Injection Molding: Adaptive Shot-Size Control Now Available for Thermosets

KraussMaffei now offers its APC plus adaptive process control for thermoset injection molding. Previously applicable only to thermoplastics, APC plus is designed to maintain shot-weight consistency despite material variations and changes in ambient conditions. The software measures viscosity and adjusts the injection changeover point and holding pressure of the current shot, based on a predicted injection volume. The “plus” designation differs from the earlier-generation APC function by including a library of materials data such as melt density and melt compressibility, which are critical to consistent cavity filling and packing.

Now, APC plus is available for molding free-flowing thermosets such as granular phenolic, melamine, urea, unsaturated polyester and epoxy molding compounds, as well as polyester BMC/SMC and liquid or solid silicones. KraussMaffei says the adaptive control is all the more necessary for thermosets because of high fiber/filler contents (up to 80%), more pronounced batch-to-batch variations than with thermoplastics, and the absence of a check valve to prevent precuring in the barrel. Due to the high filler contents and low molding temperatures, thermoset compounds are much less compressible than thermoplastics. As a result, minimal deviations of the start of filling are not visible to machine operators.

The thermoset capability of APC plus was proven at German molder Baumgarten automotive technics GmbH, which helped develop the new functionality. Baumgarten has been using APC plus for a year to mold phenolic oil-pump adjusting rings (pictured) in a three-shift operation and reportedly has been able to reduce scrap significantly.