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Predicting metal molding success
Joseph Ogando, Materials Editor -- Design News, April 23, 2001
Morristown, NJ —Anyone who designs an injection molded part has to grapple with two great unknowns: Will the mold fill? And if it does, what's the best way to fill it? Enter mold-filling simulation software, which predicts a part's molding prospects from its CAD model. While off-the-shelf analysis software has traditionally targeted plastic parts, engineers at Honeywell Corp. have now applied the same simulation methods to metal injection molding (MIM).
To simulate the molding behavior of Honeywell's PowderFlo MIM materials, the company's simulation experts use MPI/3D from Moldflow Corp. (Wayland, MA). "The software has been doing a great job in predicting how a part will fill, the location of the weld lines, and the best gating scenarios," says Craig Scott, a Honeywell applications engineer who specializes in CAE and process simulation. He adds that much of the software's value comes from its knack for revealing the flow patterns that contribute to warp. "This ability has saved us a lot of time and money," he says, explaining that warp appears late in the design process and can trigger expensive tooling changes.
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| Off-the-shelf molding simulation software for plastics has now been applied to metal injection molded parts-- like this turbine blade. |
According to Scott, flow analysis suits MIM for the same reason it suits plastics. It flags molding problems very early in the design process—while the part still flickers on someone's workstation. "It helps us reduce the number of design iterations and avoid costly tooling modifications later on," he says. Over the past year, Honeywell has used the software on numerous parts that would formerly have reached the prototype stage without any certainty of molding success. These jobs included a 200-gram nickel alloy turbocharger rotor and a 62-gram Hastelloy combustion swirler for an aircraft engine.
One key to Honeywell's success with filling analysis has been its reliance on true-3D code rather than code that relies on midplane representations—the so-called "21/2D" approach. Scott points out that the majority of MIM parts feature relatively thick sections that exceed the 6 to 8 mm practical limitation of midplane simulations. "When we tried a 21/2D analysis, it returned some funny results," he says.
Tailoring Moldflow's software to MIM did require some preliminary work. Scott reports that Honeywell, with Moldflow's help, had to characterize the rheology of the PowderFlo materials, which consist of various metals and alloys in a water-soluble agar carrier. With these two distinct components, the MIM materials flow differently than plastic, Scott explains. The metals also exhibited thermal conductivity characteristics that didn't mesh with Moldflow's plastic-oriented code. "A lot of thought went into accounting for the differences between our materials and plastics," he says. Once Honeywell worked around the characterization glitches, though, the software started turning out results for metal as accurate as those for plastics. Scott puts the simulation-to-reality accuracy at around 90% for all outputs save one: "Injection pressure has been more like 80%."
PowderFlo materials have now been included in the database that underlies Moldflow simulations, so the software can now be applied to any application using this family of MIM materials. Those who use other MIM feedstocks, though, shouldn't rule out simulation. While Moldflow has not yet developed a product focused on metal molding, MPI product manager Dean Piepiora says Moldflow will work with potential users to characterize other MIM systems. "If someone wants to test and try a new material, we'll help them do it," he says.
For more information about mold-filling analysis software from Moldflow Corp.: Enter 537 For more information about MIM materials from Honeywell Corp.: Enter 538
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