Abstract:
A non-blind rivet is disclosed that can be used to form a joint without the need for brazing, welding or threaded locknuts. The rivet 1 is placed in compression by opposing dies 15,20 causing a narrow region of the rivet wall to buckle forming a fold 24, the rivet thus being held to a workpiece 12 between a flange 6 and the fold 24.

Description:
BACKGROUND OF THE INVENTION 
     This invention is concerned with non-blind rivets and in particular with non-blind rivets formed with axial bores. 
     Non-blind rivets, that is to say rivets which can only be set provided there is access to both sides of a workpiece to which the rivets are to be secured, have been suggested in many different configurations and for many different purposes. 
     It is sometimes required, for example in the manufacture of vehicles, to secure a small tube to a workpiece, for example to provide a drainage hole. 
     Such tubes are often connected to primary workpieces, such as, for example, sun roofs, fuel tanks and so forth by methods such as brazing, welding, or by the use of threaded locknuts. Such known methods of connection tend to be labour intensive and are accordingly expensive. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention a non-blind rivet, adapted to be set by compressive forces, comprises a rivet body having a tubular wall surrounding an axial bore which extends from a tail end portion to a head end portion of the rivet. A head flange at the head end portion of the rivet extends outward from the body. The non-blind rivet is characterized in that the axial bore includes two portions of different diameters with a first portion having a first diameter and extending from the tail end portion, and a second portion having a second diameter greater than the first diameter and extending from the head end portion of the bore. 
     Preferably, the axial bore comprises third portion, having a third diameter less than that of the first portion, the third portion extending between the first portion of the rivet and the second portion thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example only, with reference to the accompanying drawings, in which 
     FIG. 1 shows a rivet according to a first aspect of the invention; 
     FIG. 2 shows the rivet of FIG. 1 in a hole in a workpiece; 
     FIG. 3 shows the rivet of FIG. 1, the workpiece and first and second dies; 
     FIG. 4 shows a view similar to that of FIG. 3; 
     FIG. 5 shows the rivet being set; 
     FIG. 6 shows the set rivet; 
     FIG. 7 shows a modified rivet; 
     FIG. 8 shows the rivet of FIG. 7 in a hole in a workpiece; 
     FIG. 9 shows the rivet of FIG. 7, the workpiece and first and second dies; 
     FIG. 10 shows a first stage in the setting of the rivet of FIG. 7; 
     FIG. 11 shows a second stage in the setting of the rivet of FIG. 7; 
     FIG. 12 shows the set rivet; 
     FIG. 13 shows the set rivet in use; and 
     FIG. 14 shows a third embodiment of a tail end portion of a rivet in the set condition. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a rivet 1 according to the first aspect of the invention is shown. The rivet comprises a tubular wall 2 surrounding an axial bore 3 which extends from a tail end region 4 to a head end region 5 of the tubular wall. The head end portion is provided with a head flange 6 extending outwardly from the tubular wall. 
     The axial bore 3 comprises two portions of different diameter. A first portion 7 of lesser diameter extends from the tail end portion to the head end portion of the rivet. A second portion 8 of greater diameter extends from the head end region towards the tail end portion. The first and second portions of the bore meet at a step 9. 
     Turning to FIG. 2, the rivet 1 can be seen in position in a hole 13 in a workpiece 12. The flange 6 presents an abutment surface 11 to the workpiece 12. Since the joint between the rivet and the workpiece is intended to be watertight, the abutment surface 11 is preferably coated with a sealant 10, such as a polymer. 
     In FIG. 3, the assembly of FIG. 2 is shown together with dies 15,20 that will cause the rivet 1 to deform. A first die 15, comprises a base 16 and a projection 17. The projection 17 has similar external dimensions to the first portion 7 of the axial bore and pauses therethrough, such that the base 16 of the die is in contact with the flange 6. The projection also passes into a bore 22 in a second die 20. The bore 22 in the second die has similar dimensions to the second portion 7 of the axial bore. The second die 20 also comprises an abutment surface 21 which rests on the tail end portion 4 of the rivet. 
     Once in position, the dies are moved together relative to one another, as indicated by the arrows in FIG. 4. 
     The compression forces acting on the tubular wall 2 cause the wall to collapse in the region of the second portion of the axial bore forming a fold 24, trapping the workpiece 12 between the fold 24 and the flange 6 (FIG. 5). 
     Such a rivet set in this way is shown in FIG. 6. The extent of the deformation bulge 24 is preferably limited by means (not shown) restricting the distance that the dies 15,20 can move toward one another. This will prevent oversetting of the rivet. 
     In an alternative embodiment, shown in FIG. 7, the tubular wall 2 of the rivet 1 may be provided with a third portion 30 of diameter greater than that of the second portion 8. The third portion 30 extends from the tail end portion 4 of the bore, to join the first portion 7 at a step 31, the first portion now forming an intermediate part of the axial bore 3. 
     FIG. 8 shows the modified rivet in position in a hole 13 in a workpiece 12. 
     In setting such a modified rivet, a modified second die 20&#39; is used (FIG. 9). The die 20&#39; is again provided with a base 22 through which the projection of the first die extends, and has a similar diameter to that of the first region 7 of the axial bore 3. Whereas in the previous embodiment the abutment surface 21 was only in contact with an end surface of the tail end portion 4, the abutment surface 21&#39; the present embodiment is in the form of a further projection or boss 25. The boss 25 has an external surface of similar dimensions to the diameter of the third portion 30 of the axial bore 3, and an internal diameter of similar dimensions to the first portion 7 of the axial bore. The boss 25 can thus extend between the tubular wall 2 in the region of the third portion 30 and the projection 17 of the first die 15. However, the boss 25 does not extend as far as-the step 31 joining the first and third portions of the axial bore of the rivet, but leaves a gap 26, between the abutment surface 21&#39; and the step 31. 
     When the dies are moved together relative to one another (FIG. 10), the tubular wall 2 in the region of the third portion of the axial bore is weakest and deforms first, to form an external ridge 34 in the rivet. The ridge will continue to form until the face 21&#39; of the boss 25 abuts the step 31 in the tubular wall. 
     Further relative movement of the dies will cause the tubular wall in the region of the second portion of the axial bore to deform, as described in the previous embodiment (FIG. 11), by virtue of compression forces from the die 20 being transmitted via the face 31 on wall 2. 
     The fully set rivet is shown in FIG. 12. The ridge 34 may be used to attach a tube 40, or such like to the rivet, as shown in FIG. 13. 
     It will be understood that by varying the shape of the second die 20&#39;, and in particular the shape of the boss 25, a variety of shaped tail end portions can be formed, such as, for example, the flared flange 35 shown in FIG. 14.