THE 3D PRINTING SOLUTIONS COMPANY

A P P L I C AT I O N B R I E F :

FDM Sacrificial Cores and Mandrels for Composite Layups

OVERVIEW

Hollow, composite parts present a unique

manufacturing challenge. Cores are used to

create the hollow features in composite structures

when smooth internal surface finish and seam-

free construction are required. Some cores can

be easily removed because of the part’s design

geometry, but any configuration that traps a core or

mandrel inside it requires special, often sacrificial

tooling (Figure 1).

Typically, sacrificial cores are made from eutectic

salt, ceramic or urethane. These options present

several challenges:

• Can limit part geometry

• Requires machined tooling to make

• Uses harsh removal procedures

• Difficult to handle, particularly fragile components

FDM IS A BEST FITPart geometry:

• Complex, hollow parts

- Requires multi-piece molds

- Bonding that yields a seam

• Replace other core/mandrel production methods

Part requirements:

• Quantities: 1 to 100s

• Seamless

• Wrinkle-free

• Good internal surface finish and accuracy

Composite manufacturing:

• Initial cure temperature:

- < 121 °C (250 °F)

- Can post-cure to higher temperature

• Consolidation pressure:

- < 550 kPa (80 psi)S T R ATA S Y S . C O M

BENEFITS OF FDMAverage lead time savings:

• 50% – 85%

- From design to final part

Average cost savings:

• 75% – 95%

- From design to final part

Reduced labor:

• Less tooling and setup

• No bonding of composite sections

• Hands-free core manufacturing

Improved composite parts:

• Single-piece construction

• More features, including integrated hardware

• Control over surface finish and accuracy

- Core only: part’s internal surfaces

- Core and mold: part’s internal and external surfaces

Lower risk:

• Minimal investment

• Easier to modify

• Greater durability

• Improved consistency

• Higher part yield

A P P L I C AT I O N B R I E F :

FDM Sacrificial Cores and Mandrels for Composite Layups

For these reasons, composites are more

commonly laid up in clamshell tooling. If there

is sufficient access to the interior of a closed

clamshell tool, composite material is put into the

mold and pressed against the cavity walls (Figure

2). For more complex geometries where access is

a problem, the part must be cured in two halves

and bonded together. This results in a seam that

weakens the part.

APPLICATION OUTLINE

Sacrificial cores yield several performance

advantages when used in place of clamshell

tooling. For example, because the composite

fabric is laid up on a male core, it can be favorably

oriented and overlapped to create a seam-free

part with optimal mechanical properties (Figure 3).

Using a male tool also eliminates interior wrinkles,

and provides control over interior accuracy and

surface finish.

Figure 1: Composite performance racing part with hollow ports and chambers.

Figure 2: Two-piece clamshell tooling and composite duct.

Figure 2: Two-piece clamshell tooling and composite duct.

ULTEM® 9085 RESIN SUPPORT FOR SACRIFICIAL CORES

ULTEM 9085 resin is a strong, high-temperature thermoplastic that uses a support material which may be used for sacrificial cores. Exposing it to acetone embrittles the material, allowing it to be extracted. This option is ideal when molding or curing temperatures exceed the limits of FDM soluble support materials, or when parts contain aluminum inserts that may be corroded by the support removal solution.

FDM SACRIFICIAL CORES AND MANDRELS FOR COMPOSITE LAYUPS / 2

A P P L I C AT I O N B R I E F :

FDM Sacrificial Cores and Mandrels for Composite Layups

FDM® is an additive manufacturing process that

builds plastic parts layer by layer, using data from

computer-aided design (CAD) files.

Sacrificial cores made with FDM technology use

the same soluble material that’s used as support

structure for FDM parts. However, unlike other

core materials that require harsh methods for

removal from the composite, FDM soluble cores

are easily washed away in a detergent solution

(Figure 4). This reduces the risk of damaging the

part during core extraction. Additionally, FDM

provides a much higher level of design freedom

than other types of technologies. This allows the

creation of more robust, complex cores that result

in composite parts with improved performance

and functionality (Figure 5).

FDM soluble cores are strong enough to withstand

the temperatures and pressures associated

with composite manufacturing processes. And,

because the core is produced in an automated

process and the composite can be laid up directly

on the soluble core, much of the tooling and labor

is eliminated. This yields substantial reductions in

lead time and cost.

PROCESS OVERVIEW

The first step is to design a 3D model of the core

geometry. During pre-processing of the digital

data, there are two modifications required to

ensure ease of core removal. First, the core is

produced with an internal structure that makes

it mostly hollow. Second, the soluble material

normally used for support structures replaces the

standard FDM thermoplastic.

Integrating FDM soluble cores into the composite

manufacturing process is straightforward with

minimal modifications. The composite curing

FDM SACRIFICIAL CORES AND MANDRELS FOR COMPOSITE LAYUPS / 3

Figure 4: Soluble core dissolves in a support removal bath (SR-30).

Figure 5: Composite duct — no seams, no interior wrinkles.

A P P L I C AT I O N B R I E F :

FDM Sacrificial Cores and Mandrels for Composite Layups

cycle is unchanged as long as the cure temperatures

and pressures are within the specifications of the

FDM material. After curing, simply wash away the

core by soaking the part in a support removal bath.

CUSTOMER STORY

Champion Motorsport’s legacy of performance

on the racetrack drives the performance of its

aftermarket products. The Le Mans-winning team

develops, perfects and proves its technology on

the track and then leverages it to create aftermarket

Porsche equipment.

When manufacturing a turbo inlet duct for the

Porsche 997 Turbo, Champion used sacrificial FDM

cores to overcome the challenges of making this

high-performance carbon fiber part (Figure 6).

“We substantially improved the quality of carbon

fiber turbo inlet ducts and other aftermarket parts

by making them with FDM soluble cores,” said

Chris Lyew, lead mechanical engineer for Champion

Motorsport.

Lyew adds, “The use of FDM soluble cores makes

it possible to mold the duct in a single piece that

is much stronger than parts produced by bonding.

Every FDM soluble core is exactly the same so it’s

easy to maintain the internal finish of the duct. Also,

FDM soluble cores are produced in less time and

at a lower cost than sand cores because they don’t

require a mold.”

FDM SACRIFICIAL CORES AND MANDRELS FOR COMPOSITE LAYUPS / 4

Figure 6: Carbon fiber turbo inlet duct (black) for Porsche engine with matching soluble core (SR-30).

A P P L I C AT I O N B R I E F :

FDM Sacrificial Cores and Mandrels for Composite Layups

Application compatibility:

(0 – N/A, 1 – Low, 5 – High)

• FDM: Idea (0), Design (0), Production (5)

• PolyJet™: Design (0), Production (0)

Companion and reference materials:

• Technical application guide − Document

• Application brief − Document

• Video − Commercial − Success story − How It’s Used

• Referenced processes − Best Practice: Removing Soluble Supports − Best Practice: Bonding − Best Practice: CAD to STL

CUSTOMER PROFILE

Forward-thinking designers,engineers and manufacturers of composite parts for:

• Aerospace, automotive, marine, robotics

• Performance sports

• Medical prosthetics/orthotics

Characteristics:

• Low-volume manufacturing

- Challenging, hollow composite parts

• Open to change or seeking innovation

Traditional technology obstacles:

• High labor demands

- Limited design freedom

- Configured to allow core removal

• Tooling

- High cost

- Long lead time

- Many mold components

- Cores hard to work with

- Inconsistent core features

- Difficult core removal processes

• Reduced part strength with clamshell molding

REFERENCE COMPANIES

FDM SACRIFICIAL CORES AND MANDRELS FOR COMPOSITE LAYUPS / 5

info@stratasys.com

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Rehovot 76124, Israel

+972 74 745-4000

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The information contained herein is for general reference purposes only and may not be suitable for your situation. As such, Stratasys does not warranty this information. For assistance concerning your specific application, consult a Stratasys application engineer. To ensure user safety, Stratasys recommends reading, understanding, and adhering to the safety and usage directions for all Stratasys and other manufacturers’ equipment and products. In addition, when using products like paints, solvents, epoxies, Stratasys recommends that users perform a product test on a sample part or a non-critical area of the final part to determine product suitability and prevent part damage.

For more information about Stratasys systems, materials and applications, call 888.480.3548 or visit www.stratasys.com

THE 3D PRINTING SOLUTIONS COMPANY

CONTACT:

To obtain more information on this application, contact:

Stratasys Appl icat ion Engineer ing

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