Process for manufacturing a diaphragm accumulator

Abstract

A process for manufacturing a diaphragm accumulator (12), at least consisting of two adjacent housing parts (14, 16) which are permanently joined to each other along a common weld seam or joint profile (36) in a joining step by means of friction stir welding in order to form an accumulator housing (10), characterized in that before the friction stir welding operation is carried out by means of a welding tool (40) which is set in rotation and plunges with a specifiable pressing force into the weld seam and joint profile (36), at least one housing part (16) is provided with a diaphragm unit (19) by inserting the latter into said housing part (16), the diaphragm unit (19) having a movable separating diaphragm (20), and in that a support device (34) is additionally inserted between the weld seam and joint profile (36) and the diaphragm unit (19), the support device (34) covering the weld seam and joint profile (36) with a specifiable excess length in such a way that the support device (34) exerts a supporting force that counteracts the pressing force of the welding tool (40).

Description

[0001] Proceedings

[0002] The invention relates to a method for manufacturing a membrane storage device, at least consisting of two adjacent housing parts which are permanently joined together in a joining step by means of friction stir welding along a common seam or connection path to form a storage housing.

[0003] Storage devices with a storage housing, known as hydraulic accumulators, are readily available on the market in a wide variety of designs. These accumulators serve, among other things, to store specific volumes of pressurized fluid in hydraulic systems and return them to the system as needed. Hydraulic systems with hydropneumatic accumulators featuring a diaphragm separator are particularly common. The diaphragm, or separator, separates a fluid chamber (the working chamber) from a gas chamber (another working chamber). The diaphragm effectively decouples the gas and liquid chambers. Nitrogen gas is the preferred working gas. The fluid chamber is typically connected to a hydraulic circuit within the system, so that when the pressure in the hydraulic circuit increases, the accumulator absorbs the pressurized fluid, compressing the gas in the process.As the pressure decreases, the previously compressed gas expands again, displacing the fluid back into the hydraulic circuit. The use of hydraulic accumulators for this type of energy storage is just one example; other applications are possible, such as smoothing or damping hydraulic pulsations. Furthermore, they can be used in suspension systems, including for weight compensation, and allow for leakage and volume compensation in hydraulic systems. Additionally, they have proven effective as a safety reserve in emergency operation scenarios.

[0004] DE 2015 012 357 A1 discloses a hydraulic accumulator, particularly in the form of a membrane accumulator, comprising at least two housing parts of an accumulator housing in which a separating element, particularly in the form of a separating membrane, separates two fluid or media chambers from one another and is connected to one housing part along a weld seam by at least one media connection part, wherein the connection part engages at least partially in a receiving chamber formed in one housing part along a housing opening, and wherein the adjacent wall surfaces of the housing part and the connection part are connected to each other by means of the weld seam in the receiving chamber. The two housing parts are joined end-to-end along a seam or connection path by a further weld seam, which can be produced by electron beam welding or laser beam welding without welding filler materials.To prevent weld spatter from unintentionally reaching the inside of the storage housing with its sensitive elastomeric separating membrane during the welding process, the weld seam to be produced is completely covered on the inner circumference by an annular projection of one of the two storage housing parts. In DE 41 31 524 A1, a seam or connection between the two storage housing parts of a membrane storage device is covered inwards by an annular connecting element during the welding process, particularly using an electron beam welding process, to prevent the ingress of weld spatter. Simultaneously, the annular connecting element is firmly connected to the inside of the storage housing during welding and, before the two housing parts are welded together, is clipped to a partially flexible retaining ring to which the hemispherical separating membrane is movably hinged for operation within the storage device.

[0005] DE 10 2014 005 51 1 A1 discloses a storage device, in particular in the form of a hydraulic accumulator, comprising a storage housing consisting of at least two housing parts which at least partially define a working space in the storage housing, in which a separating device is movably guided to separate two media spaces from each other and is held in a fixed position in the storage housing at a predetermined fixing point by means of a holding device, wherein the holding device applies the separating device to at least one of the housing parts in a contacting manner with a defined contact force in the area of ​​the fixing point, while maintaining a constant or substantially constant wall thickness.

[0006] During assembly, the two shell-like housing parts are first partially nested, and the free edge of the larger-diameter housing part is folded over onto a defined top surface of the smaller-diameter housing part using a crimping or flanging process with a predefinable crimping force. In this way, the two (storage) housing parts are permanently and fluid-tightly joined by a flanging process, as an alternative to welding. A generic method for manufacturing a membrane storage device is known from CN 106742074 A, consisting at least of two adjacent, semicircular, thin-walled housing shells that are permanently joined together in a single joining step by friction stir welding along a common seam or connection path to form a storage housing.Prior to this joining step using friction stir welding, a thin-walled, elastically compliant separating membrane is pre-bonded to one of the two housing shells using TIG welding. The well-known membrane accumulator is constructed of lightweight aluminum and serves as a container for storing propellant for spacecraft.

[0007] AT 1 1066 U 1 discloses a pressure tank made of metal, in particular in the form of a high-pressure tank made of aluminium for gas-powered vehicles, which is composed of at least two parts connected to each other via a friction stir weld, wherein the pressure tank is equipped with at least one wall thickness thickening adjacent to the friction stir weld for the outlet of the friction stir tool to the outside towards the environment.

[0008] Based on this prior art, the invention aims to further improve known solutions while retaining their other advantages, in particular to connect two adjacent housing parts of a storage housing for a membrane storage device in a reliable and cost-effective manner and in a way that is easy to assemble. A method with the features of claim 1 and claim 6, each in its entirety, achieves this objective.

[0009] By providing, according to the characterizing part of claim 1, at least one housing part with a membrane unit by inserting the membrane unit into this housing part, which has a movable separating membrane, and by additionally inserting a support device between the seam and joint and the membrane unit, which covers the seam and joint with a predefinable overhang in such a way that the support device provides a support force that counteracts the pressure force of the welding tool, an alternative method to electron beam welding or laser beam welding is created that does not require welding filler materials;Friction stir welding alone does not cause cracks or pores in the adjacent material sections of the two housing parts being joined, due to the comparatively low heat input. Because of the low heat input, there is also no distortion within the weld seam, yet high strength is achieved. Furthermore, a homogeneous material structure is formed in the weld area.

[0010] However, during friction stir welding, the rotating welding tool exerts high compressive forces on the housing parts being joined, which can lead to buckling or other deformation of the housing parts or the storage housing itself. To counteract this damaging force from the welding tool, a support structure is positioned inside the storage housing along the weld seam and joint path. This structure acts as a counterweight or abutment, stiffening the housing and its components to effectively prevent deformation or buckling during the friction stir welding process.The rotating welding tool, which engages in the seam and joint between the housing parts, exerts a high contact or engagement force on the material sections adjacent to the edges of the seam and joint. This force is reliably absorbed and compensated by the support device, which exerts a supporting force opposite to the contact force, preferably of the same magnitude (action = reaction). Furthermore, in addition to its support function, the support device can also be used to securely position the membrane unit with its separating membrane within the storage housing, even during subsequent operation.

[0011] A major advantage of friction stir welding is its ability to firmly join materials that are difficult to weld or dissimilar, such as aluminum or titanium, which are particularly lightweight. This allows for the lightweight construction of even highly stressed hydraulic or diaphragm accumulators. In particular, high-strength aluminum alloys with zinc, magnesium, and copper, such as alloy group 7000 and similar groups, which are age-hardenable but otherwise considered unweldable, can now be used as high-strength materials for manufacturing diaphragm accumulator housings using friction stir welding. Although the resulting accumulator housing is extremely lightweight, it is resistant to common fluid media and provides a high-pressure-resistant housing suitable for diaphragm accumulators.

[0012] In a particularly preferred embodiment of the method according to the invention, the support device is inserted into one of the housing parts in such a way that, after the joining step, its outer circumferential side comes into contact with inner wall sections in the area of ​​the weld and joint path. Due to the direct contact of the support device with the aforementioned inner wall sections of both housing parts, a particularly good support effect is achieved along a larger, annular wall area when carrying out friction stir welding using the special welding tool mentioned.

[0013] In a further particularly preferred embodiment of the method according to the invention, the membrane unit has a holding device for the separating membrane, which is brought into contact with the inner circumferential side of the support device. In this way, the support device, in addition to its supporting function, has a further function in that it securely positions the membrane unit in the storage housing or anchors it stationary in the storage housing.

[0014] In a further particularly preferred method, the support device is accommodated in an annular space, which is bounded on the outer circumference by wall sections of the housing shells and on the inner circumference by the holding device. In this way, the holding device for the separating membrane covers the support device on the inner circumference, in contact with the membrane itself, so that the holding device also provides support during the friction stir welding process, which further increases the stiffening of the component assembly along the seam and joint path during manufacturing.

[0015] In a further preferred embodiment of the method according to the invention, the support device is welded firmly to adjacent wall sections of the housing parts along the seam or joint path during friction stir welding. If the support device is formed from a support ring made of a steel material, it is difficult or even impossible to connect it to the storage housing during friction stir welding. However, the situation is different if the support ring of the support device is preferably made of aluminum or aluminum alloys, which can be very readily welded to the storage housing along the seam or joint path using friction stir welding.By defining the fixed position of the ring-shaped support device on the storage housing using friction stir welding, a fixed positioning is guaranteed, which includes the holding device of the membrane unit as soon as the holding device engages the support device in a form-fitting manner.

[0016] In a further method according to the invention for manufacturing a membrane storage device, it is provided that at least the following process steps are used to manufacture the storage device housing by means of friction stir welding: a wear-resistant welding tool is set in rotation by means of a spindle drive;

[0017] - The rotating welding tool plunges into a seam or joint between two housing parts to be joined with a predefinable contact force, thereby generating frictional heat which stirs and preferably compacts adjacent material sections along the seam or joint into a plastically deformed or doughy state by the feed of the welding tool, without reaching the melting point of the material sections.

[0018] The welding tool leaving the weld or joint path after achieving a media- and pressure-tight connection between the joined housing parts, and

[0019] The welding tool is extended from a block of material forming a housing component. This block has a preferably cylindrical outer contour and a dome-shaped inner contour. From the outside, material is partially removed to form a shell-like section with no outward angles. This shell-like section, together with the other housing component, forms the complete, shell-shaped storage housing. Friction stir welding relies on the use of a rotating pin or rod that is guided between the contact surfaces of two workpieces, in this case, the two adjacent housing components. The frictional heat generated causes the material or material pairing to plasticize, enabling the housing components to be welded together. This process creates high-quality welds that do not fatigue even after extended use.Such a method can be used in a space-saving and cost-effective manner to manufacture storage housings for hydraulic accumulators of any design.

[0020] It is preferably provided that, depending on the choice of the predefinable intervention angle from 0° to 6°, material irregularities or inclinations in the material flow at the location of the weld can also be compensated for.

[0021] In a further particularly preferred embodiment of the method according to the invention, the welding tool emerges at a different point than where it entered, particularly after leaving the weld seam and joint path. This ensures that no material damage, such as pitting or voids, can occur when the welding tool emerges or is removed from the joint. It is particularly preferred that the welding tool, during a rotation of more than 360° along the weld seam or joint path, enters a housing part adjacent to the path and emerges or retracts from the housing part upon a defined withdrawal from the material. This allows for a particularly gentle removal of the welding tool from the workpiece in the form of the housing part joint.

[0022] In a further preferred embodiment of the invention

[0023] The method envisages that the welding tool, using a multi-axis portal machine such as a milling machine, or a handling system such as a robot, moves around the stationary housing parts to be joined, or, in the case of a stationary arrangement of the welding tool, the housing parts to be joined are moved at least rotationally relative to the welding tool, or the welding tool and the housing parts to be joined perform a predefinable relative movement to each other for the welding process.

[0024] Especially when using state-of-the-art machinery, friction stir welding allows for the economical joining of components, such as membrane storage housing parts, which can have complex 3D geometries. Since no welding filler materials are required for friction stir welding, and no other consumables, such as shielding gas or flux-cored wire, are generated, the process according to the invention is extremely environmentally friendly.

[0025] In a particularly preferred embodiment of the method according to the invention, the welding tool is formed from a pin and a shoulder arranged perpendicular to it, the shoulder having a larger diameter than the pin, and the pin swirls or stirs the material parts of the housing components to be joined. The engagement pin can also be formed from a conical engagement mandrel, and the shoulder of the welding tool, which can rest flush against the material parts to be joined from the outside, controls the penetration depth of the pin. The shoulder can also have a conical or other shape.The rotating welding tool is immersed into the weld or joint along the insertion point with a predefined contact force until the shoulder rests flush against the material. This can take several seconds, allowing friction between the welding tool's shoulder and the joining partners to heat the corresponding material sections below the shoulder to just below the melting point. This temperature increase inevitably leads to a decrease in strength, causing the material to plastically degrade and enabling the mixing of the joining zone. Instead of flush contact, a predefined, defined immersion depth for the tool, corresponding to the material thickness, can also be used. In either case, the plasticized material is supported and secured by the support structure.

[0026] The invention further relates to a membrane storage device with a storage housing constructed from housing parts, manufactured according to a method as described above, wherein, according to the invention, the adjacent housing parts are connected to one another along a seam or joint profile by means of a connecting seam formed during friction stir welding, in a media- and pressure-tight manner, which is supported on its inside by a force-compensating support device, to which a membrane unit with a separating membrane is connected. In particular, membrane storage housings can be manufactured in this way from lightweight but difficult-to-weld materials, such as aluminum.

[0027] The inventive method and a membrane storage device producible therewith will be explained in more detail below using an exemplary embodiment. The diagrams show, in a general and not to scale, the

[0028] Figures 1 and 2 each show a longitudinal section of a membrane accumulator during friction stir welding and after completion of the welding process, including after the material removal of the block of material forming a housing part required for the withdrawal of the welding tool; and

[0029] Figures 3 to 6 in different views, an exemplary representation

[0030] Performing friction stir welding to produce a storage housing structure for a membrane storage tank according to Figure 2.

[0031] Figure 1 shows a longitudinal section through a storage housing 10, part of a diaphragm storage tank 12, consisting of two adjacent housing parts 14 and 16. The upper housing part 14, shown in the direction of view of Figure 1, is unmachined on its outer circumference and thus has a cylindrical outer wall 18. By machining portions of the outer wall 18, a kind of machined upper shell for the upper housing part 14 is obtained, as shown in Figure 2, with a wall thickness that is essentially the same as that of the lower housing part 16. In this respect, the diaphragm storage tank 12 shown in Figure 2 essentially represents the finished product, in which the two housing parts 14 and 16 are permanently joined together using friction stir welding, which will be explained in more detail below.

[0032] As can be seen from Figures 1 and 2, the lower housing part 16 is provided in the usual manner with a separating device in the form of an elastomeric separating membrane 20. The separating membrane 20 separates two fluid chambers 22 and 24 within the storage housing 10. Fluid chamber 22 typically contains a working gas, for example, nitrogen gas, while the other fluid chamber 24 contains a liquid, for example, hydraulic oil. Both fluid chambers 22 and 24 are provided externally with a connection for working gas 26 and a connection 28 for hydraulic oil, respectively. For the separation of the two fluid chambers 22 and 24, the flexible separating membrane 20 is designed in a cup- or bowl-shaped manner, similar to a dome.

[0033] The separating membrane 20 is inserted into the lower housing part 16 from above by means of a membrane unit 19. The membrane unit 19 has an annular retaining device 21, which, in the manner of a retaining clip 23, defines a receiving space 25 downwards for receiving an annular thickening 31 on the upper circumferential edge 30 of the flexible separating membrane 20. A fixing ring 32 is integrally attached to the retaining clip 23 above this. As shown in Fig. 2, the fixing ring 32, with its upper, outwardly projecting circumferential edge, encompasses a solid, hollow cylindrical support ring 35 of a support device 34 on its inner circumference and is connected to it, in particular, via a clip connection. The support ring 35 overlaps the separating membrane 20 with a predetermined overhang at the top and bottom, i.e., with approximately one-third of its diameter.Two-thirds of the way through a seam or connection run 36, which is bounded by the adjacent free end faces of both housing parts 14, 16 and is to be closed by friction stir welding, so that a substantially closed storage housing body is subsequently obtained, as shown in Fig. 2. In this way, the support ring 34 prevents any unwanted heat or material from being introduced onto the inside of the storage housing 10 during the welding process, which could potentially lead to damage to the material of the sensitive separating membrane 20.

[0034] Furthermore, the support device 34 with the support ring 35 allows for stiffening of the wall structure of the storage housing 10, at least in the area of ​​the seam or joint 36, so that under the influence of the welding tool 40 and its contact pressure during friction stir welding, unintended denting or undesired compression movements in the adjacent housing material cannot occur. The locking ring 32 also serves as further support, stiffening the support ring 35 further from the inside by bearing against it. This also applies in principle as shown in Fig. 1, provided that the locking ring 32 projects upwards, forming a hollow cylinder with the same inner diameter and a predefinable overhang, and the corresponding edge is not folded over to form a clip connection as shown in Fig. 2.The support ring 34 can be made of a conventional steel material; however, it can also be made of aluminum and aluminum materials, so that it is possible to connect the aluminum ring directly to the housing material of the storage housing 10 in a captive manner using friction stir welding.

[0035] Furthermore, a plate-like closure element 38 is buttoned into the bottom of the separating membrane 20 for improved sealing of the remaining fluid space 24 of the storage housing 10 against a hydraulic circuit (not shown) to which such a hydraulic accumulator or diaphragm accumulator is regularly connected via its connection 28. This design is common, so it will not be discussed further here.

[0036] Friction stir welding, also frequently referred to as friction stir welding, comprises the following essential process steps in the context of storage tank housing manufacturing. First, a wear-resistant welding tool 40 is set into rotation about its longitudinal axis by means of a (spindle) drive (not shown). Subsequently, the rotating welding tool 40 is pressed with a predefinable high contact force in the direction of the arrow according to Figure 4 into a joining gap in the form of the weld or joint path 36 between the two housing parts 14, 16, which are held together at their free end faces by a predefinable contact force.The welding tool 40 has a pin-shaped pin 42, which protrudes from a shoulder 44 arranged perpendicular to it, which has a larger diameter than the pin 42, the pin 42 serving to swirl the material parts of the adjacent housing parts 14, 16 to be joined together or to mix them in a doughy state.

[0037] The rotating welding tool 40 thus plunges into the weld or joint 36 between the housing parts 14, 16 to be joined, with a predefinable contact pressure from the free end face and from the outside. The shoulder 44, with its free end face, then rests against the outer circumference of the housing parts 14, 16, which are rotationally symmetrical about their longitudinal axis LA. During the penetration of the welding tool 40 into the weld or joint 36, the rotating welding tool 40 remains at the point of entry 1 for a few seconds. The resulting friction between the shoulder 44 and the joining partners, namely the two adjacent housing parts 14, 16, heats the storage material under the shoulder 44 until it is just below its melting point.This is accompanied by a temperature increase and consequently a decrease in strength, which plasticizes the housing material, giving it a doughy consistency. This allows for mixing within the seam or joint 36.

[0038] The starting position or insertion point is labeled 1 in Figures 1, 3, 4, and 5. The welding tool 40 is then moved continuously in a clockwise direction (indicated by arrows) as seen from Figure 5, passing positions 2, 3, and 4, until, after a revolution of slightly more than 360° from the initial position 1 and after passing over position 1 by approximately 20 degrees, position 5 is reached. During this time, the rotating welding tool 40, with its pin 42, remains within the weld line 36 between the housing parts 14 and 16. Thus, a feed movement occurs along the weld line 36, during which the rotating tool 40 is moved with high pressure along the joint line 36, continuously creating the weld.The pressure gradient that inevitably builds up between a front and a back side of the welding tool 40 due to the feed movement, together with its rotational movement, generates a transport of plasticized material around the welding tool 40, so that the pasty components of the material mix there and ultimately form the joint seam, which, according to the illustration in Figure 2, merges almost intrinsically into the other wall material of the storage housing parts 14, 16, so that a homogeneous transition between the housing parts 14, 16 results, forming the pressure-tight storage housing 10 as a whole.

[0039] The housing parts 14, 16 to be joined are rotationally symmetrical to the longitudinal axis LA of the storage housing 10 and the rotating welding tool 40 can plunge into the groove or connection path 36 between the housing parts 14, 16 with a predefinable engagement angle, preferably between 0° and 6° transverse to this longitudinal axis LA, for a joining operation, wherein in the present case an engagement angle of 0° is selected, so that the tool 40 plunges into the path 36 perpendicular to the longitudinal axis LA.

[0040] As already explained, the welding tool 40 emerges at a different point 6 to complete the welding process, which is different from the entry point 1. In particular, the weld or joint path 36 is exited at this other point 6, as can be seen especially in Figure 6. As soon as the welding tool 40, after completing a rotation of more than 360° along the weld or joint path 36, starting from station 1 and passing through the further stations 2, 3 and 4, exits at station 5, the welding tool 40, viewed in the direction of Figure 6, is moved upwards from station 5 along an arc-shaped path 46 towards station 6 and, during a defined retraction, increasingly comes out of engagement with the wall material of the upper housing part 14.After completion of the welding process along the seam or joint path 36, the welding tool 40 is rotated into the adjacent upper housing part 14 and continuously disengaged from the corresponding housing wall. This has the advantage that, upon continuous retraction of the welding tool 40 after completion of the friction stir weld along path 36, it is disengaged from the weld without any impairment of the weld in the form of pitting or void formation, etc. Preferably, a complete rotation from station 1 to station 6 takes place continuously at a constant speed and without delay.

[0041] The welding tool 40 is preferably fixed in a tool holder, such as a spindle drive, and driven by a multi-axis gantry machine, such as a multi-axis milling machine (not shown), and moved freely in space. Such a gantry machine is common, so no further details will be discussed here. It is understood that the rotating welding tool 40 also maintains its position in space, and the housing parts 14, 16 are set in rotation. The insertion and removal of the welding tool from the material is achieved by longitudinal displacement movements relative to the pin 42 of the welding tool 40. In a further embodiment, the welding tool 40 and the housing parts 14, 16 can both be moved simultaneously in relative motion to each other.

[0042] After completing the weld and turning the upper shell of the upper housing part 14, a storage housing structure 10 is obtained as shown in Figure 2, with a constant wall thickness for both housing parts 14, 16. Independently of this, a storage unit according to Figure 1 can of course also be used as the end product if required.

[0043] Friction stir welding is particularly advantageous for joining material combinations that cannot otherwise be readily welded. For example, it is especially suitable for manufacturing a storage housing 10 from aluminum and suitable aluminum alloys. Due to the absence of a liquid or vapor phase during friction stir welding, no cracks or pores, such as cavities, form in the material. While the welding pin 42 is primarily responsible for swirling the molten material, the shoulder 44, which can be visualized as a kind of half-shell, serves to isolate the ambient air from the weld seam along its path 36, which would otherwise be a disruptive factor during weld formation.

[0044] As shown in Figure 2 of the completed hydro or membrane accumulator 12, the friction stir weld created is, in terms of its microstructure, a quasi-intrinsic component of the adjacent material areas of both housing parts 14, 16, so that the weld joint is designed to be durable even under high stress.

Claims

Patent claims 1. Method for manufacturing a membrane storage device (12), comprising at least two adjacent housing parts (14, 16), which are permanently joined together along a common seam or connection path (36) in a joining step by means of friction stir welding to form a storage housing (10), characterized in that, prior to carrying out the friction stir welding by means of a rotating welding tool (40) which plunges into the seam and connection path (36) with a predefinable contact force, at least one housing part (16) is provided with a membrane unit (19) by inserting the same into this housing part (16), which has a movable separating membrane (20), and in that a support device (34) is additionally inserted between the seam and connection path (36) and the membrane unit (19), which covers the seam and connection path (36) with a predefinable overhang in such a way that the support device (34) provides a support force that counteracts the contact force of the welding tool (40).

2. Method according to claim 1, characterized in that the support device (34) is inserted in the one housing part (16) in such a way that its outer circumferential side is held in contact with inner wall parts of both housing parts (14, 16) in the area of ​​the seam and connection path (36) after the joining step.

3. Method according to claim 1 or 2, characterized in that the membrane unit (19) has a holding device (21) for the separating membrane (20), which is brought into contact with the inner circumferential side of the support device (34).

4. Method according to one of the preceding claims, characterized in that the support device (34) is received in an annular space (35) which is bounded on the outer circumferential side by inner wall parts of the housing parts (14, 16) and on the inner circumferential side by the holding device (21).

5. Method according to one of the preceding claims, characterized in that in friction stir welding the support device (34) is firmly welded to adjacent wall parts of the housing parts (14, 16) along the seam or connection path (36).

6. Method for manufacturing a membrane storage device (12) by means of friction stir welding, comprising at least the following process steps for manufacturing a storage housing (10): a wear-resistant welding tool (40) is set in rotation by means of a drive; - the rotating welding tool (40) plunges into a seam or joint path (36) between two housing parts (14, 16) to be joined with a predefinable contact force and thereby generates frictional heat which stirs adjacent material parts along the seam or joint path (36) into a plastically deformed or doughy state by the feed of the welding tool (40), without the melting point of the material parts being reached, - Exit of the seam or joint path (36) by the welding tool (40) after obtaining a media- and pressure-tight connection between the housing parts (14, 16) thus joined, and Extension of the welding tool (40) from a material block forming a housing part (14), which has a preferably cylindrical outer contour and a dome-shaped inner contour and which partially removes material from the outside into a The outer shell part is transformed into an angle-free shell part, which, together with the other housing part (16), is designed as a further shell part to form the shell-shaped storage housing (10) as a whole.

7. Method according to one of the preceding claims, characterized in that the housing parts (14, 16) to be joined are designed rotationally symmetrical to a longitudinal axis (LA) of the storage housing (10) and that the welding tool (40) plunges into the groove or connection path (36) between the housing parts (14, 16) with a predefinable engagement angle (LA), preferably between 0° and 6°, transversely to this longitudinal axis for a joining operation.

8. Method according to one of the preceding claims, characterized in that the welding tool (40) emerges at a different location (6) than where it was immersed (1) to terminate the method, in particular leaving the weld or joining path (36).

9. Method according to one of the preceding claims, characterized in that the welding tool (40) enters a housing part (14) adjacent to the weld or joint path (36) during a rotation of more than 360° and emerges from the material of the housing part (14) upon defined withdrawal.

10. Method according to one of the preceding claims, characterized in that the welding tool (40) is used with the aid of a multi-axis portal machine, such as a milling machine, or by means of a handle- a system, such as a robot, moves around the stationary housing parts (14, 16) to be joined together, or, in the case of a stationary arrangement of the welding tool (40), the housing parts (14, 16) to be joined together are moved at least rotationally relative to the welding tool (40), or the welding tool (40) and the housing parts (14, 16) to be joined together perform a predefinable relative movement to each other for the welding process. 1 1. Method according to one of the preceding claims, characterized in that the welding tool (40) is formed from a pin (42) and a shoulder (44) arranged perpendicular to it, which has a larger diameter than the pin (42) and that the pin (42) swirls or stirs the material parts of the housing parts (14, 16) to be joined together.

12. Method according to one of the preceding claims, characterized in that the rotating welding tool (40) is immersed with the predefinable contact force along the insertion point (1) into the seam or joint path (36) until the shoulder (44) lies flush on the material parts.

13. Membrane storage device (12), comprising a storage housing (10) constructed from housing parts (14, 16), manufactured according to a method according to one of the preceding claims, characterized in that the adjacent housing parts (14, 16) are joined along a seam or connection path (36) by means of a connecting seam (48) formed during friction stir welding in a media- and pressure-tight manner. are connected to each other, which is supported on its inside by a force-compensating support device (34), to which in turn a membrane unit (19) with separating membrane (20) is connected.

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