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NASA Fired Up Over 3D-Printed Engine Components

 

A NASA team is fired up about getting closer to building a completely 3D-printed, high-performance rocket engine. They demonstrated this in December by assembling additive-made complex engine parts and firing them up with cryogenic liquid hydrogen and oxygen to produce 20,000 pounds of thrust.

“We manufactured and then tested about 75% of the parts needed to build a 3D-printed rocket engine,” said Elizabeth Robertson, the project manager for the additively manufactured demonstrator engine at NASA’s Marshall Space Flight Center in Huntsville, AL. “By testing the turbopumps, injectors and valves together, we’ve shown that it would be possible to build a 3D-printed engine for multiple purposes such as landers, in-space propulsion or rocket engine upper stages.” During test firings at NASA’s Marshall Space Flight Center, 3D-printed rocket engine parts worked together successful under the same conditions experienced inside rocket engines used in space.

Over the last three years, the Marshall team has been working with various vendors to make 3D-printed parts, such as turbopumps and injectors, and test them individually. To test them together, they connected the parts so that they work the same as they do in a real engine.

“What matters is that the parts work the same way as they do in a conventional engine and perform under the extreme temperatures and pressures found inside a rocket engine,” explained Nick Case, the testing lead for the effort. “The turbopump got its ‘heartbeat’ racing at more than 90,000 rpm and the end result is … over 20,000 pounds of thrust, and an engine like this could produce enough power for an upper stage of a rocket or a Mars lander.”

Seven tests were performed, with the longest tests lasting 10 seconds. During the tests, the 3D-printed demonstrator engine experienced all the extreme environments inside a flight rocket engine where fuel is burned at greater than 3315° C to produce thrust. The turbopump delivers the fuel in the form of liquid hydrogen cooled below -240° C. These tests were performed with cryogenic liquid hydrogen and liquid oxygen, mainstays of spaceship propulsion systems. Even if methane and oxygen prove to be the Mars propellant of choice, the propellant combination of cryogenic liquid hydrogen and oxygen tests the limits of 3D-printed hardware because it produces the most extreme temperatures and exposes parts to cryogenic hydrogen, which can cause brittleness. In addition to testing with methane, the team plans to add other key components to the demonstrator engine including a cooled combustion chamber and nozzle and a turbopump for liquid oxygen.

“These NASA tests drive down the costs and risks associated with using additive manufacturing, which is a relatively new process for making aerospace quality parts,” said Robertson. “Vendors who had never worked with NASA learned how to make parts robust enough for rocket engines. What we’ve learned through this project can now be shared with American companies and our partners.”

The 3D-printed turbopump, one of the more complex parts of the engine, had 45% fewer parts than similar pumps made with traditional welding and assembly techniques. The injector had over 200 fewer parts than traditionally manufactured injectors, and it incorporated features that have never been used before because they are only possible with additive manufacturing. Complex parts like valves that normally would take more than a year to manufacture were built in a few months. This made it possible to get the parts built and assembled on the test stand much sooner than if they had been procured and made with traditional methods. Marshall engineers designed the fuel pump and its components and leveraged the expertise of five suppliers to build the parts using 3D-printing processes.

 

New, Atom-Thick Borophene in Race with Graphene

Tech Front has been following the development of graphene, that single-atom-thick material with amazing properties that may yet revolutionize Lithium batteries (see below) and other manufactured products. And while progress in making graphene affordable and usable outside the lab has been consistent, it has at times seemed slow. Now there is a second horse in the race, however—called borophene

A team of scientists from the US Department of Energy’s (DOE) Argonne National Laboratory, Northwestern University and Stony Brook University announced that it has, for the first time, created a two-dimensional sheet of boron—borophene. It’s an unusual material because it shows many metallic properties at the nanoscale even though three-dimensional, or bulk, boron is nonmetallic and semiconducting. Front-view illustration of Neutral C6v B36 borophene.

“Borophenes are extremely intriguing because they are quite different from previously studied two-dimensional materials,” said Argonne nanoscientist Nathan Guisinger, who led the experiment. “And because they don’t appear in nature, the challenge involved designing an experiment to produce them synthetically in our lab.”

One of boron’s most unusual features consists of its atomic configuration at the nanoscale. While other two-dimensional materials look more or less like perfectly smooth and even planes at the nanoscale, borophene looks like corrugated cardboard, buckling up and down depending on how the boron atoms bind to one another, according to Andrew Mannix, a Northwestern graduate student and first author of the study.

The “ridges” of this cardboard-like structure result in a material phenomenon known as anisotropy, in which a material’s mechanical or electronic properties—like its electrical conductivity—become directionally dependent, Mannix said.

Based on theoretical predictions of borophene’s characteristics, the researchers also noticed that it likely has a higher tensile strength than any other known material—including graphene. Tensile strength refers to the ability of a material to resist breaking when it is pulled apart. “Other two-dimensional materials have been known to have high tensile strength, but this could be the strongest material we’ve found yet,” researcher Nathan Guisinger said.

As they grew the borophene monolayer, the researchers discovered an advantage within their experimental technique. Unlike previous experiments that used highly toxic gases in the production of nanoscale boron-based materials, this experiment involved a nontoxic technique called electron-beam evaporation, which essentially vaporizes a source material and then condenses a thin film on a substrate—in this case, boron on silver.

The study will be published in the Dec. 18 issue of the journal Science. Borophene thus joins graphene in a developmental race of atom-thick miracle materials. We’ll watch to see which eventually takes a thin lead.
  

Lithium-Air BatteryProgress is Breathtaking

Scientists at UK’s University of Cambridge have developed a working laboratory demonstrator of a lithium-oxygen battery that has very high energy density, is more than 90% efficient, and, to date, can be recharged more than 2000 times, showing how several of the problems holding back the development of these devices could be solved.

Lithium-oxygen, or lithium-air, batteries have a theoretical energy density that’s ten times that of a lithium-ion battery. Such a high energy density would be comparable to that of gasoline–and would enable an electric car with a battery that is a fifth the cost and a fifth the weight of those currently on the market to drive over 400 miles on a single charge—theoretically, that is. However, as is the case with other next-generation batteries, there are several practical challenges that need to be addressed before lithium-air batteries become a viable alternative to gasoline.

University of Cambridge researchers have now demonstrated how some of these obstacles may be overcome, and developed a lab-based demonstrator of a lithium-oxygen battery which has higher capacity, increased energy efficiency and improved stability over previous attempts. Their research was published in the journal Science. Microscope image showing charged (left) and discharged graphene electrodes.

What Tao Liu, Clare Grey and their colleagues at Cambridge have developed uses a different chemistry than earlier attempts at a nonaqueous lithium-air battery, relying on lithium hydroxide (LiOH) instead of lithium peroxide (Li2O2). With the addition of water and the use of lithium iodide as a ‘mediator’, their battery showed far less of the chemical reactions which can cause cells to die, making it far more stable after multiple charge and discharge cycles.

By precisely engineering the structure of the electrode, changing it to a highly porous form of graphene, adding lithium iodide, and changing the chemical makeup of the electrolyte, the researchers were able to reduce the ‘voltage gap’ between charge and discharge to 0.2 volts. A small voltage gap equals a more efficient battery—previous versions of a lithium-air battery have only managed to get the gap down to 0.5–1.0  volts, whereas 0.2 volts is closer to that of a Li-ion battery, and equates to an energy efficiency of 93%.

The highly porous graphene electrode also greatly increases the capacity of the demonstrator, although only at certain rates of charge and discharge. Other issues that still have to be addressed include finding a way to protect the metal electrode so that it doesn’t form spindly lithium metal fibers known as dendrites, which can cause batteries to explode if they grow too much and short-circuit the battery.

Additionally, the demonstrator can only be cycled in pure oxygen, while the air around us also contains carbon dioxide, nitrogen and moisture, all of which are generally harmful to the metal electrode.

“There’s still a lot of work to do,” said Liu. “But what we’ve seen here suggests that there are ways to solve these problems—maybe we’ve just got to look at things a little differently.”

 

Laser Micromachining Grows Up

Laser micro-machining (LMM) is an attractive manufacturing process due to its intrinsic machining characteristics such as such as non-contact processing and capabilities to machine complex free-form surfaces in a wide range of materials. That’s the good news.

Nevertheless, state-of-the-art LMM platforms still don’t offer the repeatability, reproducibility and operability of conventional machining centers. That is to say they don’t yet offer the flexibility to realize complex machining configurations and also to combine LMM with other complementary processes in hybrid manufacturing systems and production lines. For these reasons, LMM isn’t yet considered a ‘mature’ process—unlike rival processes such as micro milling.

Four researchers—Pavel Penchev, Stefan Dimov, Debajyoti Bhaduri, and Sein L. Soo—at University of Birmingham’s School of Mechanical Engineering (Birmingham, UK) have published a paper in Volume 28 of the Journal of Manufacturing Systems that offers to bring maturity to LMM processes.

The paper, “Generic Integration Tools for Reconfigurable Laser Micromachining Systems,” presents the development of three generic integration tools for improving the system-level performance of reconfigurable LMM platforms. In particular, the research reports the design and implementation of a modular workpiece holding device, an automated workpiece setup routine and automated strategy for multiaxis LMM machining employing rotary stages.

An experimental validation of their accuracy, repeatability and reproducibility (ARR) was performed on a representative state-of-art LMM platform. The results demonstrate the flexibility and operability of the proposed tools to address important system-level issues in LMM by creating the necessary prerequisites for achieving machining ARR better than ±10 μm. The entire paper is available at http://tinyurl.com/JMS-LaserMMS

 

 


This article was first published in the February 2016 edition of Manufacturing Engineering magazine. Click here for PDF.


Published Date : 2/1/2016

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