Beijing Institute of Technology Archives - Perfect 3D Printing Filament

Beijing: 3D Printing Molybdenum Ion Thruster Components

Beijing researchers are exploring better ways to qualify ion optics, fabricating molybdenum components via additive manufacturing. Their findings were published recently in ‘3D Printed molybdenum for grids and keeper electrodes in ion thruster.

The main parts of ion thrusters are ion optics and the keeper, with optics playing a main role in the geometry of the engine. Their erosion, however, is what restricts the longevity of ion thrusters. The keeper is meant to protect the hollow cathode from ‘ion bombardment,’ causing the cathode discharge to switch on, with both metal and materials made from carbon normally used to create the necessary electrodes. Molybdenum is a common metal material used for ion optics and keeper manufacturing.

Inside of the build chamber of an SLM machine, with the fabrication piston (left), to which a build plate has been attached, and the powder delivery piston (right), on which metallic powder has been spread. The printing process starts when all the powder that is needed is loaded on the powder delivery piston, its surface flattened and aligned with the build plate on the fabrication piston.

“Among carbon-based materials, whose (Coefficient of Thermal Expansion) CTE is nearly zero and whose sputtering yield is lower than that of molybdenum, graphite is the conventional option due to its affordability and the high understanding of the industry about its fabrication methods, although pyrolytic graphite and carbon-carbon composite have also been used on several occasions for ion optics installed on significant thrusters,” state the researchers.

To streamline manufacturing of ion optics, the Beijing Institute of Technology performed a study, centered around 3D printing molybdenum for electric thrusters’ parts. It was successful and is still in development, having produced several healthy electrodes sets so far. The researchers chose selective laser melting (SLM) for the project, mainly due to its capabilities in metal printing—but also due to the level of accuracy offered, and especially for aerospace applications. Common metal materials used are titanium, aluminum, and stainless steel.

A research project at BIT created several 3D printed ion optics previously in titanium, to further examine the Additively Manufactured Ion Optics concept. Another study measured energy density, regarding:

Laser power
Laser scanning speed
Hatch spacing
Layer thickness

Molybdenum components were printed via SLM, with the research carrying on as they decided to use the materials for ion optics for mounting on ion sources in the lab, to be tested.

“Several sets of screen and accelerator grids were printed on different fabrication processes and the outputs were studied in order to verify that the SLM equipment was able to produce optics of the desired thickness and to position correctly the aperture array. The grids were examined, and it was found that they met design requirements,” stated the authors.

3D printing of the keepers is still in the development phase, although the researchers state that ‘no challenges have appeared so far.’ The researchers state that because neither the optics nor keeper are ‘especially demanded components,’ it is not necessary that the SLM molybdenum offer the same mechanical properties that they would expect from solid metal.

Four sets of screen and accelerator grids alongside several cubic samples at the end of the SLM fabrication process. After the manufacturing is completed, the components are surrounded by unsintered powder that will be removed and used for the next process.

“It was shown that both mechanical and thermal properties of SLM molybdenum approach those of the solid metal when the energy densities applied during the fabrication process get close to the maximum energy density to produce the refractory material, that is, for values about 300Jmm-3. This fact is related to the porosity of the output, which reduces as energy density increases,” concluded the researchers. “The sputtering erosion behavior of selectively laser melted materials has not been assessed yet, but it should be studied before additively manufactured components can qualify for real electric propulsion applications.”

3D printing in aerospace applications is growing more common today, as organizations like NASA develop new materials and processes, new engine alloys, and even robotics. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Effect of the bias of the scanning system over the lower region of the
build plate. The grids allocated on the lower part of the plate presented burned regions due to the excessive energy supplied by the laser.

[Source / Images: ‘3D Printed molybdenum for grids and keeper electrodes in ion thruster’]

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Researchers Make Strong, 3D Printed Expandable Origami Structures for Engineering Applications

Rearranging the same units can change a structure from one that can support a load 100 times its weight to one that will fold flat under the same load. [Image: Soft Matter]

A collaborative team of researchers from the Georgia Institute of Technology, the Beijing Institute of Technology, and Peking University are using 3D printing to directly build reconfigurable origami assemblages that can expand and fold. But even better, the 3D printed structures also have enough load-bearing capability and strength to be used in engineering applications.

In a paper published in Soft Matters, titled “3D printing of complex origami assemblages for reconfigurable structures,” the researchers explained how they used digital light processing (DLP) 3D printing to fabricate structures with hollow features.

With this method, far less support material is required for 3D printing hollow features, and softer materials, necessary for flexible structures, can be used.

The abstract of the paper reads, “Origami engineering principles have recently been applied to a wide range of applications, including soft robots, stretchable electronics, and mechanical metamaterials. In order to achieve the 3D nature of engineered structures (e.g. load-bearing capacity) and capture the desired kinematics (e.g., foldability), many origami-inspired engineering designs are assembled from smaller parts and often require binding agents or additional elements for connection. Attempts at direct fabrication of 3D origami structures have been limited by available fabrication technologies and materials. Here, we propose a new method to directly 3D print origami assemblages (that mimic the behavior of their paper counterparts) with acceptable strength and load-bearing capacity for engineering applications. Our approach introduces hinge-panel elements, where the hinge regions are designed with finite thickness and length. The geometrical design of these hinge-panels, informed by both experimental and theoretical analysis, provides the desired mechanical behavior. In order to ensure foldability and repeatability, a novel photocurable elastomer system is developed and the designs are fabricated using digital light processing-based 3D printing technology. Various origami assemblages are produced to demonstrate the design flexibility and fabrication efficiency offered by our 3D printing method for origami structures with enhanced load bearing capacity and selective deformation modes.”

Many 3D printed structures with unique properties have been inspired by origami, opening up applications in soft robotics and self-folding structures. While most origami structures mean thin sheets being joined together with binding elements like glue, the research team found a way to make several 3D assemblies in one step, without needing to connect smaller parts together. The team, led by Zeang Zhao, developed a new polymer and used geometrical design to move towards using origami for engineering structures.

To build the origami, the team developed a novel new elastomer, which makes it possible for the structure to be created from a single component. The elastic polymer material can be 3D printed at room temperature and set with UV light, which forms a soft, foldable material that can be stretched up to 100%. This material was used for the whole 3D assembly. DLP 3D printing was used to build structures, made up of various combinations of individual units of origami, without requiring any extra assembly steps.

By altering how each origami unit is connected, the structures can be designed to have different load-bearing capabilities: vitally important for applications in engineering. One of the test structures was even able to support a load that weighed 100 times more than the structure itself did. But here’s the really interesting part – just by rearranging the same individual units in a different way, the team was able to build a bridge that, under the same heavy load, would fold flat.

The structures were designed with thick panels, which were separated by hinges not unlike the creases in a piece of paper. The hinges made it possible for the angle between the panels to vary between 0° and 90°. Hinge thickness is important for a structure’s mechanical properties: if it’s too thick, it won’t fold well, while if it’s too thin, it might not be able to support the structure’s weight. In addition, the researchers made sure that the high strain and stress the structures experienced during folding was localized specifically to the hinges, so the panels would not end up deformed.

Co-authors of the paper are Zhao, Xiao Kuang, Jiangtao Wu, Qiang Zhang, Glaucio H. Paulino, H. Jerry Qi, and Daining Fang.

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[Source: Physics World]

3D printing news Sliced: United Nations, Mini, Rocket Lab, Sciaky and more

Today Sliced, our regular 3D printing news digest, features the latest educational innovations from the National Institute of Technology, Trichy, I-Form, the Advanced Forming Research Centre, the Beijing Institute of Technology and more. From industry, we see how cutting edge 3D printing applications are underway at MINI, Rocket Labs and Kleos Space. There is also an update […]