The way an injection-molded part is made largely determines its performance. During the injection-molding process, plastics are susceptible to shrinkage and warping. Moreover, filling molds with molten plastic can be problematic if the desired part contains multiple cavities or other complex features.

Many engineers, unfamiliar with analysis or pressed by tight deadlines, require outside expertise. U.S. Moldflow Consulting International, a unit of Moldflow Pty. Ltd. in Shelton, Conn., routinely receives IGES files from suppliers to large automakers who need to know in a hurry whether their designs are going to work. The files are translated into surface models using the translation and modeling tools of Strim software from Matra Datavision in Andover, Mass., then prepared for flow, cooling, and warping analyses with Moldflow software.

In an example, engineers optimize part geometry using Strim's robust translation and surface-modeling tools to evaluate the quality of the surface, repairing gaps and overlaps, eliminating extraneous details, and creating midplane surfaces. With the Moldflow program they mesh the model and perform a series of flow analyses to study how the part would fill in order to determine the optimum number and placement of gates for plastic injection. Engineers also have to know how the molten plastic will cool to predict shrinkage. These analyses are used to determine whether the finished part will become deformed during cooling.

A sidebar to the article discusses Moldflow's MF/MIDPLANE software for creating a midplane mesh.

The above was adapted from an article by Dan Deitz, Associate Editor. The full text can be found in the October 1996 issue of Mechanical Engineering magazine. ©1996 ASME International. To obtain a copy of this issue, click here.

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