Marcia Domack and John Wagner, engineers in the Advanced Materials and Processing Branch at NASA Langley Research Center, have worked with Boston-based metal fabricator Spincraft, focusing on a one-piece manufacturing process called spin forming. The team used the spin-forming technique to create a model of the forward pressure vessel bulkhead (FPVBH) of an Orion-type crew module.
NASA Tech Briefs: What is spin forming?
Marcia Domack: Spin forming is a metal fabrication method that enables us to form launch vehicle components in one piece. The way the process works is we start with a flat piece of plate, and put that essentially on a machine, kind of like a very large lathe, a piece of metal turning equipment. The plate spins in the plane, which is analogous to a record spinning on a turntable, and we use torches to heat up the material to an elevated temperature. Using a roller on the outside surface of the plate, we push it over a tool that is a shape of the component we want to make, and basically cause that material to drape over the tool and take on its shape.
John Wagner: Some of the components that we target are large, 10- to 12-foot diameter components that are made either by hogging out or machining out thick plate, a process which has a very high material scrap rate. Then, these parts are welded or riveted together. So spin-forming is a greener manufacturing process. You don’t have a lot of machining chips or wasted material, and it’s closer to the final shape. It eliminates the majority of welds, which is a good thing, because welds a lot of times are where you’ll have a lot of problems or material defects. If you can get rid of rivets, your part count is down as well. It all ends up in saving money.
NTB: How do these benefits stack up against traditional manufacturing methods?
Wagner: For example, if we just take “near-net-shape” forming in general, which is a wider area of technology that we’re pursuing, spin forming is just one of these areas. There are others, like flow forming and roll forging, but the external tank on the shuttle, for example, weighs approximately 60,000 pounds. But they have start off with 600,000 pounds of material approximately, and machine away 90 percent of the material, and you’re left with a thin shell with stiffeners. So we’re trying to get away from that high scrap rate of 90 percent into something more like spin forming, where maybe the scrap rate might be 10, 20, or 30 percent, depending on how close to near-net-shape you can get it.
Domack: From a material properties standpoint, the work that we have done with other near-net-shape fabrication processes has yielded us mechanical properties that are very close to other more traditional raw products used in the multi-piece assembly-like plate. From a material performance standpoint, these processes offer comparable properties and therefore comparable performance, but we can greatly reduce cost by eliminating lots of the steps like heavy-duty machining and the multi-piece welding inspections. We can reduce cost as well as improve the performance of the components and reduce their weight.
Wagner: And make it safer for the astronauts.
NTB: How so?
Wagner: Welded areas are typical areas where you might get a structural defect, so if you can eliminate those locations where you might have the propensity of defects, it’ll be safer for the astronauts.
Domack: We end up with a structure that has a higher reliability, which is good for design, by getting rid of those potentially defect-prone sites.
NTB: Where are we seeing spin-forming in action currently?
Domack: The process is used by commercial companies around the world to make domes for cryogenic tanks that are used on existing launch vehicles, existing rocket assemblies.
Wagner: For example, a cryogenic propellant tank is made up of barrel sections, which are the cylindrical sections typically. Then they have the ends of the tanker domes, and they used this spin forming technology, both domestically and internationally, to make these. What we were trying to do was a little bit different. The Orion configuration or module isn’t just a dome. It’s a front bulkhead, plus a barrel section. It has more contours and more radiuses of curvature. It’s more complex than, say, a dome geometry. This was a challenge for the fabricator.
Domack: It’s a well-established commercial capability to make a dome structure, which, if you look at it in cross-section, is a big arc-shaped component. We’re trying to extend this technology to the next level of development, and the next level of complexity. And if we’re successful at showing that we can make something this complex, we’re already, from a commercial standpoint, making a simple geometry and advancing this technology area, where we can make just about any shaped component that we need.
Wagner: Typically, in the work that we do, we look at both the innovative manufacturing, like the spin forming technique, but we also try to incorporate lightweight, advanced materials. The best of both worlds would be to be able to do this innovative technology, like this spin forming of the Orion crew module, and do it with a lighter weight material. The current material that we used for the demonstration article is an aluminum that has a designation of 2219 aluminum alloys, an alloy that has been around since the 1950s. There’s a more recent type of aluminum lithium alloy, alloy 2195, that’s about ten percent lighter, and ten percent or more stronger than some of the regular aluminum, like 2219. We don’t have as much experience with that material, so the next step we envision is to do this innovative forming with a lighter-weight aluminum lithium alloy.
Domack: In the long-term, the goal for a component like the Orion crew module would be to significantly reduce the weight in the vehicle and improve the performance, and do that by a combination of using this single-piece, spin-forming technology to get rid of the welds and the joints, and fabricate that from the aluminum lithium alloy. Either one by itself should gain us weight reduction in the vehicle, but when you combine the spin-forming technology with aluminum lithium, we feel like that weight reduction can be significant. Getting the weight down in the crew module allows us to add something inside, whether it’s additional personnel, like another astronaut, additional support systems for the crew module, or additional payloads.
NTB: Can you take us through that process of spin-forming a single-piece crew module?
Wagner: Originally, we’ve worked a suite of numerous near-net-shape technologies, and in the beginning, most of those were pretty standard: cylinders, and rings for attaching domes to, say, cylindrical sections. We thought that the next step would be: Could we do something that’s close to near net, using any kind of forming technology or spin-forming or flow-forming, but do it in a cone or conical section? Originally, we were trying to make a transition from straight cylindrical sections like you would have on a barrel section of a propellant tank, and a conical section like you might see in a transition region between two stages on a rocket, where it has a big diameter or small diameter. We took that idea to several companies, and we settled on trying to do that by spin forming. During the discussions with our technical colleagues at Spincraft, we mentioned almost in a joking manner, “It’d be nice ultimately, to be able to make a whole Orion crew module by spin forming this technology.” And after we examined that further, we determined that it wouldn’t be that big of push, technology-wise, to do either a conical section, or just go for broke or try to do the whole crew module that we were successful in doing?
NTB: Are there any hang-ups? Why would someone hesitate to use this method?
Wagner: One thing that we’ve found in some of the launch vehicle and aircraft industries is the mentality, and rightfully so, of “If it ain’t broke, don’t change it.” If it works well, why introduce the variable of new technology? There’s got to be a real driver for the new technology to earn its way on to either a rocket or an airplane.
Domack: The next step in our work is to quantify just how much of a benefit this kind of a single-piece construction can be over what the Orion now uses, and the many-piece, multi-piece welded construction.
NTB: Are there any other big design challenges when spin-forming?
Domack: Not so much with spin forming, but with an article like this, there’s a lot of hesitation, once a manufacturing path is established, to insert new technology, particularly technologies that significantly change how things are done. One thing we will have to address with single-piece construction is how you would add other systems to it. There are other things that have to attach to this forward pressure vessel bulkhead. If you look at the Orion crew module, or other crew capsules that are being developed, there’s a nice, smooth outer mold-line that’s on an angle. Obviously inside that, there are many systems. There are parachute systems. There are all kinds of support systems. Within all of that is a pressure vessel that the astronauts ride in. What we are making is that underlying structure. So we are planning to work on an upcoming project with the designers of all those systems. With multi-pieces: as they’re welding two pieces together, they can add in an extra flange. We’ll have to work with them to design how they would make those additions to our bulkhead.
NTB: Can you talk a bit about the partnerships that you’ve formed as you’ve been going through this spin-forming process?
Wagner: We’ve been partnered very closely initially with Lockheed Martin Michoud Assembly Facility, which is outside of New Orleans. NASA and Lockheed Martin Corporate have a Space Act Agreement that allows for the exchange of information and material and ideas between these two companies. The Space Act has been very instrumental in providing a vehicle with which we can work with our colleagues in private industry. Also, we have been working with the people who did the actual spin forming, which is Spincraft in North Billerica, MA. Marcia Domack, in particular, worked with them on a spun-form dome project a couple years ago, under the NASA Exploration Technology Development program.
NTB: Down the road, what do you see as the possibilities with spin forming in the aerospace industry?
Wagner: I think that one thing that we tried to do is demonstrate that you could use it for more than just domes. There might’ve been some isolated examples of other components, but they have not been wide ranging, and I think what we wanted to do is demonstrate that you could do different configurations (like a barrel, a cone, and a dome) all in one piece. And I think that will get people thinking about using this technology, spin forming, for things other than just cryogenic tank domes.
NTB: Can you take us through a typical day, and what you’re working on now?
Domack: Related to this project, a typical day for John and I right now is pretty dynamic, because this project of the fabrication of our forward pressure vessel bulkhead (FPVBH) has been given a lot of attention, which is great, along with some financial support to get moving with the next steps in the work. So on a day-to-day basis right now, we are working on our plans for the next steps in the work, which include material evaluations and structural analysis. We are having discussions with our partners here, along with our colleagues here at NASA Langley, in laying out those plans. We have some students working with us that are assisting with doing metallography of the parts.
Wagner: Marcia and I are both engineers, both with a materials and metallurgical engineering background. One of the things that we need to do is to look at how the process affects the material, to make sure the properties are still adequate, that the grain structure that makes up the material, the aluminum, is correct, and that we don’t have any surprises. Those kinds of things. We need to do the details. We’re working the details of the article that we made, and we’re making plans for what the next step is. We’re doing the technical planning and how we transition to this new lighter weight material. We spend a lot of time interfacing with our team, with Lockheed Martin, with Spincraft. Because the demonstration article was successful, we’ve gotten more visibility and more interested people to be on the team.
Domack: And we are collaborating with researchers at other NASA centers as well. An important part of the project that we’re undertaking now is to really understand completely what the benefits are of this technology for fabrication of these kinds of structures. We’re not working this just from the materials standpoint. We do have materials and processing people from other centers, and structural analysis types from other centers, interfacing with us, consulting with us on a frequent basis.
Wagner: The Marshall Space Flight Center in Huntsville, Alabama and the Johnson Space Flight Center in Houston, Texas, are an integral part of the team. We’ve worked closely with Marshall Space Flight Center in the past on all this type of innovative materials forming. They have a lot of expertise in friction stir-welding, a new welding process. They are a very, very important and active part of the team.
NTB: What would you say is your favorite part of the job?
Wagner: I am incredibly excited to see this article having been made. John and I have worked with near-net shape fabrication technologies for 15-plus years. We’re always looking for some new application and new things that we can make. In this particular case, we came up with an idea that did not have a project, did not have funding support, and so we’ve put a lot of time and energy into generating interest for this: finding funding for each phase, a step at a time, and over about three years, we’ve finally culminated in actually fabricating this crew module. The reception that we’ve gotten to it from the technical community has been very rewarding. It’s exciting to have the opportunity to have those who would use the technology invest in it, and really help us get to that point. And it’s a really nice-looking piece of hardware.
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