INJECTION MOLDING: Simulation for Powder Injection Molding

Modeling powder-binder segregation more accurately.

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At NPE2015, new software for improved simulation of powder injection molding (PIM) as previewed by Sigma Engineering GmbH of Germany (U.S. office in Schaumburg, Ill.). Still in development, the new module for Sigmasoft Virtual Molding is said to be a significant advance in simulating powder-binder separation in molding of metal (MIM) and ceramic powders. This allows molders to predict possible quality problems before the mold is built.

According to Sigma, one of the most common reasons for part rejection is powder-binder separation during the molding stage. However, segregation defects are discovered only at the end of the multi-stage production process when the parts are sintered, making scrap that much more costly. The new software predicts how mold and part design, process parameters, and feedstock formulation influence local concentration of metal or ceramic particles throughout the part. Regions with low particle concentration indicate where powder and binder have segregated, leading to possible aesthetic flaws or mechanical failure in the PIM application.

PIM simulation has been available for at least four years, using shear-rate gradients to predict particle segregation. This model worked well for low particle content. But when feedstock particle content rises to levels of 55-65%, factors other than shear have significant effects on segregation, Sigma says. The new model takes into account the interactions between shear rate, particle concentration, temperature gradients, and melt viscosity and their ultimate effects on the filling pattern and particle segregation.

The accompanying image shows a simulation of a watchband clasp, produced by Alliance in France, which has strict requirements for part appearance, which can be affected by particle segregation.