Method and apparatus for forming a strut

Abstract

It is disclosed a strut forming tool 3 and a method for using same. The strut forming tool (3) is configured to form an end portion (1b,1c) of an extruded tubular element (1) made of an aluminium alloy, such as a 6000 series aluminium alloy, into a connection area (12), wherein the strut forming tool (3) comprises: - a die (32) comprising an internal shaping surface (33) configured to shape the end portion (1b,1c) when the tubular element (1) and the die (32) is moved towards each other in an axial direction (A) of the tubular element (1) such that the end portion (1b,1c) is forced through the die (32); wherein the internal shaping surface (33) comprises: - a receiving section (33a) configured to receive the end portion (1b,1c) of the tubular element (1); - a final section (33c) with a cross-sectional area configured to define a cross-section of the connection area (12), wherein the connection area (12) comprises a flattened area (12a) and preferably at least one side wing (12b); and - a shaping section (33b) configured as a gradual transition from the receiving section (33a) to the final section (33c) and configured to convert the relative axial movement between the tubular element (1) and the die (32) into radial periphery compression forces on the end portion (1b,1c).

Description

[0001] Method and apparatus for forming a strut

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method and an apparatus for forming a strut for automotive vehicles, in particular to the end forming of such struts.

[0004] BACKGROUND ART

[0005] Struts is a solution for car suspensions and structural systems. The use of tubular struts is an effective way of improving the stiffness of a body. Struts are typically made from tubular elements with flattened end portions forming connection areas allowing the strut to be attached (most often bolted) to structures. The stiffness of the connection area is therefore of high importance.

[0006] To increase the stiffness of the connection area, a local stiffener can be inserted at the end as suggested by GB287023. Another way of increasing the stiffness of the connection area is disclosed in document W02020 / 104383, wherein the wall thickness is increased in an end portion of the tubular element before flattening. Yet another way of increasing the stiffness of the connection area is disclosed in document WO2019 / 193099, wherein an end portion of the tubular element is folded before flattening. The flattening of the end portion into a connection area is performed by squeezing the tubular element in the radial direction, as illustrated in Figs. 3a-4b. Some examples of resulting connection areas are shown in cross-section in figs. 5a-5e. Providing side wings on the connection areas, as exemplified in Figs. 5b-5e, will also increase the bending stiffness of the connection area.

[0007] It is known from cold forging processes that aluminium alloys can be highly formable if the material undergoing the forming process are kept under compression. During a traditional flattening process for struts, some parts of the end portion will be compressed, while other parts of the end portion will be under tension, ref. Fig. 5g. In the tensioned parts the material will be locally elongated. If the material cannot be sufficiently elongated as required to undergo the forming process, cracks will occur. Such cracks are undesirable as they will significantly reduce the strength of the connection area.

[0008] Cracks are usually not an issue when end portions of tubular elements are produced from a low or medium strength aluminium alloy not being in a tempered or cold worked condition, typically having a tensile strength below 250 MPa and elongation higher than 18 %. However, due to insufficient elongation in the material, cracks will typically occur when end portions of tubular members made of high strength alloys, tempered, or cold worked material are flattened in this process. The known forming process is therefore unsuitable for materials not having sufficient elongation. However, it is desirable to make struts of alloys with reduced elongation caused by having been pre-tempered or pre-cold worked to achieve an improved connection between the strut and the car frame and / or to optimize the manufacturing process. The advantage obtained through pre-cold working is normally obtained through eliminating the tempering process, whereas the advantage of forming pretempered materials is obtained through eliminating tempering of finish fabricated parts and components.

[0009] The present invention is directed to a method and an apparatus that may solve or at least reduce at least one of the aforementioned problems or challenges. SUMMARY OF INVENTION

[0010] The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention.

[0011] The invention relates to a strut forming. The strut forming tool is configured to form an end portion of an extruded tubular element made of an aluminium alloy, such as a 6000 series aluminium alloy, into a connection area.

[0012] The strut forming tool comprises a die and the die comprises an internal shaping surface configured to shape the end portion when the tubular element and the die is moved towards each other in an axial direction of the tubular element such that the end portion is forced through the die.

[0013] The die may be one piece or a plurality of pieces. A plurality of pieces may be assembled or spaced apart to form the die. The shaping surface may thus be one surface or the sum of a plurality of surfaces.

[0014] The internal shaping surface comprises: a receiving section configured to receive the end portion of the tubular element; a final section with a cross-sectional area configured to define a cross-section of the connection area, wherein the connection area comprises a flattened area and preferably at least one side wing; and a shaping section configured as a gradual transition from the receiving section to the final section and configured to convert the relative axial movement between the tubular element and the die into radial periphery compression forces on the end portion.

[0015] The strut forming tool will prevent or at least reduce the tension in the material of the tubular element caused by the forming process. Thus, the strut forming tool allows forming of tubular elements made of materials having reduced elongation / formability without the risk of cracking the material. An improved fabrication process is thus obtained.

[0016] The shaping surface can be configured to control local material flow in selected parts of the end portion during the forming process. In this context controlling should be understood as encompassing a reduction as well as a complete prevention of the local material flow. The controlling will thus cause a reduction, or preferably a complete prevention, of the tensile stresses arising during the forming process. The control may be in one or more directions and should be selected to reduce, or preferably prevent, cracks from building in the material because of the forming process.

[0017] The shaping surface may be configured to completely encircle the end portion during forming.

[0018] The material of the tubular element will typically be pre-tempered or cold worked before the end portion is shaped. The strut forming tool allows forming of the end portion of such tubular elements, typically having less than 18 % elongation, without cracking the material.

[0019] When produced from a high strength alloy, the material of a tempered or cold worked tubular elements typically has a tensile strength above 300 MPa. The strut forming tool allows forming of the end portion of such tubular elements without cracking the material.

[0020] The strut forming tool may comprises a holder configured to hold the tubular element. The die and the holder will then be configured to be moved towards each other during the forming operation. One of them can be fixed while the other is free to move, or both may be free to move.

[0021] The strut forming tool may comprise a plurality of dies, i.e. two or more dies. If the strut forming tool comprises two or more dies, two connection areas may be formed on the tubular element at the same time. Two of the dies may be identical to form identical connection areas at both ends at the same time. If two connection areas are to be formed at the same time, the two dies can be moved towards each other in an axial direction of the tubular element.

[0022] The tubular element will typically be straight. If the tubular element is bent or if one or both connection areas are bent, the holder may preferably be used in combination with one or two dies.

[0023] The end portion has an initial periphery on entry into the shaping section. The shaping section is configured to shape the connection area to have a periphery which is smaller than the initial periphery of the end portion.

[0024] After being extruded, the tubular element may go through one or more processes prior to being formed by the strut forming tool. Such processes may involve changing (e.g. expanding) the periphery of the end portion or the entire tubular element as compared to when it was extruded. The shape of the extruded hollow tubular element may be e.g. round, oval, flat oval. The initial periphery of the end portion should in any case be understood as the periphery of the end portion when it enters the die.

[0025] The shaping section comprises a shaping section inlet and a shaping section outlet. The end portion enters the shaping section at the shaping section inlet and leaves the shaping section at the shaping section outlet. The shaping section inlet defines a first periphery, and the shaping section outlet defines a second periphery. Wherein the second periphery should be smaller than the first periphery.

[0026] The connection area is gradually formed as the tubular element is forced through the die. The shaping surface of the die is configured to compress the periphery of the part of the end portion being shaped. This compression reduces tension in the material such that cracking is avoided. The shaping surface also cause the axial movement to build up compression stresses during the forming process. Whereas with the prior art strut forming techniques, increased tension stress is caused when the material is formed, and in particular when it is pulled down into the lower tool.

[0027] The material of the extruded tubular element will typically have a grain structure wherein the grains are oriented in the longitudinal extrusion direction of the tubular element. This grain structure orientation reduces the elongation measured 90 degrees to the extrusion direction. This grain structure therefore limits the formability across the extrusion direction. The material is therefore prone to cracking when outer radiuses are formed, e.g. when forming connection areas on end portions of the tubular element. The risk of cracking is eliminated by the compression applied to the material during forming by the forming tool.

[0028] After forming, an outer part of the end portion has been shaped into a connection area. Adjacent the connection area, a transition area is formed. The transition area is a gradual transition between the connection area and the part of the tubular element that is not formed by the forming tool, such as an intermediate portion.

[0029] The connection area to be formed is configured for connection to another component or assembly, such as a car frame.

[0030] The connection area preferably comprises a hole for a bolted connection.

[0031] By being through-going, the shaping surface will allow the end portion to exit the die after shaping. The connection area can then be made to have any required length. Alternatively, the die can be adapted to the required length of the end portion.

[0032] The tubular element / strut and the die can be moved away from each other in the axial direction of the tubular element / strut to release the connection area from the die after forming or if the die is made of 2 or more parts it can be separated after end forming and as such release the formed connection area.

[0033] The strut forming tool should be made of a stronger material than the tubular member.

[0034] Friction between the die and the tubular element can preferably be lowered by means of lubricant. It is also preferred that the surface roughness of the die is selected to lower friction.

[0035] The connection area formed with the strut forming tool can be a finished connection area. However, it may also be a semi-finished connection area that will subsequently undergo additional forming (e.g. bending or further flattening to squeeze the walls onto each other). The subsequent shaping can involve a radial force, e.g. as described in the prior art. However, the critical shaping, i.e. the shaping that would normally cause cracking, is performed with the strut forming tool. As such, the strut forming tool may be used to form both a finished strut and a semi-finished strut.

[0036] The semi-finished strut having one end portion formed to a connection area may have to be formed at the opposite end portion also. The opposite end portion can then be formed by means of the same strut forming tool or by means of a similar strut forming tool configured to from a connection area with a different geometry.

[0037] The cross-section and the cross-sectional area is in a plane perpendicular to the axial direction of the tubular element / strut.

[0038] No parts of the shaping surface should be perpendicular to the axial direction of the tubular element.

[0039] The receiving section may comprise a funnel shape.

[0040] The receiving section may have a cross-sectional area corresponding to the cross-section of the end portion of the tubular element, typically being circular or semi-circular.

[0041] The receiving section preferably tapers from a first cross-sectional area, that is greater than the cross- sectional area of the end portion, to a second cross-sectional area, that is equal to the cross-sectional area of the end portion.

[0042] The shaping section may be configured to straighten out two wall portions of the tubular element and bring the wall portions closer together, preferably into contact with each other, to form the flattened area.

[0043] In the flattened area two wall portions of the tubular element are straightened out and brought closer to each other, preferably into contact with each other. The cross-sectional area of the final section may thus be configured to define a cross-section of the connection area comprising a flattened area wherein two wall portions of the tubular element are straightened out and brought closer to each other, preferably into contact with each other. The two wall portions of the flattened area are preferably parallel.

[0044] The connection area may comprise one side wing. The side wing may be a single side wing or a double side wing. The side wing is typically arranged at an end of the flattened area.

[0045] In the side wing, two wall portions of the tubular element are bent and brought closer to each other, preferably into contact with each other.

[0046] The side wing may be formed in a wide variety of shapes. However, the side wing is always bent relative to the flattened area. The shaping section may be configured to shape the connection area to comprise two side wings arranged on opposite sides of the flattened area.

[0047] The connection area may comprise two side wings arranged on opposite sides of the flattened area. The two side wings may be single side wings, double side wings or a combination of the two.

[0048] A single side wing extends in one direction relative the flattened area. Whereas a double side wing extends in two directions relative the flattened area.

[0049] When a connection area comprises two side wings, the side wings will typically be angled relative each other but may also be parallel.

[0050] The shaping section may be configured to shape the cross-section of the connection area to comprise one or more radiuses, wherein the one or more radiuses are smaller than two times a wall thickness of the connection area.

[0051] The cross-sectional area of the final section may thus be configured to define a cross-section of the connection area that comprises one or more radiuses, wherein the one or more radiuses are smaller than two times the wall thickness of the connection area.

[0052] The radius and the wall thickness should be measured at the same place on the connection area.

[0053] Some of the radiuses will often be smaller than lx the wall thickness.

[0054] If two wall portions of the tubular element are brought into contact with each other, the wall thickness should still be considered the thickness of one of the wall portions.

[0055] Radiuses will be located at opposite ends of the flattened area, and in the side wings when present. During a forming process, tension typically builds where outer radiuses are formed, and compression typically builds where inner radiuses are formed.

[0056] When an outer radius is formed, it is increasingly important to build up the radial compression (to avoid cracks) as the radius gets smaller. The need for compression is therefore less at the beginning of the forming as compared to later stages of the forming. The need for compression is thus less at the part of the shaping section close to the receiving section as compared to the part of the shaping section close to the final section. When the final section is reached, the forming is completed and there is no longer a need for compression. The cross-sectional area of the final section can therefore be unchanged throughout the final section.

[0057] When the flattened area is formed, it is of less importance to build up radial compression. The material can withstand cracks even if some parts are not under radial compression where the flattened area is formed.

[0058] The cross-section of the connection area defined by the final section may have a height and a width, wherein the width is equal or greater than two times the height.

[0059] The invention relates to a method of forming a strut. The method is using a strut forming tool as described herein.

[0060] The method comprises the steps of: providing an extruded tubular element made of an aluminium alloy, such as a 6000 series aluminium alloy, and comprising two end portions on opposite sides of an intermediate portion; moving the die and the tubular element towards each other in an axial direction of the tubular element such that the end portion enters the shaping surface; and forming a connection area by means of forcing the end portion through the die, wherein axial movement between the tubular element and the die is causing the shaping surface to radially compress a periphery of the end portion.

[0061] The forming of the end portion of the tubular element into a connection area is performed by gradually shaping the end portion, starting from an outermost part of the end portion, moving in an axial direction of the tubular element towards the intermediate portion.

[0062] This method provides the same effects and advantages as the strut forming tool.

[0063] The tubular element and connection area referred to in connection with the method may have the same features as those referred to with the forming tool.

[0064] If the strut forming tool comprises a holder, the method may comprise the step of attaching the tubular element to the holder prior to the forming step.

[0065] If the strut forming tool comprises two or more dies, two connection areas may be formed simultaneously during the forming step.

[0066] The method may comprise repeating the forming step to form another connection area on the tubular element.

[0067] The forming step may be performed by means of cold forming.

[0068] The method will typically comprise the step of pre-tempering or pre-cold working the tubular element prior to forming.

[0069] The present method makes it possible to temper in the tubular element prior to forming its ends into connection areas. This will lower the production / handling cost and result in less scrap caused by handling damages. The tubular element may for example be tempered in an as-extruded condition prior to forming.

[0070] The strut forming tool may be configured such that the holder and the die can be brought into contact with each other. The method may comprise bringing the holder and the die into contact with each other.

[0071] The method may comprise the step of moving the holder and the die away from each other to retrieve the finished or semi-finished strut.

[0072] The method may comprise the step of squeezing the connection area after forming. The squeezing may involve bringing the wall portions of the flattened area even closer together, preferably into contact with each other. The squeezing may involve bringing the wall portions of the side wing(s) even closer together, preferably into contact with each other. The squeezing may also involve reducing one or more radiuses of the connection area.

[0073] The method may comprise the step of forming a hole in the connection area. The hole can receive a bolt for mounting the strut to an automotive structure. The hole can be obtained by punching or drilling a hole in the formed connection area.

[0074] The method may comprise the step of bending the tubular member at the end portion, such that the intermediate portion has a first longitudinal central axis and the end portion has a second longitudinal central axis, wherein the second longitudinal central axis is offset or at an angle with respect to the first longitudinal central axis. The connection area of the strut can then be aligned with the connection area of the structure to which the strut is to be attached. Bending is preferably performed after forming of the connection area. Alternatively, the bending and forming can be performed simultaneously.

[0075] BRIEF DESCRIPTION OF DRAWINGS

[0076] The following drawings are appended to facilitate the understanding of the invention. The drawings show embodiments of the invention, which will now be described by way of example only, where:

[0077] Fig. 1 shows an axial cross-sectional view of a tubular element;

[0078] Figs. 2a-b show a perspective view of a strut, or at least a part of a strut, and a transverse cross- sectional view of the strut;

[0079] Figs. 3a-b show an axial cross-sectional view and a transverse cross-sectional view of a tubular element positioned in a prior art forming tool;

[0080] Figs. 4a-b show the same tubular element and prior art forming tool as figs 3a-b wherein the prior art forming tool has shaped a connection area at one end portion of the tubular element by means for forcing an inner tool piece towards an outer tool piece in a radial direction of the tubular element;

[0081] Figs. 5a-f show transverse cross-sectional views of different embodiments of a connection area;

[0082] Fig. 5g shows a detail of Fig. 5c on which it is indicated where tension and compression is formed when a connection area is formed with a prior art forming tool as exemplified in Figs. 3a-4b;

[0083] Fig. 6a shows an axial cross-sectional view of a tubular element positioned in a strut forming tool according to the invention;

[0084] Fig. 6b shows the same tubular element and strut forming tool as Fig. 6a wherein the strut forming tool has shaped a connection area at one end portion of the tubular element by means for forcing the tubular element through a die in an axial direction of the tubular element;

[0085] Fig. 6c shows the same tubular element and strut forming tool as Fig. 6b wherein the die is removed from the formed connection area;

[0086] Fig. 6d shows an axial cross-sectional view of the die;

[0087] Fig. 7a shows a side view of a part of a strut;

[0088] Figs. 7b-e show transverse cross-sectional views of different parts of the strut in Fig. 7a;

[0089] Fig. 8a shows a perspective view of a strut with an angled connection area; and

[0090] Figs. 8b-d show a top view, a front view, and a side view of the strut in Fig. 8a.

[0091] DETAILED DESCRIPTION

[0092] In the following, embodiments of the invention will be discussed in more detail with reference to the appended drawings. It should be understood, however, that the drawings are not intended to limit the invention to the subject-matter depicted in the drawings.

[0093] In the preceding description, various aspects of the disclosure have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the invention and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.

[0094] The automotive industry continuously strives toward weight and cost saving solutions. Therefore, it is of great interest to find solutions that allow for light-weight materials, such as aluminium, to be used. However, when using aluminium, the design requirements must receive an increased focus to obtain load-bearing members that can fulfil the requirements put thereon. In struts mounted in automotive structures, the connection areas are subject to the highest local stresses. This is particularly pronounced when the axis of connection area is not in line with the axis of loading.

[0095] Struts typically have connection areas for attachment to an automotive structure, where the connection area is a flattened part of the strut. To improve stiffness, the connection area can be formed with side wings.

[0096] Fig. 1 shows an axial cross-sectional view of a tubular element 1. The tubular element 1 comprises an intermediate portion la and two end portions lb,lc. The tubular element 1 is extruded. The periphery of the two end portions l,b,lc and the intermediate portion la is therefore the same.

[0097] Due to the extrusion process, the material of the tubular element 1 has a grain structure wherein the grains are oriented in the axial direction A of the tubular element 1. This is also the direction in which the tubular element 1 was extruded. This grain structure makes the material easier to form in the axial direction A, parallel with the grain orientation, than in a radial direction R, perpendicular to the grain orientation. In the direction perpendicular to the grain orientation, the material has a reduced elongation. The reduced elongation increases the risk of cracks forming in the material during a shaping process, e.g. when making a strut 10.

[0098] Fig. 2a shows a perspective view of a strut 10, or at least a one end of the strut 10. This strut 10 is made from a tubular element 1 as illustrated in Fig. 1. A connection area 12 is formed at the end of the strut 10. In Fig. 2a only one connection area 12 is illustrated. However, a strut 10 will typically comprise two connection areas 12. Struts 10 can also be made to any required length.

[0099] The connection area 12 is formed at the very end of the strut 10. The connection area 12 adjoins a transition area 13 which makes a gradual transition to an adjoining intermediate area 11. At the opposite end of the intermediate area 11, a second transition area 13 will typically lead to a second connection area 12.

[0100] A hole 14 will typically be made in the connection area 12 to provide a bolted connection such that the strut 10 can be connected to a frame or similar. Alternatively, the connection area 12 can be connected in any other suitable manner that is available to the skilled person.

[0101] Fig. 2b shows a transverse cross-sectional view through the connection area 12 of the strut 10 in Fig. 2a. The connection area 12 has a flattened area 12a. The connection area 12, may have side wings 12b as illustrated in Fig. 2a and Fig. 2b. The connection area 12 has a height h, a width w, and a periphery Pc.

[0102] Fig. 3a show an axial cross-sectional view of a prior art forming tool 2. The prior art forming tool 2 is used to form the end portion lb,lc into a connection area 12 and thus making the tubular element 1 into a strut 10. Fig. 3b shows a transverse cross-sectional view of the forming tool 2 in Fig. 3a.

[0103] The forming tool 2 comprises an inner tool piece 21 and an outer tool piece 22. To form the connection area 12, the tubular element 1, and in particular the end portion lb thereof, is first placed on the outer tool piece 22. The inner tool piece 21 is then placed on top of the tubular element 1, as illustrated in Figs. 3a-b. The next step is to force the inner tool piece 21 towards the outer tool piece 22, i.e. in the radial direction R of the tubular element 1 (also indicated as the Z-direction in the figures).

[0104] Fig. 4a and Fig. 4b show the same forming tool 2 as in figs 3a-b. In Figs. 4a-b the inner tool piece 21 and the outer tool piece 22 have been forced towards each other such that a connection area 12 has been formed. This connection area 12 is of the same type as the connection area 12 illustrated in cross-section in Fig. 5c. A detailed view (detail A) of this connection area 12 is illustrated in Fig. 5g.

[0105] Fig. 5g illustrates where the material is under tension T and compression C during the forming process illustrated through Figs. 3a-4b. Where outer radiuses ro are formed, the material is under tension T; and where inner radiuses ri are formed, the material is under compression C. This tension will cause cracks in the material if the material does not have sufficient elongation.

[0106] When forming a connection area 12 from an extruded tubular element 1 made of a 6000 series aluminium alloy with the forming tool 2, cracking was a frequent issue due to insufficient elongation. The present invention therefore provides a strut forming tool 3 and a forming method allowing connection areas 12 to also be formed from aluminium alloys with elongation below 18 %. These materials can be pre-tempered or pre-cold worked prior to the forming of connection areas 12.

[0107] Fig. 6a shows an axial cross-sectional view of a strut forming tool 3 according to the invention. The strut forming tool 3 is used to form the end portion lb,lc into a connection area 12 and thus making the tubular element 1 into a strut 10.

[0108] The strut forming tool 3 comprises a die 32 and optionally a holder 31. To form the connection area 12, the end portion lb of the tubular element 1 is first introduced into the die 32. The next step is to force the end portion lb through the die 32 in the axial direction A of the tubular element 1 (also indicated as the Y-direction in the figures).

[0109] Fig. 6b shows the same strut forming tool 3 as in Fig. 6a. In Fig. 6b the end portion lb has been forced through the die 32 such that a connection area 12 has been formed. The strut forming tool 3 can be used to form connection areas 12 of the types formed by the prior art forming tool 2, including but not limited to the embodiments illustrated in Figs. 5a-f.

[0110] Fig. 6c shows the same strut forming tool 3 as in Fig. 6b. In Fig. 6c the die has been removed from the formed connection area 12. The die 32 can be forced over a tubular element 1 e.g. hold in place by the holder 31. Or the tubular element 1 can be forced through a die 32 being fixed. Two connection areas 12 can also be formed at the same time by means of two dies 32.

[0111] Fig. 6d shows an axial cross-sectional view of the die 32. The die 32 comprises an internal shaping surface 33. The shaping surface 33 is configured to gradually shape the end portion lb into a connection area 12 as the end portion lb is forced through the die 32. The internal shaping surface 33 comprises: a receiving section 33a, a shaping section 33b, and a final section 33c. The receiving section 33a is configured to receive the end portion lb of the tubular element 1. The final section 33c has a cross-sectional area configured to define a cross-section of the connection area 12. The shaping section 33b is configured as a gradual transition from the receiving section 33a to the final section 33c. The shaping section 33b will convert the relative axial movement between the tubular element 1 and the die 32 into radial compression forces on the periphery P of the end portion lb. The compression forces acting on the periphery P during the forming process will prevent or at least reduce tension T building in the material. Thus, the strut forming tool 3 allows forming of tubular elements 1 made of materials having reduced elongation / formability without the risk of cracking the material. This also allows the material to be tempered in prior to the forming process, which will speed up the fabrication process.

[0112] When a connection area 12 is formed with the prior art forming tool 2, the material is free to flow out / relocate in available space between the inner tool piece 21 and the outer tool piece 22. Whereas when a connection area 12 is formed with the strut forming tool 3, the material flow can be restricted in needed directions throughout the forming process, or at least through selected parts of the forming process. The free material flow would typically cause tension T to build in the material, whereas the restricted flow provided by the shaping surface 33 will reduce or prevent tension T from building in the material.

[0113] In the illustrated example, the internal shaping surface 33 completely encircles the end portion lb.

[0114] In the illustrated example, the die 32 is one piece. However, a plurality of pieces may constitute the die 32. As such, the shaping surface 33 may be one surface or a combination of a plurality of surfaces.

[0115] When entering the shaping section 33b the end portion lb has an initial periphery Pi, as indicated in Fig. 6a. As the end portion lb is forced through the die 32 the periphery P will change. And when the end portion lb has passed through the shaping section 33b the end portion lb has been formed into a connection area 12. The connection area 12 has a periphery Pc, as indicated in Fig. 6c, that is different from the initial periphery Pi. The shaping section 33b is configured such that the periphery Pc of the connection area 12 is smaller than the initial periphery Pi of the end portion lb.

[0116] The shaping section 33b is configured to straighten out two wall portions of the tubular element 1. The tubular element 1 is typically circular in cross-section but may have other geometries as required. During or after the straightening, the shaping section 33b will bring the wall portions closer together, preferably into contact with each other. In that way a flattened area 12a of the connection area 12 is formed. The shaping section 33b is preferably also configured to form one or two side wings 12b on the connection area 12.

[0117] The shaping section 33b may be configured to form a finished connection area 12 or a semi-finished connection area 12. A semi-finished connection area 12 can subsequently be squeezed or undergo other shaping operations which are not prone to cracking of the material, e.g. to bring the wall portions into contact with each other.

[0118] The shaping section 33b is configured to shape the cross-section of the connection area 12 to comprise one or more radiuses r. The radiuses r can be smaller than two times a wall thickness Wt of the connection area 12. Fig. 5f illustrates an embodiment of the connection area 12 wherein the radius r equals one wall thickness Wt.

[0119] Fig. 7a shows a side view of a part of a strut 10 having a connection area 12 which is formed by a strut forming tool 3 according to the invention. The connection area 12 is, seen from a side view, aligned with a centreline of the intermediate area 11. However, such alignment is optional. The connection area 12 can be arranged higher or lower relative to the centreline of the intermediate area 11.

[0120] Figs. 7b-e show transverse cross-sectional views of different parts of the strut 10 in Fig. 7a. The crosssection denoted E-E goes through the intermediate area 11 of the strut 10. This cross-section will typically be the same as extruded. The cross-section denoted D-D goes through the transition area 13. In this cross-section the periphery P has changed as compared to as extruded. The cross-section denoted C-C is close to the connection area 12. Two wall portions have been straightened and brought closer together. Two side wings 12b have also been shaped. The cross-section denoted B-B goes through the connection area 12. Two wall portions have been brought into contact with each other in the flattened area 12a. The wall portions at the side wings 12b have also been brought into contact with each other. Furthermore, radiuses r have been shaped in the side wings 12b and in the transition between the flattened area 12a and the side wings 12b.

[0121] The four cross-sections of Figs. 7b-e also illustrates four stages of a forming process with the strut forming tool 3. Fig. 7e shows a cross-section corresponding to an end portion lb as it enters the die 23 or the shaping section 33b. Fig. 7d shows a cross-section corresponding to the end portion lb at an early stage of the shaping process. Two wall portions are starting to straighten out. Fig. 7c shows a cross-section corresponding to a semi-finished connection area 12. The remaining shaping could be performed by other means than the strut forming tool 3. However, the final shaping could be performed by the strut forming tool 3, resulting in the cross-section illustrated in Fig. 7b which is a finished connection area 12.

[0122] Figs. 5a-f show transverse cross-sectional views of different embodiments of a connection area 12 that can be made with the strut forming tool 3.

[0123] As illustrated, the connection area 12 should always have a flattened area 12a. The number of side wings 12b can be zero, as illustrated in Fig. 5a. Or the number of side wings 12b can be one, as illustrated in Fig. 5b. Or the number of side wings 12b can be two, as illustrated in Figs. 5c-f.

[0124] The side wing 12b can be a single side wing 12b, as illustrated in Figs. 5b-d. Or the side wing 12b can be a double side wing 12b as illustrated in Fig. 5e.

[0125] The side wing 12b can be hollow, as illustrated in Fig. 5e-f. Or the side wing 12b can be closed as illustrated in Figs. 5b-d.

[0126] Two side wings 12b can be parallel, as illustrated in Figs. 5d-e. Or the side wings 12b can be symmetric, as illustrated in Figs. 5c and 5f.

[0127] The side wings 12b are angled relative the flattened area 12a. The angle can be selected as required. Two side wings 12b can have different angles relative the flattened area 12a.

[0128] The connection areas 12 shown in Figs. 5a-f are all examples of finished connection areas 12, i.e. connection areas 12 that do not require further shaping prior installation.

[0129] Fig. 8a shows a perspective view of a strut 10 with an angled connection area 12. Figs. 8b-d show a top view, a front view, and a side view of the strut 10 in Fig. 8a. The connection area 12 has an axial direction Ac which is different from the axial direction A of the intermediate area 11. The connection area 12 can be angled relative the intermediate area 11 as required. To achieve this angle, bending is preferably performed after the connection area 12 has been formed.

[0130] The hole 14 is preferably also made after the connection area 12 has been formed. LIST OF REFERENCE NUMBERS

[0131] 1 Tubular element la Intermediate portion lb, lc End portion

[0132] 10 Strut

[0133] 11 Intermediate area

[0134] 12 Connection area

[0135] 12a Flattened area

[0136] 12b Side wings

[0137] 13 Transition area

[0138] 14 Hole

[0139] 2 Forming tool, for radial end forming

[0140] 21 Inner tool piece

[0141] 22 Outer tool piece

[0142] 3 Strut forming tool, for axial end forming

[0143] 31 Holder

[0144] 32 Die

[0145] 33 Internal shaping surface

[0146] 33a Receiving section

[0147] 33b Shaping section

[0148] 33c Final section

[0149] C Compression h Height, of the connection area

[0150] A Axial direction, of the tubular element / strut

[0151] Ac Axial direction, of the connection area

[0152] P Periphery

[0153] Pc Periphery, of the connection area formed by the strut forming tool

[0154] Pi Initial periphery, of the end portion

[0155] R Radial direction, of the tubular element r Radius ri Inner radius ro Outer radius

[0156] T Tension w Width, of the connection area

[0157] Wt Wall thickness

[0158] X First horizontal direction

[0159] Y Second horizontal direction

[0160] Z Vertical direction

Claims

CLAIMS1. A strut forming tool (3) configured to form an end portion (lb,lc) of an extruded tubular element (1) made of an aluminium alloy, such as a 6000 series aluminium alloy, into a connection area (12), wherein the strut forming tool (3) comprises:- a die (32) comprising an internal shaping surface (33) configured to shape the end portion (lb,lc) when the tubular element (1) and the die (32) is moved towards each other in an axial direction (A) of the tubular element (1) such that the end portion (lb,lc) is forced through the die (32); wherein the internal shaping surface (33) comprises:- a receiving section (33a) configured to receive the end portion (lb,lc) of the tubular element (1);- a final section (33c) with a cross-sectional area configured to define a cross-section of the connection area (12), wherein the connection area (12) comprises a flattened area (12a) and preferably at least one side wing (12b); and- a shaping section (33b) configured as a gradual transition from the receiving section (33a) to the final section (33c) and configured to convert the relative axial movement between the tubular element (1) and the die (32) into radial periphery compression forces on the end portion (lb,lc).

2. The strut forming tool (3) according to claim 1, wherein the material of the tubular element (1) is pre-tempered or pre-cold worked and has an elongation less than 18 %.

3. The strut forming tool (3) according to claim 1 or 2, wherein the strut forming tool (3) comprises:- a holder (31) configured to hold the tubular element (1).

4. The strut forming tool (3) according to any one of claims 1-3, wherein the end portion (lb,lc) has an initial periphery (Pi) on entry into the shaping section (33b), wherein the shaping section (33b) is configured to shape the connection area (12) to have a periphery (Pc) which is smaller than the initial periphery (Pi) of the end portion (lb,lc).

5. The forming tool (3) according to any one of claims 1-4, wherein the shaping section (33b) is configured to straighten out two wall portions of the tubular element (1) and bring the wall portions closer together, preferably into contact with each other, to form the flattened area (12a).

6. The forming tool (3) according to any one of claims 1-5, wherein the shaping section (33b) is configured to shape the connection area (12) to comprise two side wings (12b) arranged on opposite sides of the flattened area (12a).

7. The forming tool (3) according to any one of claims 1-6, wherein the shaping section (33b) is configured to shape the cross-section of the connection area (12) to comprise one or more radiuses (r), wherein the one or more radiuses (r) are smaller than two times a wall thickness (Wt) of the connection area (12).

8. A method of forming a strut (10), using a strut forming tool (3) according to any one of claims 1-7, wherein the method comprises the steps of:- providing an extruded tubular element (1) made of an aluminium alloy, such as a 6000 series aluminium alloy, and comprising two end portions (lb,lc) on opposite sides of an intermediate portion (la);- moving the die (32) and the tubular element (1) towards each other in an axial direction (A) of the tubular element (1) such that the end portion (lb,lc) enters the shaping surface (33); and- forming a connection area (12) by means of forcing the end portion (lb, lc) through the die (32), wherein axial movement between the tubular element (1) and the die (32) is causing the shaping surface (33) to radially compress a periphery (P) of the end portion (lb,lc).

9. The method according to claim 8, wherein the forming step is performed by means of cold forming.

10. The method according to claim 8 or 9, wherein the method comprises the step of:- pre-tempering or pre-cold working the tubular element (1) prior to forming.

11. The method according to any one of claims 8-10, wherein the method comprises the step of:- squeezing the connection area (12) after forming.

12. The method according to any one of claims 8-11, wherein the method comprises the step of:- forming a hole (14) in the connection area (12).

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