A Simple Press for Complex Parts

October 1, 2001
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A new press developed for powder metallurgy applications is showing promise for efficiently producing high quality, complex-geometry ceramic parts in net shapes.

Author Glenn Beane stands near the new press (left), which is about the size of a small refrigerator, compared to the up-ended tractor-trailer size of the traditional compaction press in the middle.
Since the advent of compaction technology in the early 20th century, press design has improved incrementally but has always been in the form of very large, fixed, hydraulic or mechanical gravity-fed presses. The traditional analog apparatus controlling the process of bringing the powder into the press and then compressing it into the desired shape results in many parts that have to be machined to make them usable or, in too many cases, have to be discarded entirely, greatly reducing the yield and efficiency of the system. The size and the range of geometries—i.e., the complexity of parts that can be manufactured in these systems—have often been limited by the design of these production systems.

Late last year, a fully digitally controlled press, totally powered by hydraulics, was introduced.* The new system is about the size of a refrigerator, rather than the huge, up-ended tractor-trailer size of most traditional compaction presses. Initially developed specifically for the powder metallurgy industry, the system has recently been proven to successfully produce complex-geometry ceramic parts as well. The new system produces parts with much greater green strength, lower and more uniform shrinkage, and minimal ejection/deflection cracking.

Although the new system incorporates dozens of individual innovations, the real key to the success of the new technology is in replacing brute force with intelligence and art with digital technology. From the carefully calculated weighing of the powdered materials, to the “fluidization” of the materials that assures uniform distribution of materials in the die cavity, to the digitally controlled pressure system, each step applies a level of intelligence that requires far less size and weight than a traditional press—while producing a superior product. The digital control also makes possible highly accurate, constant quality control, as well as remote diagnostics and troubleshooting.

The new system, recently named one of three “Inventions of the Year” by TIME Magazine, offers ceramic manufacturers the potential to expand the design envelope, producing higher-quality parts and a larger range of parts with little or no post-press machining, while affording dramatically lower downtime for presses.

Accurate Measurement

Traditional presses measure the powdered material for each part by volume. This method of measurement results in variations in the actual weight of the material, and these variations can have serious implications for mechanical tolerances and create unacceptable differences in performance from one part to another.

The new system, by contrast, measures the powder by weight, ensuring that measurements are consistent to within ±0.1 gram and as fine as ±0.04 gram, regardless of the part size, versus a typical weight variation reported at 5 to 8% per part. The result is reliable consistency in density—a key requirement for high performance from one part to another. Higher density can also be achieved compared to conventional pressing technologies—compaction pressures have reached 50 tons per square in. (TSI) in initial production runs with ceramic materials, and a potential of 65 TSI is possible.** This compares with the 5 to 10 TSI achieved with traditional ceramic compaction presses.

A ceramic part pressed at 50 tons per square in. using the new compaction pressing technology.

Fluidization

Once the powder has been measured, it is placed in the die for pressing. With traditional presses, this process, too, can introduce inconsistencies in the amount of material in different parts of the die, resulting in variations in structural performance and density from one segment of the resulting part to another. The apparent size of the part may be consistent, but the density can vary, making its strength greater or less from segment to segment.

The new technology solves this problem by “fluidizing” the powder before pressing. Once in the die, a rapid flow of air is introduced to the die, turning the powder into a fluid. When the fluidized powder settles, it settles uniformly throughout the die, assuring uniform performance throughout the part.

By combining an accurate method of measuring inflow to the system—the weight system—and a method of assuring even distribution of the materials in the press—fluidization—the new technology reliably produces parts that require little or no after-press machining.

Docking Station Architecture

A key factor in reducing the size of the press was the concept of the “docking station,” which separates the energy source from the press itself. In traditional presses, each piece of equipment has its own power source, typically an electric motor that drives a flywheel. The motor and flywheel add a great deal to the size and weight of a traditional compaction press.

In the new system, the power is hydraulic and comes from a separate and remote power system that is digitally controlled. While tapping into a common hydraulic power system, each punch—the top and bottom faces of the manufactured part—is independently controlled. Each level of a punch (up to eight levels) has its own position transducer and its own pressure transducer. This allows each part of the press to monitor and manage its own piece of the manufacturing process, all within a total manufacturing system that manages the entire process.

The docking system also allows manufacturers to quickly remove a press from service—unplugging it from the hydraulic, electric and electronic connections in the docking station—and replace it with another. With traditional compaction presses, several days of downtime are often required for retooling when the manufacturing regime shifts from one part to another. With the new system, this type of changeover can be accomplished in a matter of hours, rather than days.

Lights-Out Manufacturing and Remote Diagnostics

Further benefits of the fully digital control of the press system are the flexibility it provides for operating the press. Because its operation is constantly monitored by the sensors and the computer software, the press can run 24 hours a day, seven days a week with just one shift of workers—true lights-out manufacturing. Traditional presses, by contrast, require the constant presence of an operator.

If any problems arise with the new system when no operator is present, the system’s computer can call or “beep” an operator who may be able to diagnose and solve the problem remotely. Otherwise, the operator can go in to the factory to make the fix or simply shut the system down until the next business day. If the problem is too difficult for the operator to address, off-site support staff can use the same remote diagnostics and troubleshooting tools from virtually any location.

The digital, computer-controlled system also allows manufacturers to draw on the much larger pool of potential employees with computer experience rather than the much smaller pool of experienced traditional press operators. And the small size means that a manufacturer can move a press from one location to another easily to respond to changing business opportunities—in North America or abroad.

Putting Theory into Practice

While all these benefits may sound appealing, few of today’s companies can afford to invest in “experimental” technologies. For that reason, the company that invented the new press system began a series of tests with Ferro Corp. several months ago to prove the feasibility of the press in ceramic manufacturing. According to Ferro, this new technology shows a great deal of promise.

“For Ferro, advances in pressing are extremely important, since our customers often ask us to investigate complex parts that, unfortunately, we just cannot manufacture using traditional technologies,” explained Jyoti Chakraverty, new product development manager for Ferro’s North American Ceramic Division.

“Our initial findings [with the new press] have been extremely positive. Although further research and collaboration are necessary, Ferro may soon be able to press even the most complex shapes requested by our customers, including some that currently would not be possible using existing technologies,” Chakraverty added.

For More Information

For more information about the new pressing technology, contact Glenn Beane at Mii Technologies LLC, 17 Interchange Dr., West Lebanon, NH 03784; (603) 298-0422; fax (603) 298-0425; e-mail glenn.beane@miitechnologies.com; or visit www.miitechnologies.com.

*The new technology is commercially available through Mii Technologies LLC
**Although ceramic materials have yet to be tested at 65 TSI, metal powders of largely the same physical characteristics are regularly pressed at this level of pressure.


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