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# AUTOMATIC LAYING OF UNIDIRECTIONAL C.F.C. ON DOUBLE CONTOURED SURFACES

## Obiettivo

The mathematical model of the tape deposition provides the trajectories (to be transferred to the numerical control of the robot) of the centrelines of the tapes over the surface of the panel (eg fuselage). It is also required to provide suitable computation criteria for the gap and overlay of the edges of contiguous tape. The program needs to be organised for the whole surface and for several deposition directions.

The construction of the mathematical model was organised in 3 steps: the deposition over a rotational paraboloid, the analytical representation of the real surface, and the deposition over the real panel surface. Because of the simplicity of rotational surfaces, it is possible to obtain relatively simple expressions of the differential equations which provide the trajectory of the centreline of the tape. The theoretical description concerning the influence upon the lay up process of the tape of the width of the tape, of the local curvature, of the gap and overlap of adjoining tapes and of the lay up start angle have been obtained for the rotational paraboloid.

The theoretical results have been tested by experiment. A first series of experiments was with the deposition of one tape, following the centreline of the tape as calculated by the model, and a second was with the simultaneous deposition of 3 tapes following the prescribed trajectory of the central tape axis. Both series of experiments were done over a cone and a paraboloid model.

The mathematical model provides a provision with an allowance of one millimetre of the edge of the tape. It is possible to obtain gaps of one millimetre or less, using a 25 mm wide tape laid over the areas where the curvature attains the largest values. The lay up head does not require autoadaptativity, it simply needs to be controlled over 5 axes. It is not possible to avoid gaps over a surface with double curvature, or to avoid a difference between the ideal deposition angle and the real one.

A mathematical model has been derived of the tape lay up process over a general surface, which has been analytically approximated by means of locally tangential paraboloids. A software program was organised to provide the various trajectories starting from a given surface at fixed number and orientation of the layers. The program also provides the computing of the gaps and of the length of the tape necessary to cover the surface. The surface itself was defined by a multipatch representation (eg a Bezier type), generated by a computer aided design system. A closed analytical representation is not available as it would be necessary to provide the lay up trajectories. The global representation of the surface is obtained by classical cubic splines which allows, by standard techniques, the representation of the surface and the derivation of nonlinear differential equations which define the trajectories of the centrelines of the tape.

A lay up tool was designed to be used for the laying of unidirectional fibre composite tapes on double curved aircraft panels. It performs 2 processes: the tensioning and guidance of the bundle of 3 tapes.

Machines of the JO'MACH series were assembled and prepared, by locking the lay up tool to the twist head and clamping the moulds to the work table.

The feasibilty of the deposition process with a carbon fibre composite tape of 25 mm width was proved, the gaps were within admissible values, and there were no overlaps or wrinkles. It is possible to use a 5-axis numerically controlled robot (like a JO'MACH) to handle the ATL, making it as simple as an end effector, thus avoiding any need for axis autotracking. The tape laying head was developed in line with the lay up requirements. The ATL was drawn up as an end effector to be hydraulically clamped to the JO'MACH twist head taking advantage of the JO'MACH wrist a-axis and c-axis for its handling.

Very good results were obtained laying up one single tape. No wrinkles or overlaps occured and the gaps were close to the computed value. The lay up of the bundle of 3 tapes showed the lateral tapes moving away from the central one and curling themselves around the reeds. This occured because the composite tape was the one made with thin supporting paper. The gaps between 2 laid up bundles of 3 tapes were 4 to 8 mm in some directions.

It was decided to lay up the multilayer with a single tape in order that the gaps would be uniformly distributed. The next stage was to produce the multilayer with unidirectional carbon fibre tapes laid up on a metal mould. After curing, ultrasonic tests showed that the laminate was of good quality.

Improvements on the behaviour of the tape were obtained by selecting the most appropriate carrier paper and film separator.

Pre-preg tapes meeting the requirements of the automatic laying process on double contoured surfaces were developed. Necessary improvements were made in the pre-preg production and in the selection of the most appropriate carrier paper and film separator.
COMPOSITE MATERIALS INCLUDING IN PARTICULAR UNIDIRICTIONAL CARBON FIBRE COMPOSITES ARE BECOMING MORE AND MORE IMPORTANT IN THE AIRCRAFT INDUSTRY.
TO ACHIEVE AN ADEQUATE PRODUCTION THROUGHPUT, IT IS ESSENTIAL TO AUTOMATE THE LAYING PROCESS AND, TO THIS END, UNIDIRECTIONAL COMPOSITE TAPE IS PARTICULARLY WELL SUITED.

THE OBJECTIVE OF THE PROJECT IS TO ACHIEVE AN AUTOMATIC LAYING ON DOUBLE CONTOURED SURFACES FOR THE MANUFACTURE OF AIRCRAFT COMPONENTS LIKE FUSELAGE PANELS.

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### Meccanismo di finanziamento

CSC - Cost-sharing contracts

### Coordinatore

BASF AG
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Indirizzo
Carl-Bosch-Straße 38
67063 Ludwigshafen
Germania

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