Creating soluble cores with additive manufacturing

You might say that, with its wide adoption as a soluble core for carbon-composite-part production, additive manufacturing support materials have added a valuable side hustle to their day job. It's easy to see why — water-soluble support materials offer key advantages over conventional methods used to create internal cavities in composite parts manufacturing.

Soluble core use for composites is ideally suited for applications like the complex ducting found in aerospace and auto racing. As materials and printers continue to evolve, soluble cores are worth exploring for any application where the optimum solution centers on complex voids. 

Composite parts are created from layers of material (the "fiber") and a binding resin, which are then shaped by winding, wrapping, or molding over a core, pattern, or mandrel.

Creating hollow parts can present challenges with traditional methods; removing internal supports can be difficult, and complex cavities are ruled out entirely.

The solution is a soluble, or sacrificial, core. After printing, the soluble core is the form around which the carbon fiber is set. After curing in an autoclave, the core is simply washed out.

Soluble cores are ideal and, in many cases, the only solution for creating the complex ductwork found in aerospace and auto racing.

Soluble cores open up new options for implementing complex internal geometries, but the process offers numerous advantages over standard techniques for building simpler forms.

The time savings for soluble core vs. clamshell construction tends to be dramatic. Many report savings of up to 95% in lead time and labor required with a move to soluble core.

A soluble core eliminates the mold creation, cure, and final bonding steps needed when using a clamshell mold technique. And because you simply wash away your core after the part is cured, you also eliminate the risk of damage during core extraction. Further benefits: no potential weakness at the seams and a smoother interior surface.

A soluble core also eliminates the additional tooling that other material processes — such as eutectic salt, ceramic, and urethane, or memory bladders — require.

In short, the advantages of faster time-to-part, design freedom, and cost savings that have made additive manufacturing a mainstay in jig and fixture production are just as applicable to the use of soluble cores for composite-part manufacturing.

Historically, most support materials have temperature (250°F, 121°C) and pressure (50 ps, 345 kPa) limits that effectively ruled out their application as soluble cores. Today, new materials like AquaSys 180® — which can be printed at chamber temperatures up to 180°C, has thermal stability up to 130°C, and pressure compatibility up to 7 bar —are expanding the application envelope.

Today, AM soluble core usually refers to its application as a layup tool for autoclave or out-of-autoclave processes.

Auto racing and aerospace are characterized by high engineering-performance demands and low production volumes, and additive manufacturing plays well to those requirements.

The two industries have a shared history, sometimes using the same suppliers and in the case of Boeing and Lotus Formula 1, direct collaboration. Boeing has worked for nearly 20 years now with the Lotus team to develop and implement 3D printing technologies. The Lotus team brought fast development capability that Boeing’s OEM suppliers couldn’t match; the partnership has helped speed development cycles.

Speaking of faster, Swift engineering designed and built a single-engine business jet in just 200 days, from commission to first flight. Design, composite tooling, and parts were fabricated and assembled in San Clemente at Swift’s Advanced Composite Manufacturing Center. One piece of this swiftly constructed puzzle was a complex, hollow inlet duct, which the team created using an AM-produced sacrificial tool.

It’s exciting to see what an innovator like Swift can do, but the more mundane impetus of financial pressure is likely to be the primary driver of increased adoption of composite parts in aerospace. The issue is weight.

Higher fuel costs are the Achilles heel of the commercial airline industry. Every pound counts, as every flyer who’s tried to maximize their baggage allotment knows. But weight can be saved elsewhere too, and thus the market for composite aero-engine components has nearly tripled since 2005, according to a recent aerospace industry report.

If you're watching a Formula 1 race, you're looking at some sophisticated composite engineering at work. Motorsport teams tend to keep their engineering breakthroughs to themselves, but Champion Motorsport serves a slightly less competitive customer. They've shared the story of how they create their carbon-composite turbo-inlet ducts using a soluble core.

Chris Lyew, lead mechanical engineer at Champion Motorsport, explained, “The performance of the vehicle depends on a smooth internal surface, while the customer expects a beautiful external surface.”

Traditional methods for creating a sacrificial core — clamshells, bladders, or a sacrificial sand core — couldn’t deliver on those requirements, but a soluble core from a material like AquaSys 180 is ideal for this application.

Soluble-core use is a mature technique in automotive and aerospace applications, but it’s a technology with wider potential that's being used as a supporting technique with investment casting, making more intricate cavity patterns possible, and reducing or eliminating additional machining. Others have experimented with soluble cores in concrete and matrixed materials as well as metal resins.

You can think of soluble core as another arrow in your design for additive manufacturing (DFAM) quiver. DFAM looks at a design differently, reconsidering an object and rethinking its construction, perhaps with fewer parts, or one with very different boundaries and connections.

Whether your objective is a wholesale reinvention of a part or simply bringing production efficiency to a current one, soluble core offers a great new option.