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.