[0001] The present invention relates to a blind rivet arrangement for producing a blind rivet joint, said blind rivet arrangement having a rivet body and having a mandrel, wherein the rivet body comprises a rivet head, a rivet shank and a continuous rivet bore, wherein the mandrel comprises a mandrel head and a mandrel shank which is inserted in the rivet bore, wherein the rivet bore comprises a first bore cross section in the region of an end of the rivet shank which is opposite the rivet head, and wherein the mandrel shank comprises a first shank cross section in a first mandrel region adjacent to the mandrel head.

[0002] In addition, the present invention relates to a blind rivet joint having at least two workpieces and having a formed blind rivet arrangement of the above-described type.

[0003] Such types of blind rivet arrangements are known from document WO 2009/098431 A1 and are used to join workpieces, access only being possible from one side (the visible side). In this case, the blind rivet is inserted with the blind-side mandrel head through previously realized bores in the workpieces to be joined. The setting or jointing operation then follows by the mandrel being pulled in the direction away from the workpiece arrangement (for example by means of a blind rivet tool) on the visible side. This leads on the blind side to deforming of the rivet shank and to forming a blind head which abuts against the blind-side workpiece surface after setting. As a rule, the mandrel shank comprises a predetermined breaking point in this case such that the mandrel shank protruding on the visible side breaks off once the setting operation has been carried out and is able to be removed.

[0004] The first shank cross section, in this case, is preferably adapted to the first bore cross section. Said adapting can be used for locking the rivet body and the mandrel in a mechanical manner. This can prevent the rivet mandrel becoming inadvertently detached from the rivet body prior to the jointing operation. In this case, for mechanical locking it is known to provide profiled expanding in the region of the first shank cross section, into which profiled expanding material of the rivet body is brought by means of radial impressing. The profiled expanding is formed in particular by radial projections.

[0005] The bore cross section of the rivet body, in this case, is uniform over the length of the rivet bore. The bore cross section, in this case, is designed such that the type and manner of the setting operation in the respective application is established in view of the required tensile and shear strength of the rivet. When the bore cross section is enlarged, the shank cross section also has to be correspondingly enlarged.

[0006] If, as a result of the processing technology a small shank cross section is required, numerous problems can occur. On the one hand, mechanical locking by means of radial impressing can only be effected as a result of very deep impressing. As a result, only comparatively low holding forces are able to be realized. The deep impressing, in this case, can result in preliminary damage to the rivet body or even in said rivet body shearing off.

[0007] In addition, there is a centring problem as a result of a large amount of play between the inner circumference of the rivet bore and the outer circumference of the mandrel shank. In particular, there can be larger amounts of centre offset between the mandrel and the rivet bore. This can result in increased misalignments. As a result, once again, problems can arise working with the rivet, in particular when the mandrel shank has to be inserted into a pulling mechanism which is only slightly larger than the shank cross section. In this connection, it is possible that sometimes the rivet mandrel is no longer trapped by a bore of the pulling mechanism.

[0008] In the case of excessive play between the rivet bore inside diameter and the mandrel shank outside diameter, greater misalignments of the set rivets can be reckoned with. This can result in deviations in the rotational symmetry when deforming the rivet shank and, as a consequence, in misalignments of the set blind rivet.

[0009] Against said background, it is an object of the invention to provide an improved blind rivet arrangement and an improved blind rivet joint, at least one of the above-mentioned disadvantages being overcome.

[0010] Said object is achieved in the case of the blind rivet arrangement named in the introduction in that in a second mandrel region which projects out of the rivet bore, the mandrel shank comprises a second shank cross section which is smaller than the first shank cross section.

[0011] A mandrel according to the invention comprises, as a consequence, a first mandrel region with a first shank cross section and a second mandrel region with a second shank cross section, the second shank cross section being smaller than the first shank cross section.

[0012] The first shank cross section can be used in conjunction with the first bore cross section of the rivet bore in order to centre and/or to guide the mandrel with reference to the rivet body. In addition, mechanical fixing, for example by means of radial impressing, can be effected in said first mandrel region.

[0013] The second shank cross section, in contrast, can be clearly smaller such that the blind rivet arrangement can also be used in the case of application requirements where small mandrel diameters are needed. [0014] Exact centering of the mandrel shank with reference to a longitudinal axis can be effected in one embodiment just as a result of the interaction between the first bore cross section and the first shank cross section. In other aspects of the invention, this is possible as a result of these and/or further measures.

[0015] Consequently, decoupling of the previous dependence of the mandrel cross section on the bore cross section is possible as a result of the invention. As mentioned, demands of the processing technology for certain mandrel cross sections in the region to the interface to the processing device can be met as a result. In addition, targets for material and consequently cost saving can be realized. In addition, it is preferably possible to develop the blind rivet arrangement in an optimum manner specific to the application. In particular, it can be possible to design the rivet bore in the region relevant for forming the blind head in view of the requirements for the rivet joint. The quality demands on the rivet joint can thus be optimized where applicable.

[0016] The object is consequently completely achieved.

[0017] The transition between the first and the second mandrel region (that is the transition between the first and the second shank cross section) can be effected at an arbitrary point (when seen in the axial direction) inside the rivet mandrel.

[0018] It is particularly preferred, however, when said transition is realized in the region of the predetermined breaking point.

[0019] On the one hand, the mandrel can be manufactured in a simple manner as a result. In addition, it is possible to adjust the breaking force of the predetermined breaking point in a comparatively simple manner.

[0020] According to a further preferred embodiment, in the region of the first mandrel region the mandrel shank comprises an outer-circumferential profiling which engages with the inner circumference of the rivet bore. [0021] A profiling of this type can be formed, in particular, by radial projections which proceed from the outer circumference of the first shank cross section.

[0022] A profiling of this type enables mechanical locking between the mandrel and the rivet body by radial impressing being effected in the region of the first mandrel region, that is to say an impressing force is applied from outside onto the rivet body which presses the material of the rivet body into the profiling.

[0023] The shank cross section and the bore cross section can have an arbitrary cross sectional form, but are preferably realized in a circular manner such that the cross sections are defined by their respective diameter.

[0024] It is particularly preferred, in this case, when the ratio between the diameter of the first shank cross section and the diameter of the first bore cross section is within a range of between 0.08 and 0.99, in particular within a range of between 0.87 and 0.97.

[0025] In the case of a diameter ratio of this type, on the one hand radial impressing and consequently mechanical locking is possible, it being possible to realize high holding forces. On the other hand, it is possible to realize comparatively good centring or guiding of the mandrel in the rivet body as a result.

[0026] The ratio between the diameter of the first shank cross section and the diameter of the second shank cross section is preferably within a range of between 1.01 and 3, in particular within a range of between 1.05 and 2.5 and in a particularly preferred manner within a range of between 1.1 and 1.85.

[0027] It is possible to realize blind rivet arrangements for a wide spectrum of different applications within said ranges. [0028] In addition, it is advantageous overall when the first mandrel region extends over an axial length which is greater than 0.2 times the axial length of the rivet bore and/or is smaller than 0.6 times the axial length of the rivet bore.

[0029] The mandrel is guided well in the rivet body in the region of the first mandrel region as a result of such an axial length. Misalignments can already be excluded in an extensive manner as a result.

[0030] According to a further preferred embodiment, which represents an invention in itself in conjunction with the preamble of Claim 1 , in the region of the rivet head the rivet bore comprises a second bore cross section which is smaller than the first bore cross section and which is adapted to the second shank cross section.

[0031] Optimized centring and guiding can be set up for the second mandrel region as a result of said measures.

[0032] In addition, the arrangement of a transition between the first bore section and the second bore section inside the rivet bore makes it possible for a residual rivet mandrel to be able to be locked in a targeted manner in the rivet body. This can have a positive influence on the locking force of the residual rivet mandrel.

[0033] A further advantage can consist in that in the case of soft materials, deformation of the rivet body can be stopped and consequently adjusted in a targeted manner as a result of the design of the geometry of the transition. As a result, the achievement here is that very soft workpieces (such as, for example, thin sheet metal, cardboard, leather, CFRP, etc.) are not deformed during the setting process. The limiting of the deforming, in this case, can be stopped so early that even a joint with play can be realized such that the blind rivet joint is able to act as a rotational axis. Unlike the conventional prior art, the blind rivet arrangement can also consequently be set in a displacement-controlled manner, for example in dependence on whether a transition on the mandrel slips onto a transition on the rivet bore. [0034] To achieve at least one of the abovementioned targets, it is preferred when the axial length of the region of the rivet bore with the second bore cross section is greater than or equal to 0.4 mm, and preferably is greater than or equal to the axial height of the rivet head.

[0035] In addition, it is preferred when an axial spacing is set up between the first mandrel region and the transition between the bore cross sections of the rivet bore. As a result, the mandrel is not guided in said intermediate region. In other words, the mandrel is preferably guided both in its first mandrel region adjacent to the free end of the rivet body and in a second region adjacent to the rivet head. Ideal centring of the mandrel with reference to the rivet body can be achieved as a result, even when the mandrel, in a second mandrel region comprises a smaller shank cross section than in its first mandrel region.

[0036] According to a particularly preferred embodiment, in this case, the ratio between the diameter of the first bore cross section and the diameter of the second bore cross section is within a range of between 1.01 and 3, in particular within a range of between 1.05 and 2.5 and in a particularly preferred manner within a range of between 1.1 and 1.85.

[0037] With said range of diameter ratios, rivet mandrels with corresponding ratios between the first shank cross section and the second shank cross section can be guided and centred in an ideal manner.

[0038] In addition, it is advantageous when a transition from the first to the second bore cross section is arranged closer to the rivet head in the axial direction than the predetermined breaking point.

[0039] In particular, in combination with the feature that the transition between the first and the second mandrel region is formed in the region of the predetermined breaking point, a non-guided portion can be set up as a result inside the rivet bore be- tween the first mandrel region and the second mandrel region, which can support a deforming of the rivet body to form the blind head.

[0040] In general, the blind rivet arrangement according to the invention can be used for every kind of design of blind rivet.

[0041] However, it is particularly preferred when the blind rivet arrangement is a body-folding blind rivet arrangement. Such types of body-folding blind rivet arrangements can be used in particular for the purpose of joining workpiece arrangements of different axial thickness together. As a consequence, compensation for different clamping thicknesses can be effected.

[0042] It is particularly preferred, consequently, when the rivet shank comprises a head forming portion which is realized for the purpose of forming a blind head when producing the blind rivet joint, and comprises a folding portion which is arranged between the head forming portion and the rivet head and is realized for the purpose of forming a body fold when producing the blind rivet joint in order to compensate for a clamping thickness.

[0043] These types of blind rivet arrangements are also called variable grip rivets. In addition, such types of blind rivet arrangements make it possible to minimize mechanical load on faces and edges of workpieces in the axial and/or radial direction, in particular when at least one of the workpieces is a plastics material, such as, for example, a thermoplastics material, a thermosetting plastics material, a CFRP or the like, or also another soft workpiece.

[0044] An example of a body-folding blind rivet of this type is known from document DE 10 2010 017 296 A1 , the disclosure content of which is to be included fully in the present case by reference. [0045] It is particularly preferred, in this case, when in the region of the contact face against a visible-side workpiece surface, the rivet head comprises an axial recess for receiving at least part of the body fold formed when producing the blind rivet joint.

[0046] A body-folding blind rivet of this type is known from the earlier German Patent Application with Application Number DE 10 2012 016 592.7, the disclosure content of which is to be included fully in the present case by reference.

[0047] As a result of realizing the axial recess in the rivet head, it is possible, in particular, to join even soft workpieces together or workpieces which are mechanically less loadable, a relatively large clamping region nevertheless being realized. In particular, the achievement here can be that the workpiece arrangement is not damaged during the setting operation, it being possible to keep any radial widening of the rivet body in the head region within tight limits. As a result, the spacing between the edges between the body shank outside diameter and the inside diameter of the bore in the workpieces can be minimized.

[0048] In general, the invention can also be claimed in the form of a mandrel for a blind rivet arrangement of the abovementioned type, wherein the mandrel comprises a first mandrel region and a second mandrel region, wherein the mandrel comprises a smaller shank cross section in the region of the second mandrel region.

[0049] In a corresponding manner, the invention can also be claimed by a rivet body for a blind rivet arrangement which comprises a rivet bore, wherein in a region adjacent to the rivet head a bore diameter is smaller than in the region of an end of the rivet shank, and/or can be claimed in the form of a method for producing a blind rivet joint, wherein a setting operation is effected in a displacement-controlled manner.

[0050] In addition, the above object is achieved by a blind rivet joint with at least two workpieces and with a formed blind rivet arrangement of the above-described type. [0051] All in all, the invention enables the decoupling of the previous dependence of the rivet mandrel diameter on the body bore in the case of blind rivets, in particular in the case of body-folding blind rivets. A displacement-controlled processing of the blind rivet is made possible in contrast to the prior art.

[0052] In addition, in the case of the invention at least one of the following advantages is achieved. The rivet mandrel diameter is adaptable to the processing device in a manner which is not dependent on the application. There is reduced material use in the case of the rivet mandrel and/or in the case of the rivet body. The design of the rivet bore can be effected in a manner which is specific to the application. There is optimized straightness of the set rivet as a result of guiding the mandrel. The function of a body fold in an axial recess of the rivet head is possible. Secure fixing of the rivet body on the mandrel is possible. A design is possible with play or clamping suitable for an application, including displacement-controlled setting. Damage in the case of soft joining materials such as CFRP, cardboard, leather, etc. can be prevented.

[0053] It is obvious that the aforementioned features and features yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or standing alone without departing from the framework of the invention.

[0054] Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description, in which:

Fig. 1 shows a schematic longitudinal sectional view of a first embodiment of a blind rivet arrangement according to the invention;

Fig. 2 shows a longitudinal sectional view through a rivet body of a blind rivet arrangement according to a further embodiment of the present invention;

Fig. 3 shows a blind rivet arrangement using the rivet body of Fig. 2 during a setting operation; and Fig. 4 shows the blind rivet joint completed by means of the blind rivet arrangement of Fig. 3.

[0055] Fig. 1 shows a schematic representation of a longitudinal section of a first embodiment of a blind rivet arrangement according to the invention which is designated in general by the reference 10.

[0056] The blind rivet arrangement 10 comprises a rivet body 12 and rivet mandrel 4. The blind rivet arrangement 10 can be used for the purpose of joining a workpiece arrangement which includes at least one first workpiece 16 (visible-side workpiece) and one second workpiece 18 (blind-side workpiece).

[0057] The rivet body 12 comprises in a known manner a rivet head 20 which includes a contact face 22 for abutment against a top surface 24 of the visible-side workpiece 16. The rivet head 20 merges into a rivet shank 26 which can be inserted into a workpiece bore 28 in the workpiece arrangement. The rivet body 12 is penetrated by an axially continuous rivet bore 30.

[0058] The mandrel 14 comprises a mandrel head 32 which is realized for abutting against an end surface 34 of the rivet shank 26. In addition, the mandrel 14 comprises a mandrel shank 36 which is guided through the rivet bore 30 and extends out of the rivet head 20 on the visible side.

[0059] The rivet mandrel 14 also includes a predetermined breaking point 38.

[0060] To produce a blind rivet joint, the rivet shank 26 is inserted into the workpiece bore 28, as shown in Fig. 1. An axial pulling force is then exerted onto the mandrel 14, as is shown in the case of F^ and the rivet head 20 is held by means of a second force F ₂ which is in the opposite direction to and is greater than F^. [0061] By the mandrel head 32 abutting against the end surface 34 of the rivet shank 26, the latter is deformed on the blind side such that a blind head is formed. The force F-, , in this case, is adjusted or increased, as a rule, such that once the blind head has been completed the mandrel 14 breaks at the predetermined breaking point 38 and can be pulled out of the completed blind rivet joint.

[0062] The mandrel 14 comprises a first mandrel region B^ and a second mandrel region B ₂ . The first mandrel region extends from the mandrel head 32 inside the rivet bore 30 as far as up to the predetermined breaking point 38. The second mandrel region B ₂ extends from the predetermined breaking point 38 out of the rivet head 20. In the first mandrel region Bi the mandrel shank 36 comprises an outer diameter D ₂ which is adapted to a first bore diameter of the rivet bore 30. The diameters and D ₂ are adapted to one another such that the mandrel 14 can be locked inside the rivet body 12, for example as a result of radial pressing. For this purpose, it can advantageous when radial projections 42 or another form of profiling are provided on the mandrel shank 36.

[0063] In the second mandrel region B ₂ the mandrel shank 36 comprises a second shank diameter D ₃ which is smaller than the first shank diameter D ₂ .

[0064] In the region of the rivet head 20, the rivet bore 30 comprises a second bore diameter D ₄ . The second bore diameter D ₄ is smaller than the first bore diameter Di. In addition, the second bore diameter D ₄ is adapted to the second shank diameter D ₃ . The axial region over which the rivet bore 30 has the smaller second bore diameter D ₄ extends preferably through the entire rivet head 20 and over and beyond this preferably in the direction of the rivet shank 26 by a length which is designated in Fig. 1 by the reference U.

[0065] The axial height of the rivet head is designated by the reference U in Fig. 1 . The axial length of the rivet shank 26 is designated by the reference L ₂ in Fig. 1 , and the spacing between the contact face 22 and the predetermined breaking point 38 is designated by the reference L ₃ in Fig. 1 . The outer diameter of the rivet shank 26 over the entire length is preferably uniform and is designated by the reference D ₅ in Fig. 1. [0066] The transition between the first bore portion with the first bore diameter D ₂ and the second bore portion with the second bore diameter D ₄ is formed by a step or a transition which is designated by the reference 40 in Fig. 1 .

[0067] In general, the achievement with the blind rivet arrangement 10 of Fig. 1 is that in the region projecting out of the rivet body 12 the rivet mandrel 14 can have a comparatively small diameter. Nevertheless, the mandrel 14 can have a relatively large diameter in the first mandrel region In the first mandrel region B1 the mandrel is guided and centred in an axial manner with reference to the rivet body 12. In addition, the diameters D3 and D4 are adapted to one another such that the mandrel is also guided or centred in said axial region by the rivet body 12.

[0068] The mandrel can be non-guided between said regions inside the rivet body 12.

[0069] The spacing between the transition 40 and the predetermined breaking point 38 can be chosen such that a displacement-controlled setting is possible in such a manner that the first mandrel region Bi impacts against the transition 40 during the setting operation, as a result of which a breaking open of the predetermined breaking point 28 can be introduced. As a result, the setting operation can be realized such that a predefined clamping thickness is realized.

[0070] Figures 2 to 4 show a further embodiment of a blind rivet arrangement 10' which, with regard to design and method of operation, corresponds in general to the blind rivet arrangement 10 of Fig. 1. Identical elements are consequently characterized by identical references. Essentially the differences are explained below.

[0071] On the one hand, in the region of the rivet head 20, the rivet body 12' shown in Fig. 2 comprises an axial ring-shaped recess 44 which can serve for receiving at least part of a body fold. The axial depth of the axial recess 44 is designated by the reference L ₅ in Fig. 2. Said axial depth L ₅ is smaller than the axial height of the rivet head 20. An outer diameter of the rivet head 20 is designated by the reference D ₆ and an outer diameter of the axial recess 44 is designated by the reference D ₇ .

[0072] The spacing between the bottom of the axial recess 44 and the transition 40 is designated by the reference L ₆ . Said region also forms a folding portion 46 of the rivet shank 26.

[0073] In addition, on the end opposite the rivet head 20 the rivet shank 26 comprises a head forming portion 50. A rigid portion 48, the length of which is designated by the reference L ₇ , is provided between the head forming portion 50 and the folding portion 46. The axial length of the head forming portion 50 is designated by the reference U.

[0074] The head forming portion 50 includes a first forming portion 52 with an axial length L ₉ , a second forming portion 54 with a second axial length L ₁₀ and a third forming portion 56 with an axial length L^. The first forming portion 52 is adjacent to a blind-side end 58 of the rivet shank 26. The third forming portion 56 is adjacent to the rigid portion 48. The axial lengths L ₉ , l_i ₀ and can be approximately the same size. The middle second forming portion 54 comprises a greater strength than the first forming portion 52 and the second forming portion 56. The folding portion 46 comprises the least strength of the portions 46, 48 and 50.

[0075] Fig. 3 shows the blind rivet arrangement 10' during a setting operation. It can be seen that a blind head 60, which is formed by deforming the head forming portion 50, is formed during the setting operation.

[0076] Fig. 4 shows the completed blind rivet joint 64, it being possible to see that, for adapting to the clamping thickness, the folding portion 46 has formed a body fold 62 which is arranged at least in part inside the axial recess 44 of the rivet head 20 of the rivet body 12'. [0077] In addition, Fig. 4 shows by the reference L ₁₂ the axial height of the body fold 62 which is preferably smaller than or equal to the axial depth L ₅ of the axial recess 44.