Abstract:
The invention relates to a rivet for connecting parts, in particular aircraft components, through which holes are formed, the rivet including a sleeve part, which has a rivet head with an axially extending cavity and an adjoining or is composed of such rivet head and a rivet mandrel having an essentially cylindrical base body and a widened rivet mandrel head in relation to the diameter thereof and which passes through the sleeve part and along the cavity with its base body. So that a cost-effective connection with improved loadability can be produced between workpieces, even when they have holes of different sizes for the rivet, the rivet mandrel according to the invention has ribs running axially on the cylindrical base body.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a rivet for connecting parts, in particular aircraft components, through which holes are formed, the rivet including a sleeve part having a rivet head with an axially extending cavity and an adjoining shank, is composed of such rivet head and a rivet mandrel having an essentially cylindrical base body and a widened rivet mandrel head in relation to the diameter thereof and which passes through the sleeve part and along the cavity with its base body. 
     2. Description of Background and Other Information 
     Rivets of the aforementioned type are produced in large production runs and have a wide application in joining workpieces. In particular, when workpieces made of different materials are to be connected and techniques such as soldering, welding or adhesive bonding cannot be used to join the workpieces, joining using rivets of this type represents a practicable alternative method of connection. The workpieces to be connected are thereby first provided with bored holes and the workpieces are placed against one another, ideally with axially aligned orientation of the axes of the holes. Subsequently, a rivet head of a sleeve part is placed on a borehole of the first workpiece and held there in a fixed manner, and a rivet mandrel penetrating the bores is drawn through the fixed rivet head and a shank optionally adjoining it, until the widened rivet mandrel head thereof comes to bear against the second workpiece or the widened rivet mandrel head has deformed an end-side sleeve part with the formation of a non-positive connection. Non-positive connections of this type are often found, e.g., in aircraft construction, where individual components of different types of materials are combined with one another. 
     In order to join together different types of workpieces by riveting, it is necessary, as mentioned, to provide them with bores in which there is space for a rivet. In practice, in this context the case often occurs that two bores that are provided to accept a rivet have different bore diameters. If the necessary bores are produced separately in the workpieces, it is difficult to obtain exactly the same bore diameters. But even when workpieces that are to be connected and are made of different types of materials are placed one on top of the other and respectively corresponding bores are produced in one step or through a single drilling operation, the bores thus produced can have different bore diameters due to different material properties. Furthermore, the type of drilling operation can thereby have an impact on the size and shape of corresponding bores, as is known, e.g., for laser drilling. 
     If workpieces with different bore diameters are joined together by riveting, the result is that the rivet in the bores cannot bear against all the bore walls or against both workpieces. A connection between the workpieces therefore occurs at least mainly only through a non-positive closure, and one workpiece has a looseness in a plane perpendicular to the bore axes. A loadability of the rivet connection is correspondingly limited. 
     Attempts have been made according to the prior art to avoid this disadvantage by reaming the necessary bores. However, a reaming operation represents an additional step, which is time-consuming and costly and, in particular in the connection of aircraft components, when thousands of bores are to be reamed on one component, this can significantly reduce productivity. 
     SUMMARY OF THE INVENTION 
     Based on the prior art described above, the invention provides a rivet of the aforementioned type with which a cost-effective connection with improved loadability can be produced between workpieces, even when such workpieces have bores of different sizes for the rivet. 
     More particularly, a rivet according to the invention is of the aforementioned type, except that the rivet mandrel has ribs running axially on the cylindrical base body, which ribs, in a particular embodiment, are arranged between the rivet mandrel head and the cavity. 
     A rivet according to the invention in particular has the advantage that, when workpieces are connected by drawing the rivet mandrel into or through the rivet head, the rivet, due to the ribs provided on the cylindrical base body, bears against both bore walls or workpieces at least in some sections, even with bores of different sizes in the workpieces, and a connection can be easily produced via a non-positive or also via a positive component. Positional inaccuracies caused by an orientation of the bore axes that are not axially aligned can also be offset thereby. 
     The ribs provided according to the invention are also advantageous from another aspect, because with a placement process by forming material of the workpieces to be connected, or material of the sleeve part, such material can flow into the free spaces present between the ribs so that drawing in the rivet mandrel compared to a conceivable conical embodiment of a rivet mandrel is facilitated or even made possible at all. 
     It is thereby advantageous with respect to a uniformly high loadability of a rivet connection when the ribs are arranged in a rotationally symmetrical manner to a longitudinal axis of the rivet mandrel. 
     It is also favorable in order to utilize or maximize effects of the ribs over the greatest possible length when the ribs adjoin the rivet mandrel head. 
     As has been shown in tests, it can also be favorable with respect to the largest possible contact surface with an average surface pressure between the rivet mandrel and the shank or the workpieces and consequently a high loadability in terms of strength of a rivet connection, if the ribs at least in some areas have a circular arc shape or, in particular, an acute-angled rib outer contour. 
     In order to make it possible to draw in the rivet mandrel with a low expenditure of force, the ribs can also be embodied at least in part with wedge surfaces. Alternatively, the ribs can be embodied along their axial extension with essentially the same cross section, which is advantageous with respect to a high surface pressure between ribs and workpieces or the shank of the sleeve part. It is also possible for the ribs, seen from the rivet mandrel head in the direction of the rivet head, to first have an area with a constant cross section to which a sloped or wedge-shaped area adjoins. It is thereby possible to draw in the rivet mandrel easily with high surface pressure at the same time. 
     A rivet mandrel of a rivet according to the invention can be embodied as hollow. However, it is advantageous if the rivet mandrel is solid, because the rivet mandrel can then better withstand radial forces acting thereon, the rivet connection having a higher rigidity, and a greater tensile force thereby can be exerted on the rivet mandrel while it is being drawn in, without the rivet mandrel being damaged. 
     The ribs can be applied to the rivet mandrel after manufacture, e.g., by soldering or adhesive bonding or another type of connection technique or mechanism. However, every connection point represents a potential weak spot under stress. Therefore, in a particular embodiment, the rivet mandrel is embodied as one-piece. Rolling or cold working are suitable and simple methods for producing a solid rivet mandrel with ribs running axially. 
     It has proven useful in a manner to be particularly emphasized if the sleeve part has a shank having a constant outside diameter, the first end of which shank adjoins the cavity of the rivet head and the second end of which shank is in contact with a rivet mandrel head having at least the same outside diameter, that the shank be embodied in the direction from the first end to the second end with an expansion area having a constant inside diameter and an adjoining compression area having an at least partially increased inside diameter, and the ribs bearing in an area corresponding to the compression area of the shank. 
     With this variant in a blind-rivet embodiment, an excellent surface pressure can be achieved between the rivet mandrel and the shank as well as between the shank and the workpieces after a placement operation due to the ribs. The ribs make it possible on the one hand for the rivet mandrel to be drawn in with a lower expenditure of force compared to the prior art, because the material of the shank can in part flow into free spaces between the ribs and, through the deformation, a consolidation is achieved which is so high that a highly loadable connection is achieved, although drawing in the rivet mandrel is not made more difficult or impeded. On the other hand, while being drawn in, the ribs at the same time produce an expansion of the shank at least in parts and press it against the bore walls in the workpieces producing a positive connection, so that after the placement operation the shank and the rivet mandrel as well as the shank and the workpieces are firmly connected to one another. A non-positive connection as well as an excellent positive connection is thus produced between the rivet mandrel and the shank on the one hand and between the shank and the workpieces on the other hand. 
     For special purposes, e.g., when the rivet head and the shank are subjected to greatly divergent stresses after the placement of the rivet, it can also be provided for the rivet head and the shank of the sleeve part to be made of different materials. For example, the rivet head and the shank of the sleeve part can be produced separately as single components that, together with a rivet mandrel form a kit, which are assembled only upon production of a rivet connection. In this case the single components can be made of different materials that are selected according to the stress to be expected on the single component. It is also possible for the rivet sleeve to be made of one material and to have different properties in the area of the rivet head than in the area of the shank, e.g., after a locally limited heat treatment or a thermo-mechanical treatment of the rivet head. 
     When an inner surface of the shank in the compression area is formed according to a surface of the rivet mandrel in the area of the same embodied with ribs, a particularly high surface pressure can be achieved between the shank of the sleeve part and the workpieces as well as between the shank and the rivet mandrel. In this variant of a rivet a non-positive closure as well as a full-surface positive closure is achieved, which leads to highly loadable rivet connections. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in greater detail with reference to the appended drawings, which illustrate exemplary embodiments of the invention, whereby: 
         FIG. 1  illustrates a rivet mandrel of a rivet according to the invention; 
         FIG. 2  illustrates a blind rivet before a placement process; 
         FIG. 3  illustrates a blind rivet after a placement process; 
         FIG. 4  illustrates a rivet having a countersunk-head after a placement process; 
         FIG. 5   a  illustrates a rib located on a base body of a rivet mandrel, which rib is embodied with an essentially identical cross section along its axial extension; 
         FIG. 5   b  illustrates a rib located on a base body of a rivet mandrel, which rib is embodied with a flat wedge surface and an essentially circular arc-shaped rib outer contour; 
         FIG. 5   c  illustrates a rib located on a base body of a rivet mandrel, which rib is embodied with a curved wedge surface and an acute-angled rib outer contour; 
         FIG. 6  illustrates a partial representation of a rivet according to the invention, the sleeve part of which is composed of several component parts; and 
         FIG. 7  illustrates another rivet, the sleeve part of which is composed of several component parts, in a partial representation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows by way of example a rivet mandrel  2  as it is used in a rivet according to the invention. The rivet mandrel  2 , which is generally made of a metallic material and is advantageously produced entirely from a high-strength steel alloy in a solid manner, has an essentially cylindrical base body  26  with a longitudinal axis X and a diameter D. Grooves  23 , located in planes perpendicular to the longitudinal axis X and extending around the axis X, can be provided on the base body  26 , as shown in diagrammatic form in  FIG. 1 , via which grooves the rivet mandrel  2  is brought into connection with a rivet head during placement of the rivet or is connected to a rivet head in a positive manner after placement. In a particular embodiment, the grooves  23  are embodied asymmetrically, in order to increase an initial tension. Furthermore, grooves  25  are provided via which the rivet mandrel  2  can be drawn with a placement device. Furthermore, the rivet mandrel  2  has a predetermined breaking point  24 , at which the rivet mandrel  2  is designed to break at the end of a placement process or after the production of a rivet connection, so that the end of the rivet mandrel  2 , in a particular embodiment, is approximately flush with a head of a rivet. In addition, on one end the rivet mandrel  2  has a rivet mandrel head  21  that is widened with respect to the diameter D of the base body  26 , to which rivet mandrel head ribs  22  adjoin. The ribs  22  run axially or parallel to the longitudinal axis X of the rivet mandrel  2  and are arranged in a rotationally symmetrical manner around the longitudinal axis X, a number of the ribs  22  depending on the diameter D of the cylindrical base body  26  and, e.g., with a diameter D of 10 mm, lying between four and ten, so that, on the one hand, the rivet mandrel  2  can be drawn in well but, on the other hand, a high surface pressure is also achieved between the rivet mandrel  2  and a shank or workpieces. As shown in both  FIGS. 1 and 2 , the ribs  22  project radially beyond non-ribbed portions of the base body  26  of the rivet mandrel. 
       FIG. 2  shows a cross section of a blind rivet according to the invention with a rivet mandrel  2  according to  FIG. 1  after insertion in bores of two workpieces  3 ,  4  to be connected, but before a placement of the rivet. In addition to the rivet mandrel  2  described, the blind rivet comprises a sleeve part  1  with a rivet head  11  and a shank  12 , which with one end  121  adjoins the axially extending cavity of the rivet head  11 . The shank  12  is embodied with a constant outside diameter. The rivet mandrel head  21  of the rivet mandrel  2  is placed in the area of its second end  122 , the rivet mandrel  21  in the mating area on the shank  12  having the same outside diameter as the shank and subsequently being embodied in a tapering manner. This makes it possible to insert the rivet, even if the workpiece  3  is not accessible. 
     In the interior, the shank  12  of the sleeve part  1  has an axially extending cavity that is continuous with an axially extending cavity of the rivet head  11  of the sleeve part, as shown in  FIG. 2 . More specifically, the sleeve part  1  has an essentially cylindrical cavity in the area of the rivet head  11  and the expansion area A of the shank  12  adjoining it, which cavity accepts the correspondingly dimensioned cylindrical base body  26  of the rivet mandrel  2 . In a compression area S adjoining the expansion area A, the shank  12  is embodied with an increased inside diameter compared to the expansion area A, in order to provide space for the ribs  22  of the rivet mandrel  2 . The increased inside diameter of the shank  12  is designed such that the ribs  22  bear against the shank  12  inside at some points. The individual parts of the rivet are then no longer disengaged from one another, which facilitates the handling of the rivet during an assembly. 
     The situation shown in  FIG. 2  occurs, as mentioned, before the placement of the rivet, therefore before the rivet mandrel  2  is drawn into the sleeve part  1 . If the bores necessary for the rivet in the workpieces  3 ,  4  have different bore diameters, the shank  12  does not bear against both workpieces  3 ,  4 , but has a free spacing  31  from a workpiece  3  and optionally also from a workpiece  4 . 
     If the rivet mandrel  2  is now drawn into the sleeve part  1  by drawing on grooves  25  while holding the sleeve part  1  on the rivet head  11 , the rivet mandrel head  21  placed on the shank  12 , with the rivet mandrel head  21  having a size, transverse to an axial extent of the sleeve part  1 , that at least covers an entirety of the end of the shank  12 , causes a compression or deformation of the shank  12  on its second end  122 , so that it is folded and a driven head is formed, as shown in  FIG. 3 , the rivet mandrel head  21  being spaced from the connected workpieces  3 ,  4  by a distance of twice the wall thickness of the second end  122  of the shank  12 . As such, the radially projecting ribs  22  create an expanded area of the shank  12  beneath the folded end  122  through the thicknesses of the workpieces  3 ,  4  to the rivet head  11 .  FIG. 3  shows the ribs extending axially without interruption through the thicknesses of the workpieces. In other words, at the same time as the shank  12  on its second end  122  is being compressed and deformed, the ribs  22  adjoining the rivet mandrel head  21  penetrate into the area of the shank  12  having a smaller inside diameter and produce an expansion of the shank  12  there, i.e., along an axially extending portion of the shank, where the outside periphery of the shank is increased from the initial diameter, so that the looseness provided by the free space  31  present between the shank  12  and workpiece  3  is eliminated. During expansion, if the solid rivet mandrel  2  bears against the shank  12  only in the area of the ribs  22 , excess material of the shank  12  can also be forced into free spaces between the ribs  22 , so that a good positive closure and a favorable stress distribution in the rivet and the workpieces  3 ,  4  is achieved. Because the shank  12  is thin-walled at its end  122 , and the rivet mandrel  2  easily slides into the shank  12  due to the ribs  22  shaped in an elongated manner, only slight force is necessary to place the rivet. At the end of the placement process the looseness  31  between the shank  12  and the spacing  6  between the workpieces  3 ,  4  are finally no longer present and the workpieces  3 ,  4  are connected to one another in a non-positive and positive manner. 
     After the placement of the rivet, the base body  26  bears against an inner surface  13  of the rivet head  11  and against the shank  12  essentially over the entire surface. This configuration is shown in  FIG. 3 . In this connection it is favorable, as mentioned, if the grooves  23  are embodied asymmetrically or in a sawtooth manner in cross section, as can be seen from the enlarged section of  FIG. 3 . 
     A looseness can also be present between the workpiece  4  and the shank  12  before the placement of the rivet. In such a case, during placement of the rivet a gap between the shank  12  and the workpiece  3  as well as a gap between the shank  12  and the workpiece  4  are closed due to the deformation of the shank  12 . Likewise, the invention covers variants in which the shank  12  is embodied with a constant wall thickness. 
     Alternatively to the embodiment shown in  FIGS. 2 and 3 , it is possible with otherwise identical geometric design to apply the ribs to the shank  12  instead of to the rivet mandrel  2 , but this is also associated with higher production costs, because recessing ribs into the shank is more complex than recessing ribs in an outer side of the rivet mandrel. 
       FIG. 4  shows a rivet according to the invention, in which the sleeve part  1  comprises only a rivet head  12 , no shank being present, after the placement of the rivet. The rivet mandrel  2 , which is equipped with a rivet mandrel head  21  embodied as a countersunk head, renders possible a flush installation in the area of a surface of the workpiece  3 . With this embodiment variation, the ribs  22  of the rivet mandrel  2  bear directly against the workpieces  3 ,  4 , which are deformed on the bore side through the placement of the rivet, and thus produce a positive closure. 
       FIGS. 5   a ,  5   b , and  5   c  show possible embodiments of ribs  22 , which have proven to be of value in tests. As shown in  FIG. 5   a , a rib  22  can be embodied with an essentially identical cross section along its longitudinal extension and an approximately circular arc-shaped rib outer contour  221 . During the placement of a rivet according to  FIG. 2 , the circular arc-shaped front surfaces  222 ,  223  running parallel to the longitudinal axis X of the rivet mandrel  2  slide along the shank  12  and expand it. Simultaneously, material of the shank  12  can flow into the free spaces present between the ribs  22  and lie against the rib side surfaces  224  there. 
     In an embodiment further improved over the embodiment according to  FIG. 5   a , each of the axially extending ribs  22  according to  FIG. 5   b  can also be embodied with a front surface  223 , each of the surfaces  223  tapering in a direction away from the rivet mandrel head  21  that acts as a wedge surface and facilitates a sliding of the rivet mandrel  2  when drawn in. 
     Finally,  FIG. 5   c  shows a particularly favorable embodiment of ribs  22 . A high surface pressure or optimization of stresses in the rivet and the workpieces  3 ,  4  with good drawing-in properties of the same are given with this type of shape of ribs  22 . 
     In a further possible embodiment, the ribs  22  can also be graduated and/or embodied with different cross sections. 
     The ribs  22  are embodied with a length L 1  and a width such that when the rivet mandrel  2  is drawn in an expansion of the shank  12  or of the workpieces  3 ,  4  occurs. If a length of the ribs is at least 25%, and more than 40% in a particular embodiment, of the length L of the base body  26  between the rivet mandrel head  21  and a predetermined breaking point  24  and/or the ribs  22  in the rib area B ( FIG. 1 ) cover at least 40%, and more than 50% in a particular embodiment, of the outer surface of the base body  26 , a particularly effective expansion of the shank  12  and an inflow of material between the ribs  22  that is advantageous for a high surface pressure can be achieved. 
     Finally,  FIGS. 6 and 7  show variants of a rivet according to the invention, which have proven to be advantageous with respect to the closing of an axial gap  6  (see  FIGS. 1 ,  6 ,  7 ). In these variants the sleeve part  1  comprises a shank  12  that is composed of several parts, so that before and/or during a shaping of a driven head an axial force acts on a workpiece  3 . For example, with the variant shown in  FIG. 6 , when the rivet mandrel  2  is drawn in, the upper sleeve  123  is expanded by the ribs  22 , the gap between the sleeve and the top sheet  3  is closed and, subsequently, the upper sleeve  123  together with the top sheet  3  are carried along and the gap  6  between the sheets is bridged before the upper sleeve  123  as well as the lower sleeve  124  are expanded even more and a loadable positive closure is produced. 
     In the variant shown in  FIG. 7 , it is ensured in a similar manner that a force acting axially is exerted on the workpiece  3  even before an expansion of the shank  12  in the direction of the workpieces  3 ,  4  and an embodiment of a positive closure, so that the gap  6  can be closed. Instead of this type of a multiple-part embodiment of the shank, it can also be embodied in one piece with a predetermined breaking point or one or more predetermined deformation points.