GB2273256A

GB2273256A - Superplastic formed hollow components

Info

Publication number: GB2273256A
Application number: GB9324684A
Authority: GB
Inventors: Wolfgang Betz
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1992-12-09
Filing date: 1993-12-01
Publication date: 1994-06-15
Also published as: FR2698812B1; SE9303492L; ITMI932552A0; ITMI932552A1; DE4241421A1; DE4241421C2; SE9303492D0; IT1265254B1; GB9324684D0; FR2698812A1

Description

1 & 2273256 1 PROCESS FOR THE PRODUCTION OF HOLLOW COMPONENTS AND

APPLICATIONS OF THE PROCESS The invention relates to a process for the production of hollow components, in the case of which a smooth or preformed sheet stack, consisting of at least one upper sheet, a lower sheet, a mould seam and a partial layer of separating medium in the mould seam is first diffusion welded at areas of the mould seam that are without separating medium and is then blow formed in a closed heated mould by means of the action of a gas pressure between the upper sheet and the lower sheet.

Blow forming is a forming technique that is known from US-PS 4.184,000, in the case of which the material to be formed. preferably sheet metal. is brought into the desired shape by the pressure of a fluid medium, preferably gas. In this connection, the sheet that is to be formed is pressed against a heated female mould. In thig connection, the pressure chamber is sealed in a blow forming machine by means of the pressure exerted by a press on the edge of the sheet of metal. This has the drawback that, in particular in the case of components with large surfaces, high mould clamping forces need to 1 2 be applied, such that only correspondingly expensive and complex blow- forming machines can be used.

A blow-forming process of this type for components having small surfaces is known from US-PS 4,526,312, in the case of which process a sheet stack is diffusion welded by means of high mould clamping forces of a press and simultaneous heating of a lower, upper and separating sheet with partial separating medium areas. This process has the drawback that as the surface of the sheet stack increases, the press, the press tools and the heating device for a diffusion welding process can only be produced at a considerable technical cost. In addition to the above, the plan parallelism and the adjustment of the pressing tools that are necessary for the diffusion welding can hardly be overcome.

It is the object of the invention to provide a process of the above mentioned type that overcomes the drawbacks and of state of the art and enables hollow components that have large surfaces to be diffusion welded without mechanical pressing tools.

According to the invention, this object is achieved in that a process according to the preamble of claim 1 includes the following process steps:

a 3 (a) after the application of a separating medium in partial areas of the mould seam between the upper sheet and the lower sheet these are connected at their external edges, in a manner sealed with respect to gas, to form a sheet stack, and a gas supply to the mould seam is incorporated between the sheets of the sheet stack during the welding of the external edges; (b) subsequently, the mould seam is evacuated via this gas supply, sealed, and welded in a hot isostatic pressing process, and subjected to an explosion compression process at the diffusion welding temperature of the sheets of the sheet stack in the areas without the separating medium.

The process has the advantage that components can be produced with the use of less energy than has hitherto been the case with blow-formed components. Furthermore, sheet stack surfaces, that cannot be managed using previous mechanical pressing tools, can be diffusion welded. For the actual blow-forming, a simple box mould with a mould seam for tensioning the sheet stack is advantageously sufficient, since the diffusion welding is advantageously performed separately from the blow- forming step in a hot isostatic press or an explosion connection 4 system. The explosion compression has the additional advantage with respect to a hot isostatic pressing that in the case of explosion connections, there are no restrictions to be taken into consideration with respect to the operating space, and thus the sheet stacks to be connected are not restricted as regards their surface expansion.

Since the box mould only needs to accommodate the forming energy for the blow-forming, simple connection media between the mould parts are sufficient, and the costs for the development of large pressing systems can be reduced. The shape and size of the box, thus become the shape and size of the component, are thus made independent of the size of the mechanical press.

The output can be increased many times in comparison with the conventional blow-forming machine since the diffusion welding temperature does not need to be reached in the blow-forming machine.

Furthermore, double walled components, as are used in engine constructions or casings, flaps or combustion chamber walls or in aeroplane construction for rudder flaps or rudders, or in vehicle construction.for supporting structures, doors and bonnets, can be mass 0 11 produced.

In another embodiment of the process, a hot roller system is used for the diffusion welding. This has the additional advantage that repetetive partial areas that are enclosed in a manner sealed with respect to gas between an upper sheet strip and a lower sheet strip, can be diffusion welded. The repetetive areas can subsequently be processed to form individual components in blow-forming systems. In this manner, large amounts can be diffusion welded economically.

A further preferred embodiment of the process consists in that, after the evacuation and before the hot isostatic pressing. the sheet stack is rolled up to utilise the working space, and is diffusion welded in the rolled state. In contrast to conventional processes, the sheet stack need not already have the processing shape for a blow-forming device for the diffusion welding, but rather, may, advantageously, be adapted to the measurements of the hot isostatic press or an explosion connection device or a hot roller structure as a sheet stack.

The sheet stack may, if required, advantageously be processed to form a ring, sphere, dome or other pre-form 6 before the blow-forming. When the mould seam is evacuated, a cleaning of the mould seam is advantageously achieved, and the leaktightness is tested.

Preferably, a female mould of the component is formed as an upper and lower mould in the shape of a box for the blow-forming of the sheet stack, and the separating surface between the upper and lower mould is adapted to the moulded basis of the component. This has the advantage, that, after the blow-forming, the upper and lower moulds can be separated safely.

The box mould is advantageously held together for the blow-forming by means of screwing, clamping or welding the upper and lower moulds, such that they can not be opened by inflation forces. Between the upper and lower mould, the box mould has a groove that is adapted to the sheet stack. which groove retains the sheet stacking position during the blowforming by means of a tension that is introduced when the upper and lower moulds are connected.

The upper and lower moulds of the box mould are, advantageously, made of seperable mould elements of ceramic material, which is particularly advantageous when the upper and lower moulds are heateduntil they are in 0 a 7 the range of the creep temperature of the sheet stack. Heating elements are provided in the box mould for heating the upper and lower moulds.

The heating of the box mould and/or the sheet stack into the range of the material creep temperature of the sheet advantageously makes the pressing of the sheet into the upper and lower moulds easier.

Welding techniques are preferably used to connect the edges of the sheet stacks, which advantageously leads to a connection that is sealed with respect to gas.

Prior to the connection of the sheets to form a sheet stack, a separating medium is applied to the contact surfaces of the sheets, wherein oxide films, ceramic layers or inorganic high temperature varnishes are preferably applied to the surface as the separating medium. These make the separation of individual sheets easier in the case of blow formation and prevent unintentional friction welding, cold welding or diffusion welding of partial areas.

Using this process, casing components of gas engines and doubled walled components of engines or aircraft or vehicles are produced. In this manner, the inner and the 8 outer casing sections or segments thereof, for conducting cooling air between casing walls, can be produced in a single blow-forming step. In the case of rudder flaps or rudders or segments of these components, the suction and pressure sides can be formed simultaneously. Material reinforcements or structural reinforcements can be incorporated at the same time in that, before the blowforming, intermediate layers are advantageously placed between the sheets in the case of inner structural reinforcement of a double-walled component, or in that additional sheets are advantageously mounted on the sheet stack from the exterior in the case of external material reinforcement. In the case of vehicles, supporting structures, doors or bonnets can be produced in an economic manner using this process.

Fig.1 shows an example of an embodiment of a box mould for performing the process.

Figure 1 shows an example of an embodiment of a box mould 1 for performing the blow-forming process. For this purpose, two smooth or preformed sheets 2 and 3 are first covered over on the surface with a separating medium in the areas 5 and 6, and then connected at the exterior edges 4 in a manner sealed with respect to gas to form a sheet stack 10 by means of a weld seam 11. In this 1 1 9 connection, two gas supplies 7 and 8 are incorporated in the mould seam 9 between the upper sheet 2 and the lower sheet 3 of the sheet stack 10. The smooth or preformed sheet stack 10 is evacuated via the gas supplies 7 and 8 and then subjected to diffusion welding of the areas of the weld seam 9 that do not have separating medium in a hot isostatic press. Subsequently, the smooth or preformed and diffusion welded sheet stack 10 is tensioned between a lower mould 12 and an upper mould 13 of the box mould 1 at its welded edges 4, where the lower mould 12 and upper mould 13 are tensioned in relation to one another by means of the screws 14.

Finally, the box mould 1 is heated by means of the heating rods 15 to 3% below the melting temperature of the sheet stack 10, and gas pressure is applied to the gas supplies 7 and 8. The bulges 16 and 17 then expand in the separated areas 5 and 6 and form cooling channels for a double walled engine casing or reinforcing seams for two mirror symmetrically disposed sheet parts 2 and 3 for example.

The lower mould 12 and upper mould 13 consist of ceramic elements, which are held together by steel casings 18 and 19 via screw connections.

Claims

CLAIMS:

1. Process for the production of hollow components, in the case of which a smooth or preformed sheet stack consisting of at least one upper sheet, one lower sheet, one mould seam and a partial separating middle layer in the mould seam is first diffusion welded at areas of the mould seam that are without separating medium, and is then blow formed in a closed, heated mould by the action of a gas pressure between the upper sheet and the lower sheets, characterised in that:

(a) after the application of a separating medium in partial areas of the mould seam between the upper sheet and the lower sheet these sheets are connected at their external edges in a manner sealed with respect to gas to form a sheet stack, and a gas supply to the mould seam is incorporated between the sheets of the sheet stack during the welding of the external edges; (b) subsequently, the mould seam is evacuated via this gas supply, is sealed, and is welded in a hot isostatic pressing process or an explosion compression process at the diffusion welding temperature of the sheets of the sheet stack in the areas without separating medium.

r-, 1 1

2. Process for the production of hollow components, in the case of which a smooth or preformed sheet stack consisting of at least one upper sheet, one lower sheet, one mould seam and one partial area of separating medium in the mould seam is first diffusion welded in the areas of the mould seam that is without separating medium, and is then blow formed in a closed, heated mould by the action of a gas pressure between the upper sheet and the lower sheet, characterised in that the diffusion welding is performed as follows:

(a) after the application of a separating medium in partial areas of the mould seam between the upper sheet and the lower sheet, these are connected at their external edges in a manner sealed with respect to gas to form a sheet stack, and a gas supply to the mould seam-is incorporated between the sheets of the sheet stack during the welding of the external edges; (b) subsequently, the mould seam is evacuated via 4 this gas supply and is sealed and the sheet stack is welded in a hot roller system at the diffusion welding temperature of the sheets in the areas without separating medium.

12

3. Process according to claim 1 characterised in that after the evacuation process and before the hot isostatic pressing, the sheet stack is rolled up for maximum usage of the working space, and is diffusion welded in the rolled state.

4. Process according to any one of claims 1 to 3, characterised in that a female mould of the component for blow-forming the sheet stack is formed as the upper mould and lower mould in a box mould, and in that the separating surface between the upper mould and lower mould is adapted to the moulded basis of the component.

5. Process according to any one of claims 1 to 4, characterised in that the box mould is held together by screwing, clamping or welding the upper mould and lower mould during blow forming.

6. Process according to any one of claims 1 to 5, characterised in that after the tensioning in the box moulds, the female moulds and/or the sheet stack is/are heated until, at most, the range of the critical temperature of the sheet casing.

7. Process according to any one of claims 1 to 6, characterised in that oxide films, ceramic layers or I.

7 13 inorganic high temperature varnishes are applied to the surface as a partial separating layer prior to the edge connection of the sheets to form a sheet stack.

8. Process according to any one of claims 1 to 7, characterised in that one or more intermediate sheets, which are partially coated with the separating medium, are introduced into the mould seam prior to the welding of the external edges of the upper sheet and the lower sheet, which intermediate sheets, after the hot isostatic pressing during the blow-forming of the sheet stack, advantageously clamp a supporting structure between the upper sheet and the lower sheet with their areas that are not diffusion welded.

9. Application of the process according to any one of claims 1 to 8 for the production of components having large surfaces and double walls and preferably being supporting components of engines, aircraft or a vehicle.