New research provides guidance for optimized thermoplastic composite overmolding

Overmolding is a technology in which a thermoplastic composite laminate is thermoformed and subsequently injection overmolded. This near-net-shape manufacturing process is well suited for automated large series production of complex 3D structures with excellent structural performance and a high level of function integration.

However, the industry lacks process design tools. Responding to this need, researchers at the ThermoPlastic composite Research Center (TPRC, Enschede, Netherlands) analyzed the overmolding process, focusing on the bond strength between the overmolded composite laminate and the injected polymer resin/reinforced composites. Using process modeling and mechanical testing, they evaluated both a single-step and a dual-step process. Results showed distinctly different process mechanisms and resulting material structure and mechanical performance in the overmolded composite parts.

Starting from De Gennes' classical reptation theory for reptation and healing of amorphous polymers, an alternative approach was developed to describe the strength development for semi-crystalline materials. A rudimentary description of the degree of melting was implemented to predict the bond strength as a function of the thermo-mechanical history at the interface during forming and subsequent resin injection for PA6 and PEEK, both semi-crystalline matrix materials.

The full article, “Analysis of the Thermoplastic Composite Overmolding Process: Interface Strength” can be found in Frontiers in Materials. Read more about TPRC’s overmolding research here.

Reptation

Reptation—motion of long linear, entangled macromolecules amorphous polymers. SOURCE | Carl Henderson, Wikimedia Commons.

A theory proposed by Piere Gill deGennes in 1971 and later extended to the tube model by Maasai Doi and Sam Edwards. It describes the thermal motion of long polymer chains in concentrated solutions and melts, postulating that individual polymer chains, constrained by their neighbors, move primarily along their own contours in a snakelike fashion. Hence its name, derived from the Latin reptare, to creep. Reptation-based models have reportedly been successful in reconciling a wide range of experimental observations and are broadly in agreement with more recent computational results.

REFERENCES | “Activated reptation: Coupling of polymer dynamics to density fluctuations” and “Reptation and Tube Model” from polymerdatabase.com