Carbon Foam Composite Tooling
Technology Overview
Construction of aircraft, spacecraft, missile parts, automobiles, and sporting goods equipment is rapidly moving to carbon fiber-reinforced thermoset and thermoplastic resins, resulting in higher strength-to-weight ratio, higher stiffness, and less susceptibility to corrosion and fatigue.
CFOAM® -based carbon foam composite tooling offers an alternative to conventional Invar®, steel, and aluminum tools - simplifying tool design and reducing the time to build a tool.
Tooling must be low cost, rigid, durable, thermally stable - offer a low CTE (coefficient of thermal expansion), and, in many cases, be lightweight.
For dimensional stability of the tool, the CTE must closely match the part being produced. CFOAM carbon foam has a very uniform thermal expansion when compared with Invar® 36 and 42. This enables post curing of the composite parts on the tool with high temperature BMI resins.
Touchstone performed a comprehensive benefit analysis comparing the use of CFOAM® carbon foam versus Invar®, aluminum, and steel tools. The finding identified that the use of CFOAM carbon foam would not just be a suitable alternative to the current method, but also provide the following advantages:
Low coeffecient of thermal expansion for composite tooling more closely matching composite part
Lower fabrication costs
Lighter weight tools
Tooling easier to modify or repair
Improved performance durability
Increased autoclave part throughput due to low mass tooling
Touchstone has developed unique process methods critical for manufacturing carbon foam composite tooling. Both rapid and durable tooling methods have been developed. Tool performance was tested and evaluated. Important developments were made in tooling surface coatings, including continuous and chopped fiber with BMI resins. CFOAM® carbon foam composite tools are currently in-service today and are successfully being used at commercial composite lay-up production facilities. |
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Fabrication Techniques
Block Bonding
Dimensions for the tool will be necessary before any work can begin. When the size and shape are determined, CFOAM carbon foam blocks are then stacked to the desired finished part geometry.
Use the CFOAM carbon foam bonding adhesive to adhere all of the blocks together in the proper form. Use a notched trowel to ensure a sufficient amount of adhesive has been applied. Apply the adhesive to both the surface and the edges where any of the blocks are touching each other and follow the adhesive curing instructions.
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Rough Machining After the adhesive has dried, the resulting CFOAM carbon foam block can be machined into the proper shape. However, this machined product should be undersized from the actual dimensions to allow room for the composite surfacing material. The specific under-cut will vary depending upon the type of surface being applied. Several different surfacing materials have been developed and tested. Consult Touchsone's technical support for additional information regarding specific surfacing material. |  |
 | Adding Composite The unfinished tool is now ready for the application of the adhesive and surfacing materials applied to the surface of the rough machined CFOAM carbon foam. Apply adhesive film (cut to size) to the bottom of the tool. In this example, a bi-directional carbon pre-preg is used. The weight of this material varies, and should be adjusted as needed. The amount of material will primarily be driven by the durability and handling requirements of the tool. The pre-preg is now cut to size and applied to the bottom of the tool. This is cut slightly larger than the actual measurements to allow for trimming. Each individual piece is trimmed before the next layer is applied. |
Once all the pieces are applied to the bottom, begin working on the sides of the tool. The adhesive film is applied as before and the same process is followed until all sides are covered. Flip the tool over and apply the adhesive to the top surface. This process can be done in sections if the tool has a complex geometry to to ensure that if adheres properly. Press firmly onto the tool to avoid air pockets behind the adhesive. The tool is now ready for the applicatoin of surface material. As with adhesive, it should be applied in sections per the engineering ply layout. |  |
| Final Preparation and Processing The tool is now ready to be placed into a vacuum bag and autoclave cured. Vacuum bagging materials and procedures are dependent upon specific resin systems and may also be varied depending upon part geometries. |  |
The tool is now ready to be placed into the autoclave. Attach a vacuum line to the tool inside the autoclave, seal the door, shut and set the program to the manufacturers surface curing temperatures. |  |
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Remove the composite tool from the autoclave and the vacuum bag. It is now ready to be machined to final size. When the composite tool is completed in the mill, a seal coating is applied to the top surface. This will fill any pinholes or scratches on the surface. Finally, the tool is wet sanded for a polished finish. |
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The surface hardness on this kind of tool has been measured to be 83 Rockwell B, which is comparable to many Invar® tool surfaces. |
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How To Get Started Touchstone provides custom CFOAM carbon foam billets: |  |
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Bonded CFOAM carbon foam blocks laid up to specified dimensions: |  |
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Custom machined CFOAM carbon foam parts: |  |
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A complete composite tool: |  |
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Invar® is a registered trademark of CRS Holding, a subsidiary of Carpenter Technologies. |
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