Conventional simulations performed prior to producing injection-molded components are based on the assumption that mold temperature remains fixed and constant over time. This method, however, ignores the complex thermal processes that take place within the mold that are governed by the heat-transfer properties of the materials present throughout the system, including the polymer melt, runner system, inserts, mold, and isolation materials. Pursuing a new approach, Sigma Plastic Services Inc. (Schaumburg, IL) has developed 3-D software that allows injection molders to calculate multiple consecutive production cycles accurately, simulating the thermal interactions that occur throughout all of the components in the mold.

Sigmasoft software drives new mold designs, develops molding processes, or solves molding problems, according to Matt Proske, applications manager at Sigma Plastic Services. It is employed to visualize and understand what is going on in any area of the mold or polymer part at any point during the manufacturing process. "It's sort of like a user-friendly CAT thermal imaging scanner for injection molders," Proske comments. "At any point in time, you can see everything that is happening anywhere in the mold, but with the added benefit of being able to use it to predict the future outcome of a molding trial without actually building the mold."

Traditional simulation programs were developed for use by analyst groups to validate part designs based on complex meshing operations, Proske explains. Unlike such programs, Sigmasoft dispenses with time-consuming and tedious meshing steps, enabling engineers with process knowledge to perform multicycle simulations involving the complete mold and the entire molding process. "A multicycle process simulation calculates the coupled heat and fluid flow through the entire mold over the course of multiple consecutive cycles," Proske says. "The mold and process work together to produce a part, and this relationship is critical for part quality. The mold temperature influences solidification rates, which influence such factors as crystallization or part temperature at mold open, both of which influence the final shape of the part."

Medical parts require tighter tolerances than parts used in other industries, Proske notes. By including the entire mold and process in a virtual production setup, these tight tolerances are more easily achieved during production. "During process simulation, much more information is available, and problems can be corrected before the mold is built, resulting in a mold and a process that were developed for each other."

"Sigmasoft can be used to validate part designs," Proske says, "but its true intention is to develop a mold and process simultaneously in order to produce quality parts the first time you run the mold."