Soluble Cores with a 3D Printer

Application Outline

Composite parts are manufactured by winding, wrapping, molding and laying up various combinations of materials and resin systems on molds, bucks, patterns, cores and mandrels. Producing hollow composite parts that trap the pattern can present a manufacturing challenge. 

This new approach provides substantial improvements for low–volume production by replacing the mold with an FDM soluble core. Soluble cores substantially reduce delivery lead time and labour expenses by eliminating the need for making a mold and also reducing the time required for laying up the part. Instead of the tedious process of laying up the two mold halves, then laying up the part in each half, and then bonding the two halves together, the composite cloth can be wrapped around the soluble core. After the part has cured, the core is simply dissolved using a supplied dishwasher component.

The nature of additive manufacturing makes it possible for FDM to produce much more complex geometries than are possible with other cores. In many applications, greater design freedom generates performance improvements and cost reductions. FDM soluble cores are strong enough to withstand the loads of composite manufacturing processes and there is no risk of damaging the part during core extraction because the core simply melts away as it soaks in a liquid bath. 

Process Overview

Manufacturing FDM soluble cores requires two changes to the standard FDM process. First, the core is designed to make its internal structure mostly hollow. Second, the strong thermoplastic of a standard FDM part is replaced with a soluble material that is normally used for the construction of a part’s support structures. The core can be designed in two different ways. One way is to create a solid 3D model and use the sparse fill option, while in Insight — the Fortus build prepartion software — to automatically create an internal structure that minimizes the internal volume of the core. The second approach is to create (in CAD) an internal structure that keeps the core stable under the temperatures and pressures of composite molding while promoting flow of the solution to accelerate core removal. Both of these approaches minimize material consumption, build time and washout time.

It’s relatively simple to integrate FDM soluble cores into the manufacturing process. No modifications to the process are needed prior to composite curing and core removal. The cure cycle is also unchanged, but temperatures must be limited to avoid distortion. In general, composite parts with FDM cores must be cured at temperatures below 250 °F (121 °C) and at pressures less than 50 psi (345 kPa). The only process change is that, after the composite part has cured, the core is removed by dissolving it in a solution bath. To do so, the part is placed in the Stratasys WaterWorks soluble support system.