Process Simulation Modeling in LSR Injection Molding with Reactive Viscosity Techniques

Complex rheology evaluation of Dow Corning’s XIAMETER^® Brand Liquid Silicone Rubber (LSR) is studied by applying techniques in reactive viscosity measurement. Reactive viscosity measurements, compiled with other physical data on these materials, can be data fitted and formatted for use by SOLIDWORKS^® Flow Simulation, Autodesk Moldflow^® Simulation, and SIGMASOFT^® 3D Simulation software products. New techniques in measuring reactive viscosity using Alpha Technologies rheometry instruments are shown to enhance the accuracy of modeling LSR flow in computer simulation software. The software available from these and other sources have recently improved their reactive modeling techniques to a high degree of accuracy by using reactive rheology data fitted to “multi-point data” sets that provide real-world results unlike ever before.

Algorithm data fitting based on these reactive models considers the complexity of thermoset “cure” behavior in creation of the “multi-point data” sets. A reactive modeling method of this complexity considers (1) the degree of cure, (2) the temperature, (3) the shear-rate, and (4) the structural rebuild time. This builds a four dimensional contour plot of flow behavior within the normal LSR injection process window typically used in efficient LSR injection molding processes. At degrees of cure just above two percent, the onset of gel-flow behavior begins. Older software modeling techniques did not take into account the gel-flow behavior, and merely provided a “single-point data” at an uncured or “gel-free” state. Without considering gel-flow behavior in the simulation model, real-world simulation is not possible because injection molding of LSR operates across the gel-flow range of 3 to 5 percent, with as much as 40 percent degree of cure.

It is important to consider the relevance of these new flow simulation methods in computer aided designs and how best to adopt them into LSR injection mold simulations—particularly in the designs that use LSR. This paper will show how using “multipoint data” sets can save time and money for the Mold Designer.