Dr. Matthew Davies is a mechanical engineer at the National Institute for Standards and Technology (NIST), where he leads several high-speed machining projects. Aerospace machine and parts manufacturers can learn new ideas and new processes from the military manufacturing projects in which NIST is involved.

Over the years, NIST has helped lay the foundation for prosperity and technological advancement in the United States. NIST research has been used to improve military machining techniques, and private manufacturers have much to learn from their findings as well. In 1989, NIST founded the Manufacturing Extension Partnership (MEP) in an effort to offer technical assistance and the latest business practices to the nation's smaller manufacturers. Today, manufacturers and machine shops in the aerospace industry have a lot to learn from NIST's research in high-speed machining.

As NIST continues its research in high-speed machining, military and private sector manufacturers alike will continue to learn from their invaluable developments, such as laser sintering. Laser sintering is a process which heats powder into layered shapes for prototype development, driven by CAD/CAM technology.

LASER SINTERING FOR LESS WEAR AND LESS WASTE

Cross-military high-speed machining techniques that are applicable to aerospace manufacturing primarily involve 6AL-4V titanium machining, according to Matthew Davies. Since titanium does not process like aluminum in high-speed applications, tool wear can be significant. "This is a very complex problem," says Davies. "If you start with something that is already pretty thin to begin with, you have to worry about the dynamics of that part during machining. If not done correctly, part vibrations will cause significant chatter."

But this issue extends beyond titanium. "Even in aluminum, you really do not want to start with huge plate. You would prefer not to recycle 95 percent of your aluminum all the time." To counteract that, Davies says, many machinists start with near-net-shape billets or forgings. "The problem with starting with forgings is you do not know the residual stress patterns in the material to begin with, so your parts will warp on you more than they will if you start with plate."

To counteract this problem, Davies and his team have been exploring new aerospace manufacturing processes, including combinations of near-net-shaped processes like laser sintering. In this particular type of application, laser sintering is used a bit differently, as it produces a part from a block of material that is nearer the shape of the desired part than just a standard block of metal. It is a process long utilized by the military. The benefits of laser sintering are a more efficient use of material and a reduction in tool wear in high-speed machining applications.

TRAINING FOR THE SMALLER AEROSPACE MACHINE SHOP

Davies says limited government funding to NIST has held back volumes of research for smaller aerospace manufacturing shops. But he is also quick to point out that education and training are areas where the small shop can truly benefit from NIST's findings.

High-speed machining courses through the American Society for Precision Engineering and the Society for Manufacturing Engineers offer the small precision shop user experience-based training in high-speed machining. These course, up to four hours in length, attempt to describe in more detail what the small shop should think about. Issues on HSK vs. CAT tooling as well as the length of cutters are current hot topics. Such training offers new approaches necessary to maximize benefit from the high-speed machines lining so many machine shop floors today.

NEW MACHINES CALL FOR NEW PROCESSES

"If a small shop gets into high-speed aerospace machining, it is going to find itself using half-inch end mills at four times the speed, or even ten times the speed it used to use them, taking lighter cuts and going faster," says Davies. " But it does not help the small machine shop operation to buy a high-speed machine and use a one-and-a-half inch cutter at 2,000 rpm." Davies says that is typically what many machinists do because it is how they are familiar with operating.

"Not many companies continue to develop new software like the Makino Super Geometric Intelligence 3 control technology. Many of the databases that are in machine software packages are old, and have not been updated substantially since the '70s. So, recommended speeds from those programs are not necessarily the ones to use."

"One example is a high-profile component job NIST is doing currently with pure molybdenum," says Davies. "The recommendation from the machine software database was to machine at very low speeds and go as slowly as possible. However, we noticed that if we did speed up the process, we got much better behavior out of modern high-speed machining. So we ended up speeding up the process substantially, probably four to five times the recommendation, and we got much better results."

For the small shop interested in high-speed machining, it can simply be a matter of retraining for many machinists used to the methods of conventional machining. The first instinct of many machinists when faced with chatter problems, for instance, is to turn down the spindle speed. But Davies warns that this isn't always the best approach. "When you deal with chatter problems by turning down the spindle speed, you end up using your machines at only 25 percent capacity."

BIG THINGS TO COME

The NIST continues to pursue machining developments for the military and beyond. "One big project NIST has been working on for the past three years with the U.S. Navy is the Naval Foundry and Propeller Center in Philadelphia," says Davies. The Naval Foundry and Propeller Center is responsible for the manufacture of propulsion system components for ships and submarines, in which castings of up to 110,000 pounds are machined down to about 80,000 pounds with five-axis machine tools. The center is currently facing slow manufacturing due to outdated processes, something NIST is working hard to help them correct.

"And, they are often hand-finished in critical areas because the older machines are not fast enough to do the type of finish work that is being done in the die/mold industry," Davies says. "It is similar to the technological gap that occurred with die/mold issues in the auto industry a decade or two ago. The Navy wants to transition the Naval Foundry and Propeller Center to high-speed machining and we are going to assist them." As NIST continues its research in high-speed machining, military and private sector manufacturers alike will continue to learn from their invaluable developments.

For additional information about NIST, the National Institute of Standards and Research, contact them by phone at 301-975 NIST (6478). Or, visit their Website at www.nist.gov.

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