Present invention relates to a process for bending to a curved contour of a light-weight cellular plate, of the "honeycomb"-plate type, where three plate layers are connected to each other in pairs via layers of glue, comprising a first outer layer of thin-walled plate material, preferably of light metal, and a second, opposite outer layer of thin-walled plate material, preferably of light metal, together with a third, intermediate layer of transversely extending, cellular material, preferably of light metal, the cellular plate being arranged on a convexly curved moulding means and being subjected thereafter to bending against the moulding means during stretching of the first outer layer relative to the second outer layer.

Hitherto bending of this type of cellular plate has been effected to a large degree by making incisions or recesses in certain portions of one outer layer of the plate, so that the middle cellular layer can be correspondingly folded together a corresponding distance locally in a,'direction sideways of the main direction of the cells. Simultaneously with this the layer in which the recesses or incisions are cut out is weakened, since the through structure of the outer layer is broken and this must be compensated for by suitable means, such as filling of extra filling material (adhesive or the like) in adjacent parts of the cellular plate.

With the present invention the general aim is a simple and effective bending of cellular plates without making incisions or recesses in one outer layer of the cellular plate.

Hitherto various ways of solving this problem have been attempted. In US 3,788,177 there is shown a process for stretch shaping a cellular plate into a curved contour

over a convexly arched moulding means. In such a solution one is dependent on special clamping means for accurately maintaining each opposite outer layer of the cellular plate. By means of accurately regulating the tension one can ensure in a simple, but direct manner that the layer of the cellular plate, which forms an abutment against the moulding means, is subjected the whole time to a certain minimum tension along the surface of the mould, while the outermost layer of the cellular plate is subjected to an equivalently greater tension with a greater extension following from this and equivalent permanent stretch deformation of the same.

In US 2,842,594 bending is shown of a solid work piece, made of metal, which is mounted by means of special clamping means between two oppositely movable hydraulic tensioning means. A convexly curved moulding means is pressed against the metal piece in a direction transversely of the direction of stretch of the metal piece by relative movement between the moulding means and the tension means with the associated metal piece. By means of special tension regulating means the tension of the tension means can be regulated correspondingly as in the afore-mentioned US 2,824,594, so that a controlled stretch is achieved in the different layers of the metal piece during bending of the latter.

In US 3,060,561 a sandwich plate is shown, comprising two opposite, plane, thin-walled outer plates and an intermediate thin-walled plate, which extends corrugated between the outer plates. It is proposed to fasten the sandwich plate to a plate-shaped thin-walled, elastically flexible support means, by connecting opposite extensions of the one of the two outer plates to the plate-shaped support means in rigid connection by means of fastening pins. The two transverse support bars are received in an intermediate space which is defined within the sandwich plate between the support means and the said one outer plate, which at opposite ends is bent about each

of its support bars and disposed flush with the support means. Thereafter the support means and associated support bars, together with the sandwich plate, are bent about in a manner not mentioned further into a permanently bent condition by stretching the said one outer plate, while the other outer plate and the corrugated plate are supported in the support means. Finally the bent sandwich plate must be removed from the support plate by cutting.

In DE 24 32 929 B2 there is shown a process for bending a sandwich plate having a core of corrugated plate in that the metal layer of the sandwich plate, which is to be subjected to the largest tension during the bending, is heated to a temperature where the tensile strength of the metal exceeds the elastic limit at the associated tension loading.

According to the invention the particular objective is to be able to bend the cellular plate by means of pressure means instead of tension means. In this connection a far simpler apparatus and far simpler operative conditions can be achieved. Firstly the use of complicated clamping means is avoided and secondly the use is avoided of complicated tension regulating means for continuously adjusting the tension which is exerted by associated tension means and thirdly visual monitoring of the tension regulating process is avoided.

The process is characterised in that a support means is used comprising a first flexible plate, in the form of a pressure-absorbing outer plate, and a second flexible plate, in the form of a counter pressure-absorbing inner plate, the cellular plate being located shut off in an intermediate space between the first plate and the second plate, after which the plates are arranged in the form of a plate pack in place on the moulding means and the plates are jointly clamped against the moulding means in a stationary fastening region, and the plates are thereafter jointly pressed in regions laterally outside the stationary fastening region against the moulding means.

the pressure loading being exerted successively in a lateral direction from the stationary fastening region in a direction towards the edge region of the plates.

By the process as described above an especially simple and effective treatment of the cellular plate can be achieved in that the pressure loading is exerted successively in opposite directions from the stationary fastening region, at the same time as there is exerted a tension in one outer layer of the cellular plate which is to be bent with a convex curvature. There is obtained an especially controlled and accurate and also gentle bending of the cellular plate by arranging the latter in the form of a pack between two opposite outer plates.

According to the invention special manufacturing advantages are obtained in that the first plate and the second plate are made of flexible material having limited, elastic pliability. In practice it is hereby possible to transfer a pressure loading in a uniformly distributed manner successively to the regions of the cellular plate which are to be subjected to a pressure loading. In addition the first and the second plate provide for the regions which are already bent by such successive pressure loading to be successively supported in a controlled manner in such a bent condition.

By the process according to the invention there is a special working advantage that the pack of plates is retained in a local fastening region against the convex surface of the moulding means by a first pressure means, after which the pack is pressure loaded by one or a pair of additional pressure means successively in a lateral direction from the stationary fastening region in a direction towards the edge region of the plates.

Furthermore the invention relates to a system for bending to a curved contour of a light weight cellular plate, of the "honeycomb" plate type, where three plate layers are connected to each other in pairs via layers of glue, comprising a first outer layer of thin-walled plate

material, preferably of light metal, and a second, opposite outer layer of thin-walled plate material, preferably of light metal, together with a third intermediate layer of a transversely extending, cellular material, preferably of light metal, the cellular plate being arranged on a convexly curved moulding means and thereafter being bent on the moulding means during stretching of the first outer layer relative to the second outer layer.

The system is characterised in that a support means, which comprises a first flexible, elastic plate, in the form of a pressure-absorbing plate and a second flexible, elastic plate, in the form of a counter pressure-absorbing plate, is adapted to receive and retain the cellular plate between the plates in an intermediate space suited for this, to form a pack of plates, that the moulding means is adapted, in a specific fastening region on the moulding means, to support the pack of plates, the pack of plates being adapted to be firmly clamped in said fastening region against the moulding means by means of a first pressure means, and that one or more additional pressure means are adapted to be moved successively laterally from said fastening region to edge regio (s) of the pack in a path of movement along the shape-forming convex outer surface of the moulding means during the simultaneous exertion of a pressure loading via the plate pack against the shape-forming outer surface of the moulding means.

By employing a system of moulding means and a pack consisting of the cellular plate and the surrounding support means there can be obtained in addition to an effective production arrangement and a controlled accurately designed end product a relatively simple and effective production outfit.

Particularly advantageous results are obtained according to the invention in that the first plate and the second plate jointly define the hollow space for reception of the cellular plate, the first plate and the second

plate forming a mutual supporting abutment along the periphery, just outside the cellular plate substantially flush with the outer surface of the first plate. Inter alia one has hereby the possibility to ensure a special gentle loading of the peripheral portion of the cellular plate, this if necessary being able to form a side support against equivalent side portions of the first or second plate, while the pressure forces which are transferred laterally outside the cellular plate can be transferred directly between the first and the second plate without needing to load the peripheral portion of the cellular plate.

In connection with the afore-mentioned there is a particular advantage that the first plate and the second plate are made of flexible material having a limited, elastic pliability.

Further features of the invention will be evident from the following description having regard to the accompanying drawings which illustrate a preferred embodiment, in which:

Fig. 1 shows in side view a system according to the invention in a first phase of a bending operation.

Fig. 2 shows in side view the system according to Fig. 2 in a second phase of the bending operation.

Fig. 3 shows a segment of the plate according to Fig. 2 illustrated in plan and partly in section.

Fig. 4 shows in section and schematically the plate according to Fig. 2 illustrated in section from the side.

There is shown in Fig. 1 a plate 10 of the "honeycomb" plate or bicube plate type having a cellular- forming hollow space, illustrated in a normal plane starting condition. In Fig. 2 the plate 10 is shown in an arched, that is to say curved condition.

The plate 10 consists of a first, upper layer 11 of thin-walled material and a second, lower layer 12 of thin- walled material together with a third, intermediate layer 13 (see Fig. 2) of thin-walled cellular material. In the

illustrated embodiment a plate 10 is employed of the most usual type which is marketed by Hexcel Corporation under the designation "Hexagonal Core" and which is made of thin-walled light metal. Alternatively one or more layers can be made of another suitable, metallic or non-metallic material or of a laminate of different suitable materials. The layers are glued together in pairs with a suitable adhesive to form a light weight cellular plate 10 having great rigidity and strength. The cells in the layer 13 have a hexagonal or substantially hexagonal cross- sectional form.

The cellular plate 10 is arranged between an upper flexible pressure plate 14 and a lower flexible counter pressure plate 15 to form a plate pack A. The cellular plate 10 is deposited in a cavity 15a in the counter pressure plate 15 between two end ribs 15b and 15c, the top side of which is flush with the corresponding top side of the plate 10. If desired corresponding ribs can also be present at opposite sides of the cavity between the end ribs. The pressure plate 14 is consequently adapted to be supported partly against the cellular plate 10 and partly against the included ribs 15b and 15c, and against the intermediate ribs not shown. The opposite end edges of the cellular plate 10 are adapted to be able to be placed tightly up to, but without necessarily contacting the inwardly facing surfaces of said ribs.

The plate pack A is shown in Fig. 1 in the starting position, resting against the top of a cylindrically curved moulding means 16. Alternatively the moulding means can be designed with mould surfaces having different curvatures or with certain portions having substantially rectilinear contours (not shown further) .

A first pressure means 17 in the form of a bar extends parallel to the axial direction of the moulding means 16, which runs at right angles to the plane of the drawing in Fig. 1. The pressure means 17 is adapted to be pushed in a radial direction relative to the curved

surface of the moulding means 16 inwardly towards the plate pack A and to exert a suitable clamping force in the direction of an arrow B via the plate pack A against the moulding means 16 in a limited fastening region of the plate pack A in order to firmly clamp the plate pack A in a specific position relative to the moulding means 16.

Just by the side of the pressure means 17 there is arranged a second pressure means 18 in the form of a pressure roll, which is adapted to be pressed with a radial inwardly directed pressure force as indicated by an arrow C against the plate pack 10,14,15 and also to be successively to be rolled along the pressure plate 14 from the position shown in Fig. 1 to the position shown in Fig. 2, as is indicated by an arrow D in Fig. 2.

In the preferred embodiment illustrated there is arranged a third pressure means 20 in the form of a pressure roll on the opposite side of the pressure means 17, the pressure means 20 being adapted to be moved in the direction of an arrow E, that is to say in the opposite direction to the direction of movement of the pressure means 18 as illustrated by the arrow D. There is exerted a corresponding pressure force as shown by an arrow C in the pressure means 20.

Provision is made for the elastic pressure plate 14 to have a significant wall thickness, so that an effective pressure distribution can be obtained by the pressure which is exerted from the pressure means 17 and from the pressure roll 18 and the pressure roll 20 via the pressure plate 14 against the cellular plate 10. The elastic counter pressure plate 15 has a significantly smaller wall thickness than the pressure plate 14, the counter pressure plate 15 being able to bear over a large surface area against the moulding means 16 and thereby provide effective support with a cushion effect against the cellular plate 10. The pressure plate 14 and the counter pressure plate 15 are made of a flexible material, that is to say bendable and relatively pliable, but minimally

deformable plastic material having and inherent elasticity in order to bring the material from a bent condition back to the level starting position.

According to the invention provision is made in the illustrated embodiment, wherein light metal is used in each and all layers 11-13 to ensure a permanent deformation of the cellular plate. This is guaranteed by bending and at the same time permanently deforming the cellular plate 10 in the bent form by means of a combined pressure loading across the cellular plate 10 and a tension loading in the longitudinal direction of the cellular plate 10 along the convexly curved layer 11 of the cellular plate 10. This effect is supported in that the opposite concavely curved layer 12 of the cellular plate 10 abutted against and is maintained relatively free of tension against the moulding means 16, so that first and foremost it is the layer 11 which becomes significantly deformed. However as a consequence of the stretching of the layer 11 a certain accompanying deformation of the middle layer 13 of the cellular plate 11 cannot be avoided.

During pressure loading of the cellular plate 10 between the pressure plate 14 and the counter pressure plate 15, gradually as the pressure roll 18 is rolled sideways outwardly along the plate pack 10,14,15 in a direction towards its side edge, it has been found that the cells of the cellular plate 10 become minimally deformed in the longitudinal direction, that is to say in a direction at right angles to the main plane of the cellular plate, as a result of the rigidity of the cells in this direction. Nevertheless by means of an effective tension loading which is exerted longitudinally in said first plate layer 11 one will pressure an equivalent longitudinal stretching of the plate layer 11 in that the latter can be moved in a controlled manner in the longitudinal direction within the yield point of the material. The relatively rigid, cell-formed middle layer

13 can at the same time be exposed as a consequence of the stretching of the plate layer 10 to a certain minimal deformation reckoned in a direction across the walls in the walls of the middle layer 13, while the second, lower plate layer 12 does not need to be exposed particularly to deformation forces. More specifically however it can be ascertained in practice that minimal local deformations arise across the walls of the cells, while the plate layer 12 is deformed locally in that the free-lying portion in each cell becomes bulged slightly inwards in each of its adjacent cells, as is illustrated grossly exaggerated in Fig. 4. As a result one gets hereby a minimal, strongly restricted clinching together of the plate layer 12 in the longitudinal direction.

As a result there is obtained a cold temperable, permanently formed deformation of the first, convexly curved plate layer 11 of the cellular plate 10 and an equivalently restricted permanent deformation of the cellular layer 13 and the plate layer 12.