Boeing uses LCTC process for prototype aircraft skins

Citation

(2003), "Boeing uses LCTC process for prototype aircraft skins", Aircraft Engineering and Aerospace Technology, Vol. 75 No. 2. https://doi.org/10.1108/aeat.2003.12775bab.005

Boeing uses LCTC process for prototype aircraft skins

Boeing uses LCTC process for prototype aircraft skins

Keywords: Aircraft, Prototypes, Tooling

The Boeing Aircraft Company has used its Low Cost Tooling for Composites process (LCTC), developed in conjunction with RenShape Solutions, to build a series of eight highly accurate 2.1m by 2.8m (6'-8') tools for prototyping 1 0 bismaleimide (BMI) exterior aircraft skins (Plate 3).

The project was undertaken at the Boeing Tooling Centre in Missouri, USA.

The LCTC process uses RenShape Solutions RenPaste RP 4040 syntactic epoxy patties in combination with an aluminium honeycomb substructure. This provides an extremely cost-effective rapid tooling system. The resulting models can be machined directly from CAD data and can withstand temperatures of up to l93°C for the initial supported cure of prepreg parts.

Plate 3 Boeing's LCTC process, developed in conjunction with RenShape Solutions, is being used to build BMI exterior aircraft skins

"LCTC models are ideal for prototype lay-up tools because they can be fabricated quickly in the shop without requiring the special handling and clean rooms needed for the more expensive prepreg tooling," explained Jay Byington, Senior Specialist, Tool Design Engineering at Boeing.

To fabricate each of the eight lay-up tools, a base substructure was made from 2.5 cm (1") thick aluminium plate. Selection and thickness of the base material is critical with large tools as the plate must be stiff enough to prevent deformation from the sheer weight of the model during handling.

This was especially important with these tools which had very low contours – one being almost flat.

A rough-shaped tool core was then built using lightweight, commercial grade aluminium honeycomb bonded to the base surface with a temperature resistant silicone RTV adhesive. Successive layers of honeycomb were bonded on top of the first section using a foaming adhesive until a machineable block was formed. The core was then machined with HSS cutters on a five-axis high speed mill to produce a model surface 1.25 cm (0.5") smaller than the final contour.

To form the tool face RP 4040 epoxy patties were applied to the undersized core in 165 cm-75 cm (66'-30') sections with a 2.5-3.75 cm (1'-1.5') gap left between each section to minimise tool stresses.

Within each section of the model surface, patties were kneaded to slowly push edges together and then rolled to form a uniform contour without closing the spaces between sections. It was also important to avoid pushing excess material into the honeycomb cells to prevent paste from dropping below the intended height for machining of the LCTC tool face.

The sectioned model was then cured using a stepped ramp and soak procedure provided by Vantico with the patties. Once cooled, spaces between patty sections were filled with additional RP 4040 paste and the tool was cured again.

To complete the model, carbide ball-end mills were used to machine the cured RP 4040 tool face with roughing and finishing cut speeds and feeds established to prevent chip-out and excessive dust. Before building parts, the tools were checked to verify pressure/vacuum integrity.

"With the LCTC lay-up tools, we saved time and money in producing BMI prepreg prototype skins without sacrificing dimensional accuracy," Jay concluded.

For further details contact: Vantico Ltd. E-mail: Renshape.europe@vantico.com