The invention furthermore relates to a device for producing a riveted joint with female die and male die between at least two plate-shaped components, of which the upper component or components are punched through by a punch rivet with a cutting edge arranged on the end face of its rivet shaft, which cutting edge is formed in the cutting region by an outer side extending parallel to the axis and a conical inner side of the rivet shaft, and the lowest component receives the end face cutting edge in widened form, both cutting edges being radially widened substantially to the same extent in such a way that the rear cutting edge conically widens the punch hole in the uppermost component and is riveted to this widening with interlocking fit, both the female die and the male die having a deforming piece which fits into the rivet shaft and widens the relevant cutting edge substantially to the same extent in each case.

The invention furthermore relates to a riveted joint between at least two plate- shaped components, of which the upper component or components of which are punched through by a punch rivet and the lowest component receives the end face cutting edge in widened form, both cutting edges being radially widened substantially to the same extent in such a way that the rear cutting edge conically widens the punch hole in the uppermost component and is riveted to this widening with interlocking fit.

A process is known from German Patent Application 197 01 780 for using a punch rivet with a cutting edge arranged at the end face of its rivet shaft, which cutting edge is formed in the cutting region by an outer side extending parallel to the axis and a conical inner side of the rivet shaft, the outer side extending continuously parallel to the axis over the entire rivet shaft and the punch rivet which is tubular in axial symmetrical design being provided on both sides with the same cutting edges, with a riveting tool for producing a riveted joint with a female die and male die. To this end the riveting tool has a female die and male die which have a conical piece fitting in each case into the rivet shaft to widen the relevant cutting edge of the punch rivet in each case substantially to the same extent. During the known riveting process the male die moves substantially vertically towards the uppermost sheet layer in order to punch the punch rivet vertically through the sheets to be connected. As soon as the male die in its movement towards the uppermost sheet has punched the punch rivet so far through the sheets to be connected that the region to be filled in the female die is substantially filled, the male die widens the upper edge of the punch rivet so far radially outwards by further lowering until a substantially smooth transition from upper cutting edge and upper metal surface of the upper sheet has resulted. With this plastic deformation of the upper edge region of the punch rivet a sufficiently reliable connection between punch rivet and upper sheet is produced as a result of the widening movement and pressing of the male die. As a result of the subsequent setting process of the punch rivet however, i. e. as a result of the regeneration of the upper edge region of the punch rivet in the direction of the central axis of the punch rivet, an annular gap forms and reduces the fastness of the punch rivet in the sheet and therefore the loadability of the riveted joint. This annular gap resulting from setting of the punch rivet can be disadvantageous in particular in metal connections such as aluminium/steel, for example, as moisture can easily accumulate in this annular gap.

Whilst corrosion of aluminium and steel is prevented in that the punch rivets are coated with a protective layer, this corrosion-preventing layer however does not always remain undamaged by the plastic deformation process, so in time corrosion can occur in the annular gap. Such corrosion reduces the strength of the riveted joint substantially and is disadvantageous in particular in components which have to meet certain safety requirements, for example in the manufacture of cars.

The object of the invention is therefore to create a process for producing a riveted joint with the known punch rivets, which produces a long-lasting interlocking fit with the components to be connected and to provide a tool for producing this riveted joint.

This object is achieved according to the invention by a process for producing a punch rivet connection between at least two plate-shaped components, of which the upper component or components are punched through by a punch rivet with a cutting edge arranged on the end face of its rivet shaft, which cutting edge is formed in the cutting region by an outer side extending parallel to the axis and a conical inner side of the rivet shaft, and the lowest component receives the end face cutting edge in widened form in a female die after a linear movement of a male die guided in a guide bush and an upper cutting edge remains substantially undeformed, the guide bush subsequently being lifted until at least the upper cutting edge is exposed and the axis of the male die is guided on a concentric track round the central axis of the punch rivet and in the process the male die is moved towards the punch rivet parallel to the central axis of the punch rivet and widens the upper cutting edge radially substantially to the same extent such that the upper cutting edge conically widens the punch hole in the uppermost component and is riveted to this widening with interlocking fit.

The process according to the invention builds upon the first steps of the known process for setting punch rivets in accordance with German Patent Application 197 01 780, no guide jaws which are laterally removed as soon as the cutting edge has penetrated into the upper component being used however and furthermore the riveting joint of the upper cutting edge occurring owing to a wobbling movement of the male die after this has punched the punch rivet in a linear movement in accordance with German Patent Application 197 01 780 to a certain depth into the components to be connected.

The process according to the invention in contrast uses only a guide bush in which the punch rivet is guided until it is placed on the uppermost component. After the placing of this guide bush, the male die exerts the force necessary to punch the

punch rivet through the components to be connected. As a result, a riveted joint is produced on the side facing the female die as is already known from German Patent Application 197 01 780.

Following this process step the guide bush is preferably lifted, whilst maintaining the contact between male die and cutting edge of the punch rivet until the upper cutting edge of the punch rivet is substantially exposed. In this case it may be expedient to construct the guide bush in several parts, for example in that cylindrical halfshells are arranged concentrically.

In order to form the upper widening of the punch rivet the male die is expefemale diently inclined slightly from the vertical (central axis of the punch rivet) together with the guide bush either whilst maintaining contact between male die and cutting edge, so at least a sector of the inner cone of the punch rivet is in contact with the male die, or the male die is radially offset whilst maintaining its vertical alignment with the uppermost component in order to also remain in contact at least with a sector of the inner cone of the punch rivet.

In the case of inclination of the male die, in the process according to the invention this is furthermore moved in a helical line leading in the direction of the uppermost component, so the sector which forms the contact surface between male die and inner cone of the punch rivet runs round the central axis of the punch rivet and therefore brings the external surface of the punch rivet in ever closer coincidence with the uppermost component with every 360° rotation. The movement executed in this way by the male die is a superimposition of a concentric circular path movement round the central axis of the punch rivet and a linear movement parallel to the central axis of the punch rivet towards the uppermost component, the axis of the male die moving on the external surface of a cone.

In the case where the male die is radially offset, a sector also forms a contact surface between male die and inner cone of the punch rivet and runs round the central axis of the punch rivet in the same way and forces the external surface of the punch

rivet into interlocking fit with the upper component. The movement executed in this way by the male die is a superimposition of a concentric circular path movement round the central axis of the punch rivet and a linear movement parallel to the central axis of the punch rivet towards the uppermost component, the axis of the male die moving on the external surface of a cylinder.

In a further embodiment of the process according to the invention the male die is also inclined out of the vertical (central axis of the punch rivet) and thus forms a sector as a contact surface with the inner cone of the punch rivet which runs round the central axis of the punch rivet in the same manner and forces the external surface of the punch rivet into interlocking fit with the upper component. The movement executed by the male die describes a concentric path round the central axis of the punch rivet, the axis of the male die describing a hypocycloidal path which substantially corresponds to the shape of a rosette and is designed concentrically round the central axis of the punch rivet.

With the process according to the invention a degree of pressure between punch rivet and component which is many times greater compared with the state of the art is achieved and therefore a pressing with interlocking fit occurs in the riveted joint which, even after the inevitable setting process of the punch rivet, does not lead to an annular gap forming between external surface of the punch rivet and the upper side of the component.

The helical movements of the male die are achieved by a corresponding articulating or gearing device in the drive region of the male die.

Embodiments of the invention are illustrated in the Figures, in which: Fig. la + b show the punch rivet in section and in perspective view of a continuous tubular design.

Fig. 2 to 7 show the individual production phases of the riveted joint according to the invention with the punch rivet.

Fig. 8 shows a perspective illustration of the process according to the invention in which the movement of the male die describes a hypocycloidal path.

Fig. la shows the punch rivet 1, the rivet shaft 2 of which is designed as a continuous cylindrical tube. At its two ends the rivet shaft 2 has an inner cone 3,4 in each case, which widens the rivet shaft 2 from the inside outwards and at the transition into the cylindrically extending outer side 5 forms the cutting edge 6 or 7.

The punch rivet 1 therefore has a continuous cylindrical shape substantially in the region of its inner side 8 and its outer side 5, which shape ends axially symmetrically in the two cutting edges 6 and 7.

In Fig. 2 the punch rivet 1 is held in a tool in the guide bush 12, more specifically with placement of the male die 11 on the back of the punch rivet 1. The male die 11 is also guided in the guide bush 12. The plate-shaped components 13 and 14 to be riveted are held opposite this tool having the parts 11 and 12, which components are fixed by conventional holding mechanisms. The female die 15 against which the components 13 and 14 rest during the punch and riveting process described below is arranged on the side remote from the punch rivet.

In the following phase of operation illustrated in Fig. 3 the male die 11 presses the punch rivet 1 with guidance of the punch rivet 1 in the guide bush 12 towards the component 13 which component rests in the process against the female die 15 above the component 14 underneath. Through a forward movement of the male die 11 in accordance with the arrow drawn in, the punch rivet 1 is now punched into the component 13, as illustrated in Fig. 4, the guide bush 12 guiding the punch rivet in the process. This pressure exerted by the male die 11 on the punch rivet 1 is transferred in that the male die 11 on its side facing the punch rivet 1 ends in a conical piece 16 fitting into the punch rivet, which conical piece rests with interlocking fit against the conical inner side 3 of the punch rivet 1. In the process the punch rivet 1 penetrates with its cutting edge 6 into the component 13 which thereby deforms in the direction towards the female die 15 and thereby pushes the component 14 in front of it. This procedure is brought about by the shaping of the female die 15 on its side facing the

punch rivet 1 which like the male die 11 ends in a conical piece 17. In addition to the conical piece 17 the female die 15 has the shaped pocket 18 surrounding the conical piece 17 in which the material of the component 14 is moulded when the punch rivet 1 is pushed in. As soon as this moulding process is completed, as shown in Fig. 5, the guide bush 12 is withdrawn at least until the cutting edge 7 of the punch rivet is exposed over the internal width of the bush edge.

Following on from this step the male die 11, expediently together with the guide bush 12, is pivoted out at an angle a with respect to the central axis, which up to this moment is formed by the punch rivet 1 and the male die 11, and a sector-like planar area forms as a contact surface between inner conical surface 3 of the punch rivet 1 and conical piece 16 of the male die 11. Whilst maintaining this angle a and the contact surface formed in the process the male die 11 now rotates round the central axis of the punch rivet 1 in such a way that the contact surface between conical piece 16 and inner cone 3 runs round the central axis of the punch rivet 1.

In the embodiment according to the invention (not shown) in which the formation of the sector-like planar area as a contact surface occurs as a result of an axial displacement of the entire male die, the contact surface is moved in a similar way.

A linear movement of the forward movement spindle (not shown) is superimposed on this rotating course of movement, so the male die 11 describes a helical movement in the direction towards the component 13, the outer side 5 of the punch rivet 1, i. e. the contact surface constantly, i. e. with every wobbling rotation of the male die, widening and finally being pressed, with further widening, more intensively with the upper side of the component 13 until after a number of revolutions a connection with interlocking fit is produced. Following on from this riveting process the male die 11 is withdrawn and the riveting process is concluded.

Fig. 7 shows a riveted joint which has been produced by the process according to the invention, Fig. 7a shows an enlarged detail view of Fig. 7 wherein it can clearly

be seen that a connection with interlocking fit between punch rivet outer side 5 and component 13 remains even after the setting of the punch rivet 1.

Fig. 8 shows another preferred embodiment of the process according to the invention, in which the male die is moved on a hypocycloidal path. The hypocycloidal path movement is produced by a gear not shown. During the movement of the male die on the hypocycloid a sector is formed as a contact surface between the male die and the inner cone of the punch rivet. The deforming of the punch rivet occurs on the contact surface. During the hypocycloidal path movement the male die rotates after each passing of a"rosette leaf'through the centre of the hypocycloid, which centre coincides with the central axis of the punch rivet. The linear movement of the male die (arrow direction parallel to the central axis of the punch rivet) towards the uppermost component is superimposed on this hypocycloidal movement, so the entire movement proceeds as a"wobbling movement". Fig. 8 shows a hypocycloidal path which is composed of four loops of a rosette. According to the invention the radius of curvature of the hypocycloidal movement changes constantly during the movement, so at the top of each rosette loop, when the radius of curvature is at its smallest, the deforming force of the male die with respect to the punch rivet achieves at least a local maximum. This locally increased deforming force permits the production of a particularly durable riveted joint according to the invention.