Through Thick and Thin

If you’re an injection molder or mold designer, you probably keep an eye on developments in computerized mold simulation. Perhaps you have been wondering about a phenomenon that has puzzled me, too. Why have the bulk of innovations in mold simulation over the past two years been devoted to applications that account for only 5% to 10% of the parts being molded? Why has most of the news lately concerned 3D analysis (using 3D solid mesh elements) when 90% to 95% of plastic parts can be analyzed faster with conventional 2.5D analysis?
3D simulation was developed for thick, solid parts or ones with localized thick sections. Such parts cannot be simulated as accurately with the 2.5D analysis developed for more typical “thin-shell” parts. Murali Annareddy, product line manager for Moldflow Corp., laid out for me three reasons why 3D analysis has dominated recent product debuts (see story on p. 35).

One reason is the proliferation of parts that can benefit from 3D simulation. As plastics find their way into more high-strength applications, more new parts have thin-shell geometry with some thick sections.

Second, Annareddy sees an industry-wide shift toward 3D structural analysis programs like Ansys and Abaqus. Design engineers want interfaces from mold simulation so these programs can translate predictions of molded-in stresses and fiber orientation into structural properties.

Third, Annareddy said there is a perception that 3D analysis is more accurate even for thin-shell parts. But 3D simulation is probably “overkill” for thin-shell parts, he says, because the results of 3D or 2.5D analysis would be very close, and 3D analysis takes much more computer time and memory. Moldflow’s answer will be a future release that allows users to mix regions of 2.5D and 3D analysis in the same model. Speed and accuracy: The best of both dimensions.