Lightweight structure

A lightweight structure is disclosed, in particular a lightweight structure for an aircraft which is formed from a large number of components which can be joined together by weld joining processes. According to the invention, the lightweight structure has a component thickness which is increased corresponding to the loads in the joint region of the at least one welded joint compared to a thickness of the component outside the joint region.

FIELD OF THE INVENTION

The invention relates to a lightweight structure, in particular for an aircraft, which is formed from a large number of components which can be joined together by weld joining processes.

In current production of large-scale structural components, for example fuselage shells for aircraft, skin plates or skin panels of the greatest possible size are used to produce the fuselage structure in order to minimise the number of longitudinal and transverse joints and thus to minimise the structural weight of the aircraft fuselage. The skin plates are joined together by applying stringers and frame segments to form shells and then sections which are finally joined together by a transverse joint to form the fuselage structure, and besides riveting and bonding processes, welding processes, such as in particular friction stir welding (FSW) are used as the joining process to reduce the weight of the structural components at reduced production costs by omitting the attachment elements.

Friction stir welding devices of this type have a friction stir welding head with a welding pin which rotates about its longitudinal axis and has a tool shoulder on one side or on both sides of the work piece. Due to the friction heat generated by the rotation of the welding pin and of the tool shoulder, the material in the weld formation region is plasticised, the rotating welding pin causing the stirring and thus mixing of the material of the components. The tool shoulders allow a unilateral or bilateral smoothing of the weld surface in a single operation. To ensure adequate strength in the joint regions, i.e. in the region of the longitudinal and transverse welds, a thickness of the skin plates which is dimensioned in accordance with the structural loads is necessary, and so structural components of this type have a high structural weight. It is also disadvantageous in manufacturing terms that when a transverse weld meets a longitudinal lap weld, a jump in thickness occurs which cannot be bridged by a friction stir weld.

SUMMARY OF THE INVENTION

In contrast thereto, the object of the invention is to provide a lightweight structure which allows high mechanical strength with a minimum structural weight and minimum production costs.

This object is achieved by a lightweight structure having the features of claim1.

The lightweight structure according to the invention, in particular a lightweight structure for an aircraft, is formed from a large number of components which can be joined together by weld joining processes. According to the invention, the lightweight structure has in the joint region of the at least one welded joint a component thickness which is increased corresponding to the loads compared to a thickness of the component outside the joint region. The course of the thickness is preferably configured according to the course of the load of the lightweight structure, so that a join is obtained which corresponds to the high demands made on the quality of the join, particularly in aviation. The component thickness which is adapted to the load in the joint region allows a high strength structure which is optimised in terms of weight to be achieved. Consequently, compared to the prior art, large-area lightweight structures are possible in assembly, in particular in so-called “major component assembly” (MCA) and “final assembly line” (FAL).

According to a particularly preferred embodiment of the invention, at least one component in the joint region of the welded joint is provided with a plate thickness which is increased corresponding to the loads compared to a plate thickness of the component outside the joint region.

In a specific embodiment, the welded joint is configured as a butt weld, the components to be joined together having a plate thickness which is increased corresponding to the loads compared to a plate thickness of the component outside the joint region. The plate thickness of the components in the joint region is preferably identical, thus achieving a flush abutment.

As an alternative or in addition, the welded joint can have at least one lap weld.

The components are preferably composed of a plurality of plates of a different thickness to form a load-dependant plate thickness (“tailored blank”). The advantage of this solution is that the components do not have to be machined down to the desired plate thickness in an expensive manner in manufacturing terms in order to achieve a weight-optimised structural component.

In an embodiment according to the invention, the components have a gradual thickness course, the plate thickness being configured dependent on location and as a function of the respective load.

According to the invention, the components more preferably form a skin plate of an aircraft fuselage structure, it being possible to apply profiled parts, such as stringers and/or frames to reinforce the skin plate. In this respect, it is particularly preferred if the region which has an increased plate thickness extends into a joining region of the profiled parts. The frames can be fixed directly to the skin plate by connecting clips or on the basis of the thickness course of the skin plates which is adapted to the load.

In an alternative embodiment, the component thickness of the lightweight structure which is increased in the joint region is achieved by at least one reinforcing plate to form an additional load path. In this respect, it has proved to be particularly advantageous in manufacturing terms if the components to be joined together are arranged in a common plane in the joint region, the reinforcing plate overlapping at least in portions the end portions of the components and being joined thereto by a welded joint. In this case, the skin plates can be arranged at a mutual spacing so that a tolerance-compensating transverse joint concept is achieved.

The at least one reinforcing plate is preferably configured as a sheet metal comb which is set back in the region of the stringer ends and encompasses said stringer ends in portions. The geometry of the sheet metal comb allows a compensation in tolerance for the transverse weld, without in so doing having to change the zero orientation of the stringer ends or having to use connection elements (stringer couplings). The sheet metal combs form a load path and thus allow the stringers to run out upstream of the weld region. It is therefore possible to dispense with a coupling of the stringer ends by connection elements in the section joint. In addition, the stringer ends of individual or of all oppositely arranged stringers can be joined by connection elements. This means that an even further improved component strength and reliability can be achieved.

In a specific embodiment of the invention, the first components form at least an inner sheet metal skin and the second components form an outer sheet metal skin which are joined together to form a section by a longitudinal join configured as a riveted, bonded or welded lap joint. The sections can be joined together preferably by a transverse weld configured as a butt weld, the joint region of the first sheet metal skin being set back such that the second sheet metal skin can be welded substantially up to a terminating edge. The outer skin plates are preferably each provided in the region of the transverse weld with a notch which extends from an outer edge over the terminating edge of the inner skin plate, so that the transverse weld in the region of the inner skin plates can be formed independently of the transverse weld of the outer skin plates.

A friction stir welding device comprising two tool shoulders (“bobbin tool”) can be used particularly advantageously in manufacturing terms for joining the fuselage sections, which device produces a substantially smooth surface on both sides of the lightweight structure. The two-shouldered friction welding tool can advantageously be removed after processing via the recess formed by the notches, so that no further openings are required. At least one doubler plate is preferably provided in the region of the notches to cover the recess.

Friction stir welding is particularly preferred according to the invention, as friction stir welds have an almost optimum joining structure in the weld region which is comparable with the original material characteristics of the components which have not yet been joined together. Thus, joining components by friction stir welding makes it possible to produce mechanically tough structures. As an alternative or in addition, it is possible to use laser beam welding processes and/or fusion welding processes.

Other advantageous developments of the invention are disclosed in the further subclaims.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1shows a lightweight structure1configured as a fuselage structure for aircraft and consisting of skin plates2which are joined together by riveted longitudinal joins4to form so-called fuselage shells6and these are joined together to form sections8a,8b. The sections8a,8bare then joined together to form the fuselage structure1of the aircraft by means of transverse joints10, as indicated schematically inFIG. 1. The construction of a fuselage structure1of this type is described in detail in the following with reference toFIGS. 1 to 4.

FIG. 2shows a sectional view of the fuselage structure1ofFIG. 1in the region of the sections8a,8bjoined edge-to-edge by a friction stir welding process, a wedge-shaped butt weld (transverse weld)14being formed from outside, i.e. inFIG. 2from below, during the friction stir process in a joint or weld formation region12by means of a welding pin and tool shoulders arranged on both sides of the skin plates2a,2b. According to the invention, in the joint region12of the weld, the lightweight structure1has a component thickness which is increased corresponding to the loads compared to a thickness of the construction element outside the joint region. In the illustrated embodiment of the invention, both skin plates2a,2bin the joint region12of the weld are provided with a plate thickness t2which is increased corresponding to the loads compared to a plate thickness t1of the skin plates2a,2boutside the joint region. The plate thickness t2of the skin plates2a,2bin the joint region12is configured identically, so that a flush abutment is obtained. The course of the thickness is configured to be approximately gradual corresponding to the load level, so that a join is achieved which corresponds to the high demands made on the quality of the join, particularly in aviation. Due to the component thickness adapted to the load in the joint region12, a high strength structure is provided which is optimised in terms of weight.

Profiled parts, such as stringers16a,16band frames18are provided to reinforce the skin plates2a,2b. The fuselage frames18which are indicated schematically and extend transversely to the longitudinal axis of the aircraft are fixed to the skin panel by connecting clips20, the region of an increased plate thickness t2extending up into a joining region of the profiled parts16a,20. Due to the introduction of force into the fuselage frame18, the connecting clip20is arranged in the region12of a large plate thickness t2, the stringer ends22aextending and stopping just before the weld14. The plate thickness t2is reduced to the lower plate thickness t1on the stringer side downstream of the stringer end22and the connection region of the connecting clip20. On the adjacent skin plate2b, as a result of the load which is reduced without frame connection, the stringers16bterminate in a transition region24of an intermediate thickness t3which decreases in a gradual manner towards a connection region of the stringers16bagain with reduced plate thickness t1. The stringer ends22a,22bare configured to be bent at right angles according to the course of the plate thickness and rest in a substantially planar manner against the skin plates2a,2b. To form the load-dependent plate thickness, the skin plates2a,2bare preferably composed of a plurality of plates of different thicknesses, for example by a welding process (“tailored blank”), so that the skin plates2a,2bdo not have to be machined down to the desired thickness in a costly manner in order to achieve a weight-optimised structural component1.

According toFIG. 3which shows a sectional view of skin plates2a,2bjoined by friction stir welding according to an alternative embodiment of the invention, the fuselage frames18in this embodiment are attached directly, i.e. without connecting clips, to the skin panel on the basis of the thickness path of the components which is adapted to the load. In the illustrated embodiment, the frame18is joined to the skin plate2ain the region of a large plate thickness t2by a rivet joint. On both skin plates2a,2b, due to the load which is reduced without a frame connection, the stringers16a,16bterminate in a transition region24of an intermediate thickness t3which decreases gradually in each case towards a connection region of the stringers16a,16bagain with a reduced plate thickness t1.

In the following, the formation of the transverse weld14in the region of a longitudinal join4is described by way of example with reference toFIG. 4which shows the fuselage structure1fromFIG. 1in the region of the transverse weld14and a longitudinal join4joining the skin plates2a-2d.

As can be inferred fromFIG. 4, the skin plates2a,2bform an inner sheet metal skin and the skin plates2cand2dform an outer sheet metal skin, the skin plates2a,2c;2b,2dhaving been joined together in the illustrated embodiment to form sections8a,8bby the longitudinal join4configured as a riveted lap joint. Sections8a,8bare joined by the transverse weld configured as a butt weld14a,14b, the joint region12of the skin plates2c,2dbeing set back such that the skin plates2a,2bcan be welded up to a terminating edge26. For this purpose, the outer skin plates2c,2dare each provided in the region of the transverse weld14a,14bwith a notch28which extends from an outer edge30over the terminating edge26of the inner skin plates2a,2b, so that the transverse weld14acan be formed in the region of the inner skin plates2a,2bindependently of the transverse weld14bof the outer skin plates2c,2d. A friction stir welding device with two tool shoulders can be used particularly advantageously in manufacturing terms for joining the fuselage sections8a,8b, which device produces a substantially smooth surface on both sides of the lightweight structure1. The two-shouldered friction welding tool can advantageously be removed after processing via the recess formed by the notches28, so that no further openings are required. An approximately rectangular doubler plate32is then attached to the structure by a rivet joint in the region of the notches28from an inside for covering the recess and for reinforcing the structure.

FIG. 5shows a plan view of a fuselage shell6aconsisting of two components which are configured as skin plates2a,2bof a fuselage structure1of an aircraft and are joined along their longitudinal edges by a friction stir welding process according to a further embodiment of the invention. A plurality of stringers16which are arranged in parallel and extend in the direction of the longitudinal axis of the aircraft is provided to reinforce the fuselage shell6a.

As can be seen in particular fromFIG. 6which shows a sectional view along line A-A ofFIG. 5, the longitudinal join is configured in this embodiment as a lap weld34, at least one skin plate2a,2bwhich is to be joined having a plate thickness which is increased corresponding to the loads compared to a plate thickness of the skin plate outside the joint region12. In the illustrated embodiment, the two skin plates2a,2bare each provided in the joint region12with a thickened portion which has a plate thickness t2. Downstream of the joint region12, the plate thickness t2decreases in an approximately gradual manner to a minimum thickness t1and then increases, as a function of the load, over a plurality of intermediate regions of an increasing plate thickness. The plate thickness is also increased in the region of the stringer connection to improve the introduction of force.

FIG. 7shows a plan view of the fuselage shell6afromFIG. 5which is joined to a further fuselage shell6b, having skin plates2c,2d, to form a fuselage section8. In the joint region12of the transverse joint10, the lightweight structure has a component thickness which is increased corresponding to the loads compared to a thickness of the component outside the joint region. In the illustrated embodiment of the invention, the component thickness of the lightweight structure which is increased in the joint region is achieved by a reinforcing plate arrangement which has an upper reinforcing plate36ainFIG. 7and a lower reinforcing plate36bto form a load path. The reinforcing plates36a,36bare configured as sheet metal combs which are set back in the region of the stringer ends22, encompass at a distance the stringer ends22and overlap in the region of the longitudinal join (seeFIG. 8c), the sheet metal combs36a,36beach being joined to the skin plates2a-2dby two welds38a,38bwhich extend parallel in portions and are associated with each skin plate2ato2d. The weld38aon the stringer side is configured to be set back in each case corresponding to the outer contour of the sheet metal combs36a,36bin the region of the stringer ends22. In addition to the sheet metal combs36a,36b, the stringer ends22of individual or of all mutually opposite stringers16can be joined by connection elements (coupling elements). This provides an even further improved component strength and reliability.

As can be seen fromFIGS. 8aand8bwhich are sectional views along line A-A and B-B respectively fromFIG. 7, it has proved to be particularly advantageous in manufacturing terms if the skin plates2a,2cwhich are to be joined are arranged in a common plane in the joint region12, the sheet metal comb36aoverlapping the end portions of the skin plates2a,2cin portions on the inside and being joined thereto by means of the weld38. Thus, in the joint region of the transverse joint10, the lightweight structure has a component thickness t2which is increased corresponding to the loads compared to a thickness t1of the construction element outside the joint region. Furthermore, the thickness of the skin plates2a,2cin the joining region without a stringer connection is increased in each case to a plate thickness t3compared to the plate thickness t1(cf.FIG. 8a). The skin plates2b,2dare joined accordingly by means of the sheet metal comb36b, so that it is possible to forego a description in this respect.

According toFIG. 8cwhich shows a sectional view along line C-C ofFIG. 7, a hole-free fuselage shell is achieved by means of a doubler cover plate consisting of the sheet metal combs36,36b. For this purpose, the sheet metal comb36aextends in the joint region in a common plane with the skin plate2b, an end portion of sheet metal comb36abeing overlapped by the sheet metal comb36band being joined thereto and to the skin plate2aby a longitudinal weld40, thereby forming a closed structure. Furthermore, the sheet metal comb36bis joined to the skin plate2bby a longitudinal weld42.

The lightweight structure according to the invention is not restricted to the friction stir welding process described, in fact different weld joining processes known from the general prior art can be used, such as laser beam welding or fusion welding. However, friction stir welding is particularly preferred according to the invention, as friction stir welds have in the weld region an almost optimum joining structure and thus have a high static and dynamic strength.

A lightweight structure1is disclosed, in particular a lightweight structure for an aircraft, which is formed from a large number of components2which can be joined together by weld joining processes. According to the invention, the lightweight structure1has a component thickness t2which is increased corresponding to the loads in the joint region12of the at least one welded joint compared to a thickness t1of the component outside the joint region12.