THE USE OF THERMAL EXPANSION CORES FOR NON-AUTOCLAVE PROCESSING OF PRE-PREG MATERIALS

Transcription

1 THE USE OF THERMAL EXPANSION CORES FOR NON-AUTOCLAVE PROCESSING OF PRE-PREG MATERIALS Presented by Mark Crouchen Rockwood Composites Ltd Tel

2 What is a Pre-preg? Pre-preg is a the name used where high performance fibres are preimpregnated with a suitable resin system prior to the moulding process. Pre-preg materials have a range of quality attributes which allows the moulding process to produce quality composite structures To turn a pre-preg into a component requires the correct application of heat and pressure for the appropriate time. The heat allows the resin system to cure The pressure consolidates the plies of pre-preg removing excess resin and entrapped air to achieve the desired thickness and volume fraction. Manufacture methods using pre-pregs include: Vacuum bag moulding, Autoclave Moulding, and Press moulding (bladder and compression).

3 Principles of the using thermal expanding cores to consolidate pre-preg materials. Consolidation pressure on the pre-preg is achieved through the differential expansion of materials. Tools usually hard tooling of steel or aluminium, heated in platen press or with integral heating Pressurising core material may be made of silicon rubber (200E-6), aluminium (23E-6), nylon (80E-6), PTFE (135E-6) or any other materials that have a large thermal expansion coefficient to the parent tool. As the tool heats up and expands so does the core but at a greater rate, this generates a pressure within the closed tool which consolidates the pre-preg material. During cooling, the core shrinks away from the moulded part

4 The process. Hard tooling is required Platen press processing, or stand alone tools. The process is closely associated to pressure bag moulding, where only one tooled surface is required. Can be used within a compression moulded part (however care must be taken when softer core materials are being used) Generally the cores are small in section, due to the high forces that can be generated. Larger tools often require means of restricting the thermal expansion of the core. Multiple cores can be used to good advantage in parts with complex internal cavities.

5 Advantages of thermal expansion processing Can generate high pressure (over 100psi) Can be used with complex components. Can produce a good non tooled surface. Can be a very cheap production method. Usually a very robust and consistent production method. Due to its solid nature an expanding core can be used to lay-up on. (This is difficult on a soft pressure bag) Elastomeric cores can be removed through opening much smaller than the core in its relaxed state.

6 Silicon rubber core manufacture A silicon rubber core can be moulded in the production mould tool after off setting the tool surface to compensate for the unconsolidated composite thickness, installation clearance and the intended moulding pressure often achieved by laying wax sheet in the tool to the correct thickness. Mixing of the 2 part RTV silicon material Degassing the mixed silicon (entrapped air bubbles change the bulk modulus and expansion coefficient) Pour into mould cavity and allow to cure.

7 Typical component manufacture using silicon rubber cores in a compression moulded pre-preg component Component has a central compression moulding foam core (shown white), hard extractable mandrel to form close tolerance slide-ways and silicon rubber core to form internal cavities along the length of the part

8 PTFE cores PTFE cores can provide a tooled surface to the core cavity PTFE cores do not have the inherent flexibility of a silicon cores and therefore impose restrictions on the cavity form PTFE cores may require internal heating (oil or electrical heating) to achieve fast thermal expansion Can be machined with conventional engineering processes

9 Typical Applications Missile structures Aircraft interior parts Aerospace & Defence Engine components Industrial Sorting goods Medical Where ever composites are being applied

10 Conclusion - thermal expansion cores in non-autoclave processing High quality parts can be made (i.e. low voids, good Volume Fraction (Vf), good fibre orientation, low crimp etc) Low capital investment for tooling and processing equipment Process is suitable for many component shapes, Suitable for rapid manufacture in small to medium volume. Diverse composite resin systems can be used (Phenolic, Epoxy, BMI, Cyanate Ester and VTM resins ) Time from tool design to finished tool is very quick using CAD CAM and standard engineering processes. Can be used in stand alone dedicated tooling with integral heating systems or platen press processing.

11 Any Questions?