DE102009034566B4 - Method for producing a tank for fuel - Google Patents

Abstract

Method for producing a fuel tank, wherein at least one component (1) of a tank shell of the tank is built up in layers with a generative manufacturing process in a construction direction (A), wherein - the component (1) consists of titanium or a titanium alloy and has a hollow shape, which is defined by a wall with a wall thickness, - after the layered structure of the component (1) the component (1) is further processed to produce the final dimensions of the component (1; 13), wherein the layered structure of the component (1) an energy beam (6) is directed onto a surface (5) to be constructed, on which a wire-shaped starting material (4) of titanium or a titanium alloy is provided, wherein a molten region (7) of the starting material (4) on the surface to be built (5 ) is generated with the energy beam (6), and the energy beam (6) and the wire-shaped starting material (4) to a layer (3) of the component (1), over the surface to be built up (5) are guided in a circle perpendicular to the construction direction (A) plane (B) with respect to the underlying layer changed or constant diameter, so that the component (1; 13) is constructed in a dome-like shape (1) or a cylindrical shape (13).

Description

The invention relates to a method for producing a tank for fuel. Fuel tanks, in particular fuel tanks for satellites and airplanes, are said to be made of a material that is lightweight yet has high mechanical strength. Titanium and titanium alloys are in principle suitable materials for these fuel tanks because they have these desired properties.

However, titanium and titanium alloys have the disadvantage that they are difficult to work. In the cold forming of thin titanium sheets, the degree of springback is difficult to determine in advance, so that the contour of the deformed sheet can not be determined reproducibly.

Further problems in the deformation of titanium and titanium alloys are the risk of cracking, tool wear and embrittlement of the material, especially during thermoforming, and a tendency to unevenness due to the anisotropy of thin sheets.

From the EP 0 289 116 A1 a method is known in which a component, for example a machine part, is built up in layers in a fluidized bed of a powdered titanium material by means of a laser.

From the document S.Y. Gao et al .: Research on Laser Direct Deposition Process of Ti6Al-4V Alloy, Acta Metal. Sin. (Engl. Lett), Vol. 20, No. 3, pp. 171-180, it is known to produce components for aircraft by a "laser direct deposition" process from a Ti-6Al-4V powder.

The DE 10 2007 014 948 A1 discloses a method for forming a titanium sheet, in which the titanium sheet is introduced into a sealed closed mold and pressed there against a tool contour with a combination of a heated pressure medium on one side of the titanium sheet and a negative pressure on the other side of the titanium sheet and thereby deformed.

This method has the disadvantage that the types of contours that can be made are limited. In particular, deeply contoured contours are difficult to produce with this method.

Accordingly, it is an object of the present invention to provide a manufacturing method with which a wider variety of shapes of titanium and titanium alloys suitable for manufacturing a tank, in particular a fuel tank, can be made.

This object is achieved by the subject matter of the independent claim. Advantageous developments are the subject of the respective dependent claims.

• – zumindest ein Bestandteil einer Tankschale des Tanks mit einem generativen Herstellungsverfahren in einer Aufbaurichtung schichtweise aufgebaut wird, wobei der Bestandteil aus Titan oder einer Titanlegierung besteht und eine hohle Gestalt aufweist, die durch eine Wand mit einer Wandstärke definiert ist,
• – nach dem schichtweisen Aufbau des Bestandteils der Bestandteil weiterverarbeitet wird, um die Endmaße des Bestandteils zu erzeugen,

wobei zum schichtweisen Aufbau des Bestandteils ein Energiestrahl auf eine aufzubauende Oberfläche gerichtet wird, auf der ein drahtförmiger Ausgangswerkstoff aus Titan oder einer Titanlegierung bereitgestellt wird, wobei ein geschmolzener Bereich aus dem Ausgangswerkstoff auf der aufzubauenden Oberfläche mit dem Energiestrahl erzeugt wird, und der Energiestrahl sowie der drahtförmige Ausgangswerkstoff, um eine Schicht (3) des Bestandteils (1) herzustellen, über der aufzubauenden Oberfläche kreisförmig in einer senkrecht zu der Aufbaurichtung liegenden Ebene mit hinsichtlich der darunter liegenden Schicht verändertem oder gleichbleibendem Durchmesser geführt werden, so dass der Bestandteil in einer domartigen Gestalt oder einer zylindrischen Gestalt aufgebaut wird.According to one aspect of the invention, there is provided a method of manufacturing a fuel tank, wherein

• At least one component of a tank shell of the tank is built up in layers with a generative manufacturing process in a construction direction, the component consisting of titanium or a titanium alloy and having a hollow shape which is defined by a wall having a wall thickness,
• After the layered composition of the component, the component is further processed to produce the final dimensions of the component,

wherein for the layered construction of the component, an energy beam is directed to a surface to be built, on which a wire-shaped starting material of titanium or a titanium alloy is provided, wherein a molten region is generated from the starting material on the surface to be built with the energy beam, and the energy beam and the wire-shaped starting material to form a layer ( 3 ) of the component ( 1 ) are made to be circular over the surface to be built, in a plane perpendicular to the direction of construction, with a changed or constant diameter with respect to the underlying layer, so that the component is constructed in a dome-like shape or a cylindrical shape.

It can therefore be used a generative manufacturing process for the layered construction of at least one component of a tank shell of a tank for liquids and / or gases. This ingredient is made of titanium or a titanium alloy.

With a generative manufacturing process, a part of a starting material is built up in layers. Generative production processes are processes in which components are produced directly and with the desired final contour. These parts are so strong that they can take over the mechanical-technological functions of "normal" manufactured components.

Generative manufacturing processes are also called rapid prototyping. These direct component production manufacturing methods are known in the art under a variety of names or designations such as "direct metal sintering"("DMS"),"powder metal sintering", "laser assisted metal sintering", "fusing" or "near net shaping". "Solid free form fabrication (SP)", "additive layer manufacturing" (ALM), etc. The term "rapid manufacturing" is often used in the production of higher quantities recently. In the following, however, only the term "generative manufacturing process" is to be used, but this is not meant to be limiting, for example, only to a small number.

The abovementioned generative production method has in common that the starting material is locally melted by a heat source (for example a laser or an electron beam), which is usually controlled by a CNC program, and solidifies again immediately afterwards. Thus, incrementally, following the CNC program, the 3-dimensional component geometry is built up more or less point by point or step by step in layers or in layers. As a result of the melting and solidification, the component has a cast structure which, however, is much finer-grained than conventional cast structures due to the high locally acting cooling rate.

These generative manufacturing processes allow the direct production of titanium and titanium alloy components that have a thin wall structure. The problems of springback and cracking, which can occur in the chipless deformation of sheets of titanium and titanium alloys, can be avoided. Further, constituents of titanium or a titanium alloy having an anisotropic shape can be more easily and reliably manufactured by a generative manufacturing method than chipless deformation of a sheet of titanium or a titanium alloy.

A fuel tank shell has a thin wall that forms a tank with a nearly closed hollow shape. The advantages of using a generative process for producing thin-walled titanium and titanium alloy parts are used in the invention to produce a fuel tank. The tank may be a fuel tank of a satellite, aircraft, or vehicle or space shuttle, as the material properties of titanium and titanium alloys, particularly low weight, high strength, are particularly desirable in these applications.

The invention accordingly provides a method for producing a fuel tank, in particular a fuel tank for a satellite. At least one component of a tank shell of the tank is built up in layers with a generative manufacturing process. This component is made of titanium or a titanium alloy and has a hollow shape, which is defined by a wall with a wall thickness. After building the ingredient, this ingredient is processed further to create the ingredient's gauge blocks.

The advantages of a generative manufacturing process are thus used to make titanium and titanium alloy components to produce an intermediate. This intermediate product can be further processed after its production in order to further optimize the material properties and the dimensions of the component.

In this case, an energy beam is directed to a surface to be built for the layered structure of the component. On this surface, a starting material of titanium or a titanium alloy is provided. From the source material, a molten area is generated with an energy beam on the surface to be built up, and the energy beam is guided in a defined manner over the surface to be built up to produce a layer of the component.

The term "defined" means that the energy beam is guided according to a predetermined course, which is determined, for example, by means of a CAD program. The guiding of the energy beam is typically controlled by a programmed computer.

The wall thickness of the layered constituent may be between 2 mm and 10 mm, preferably between 3 mm and 5 mm. After further processing of the component, the wall thickness can be reduced to 1 mm to 3 mm to reduce the weight of the component and to refine the contour.

The energy beam is guided so defined that the component is built up in a dome-like shape or a cylindrical shape. These components can then be joined together to make a closed tank.

In one embodiment, the starting material and hence the titanium alloy alloy is TiAl6V4. The composition of this alloy is 6 weight percent aluminum, 4 weight percent vanadium, balance titanium.

As the energy beam, one or more laser beams or electron beams or an arc may be used.

The starting material is used in the form of a wire. The use of a wire as a starting material can cause difficulties when using metallic powders occur, be avoided. A metal in wire form is not only easier to handle, but usually also cheaper, since its production is also easier.

In one embodiment, a metallic substrate is provided on which the component is built. This metallic substrate can form part of the finished fuel cup. In a further embodiment, the component is built on a subcarrier, which is later removed.

In addition, the starting material before or during the generative manufacturing process further admixtures of metallic or non-metallic, z. As ceramic materials, eg. B. may be added as a powder.

For melting the starting material a variety of possibilities is given. Usually this is done by one or more laser beams, electron beams or an arc. However, it is also possible to use a chemical, exothermic reaction, or the starting material is heated capacitively or inductively. Any combination of these different heat sources is possible.

With regard to the achievable material properties, in one embodiment of the method according to the invention, the cooling of the molten starting material takes place at a cooling rate in the temperature interval Tliquidus - T450 ° C., which is greater than 100 K / sec. Although such cooling rates inherently are inherent in the generative process, additional cooling may be used to achieve higher cooling rates.

In addition, it is advantageous if the solidification and cooling of the molten starting material takes place under protective gas or in vacuo. The shielding gas may be, for example, argon, nitrogen or a mixture of argon and helium.

Although not normally required, a heat treatment downstream of the generative production process can still improve the material properties of the structural component produced and, in particular, increase the strength and toughness. The subsequent heat treatment can typically be carried out at temperatures between 400 ° C and 1200 ° C for a period of 10 minutes to 100 hours.

Further, after the post heat treatment, the component may be subjected to rapid cooling (eg quenching in water) to room temperature followed by heat aging in the temperature range 400 ° C-650 ° C for a period of 10 minutes to 100 hours.

The use of a generative manufacturing method for producing a thin-walled tank, such as a titanium or titanium alloy fuel tank, has the further advantages of:
The generative process allows the production of components of different shapes with the same device. Consequently, all or many of the components of a fuel tank can be manufactured in one place. This avoids the problems of irregular delivery from multiple different suppliers as well as inappropriate parts sourced from different suppliers. The production chain of the fuel tank can thus be downsized.

Furthermore, due to the generative manufacturing process, changes to the tank geometries can be easily made because only the computer program that controls the energy beam and the source material needs to be changed. The additive manufacturing process thus allows for design flexibility that other manufacturing methods such as casting do not offer.

Furthermore, the use of materials is lower, since the component built up in layers is produced with almost the desired dimensions, the so-called near-net shape.

Embodiments of the invention will now be described with reference to the drawings.

1 shows a schematic representation of the layered structure of a component of a fuel tank shell according to a first embodiment,

2 shows a schematic representation of the layered structure of a component of a fuel tank shell according to a second embodiment,

3 shows a schematic representation of the further processing of the component of 2 go berserk,

4 shows a schematic representation of the welding of the components of 1 and 3 together.

1 shows a schematic illustration for explaining the layered structure of a dome-like component 1 a fuel tank for a satellite. The part 1 provides a structural component of the tank shell and thus has a hollow shape, which is defined by a thin wall.

The part 1 is made up of a titanium alloy, in particular TlAl6V4, by a generative process in the direction of arrow A in layers. The individual layers 3 are with dashed lines 2 shown in the drawing. The individual layers 3 However, they are not recognizable in the finished tank.

For producing a first layer 3 becomes a starting material 4 from TlAl6V4 on a surface to be built up 5 applied and with a focused laser beam 6 locally melted as an energy source. The molten area is denoted by the reference numeral 7 designated. The areas 8th of the ingredient 1 that melted outside this area 7 remain unmelted because of the laser beam 6 not on these areas 8th is directed, so that in these areas the temperature below the melting temperature of the starting material 4 remains.

In the first embodiment of the invention, a starting material 4 in the form of a wire 9 made of TiAl6V4, with the end of the wire 9 on the surface to be built up 5 brought and with the laser beam 6 is melted there.

The laser beam 6 as well as the wire 9 are guided in a plane B, which is perpendicular to the construction direction A, to a layer 3 of the ingredient 1 manufacture. In particular, the laser beam 6 as well as the wire 9 in a circle, with the end of the wire 9 in the molten area 7 to be led. This movement of the laser beam 6 and the wire 9 is with the arrows B in 1 shown. The movement of the laser beam 6 as well as the wire 9 is controlled by a computer program.

The molten material solidifies quickly when the laser beam 5 from this molten area 7 in the plane B is controlled away. This creates a solid area 10 a circular layer 3 of the dome component 1 , In this embodiment, the dome-shaped component 1 When assembled, a wall thickness of about 3 mm (millimeters) on.

To make the next layer of the ingredient 1 become the laser beam 6 as well as the wire 9 Guided so that they are on the surface 11 the previously prepared layer 3 hit and again in a circle with a slightly larger diameter than the underlying layer 3 in a plane B, which is perpendicular to the mounting direction A, are performed. Other layers are similarly made to the component 1 build up layer by layer or layer by layer in the direction of arrow A until it has the desired contour.

In the 1 first the closed ground 12 of the dome component 1 produced. However, it is also possible to start the dome-like shape at the open edge and build the dome-like shape inwardly, with the dome cap then being made.

The 2 shows a schematic representation of another cylindrical component 13 the fuel tank shell according to a second embodiment of the invention. The same components are shown with the same reference numerals and will not be explained further.

The part 13 is also built up layer by layer using a generative manufacturing process. The second embodiment not belonging to the invention differs from the first embodiment by the shape of the starting material 4 , In the second embodiment, the starting material 4 in the form of a powder 15 provided, which consists of a titanium alloy, in particular TlAl6V4.

A starting powder layer 14 will be on the surface 4 a carrier plate applied. The focused laser beam 6 is applied to the starting powder layer 14 to a place to be built up 5 directed, being a local area 7 the starting powder layer 14 is melted. The laser beam 6 is guided in the plane B in a circle, so that a first solid circular layer 3 will be produced.

Another layer 14 ' gets out of the starting powder 14 on the carrier plate and the first layer 3 applied and the laser beam 6 will be on the surface 11 the other starting powder layer 14 ' directed and guided so that another circular layer 3 ' on the lower layer 3 will be produced. This process is repeated and the component 13 is built up layer by layer in the direction of arrow A to the cylindrical component 13 produce with the desired height.

Generative manufacturing processes can be used to produce ingredients with the desired final contour. In one embodiment, however, the ingredients are processed further by the layered build process.

In this embodiment, the components are heat-treated to increase the mechanical strength. In particular, the ingredients are hot isostatically pressed. Thereafter, the shape and size of the components are refined by twisting and / or grinding in order to improve the dimensional tolerances and / or the surface quality. The twisting of the outer surface 17 of the cylindrical component 13 the tank shell is with the arrows 16 in 3 shown. In this step, the wall thickness is reduced from 3 mm to about 1 mm.

To manufacture the fuel tank, the individual components are joined together. 4 shows a schematic representation of the welded together cylindrical component 13 with the dome-shaped component 1 to a closed pipe 18 manufacture. The weld between the components is with the dashed line 19 shown. In another step, not shown, a second dome-shaped component is attached to the open end of the tube 18 of the 4 welded to produce a closed fuel tank. Holes through the tank shell are also made to fill the tank with fuel and guide the fuel to the engine.

By using a generative manufacturing method for manufacturing the components of the fuel tank, a thin-walled fuel tank made of titanium or a titanium alloy can be reliably manufactured. Furthermore, constituents of different shapes can be produced by the same process and consequently in the same factory. Together with the generative method, this has the advantage that the design of the fuel tank can be changed at short notice. Furthermore, special production of tanks, ie. H. Special sized tanks that deviate from the usual standard can be made by reprogramming the computer controlled laser beam and source material.

Claims (17)

Method for producing a fuel tank, wherein at least one component ( 1 ) a tank shell of the tank with a generative manufacturing process in a construction direction (A) is built up in layers, wherein - the component ( 1 ) is made of titanium or a titanium alloy and has a hollow shape which is defined by a wall with a wall thickness, - after the layered structure of the component ( 1 ) the part ( 1 ) is further processed to give the final dimensions of the constituent ( 1 ; 13 ), whereby the layered structure of the component ( 1 ) an energy beam ( 6 ) on a surface to be built up ( 5 ), on which a wire-shaped starting material ( 4 ) made of titanium or a titanium alloy, wherein a molten area ( 7 ) from the starting material ( 4 ) on the surface to be built up ( 5 ) with the energy beam ( 6 ), and the energy beam ( 6 ) as well as the wire-shaped starting material ( 4 ) to a layer ( 3 ) of the component ( 1 ), above the surface to be built ( 5 ) in a plane perpendicular to the construction direction (A) lying plane (B) with respect to the underlying layer changed or constant diameter, so that the component ( 1 ; 13 ) in a dome-like shape ( 1 ) or a cylindrical shape ( 13 ) is constructed. Method according to claim 1, characterized in that the wall thickness of the component ( 1 ) is between 2 mm and 10 mm, preferably between 3 mm and 5 mm. Method according to claim 1 or 2, characterized in that the starting material ( 4 ) consists of TiAl6V4. Method according to one of claims 1 to 3, characterized in that as energy beam ( 6 ) one or more laser beams or electron beams or an arc are used. Method according to one of claims 1 to 4, characterized in that the starting material ( 4 ) before or during the process further admixtures of metallic or non-metallic materials are added. Method according to one of claims 1 to 5, characterized in that for melting the starting material ( 4 ) a chemical exothermic reaction is used. Method according to one of claims 1 to 5, characterized in that the starting material ( 4 ) is heated capacitively, ohmically or inductively. Method according to one of claims 1 to 7, characterized in that a cooling of the molten starting material ( 4 ) in the temperature interval Tliquidus - T450 ° C with a cooling rate greater than 100 K / sec. A method according to claim 8, characterized in that the cooling rate of the molten starting material ( 4 ) is increased by an additional cooling. Method according to one of claims 1 to 9, characterized in that the solidification and cooling of the molten starting material ( 4 ) takes place under inert gas or in vacuo. Method according to one of claims 1 to 10, characterized in that for further processing of the component ( 1 ; 13 ) the part ( 1 ; 13 ) is turned off or ground. Method according to one of claims 1 to 11, characterized in that the constituent ( 1 ) with another ingredient ( 13 ) is welded from titanium or a titanium alloy. Method according to one of claims 1 to 12, characterized in that the from the starting material ( 4 ) component ( 1 ) is subjected to a subsequent heat treatment at temperatures between 400 ° C and 1200 ° C for a period of 10 minutes to 100 hours. A method according to claim 13, characterized in that the subsequent heat treatment is carried out in several stages and / or steps. Method according to claim 13 or 14, characterized in that the constituent ( 1 ) after the subsequent heat treatment of a rapid cooling to room temperature. A method according to claim 15, characterized in that after the rapid cooling, a further heat aging in the temperature range 400 ° C-650 ° C for a period of 10 minutes to 100 hours. Method according to one of claims 1 to 16, characterized in that the from the starting material ( 4 ) component ( 1 ) is hot isostatically pressed.

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