FDM Soluble Cores Simplify Production of Composite Parts

We usually focus on the durable thermoplastics that Fused Deposition Modeling (FDM) parts are built with. But FDM’s water-soluble material, which supports any overhangs or holes in a part’s geometry, is also worth learning about.

Why are soluble support materials important? They actually have more uses than just supporting thermoplastic model material. One real-world application manufacturing engineers are benefiting from is producing cores for composite parts.

Composite parts are built by winding and wrapping fiber and resin material around a core or pattern. These lightweight, high-strength parts are ideal for automotive and aerospace ductwork applications. The master patterns are traditionally made by CNC machining plastic or steel.

fdm soluble cores

An alternative is to wrap composite material around a core made out of FDM soluble material, which simply dissolves in a water-based solution.

In order to create ductwork channels, two halves need to be bonded together or if the layup is built in one piece, the core must be easily removed. Traditionally, companies employ an extractable core or build a mold in two halves and lay up each half inside of a clamshell tool. But these cores and clamshells made out of plastic or steel involve extensive labor for removal.

An alternative is to wrap composite material around a core made out of FDM soluble material, which simply dissolves in a water-based solution.

To build soluble cores, Stratasys Direct Manufacturing project engineers reverse how material is extruded from the machine, so that the 3D CAD model is built in support material and the thermoplastic acts as the support. Once the thermoplastic supports are removed by hand, the end result is a core that dissolves in water and eliminates the challenge of a core trapped inside of a part.

Soluble cores provide several advantages over machined cores, including:

Build parts faster:

Laying up composite parts in a clamshell tool is time consuming and requires the extensive labor of curing two mold halves and bonding them. Soluble cores do not involve tooling and the part can be laid up in one piece, eliminating this extra work and equipment and allowing you to build your parts in less time. Stratasys customers were able to reduce lead times by 50 to 85 percent and labor times by 75 to 95 percent when compared with clamshell tools.

Expand design freedom:

As with any FDM project, the constraints of traditional manufacturing do not apply. You can create complex designs that would not be possible with CNC-machined cores. Likewise, you can make design changes without tooling modifications; all that is needed is a new core based on the updated design.

Mitigate part damage:

Extracting a core from the interior of a part can be a challenging process and raises the risk of damaging or cracking the composite part. Soluble cores eliminate this concern because they simply melt away in a water bath without the need for extraction.

There are a few design guidelines to consider with soluble cores:

  • Pay attention to curing temperatures and pressure: We recommend soluble cores for composite applications with curing temperatures below 200 degrees Fahrenheit and pressures below 50 psi to avoid distortion.

  • Choose the right resins: Make sure the layup resin is epoxy based. Polyester resins are not compatible with the solution that dissolves FDM soluble material.

  • Adjust the density: A sparse-filled core speeds up the dissolving process by promoting the flow of water through the part. We advise creating a lattice or honeycomb core interior instead of a solid one. Stratasys Direct Manufacturing engineers can adjust your file to strike the right balance in producing a structurally-sound core that also dissolves quickly.

Soluble cores are just one example of how FDM can be beneficial for a wide range of manufacturing tooling applications.

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