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May 1, 2003

5 Min Read
A first in micromold flow analysis

UMass-Lowell researchers developed codes that empowered their Moldflow MPI software (top) to simulate the effects of the last place to fill in a micromolded part that successfully matched the known resin flow, which was determined through progressive short shots in a micromold from Miniature Tool & Die (above).

One small step has been taken in flow analysis, one that may prove to be a giant leap in the future of micromolding.

Working together with micromoldmaker Miniature Tool & Die Inc. (MTD, Charlton, MA), researchers at the University of Massachusetts-Lowell’s Plastics Engineering Dept. (UML, Lowell, MA) successfully wrote code that enabled their Moldflow flow analysis system to do something new. For the first time anywhere they were able to accurately simulate the last place to fill in a micromolded part—a last place to fill determined previously through progressive short shots of a real micropart in a real micromold.

It’s a test part with design features culled from a variety of different micromolded parts MTD has encountered. Clear PS was used for the short shot and flow analysis, though the micropart has been run in different commodities.

How small is this part? The width across the fingers on its end, the last place to fill, is .087 inch. Its longest dimension is .099 inch. Each of the two slots is .003 inch wide. It’s shot through .002-inch double-edge gating. The whole part weighs .0017g. (If you think this part is small, MTD reportedly has built a mold for micromolding as many as 520 parts/pellet.)

Paradigm Shrinking

If you look really hard, you may see the 24 cavities and cores resting in this mold’s 5-by-3-inch frame. The part, a nozzle component, was being run in a 6-second cycle in more conventional 16-cavity tooling. Because the micromold uses a toothpick-sized runner, it cycled out at 5 seconds. The result was an eight-month ROI, and, in five years’ time, a $713,000 profit, according to MTD’s Donna Bibber.

MTD’s Donna Bibber, VP sales/marketing, discussed micromold flow analysis in her presentation at Molding 2003 (Feb. 24–26, New Orleans, LA), which was titled, “Micromolding: The Growth Market for Injection Molders in the Near Future.”

“From the initial concept stages of designing micromolded components, many challenges exist to manufacture them,” she says. “Each and every step of the way, design and manufacturing engineers are paving the way by developing new technologies, or using existing technology in a way they never did before.”

Engineers usually dimension microparts in thousandths of an inch in their CAD or hardcopy drawings, for instance. Dimensioning in millimeters or microns may represent a paradigm shift in thinking, says Bibber.

Conceptualization of polymer flow in a micromold has been much more challenging. That’s because there’s no system tool designers can use—no commercial micromold flow analysis software exists.

Unconventional Thinking
“The physical properties of microfluidics offer challenges to researchers and product developers alike,” Bibber explains. “Conventional methods of simulating mold flow in macroscale principles do not apply at this scale, and therefore it is not possible to simply scale down with existing software and expect the same results as seen with larger parts.”

Dramatically different fluid mechanics are encountered in a micromold, largely because of the gate sizes through which materials are forced. Bibber says shear heat at the gates is one factor in particular that must be taken into account. Some other paradigm-shifting questions she says engineers should ask themselves include the following:

  •  What are the limitations of what’s possible to micromold (e.g., wall stock, L/D, gate sizes)?

  •  Are there any cavitation limitations?

  •  How do I handle molded microparts?

    It’s hard to believe that such a small part as this could represent a big breakthrough in moldmaking history. It’s only .099 inch long and weighs just .0017g. But it’s reportedly the smallest part ever successfully simulated in flow analysis software—potentially a macro leap in building future micromolds.

    Scientific Micromolding
    Bibber says representatives of UML interested in advancing the state of the micromolding art originally came to visit MTD after reading about the company in IMM. They asked, “What can we do to help?”

    MTD presented the project to UML. As previously reported, UML has considerable flow analysis resources at its disposal. For example, Moldflow Corp. (Lexington, MA) funded UML’s 15-station CAE classroom, in which Moldflow’s most advanced MPI software is run, software UML itself helped develop (see April 2001 IMM, pp. 13-16).

    Since the successful completion of the MTD project and the interest in micromolding it has sparked, UML has received donations of two micromolding machines—an all-electric Nissei AU3 3-tonner from Nissei’s regional representative, Ideal Plastic Systems (Woodstock, CT); and, with the help of micromolder Makuta Technics (Columbus, IN), an 18-ton Sumitomo.

    Bibber is confident that small technological steps now being made will keep pace with the quantum leaps coming in micromolding applications and growth. But she admits that there’s much work yet to be done to transform the micromolding art into a science. “Every mold we design has at least one attribute that teeters on the impossible,” she says.

    Editor’s note: To obtain copies of Molding 2003 presentations, visit Executive Conference Management Inc.’s website at www.executive-conference.com. There will be presentations from MTD and UML on micromolding at Antec 2003. MTD also will exhibit in the Polyshot booth at NPE 2003 in the East Hall, booth 9820.

    Contact information
    Miniature Tool & Die Inc.
    Charlton, MA; Donna Bibber
    (508) 248-0111; www.miniaturetool.com

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