturing processes and the outputs were studied to verify that the SLM device was capable of producing optics of the required thickness and correctly positioning the aperture array. The grids were checked and found to meet the design requirements." The authors say.
While the researchers say no challenges have emerged so far, SLM's 3D printing is still in the development phase. Since optical elements and retainers are not "particularly desirable components," SLM molybdenum does not necessarily provide the same mechanical properties as solid metals, the researchers said.
At the end of the SLM process, in addition to a few cubic samples, there are four sets of screens and accelerator grids. After fabrication, the part is surrounded by powder, which is removed and used in the next process.
"The results show that when the energy density applied during the preparation is close to the maximum energy density, the mechanical and thermal properties of SLM molybdenum are close to that of solid metal, resulting in a refractory of about 300 JMM-3. This fact is related to the porosity of the output, which decreases as the energy density increases." The researchers concluded. Sputtering corrosion behavior of selective laser-melted materials has not been evaluated, but it must be studied before additive manufactured components can be used for practical electric propulsion applications.
Scan the effects of system bias in the lower area of the construction board. Due to the excess energy provided by the laser, the grids distributed in the lower part of the plate show a burning zone.