Microgravity Helps Industry Characterize New Metal Alloys
The last time you took your new titanium golf clubs out for a few holes at the local course, it probably didn’t occur to you that the clubs were manufactured using a process that is thousands of years old. Most golf club heads are made by casting, an ancient process in which molten metal is poured into a mold, allowed to solidify, then removed from the mold and either used as is or assembled with other castings to form any number of things. The process, which is believed to have originated in the Middle East more than 5,000 years ago, is still commonly used today. In fact, the foundry, or metal casting, industry is a flourishing business, producing everything from toothbrush holders to golf club heads to components of the space shuttle. Since precise scientific knowledge about casting has been limited by interferences caused by Earth’s gravity, the process is poised to benefit greatly from research in the microgravity environment on NASA’s International Space Station.
While metal castings have been made for thousands of years, until recently, scientists still didn’t know much about the fundamental chemistry and physics of many of the metals that are used in the process. When working on a new casting process or testing a new alloy, foundry engineers usually had to use observation and trial and error to develop their methods and fine-tune their manufacturing processes. This method, while generally effective, nevertheless wastes time and expensive materials. By using precision scientific data and theoretical calculations to predict how a metal would react to the casting process, engineers could potentially reduce both wasted materials and lost time, thereby keeping pace with the increasingly sophisticated needs of the customers and keeping costs low enough to stay competitive.
Building a Vital Database
What the industry needed was a data-base containing thermophysical data for materials either currently in use or still under development. But most foundry companies are so small they cannot afford to do research themselves, so the American Foundry Society (AFS) partnered with NASA’s Solidification Design Center (SDC), a commercial space center (CSC) at Auburn University, to begin the work. Tony Overfelt, director of the SDC, explains that without an accurate database “underpinning your process engineering and research and development, then your other work lacks credibility, since you can’t convincingly interpret your data.” Building such a database is one of the primary focuses at the SDC.
The SDC is one of 17 commercial space centers that are part of the Space Product Development Program, which is in turn part of the Research Integration Division in the Office of Biological and Physical Research (OBPR). The CSCs were formed to encourage the commercial development of space through partnerships with business and academia. They are unique within NASA in that while their base fund-ing is provided by NASA, research funding comes almost entirely from private industry. The SDC itself primarily conducts research related to the foundry industry.
Filling in the Gaps
Some of that research can be done on Earth. For the past 10 years or so, the SDC has worked with Ray Taylor, who runs TPRL Incorporated in West Lafayette, Indiana, and his team of mechanical engineers to do some of this ground-based research. Taylor started working with Overfelt and the SDC in the early 1990s while doing research at Purdue University. He specializes in the collection of basic materials measurements, helping the SDC to fill in some of the gaps in their data-base with highly accurate and reliable data.
Researchers at Auburn University have done some of the ground research as well. For example, the SDC has one of only four high-temperature viscometers in the world, enabling its scientists to measure the viscosity of aluminum alloys and steels on the ground and obtain data that are useful in designing casting processes.
Scientists at Auburn and elsewhere need to study the physics and chemistry of metals and alloys both in their solid states and during melting and solidification. Unfortunately, gravity interferes with some tests and some types of metals and prevents scientists from getting high-precision data. When the interference of gravity is suppressed, as it is during orbit on the space station, scientists have a more accurate picture of those characteristics and those metals. Overfelt explains, “For example, precise viscosity measurements of low-viscosity metals like aluminum are difficult in 1 g due to buoyancy convection effects. In addition, it’s very difficult to obtain precise data about very reactive metals (titanium, magnesium, many super alloys) in crucibles [heat-resistant vessels used to melt materials] since they react with the very crucibles that contain them. Levitation experiments in low gravity provide extended times in the molten state without contact with crucibles.” Were it not for this opportunity for business to do microgravity research at NASA through the commercial space center program, the gaps in the metallurgy database of commercially important alloys might be permanent.
Going Containerless
While the SDC is involved in ground-based research, Overfelt and his colleagues are also working on experiments that will be flown on the International Space Station in 2003. They are sending up an electro-magnetic levitator, a containerless experi-ment device that levitates samples of metals and alloys which would otherwise react with their containers and thus contaminate the samples before data could be taken. While containerless research can be conducted on Earth, Overfelt asserts, “We’ll be able to have much better control of boundary conditions [in orbit]. Nice spherical samples will behave in ways that allow us to reduce our raw data to actual thermophysical properties much more precisely and accurately.” Each sample will be tested, first in its solid state and then in its molten state “to extract surface tension data . . . as a function of temperature,” Overfelt describes. For this first launch, Overfelt is testing only pure elements so that he can compare the data he gets to established data he already has. This will enable his team to carefully validate the whole system on this first flight.
For future flights, the SDC plans to incorporate a flash diffusivity device that will measure how energy diffuses through the samples. The SDC is working with Anter Corporation, a small company in Pittsburgh, Pennsylvania. Anter makes thermal diffusivity devices and has modified one design so that they can “use the standard flash approach applied to spherical samples. Flash approach has [typically] been applied [only] to very thin samples,” Overfelt describes. “We basically give it an impulse of energy on one side of the sample and measure how long it takes for that energy to diffuse through the sample. It tells us the thermal diffusivity of the material, one of the more important properties.”
By building this database of material properties, the SDC engineering team is fulfilling its goal as part of the Space Product Development Program to bring space research and business together for the benefit of everyone on Earth. Access to general information regarding research on nonproprietary alloys is available to anyone, without cost, from the SDC web site (see below). The SDC also functions as a testing lab for companies that need to have their metals or alloys characterized but do not have the facilities to do so themselves. Companies can receive the resulting data as proprietary data or allow it to be included in the general database. The benefits of the developing database to the metal industry as a whole are almost limitless.
Solid Plans for the Future
As Overfelt guides the SDC along its path of research, he keeps his eyes on the future. He intends to steer the SDC toward projects that will include work not only with the foundry industry but also with other companies that face similar challenges and as such might benefit from microgravity research. General Motors (GM) recently funded a project headed by Ken Williams, of Arena LLC in Albuquerque, New Mexico, that has resulted in groundbreaking soft-ware that will improve the quality of GM’s casting molds. This software has enormous potential both for space research and for improving any manufacturing process that involves the flow of particulates.
“And so we’re going to continue to work with the metal casting industry, expanding into the related manufacturing processes – any kind of a manufacturing process that has a fluid or a granular component where gravity has a role in distributing that process and then forcing the designers into a trial-and-error, empirical development methodology,” says Overfelt. “Anything that fits those parameters has the possibility of being improved by space experiments. I’m confident we’ll be doing other projects that are not classical metal casting projects which are manufacturing-related and which do have applications to making metal components. I think the next 10 to 20 years of space research are going to help revolu-tionize many aspects of these businesses.”
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