The present invention relates to a testing apparatus for testing a joining connection between a stud and a workpiece from which the stud projects axially. In the field of joining technology it is known for studs to be joined onto a workpiece such as a metal plate. The joining operation may be a welding operation, also referred to as stud welding. It is also possible, however, for the joining operation to be an adhesive- bonding operation or some other kind of joining operation such as a brazing process, thermoplastic welding process, etc. For the purpose of testing such a weld connection of welding studs, it is known to use a so-called torque testing tool. This tool is essentially a threaded bushing which is screwed onto an external thread of the welding stud and, in the end, is supported on the workpiece surface. This threaded bushing has applied to it a defined torque which, via the stud thread, subjects the weld connection to a combined rotary and tensile force. This mechanical test should establish whether the connection withstands a certain force without failing in the process.

The problem here is that the coefficients of friction in the thread engagement mechanism between the threaded bushing and studs can vary widely, for example in dependence upon different stud production batches, etc. It is also possible for the thread- ed bushing in the testing tool to wear over time, and this changes the coefficients of friction. Dirt can also change the coefficient of friction.

All of this results in it being possible for the actual testing force, in the case of a predetermined torque value being applied to the threaded bushing, to vary widely. In addition, depending on the frictional resistance, only some of the torque applied is con- verted into an axial tensile force. The rest of the torque acts as a rotary force on the weld connection. Since weld connections, in particular ring flange studs, can absorb a relatively high torque, even if the weld connection is weak, testing of the weld connection can give erroneous results. DE 198 37 410 A1 discloses a mechanical testing apparatus for establishing the quality of a weld of a stud welded on sheet-metal material. In the first instance here, a nut is screwed onto the stud. Thereafter, the testing apparatus is pushed on laterally such that a claw-like accommodating part engages behind the nut. A screw connection then subjects the nut, and consequently the stud, to an axial force in the withdrawal direction. The disadvantage here is that it is necessary, in order to test a joining connection, for a nut to be screwed onto the stud beforehand and for said nut to be unscrewed again following completion of the testing operation. All of this results in a complicated testing process.

DE 32 10 825 A1 discloses a tensile-testing and elongating apparatus which can test the strength of the connection between a component and a stud fitted on the same. Here too, a tension nut is screwed onto the stud in order for a testing operation to be carried out. The testing apparatus itself contains two claws which can engage behind the head of the tension nut and are coupled to a hydraulic cylinder, which can subject the tension nut to a predetermined testing force in the axial direction, as a result of which the weld connection can be tested. It is also necessary here for a tension nut to be screwed on beforehand and to be unscrewed again following completion of a testing process.

Against this background, it is an object of the invention to specify an improved testing apparatus for testing a joining connection between a stud and a workpiece from which the stud projects axially.

The above object is achieved by a testing apparatus for testing a joining connection between a stud and a workpiece from which the stud projects axially, having a supporting sleeve, which is designed to be supported axially on the workpiece in a manner concentric to the stud, having a rotary connecting member, which can be displaced axially on, in particular in the supporting sleeve and is designed to establish an axial connection to the stud by way of a rotary movement, and having a tension sleeve, which is coupled to the supporting sleeve and to the rotary connecting member such that rotation of the tension sleeve results in the first instance in an axial connection between the rotary connecting member and the stud and results thereafter in an axial movement of the rotary connecting member, in order for the stud to be subjected to an axial testing force. A testing process can thus be carried out by means of the apparatus without a separate nut having to be screwed onto the stud beforehand. Furthermore, a testing force can be generated irrespective of a coefficient of friction on the thread of the stud.

The preferably captive coupling between the tension sleeve and supporting sleeve and also rotary connecting member is such that, in a first stage, an axial connection is established between the rotary connecting member and the stud and, in a following, second stage, the rotary connecting member is subjected to an axial movement, to be precise in particular a purely axial movement without any rotary component, in order for the stud to be subjected, in this way, to a purely axial testing force. The stud is preferably a threaded stud and the rotary connecting member preferably has an internal thread. The threads are preferably fine threads.

The supporting sleeve and the rotary connecting member are preferably coupled in terms of rotation and/or can be displaced in relation to one another, preferably to a limited extent, and preferably can be displaced axially in relation to one another. The axial testing force to which the rotary connecting member, and thus the stud, is subjected in the second stage is preferably proportional to a torque to which the tension sleeve is subjected.

A testing process is carried out by means of the testing apparatus preferably by the tension sleeve being subjected to a rotary movement. This results preferably in rotation of the supporting sleeve and, consequently, preferably in rotation of the rotary connecting member, and therefore it is possible to establish an axial connection between the rotary connecting member and stud via the rotary movement of the rotary connecting member. The axial connection is established in particular by a thread engagement mechanism between the rotary connecting member and the stud. As soon as the supporting sleeve is positioned on the workpiece or the rotary connecting member is positioned on a flange or the like of the stud, to be precise in the axial direction, a frictional force established therebetween is preferably large enough for continued rotation of the tension sleeve no longer to result in continued rotation of the supporting sleeve and/or of the rotary connecting member. Instead, the testing apparatus moves into the second stage, in which the rotary connecting member is subjected to a purely axial movement, in order for the stud to be subjected to an axial testing force.

The second stage can be initiated for example by activation of a thread engagement mechanism between the supporting sleeve and the tension sleeve, for example by virtue of the supporting sleeve being positioned on the workpiece.

The object is therefore achieved in full.

According to a particularly preferred embodiment, the rotary connecting member has a connecting thread, wherein the tension sleeve and the supporting sleeve are coupled to one another via a coupling thread engagement mechanism, wherein the coupling thread engagement mechanism runs counter to the connecting thread.

Counter-running thread engagement mechanism is understood to mean that for example the connecting thread is a right-hand thread, whereas the coupling thread engagement mechanism between the tension sleeve and supporting sleeve is a left-hand thread, or vice versa.

The coupling thread engagement mechanism is preferably a particularly smooth- running thread, such as a trapezoidal thread or a ball-mounted thread.

The friction in the coupling thread engagement mechanism is preferably smaller than a friction between the supporting sleeve and the workpiece or between the rotary connecting member and the stud.

According to a further preferred embodiment, the tension sleeve and the supporting sleeve are coupled to one another via a spring arrangement. The spring arrangement may be formed, for example, by a coil spring. The spring arrangement couples the tension sleeve and the supporting sleeve in the direction of rotation preferably such that, when the tension sleeve rotates, the supporting sleeve is carried along in the direction of rotation, wherein the spring arrangement is deformed only to a slight extent, if at all.

The spring-arrangement coupling between the tension sleeve and the supporting sleeve is preferably such that the tension sleeve and the supporting sleeve can execute a number of revolutions relative to one another. In particular, it is possible for the tension sleeve and the supporting sleeve to rotate relative to one another through at least five revolutions, which results in the spring arrangement becoming increasingly deformed.

During a rotary movement of the tension sleeve, it is therefore the case that the supporting sleeve is carried along in the same direction of rotation. The carry-along action is preferably terminated as soon as the supporting sleeve is seated on the workpiece and/or the rotary connecting member is seated on a flange of the stud or the like. In this case, the spring coupling between the tension sleeve and supporting sleeve is not sufficient to overcome the frictional engagement established as a result.

In this case, preferably the coupling thread engagement mechanism between the tension sleeve and the supporting sleeve takes effect such that the tension sleeve is moved away in the axial direction from the workpiece, to be precise on account of the preferred counter-running coupling thread engagement mechanism.

It is also preferred if the tension sleeve and the supporting sleeve are coupled to one another via a coupling thread engagement mechanism and if the spring arrangement is designed such that the supporting sleeve is prestressed against a stop on the tension sleeve.

The coupling thread engagement mechanism is preferably very smooth-running, and therefore the spring arrangement generally ensures that the supporting sleeve, in the unloaded state, moves against the stop, even if this involves a number of relative movements between the supporting sleeve and tension sleeve. Furthermore, it is advantageous overall if the rotary connecting member and the tension sleeve are coupled axially via an axial bearing. Consequently, rather than rotary forces of the tension sleeve being transmitted to the rotary connecting member, they are absorbed by the axial bearing. As mentioned above, the supporting sleeve and the rotary connecting member are preferably coupled in terms of rotation, but are mounted such that they can be displaced in relation to one another preferably in the longitudinal direction, in order to allow relative movement between the rotary connecting member and supporting sleeve in particular in the second stage of the testing apparatus. Such a rotary coupling along with, at the same time, a degree of freedom in the axial direction is achieved preferably in that the supporting sleeve has at least one longitudinal slot, in which engages a rotary coupling pin which projects radially from the rotary connecting member.

According to a further preferred embodiment, the tension sleeve has an axial bore, through which engages a shank portion of the rotary connecting member, wherein a head portion of the rotary connecting member is supported axially on a coupling shoulder of the tension sleeve, preferably via an axial bearing, as mentioned above.

Movement of the tension sleeve in the direction away from the workpiece is thus converted directly, and without any transmission of frictional forces therebetween, into an axial movement of the rotary connecting member in order for it to be possible in this way, in the second stage of the testing apparatus, for the rotary connecting member, and consequently the stud, to be subjected to an axial tensile force.

Overall, it is also advantageous if the tension sleeve has a tension-sleeve base and a closure cover, which closes an axial opening in the tension-sleeve base. The closure cover here can secure in particular a head portion of the rotary connecting member axially in relation to the tension sleeve. In other words, with the closure cover removed, the shank portion can be introduced preferably into an axial bore of the tension sleeve until the head portion of the rotary connecting member is supported axially on the coupling shoulder of the tension sleeve, for example via the axial bearing. It is then possible for the closure cover to be fitted on the tension-sleeve base, in order to close the axial opening and consequently to secure the head portion of the rotary connecting member axially on the tension sleeve.

It is particularly advantageous, furthermore, if a tool-accommodating portion is formed on the closure cover.

This makes it possible for the tension sleeve to be subjected to a torque via the closure cover. The closure cover here may be designed in the form of an adapter such that a first closure cover is designed for example for accommodating a square socket with dimensions of 1 /2" and another closure cover is designed, for example, with a hexagon socket, etc.

Of course, the features which have been mentioned above and those which have yet to be explained hereinbelow can be used not just in the combination specified in each case, but also in different combinations or on their own, without constituting a departure from the framework of the present invention.

Exemplary embodiments of the invention will be described in more detail in the following description and are illustrated in the drawing, in which:

shows a schematic longitudinal-section view through one embodiment of a testing apparatus according to the invention; and

Fig. 2 shows a schematic sectional view taken along line 11-11 from Fig. 1 A testing apparatus 10 for testing a joining connection between a stud and a work- piece is illustrated in schematic form, and designated in general terms by 10, in Figures 1 and 2.

The testing apparatus 10 serves, in particular, to test a joining connection between a stud 12 and a workpiece 14. The stud 12 here is joined onto an upper side 16 of the workpiece 14, to be precise in particular by a joining connection, such as a weld connection 17. A corresponding weld bead 18 is shown in schematic form in Fig. 1. A longitudinal axis along which the stud 12 extends, and which is oriented perpendicularly to the upper side 16 of the workpiece 14, is shown at 19. An external thread 20 of the stud 12 is indicated schematically at 20.

The testing apparatus 10 has a supporting sleeve 24. The supporting sleeve 24 may be arranged in a manner concentric to the stud 12 and has at its front end, which is directed towards the workpiece 14, an annular surface 26, which can be positioned on the workpiece 14 concentrically around the weld connection 17 in order to be supported axially on said workpiece.

The supporting sleeve 24 also contains a supporting-sleeve thread 28, which is formed in an outer region at the opposite axial end of the supporting sleeve 24. The supporting-sleeve thread 28 is designed, for example, in the form of a trapezoidal thread and is realized, in particular, in the form of a smooth-running thread. 30 denotes an axial end of the supporting sleeve 24 which is located opposite the annular surface 26.

The testing apparatus 10 also contains a tension sleeve 34. The tension sleeve 34 has a tension-sleeve base 36, from which extends a sleeve portion 38 which, on its inner circumference, has a tension-sleeve thread 40 which engages with the supporting-sleeve thread 28 in order for the tension sleeve 34 and the supporting sleeve 24 to be coupled to one another in this way via a coupling thread engagement mechanism 28, 40. Fig. 1 illustrates that the end 30 of the supporting sleeve 24 strikes in the axial direction against an axial stop 42 of the tension sleeve 34. The axial stop 42 is, as will also be explained hereinbelow, designed in the form of a return-rotation stop and projects preferably in relation to an inner side of the sleeve portion 39.

In the interior of the sleeve portion 38, the tension sleeve 34 and the supporting sleeve 24 are coupled to one another via a coil spring 44. The coil spring 44 is designed to exert a rotary force between the supporting sleeve 24 and the tension sleeve 34 such that the supporting sleeve 24 can be screwed into the sleeve portion 38 of the tension sleeve 34 to the extent where the sleeve end 30 strikes against the axial stop 42, which therefore forms a return-rotation stop 42.

The tension-sleeve base 36 of the tension sleeve 34 has an axial bore 46, which merges into a coupling shoulder 48 on the axial side facing away from the supporting sleeve 24. Starting from this coupling-shoulder portion of relatively large axial diameter, the axial bore 46 then merges, via a cover shoulder 50, into an axial opening 51 in the tension-sleeve base 36. The axial opening 51 is closed by a closure cover 52, which rests on the cover shoulder 50.

A tool-accommodating portion 54 is formed at the axially free end of the closure cover 52 and may be designed, for example, in the form of a square-socket portion into which a tool 56 can be introduced, in order for rotary movements of the tool 56 to be transmitted to the closure cover 52, and consequently to the tension sleeve 34, and thus for a torque to be transmitted to the tension sleeve 34, as is shown schematically at T in Fig. 1 . The relative rotation is shown at .

As is yet to be explained hereinbelow, a testing operation takes place by the tension sleeve 34 being subjected to a rotary movement a in the right-hand direction, in which case the tension sleeve 34 is subjected to a torque T in the same direction.

The testing apparatus 10 also contains a rotary connecting member 64, which may be designed, for example, in the form of a rotary connecting sleeve 64. The rotary con- necting member 64 has a screw portion 66, which is formed by a shank portion 68 and a head portion 70.

The screw portion 66 of the rotary connecting member 64 is introduced into the tension sleeve 34 via the axial opening 51 such that the shank portion 68 passes through the axial bore 46 and such that the head portion 70 is supported axially on the coupling shoulder 48, to be precise in particular via an axial bearing 72.

With the closure cover 52 fitted in place, the head portion 70 is secured in the axial direction between the axial bearing 72 and the closure cover 52.

The shank portion 68 of the screw portion 66 of the rotary connecting member 64 extends through the axial bore 46 into the interior of the sleeve portion 38 of the tension sleeve 34 and is coupled there to a bushing portion 74 of the rotary connecting member 64, to be precise via a fixed screw connection or some other fixed, but preferably releasa- ble, connection. The external diameter of the bushing portion 74 is preferably larger than the diameter of the axial bore 46, and therefore the rotary connecting member 64 is coupled in captive fashion to the tension sleeve 34.

At its axial end which is opposite the screw portion 66, the bushing portion 74 has an internal thread 76, which is designed to be screwed onto the external thread 20 of the bolt 12. The internal thread 76 is preferably likewise a fine thread.

Two diametrically opposite radial pins 78a, 78b extend from a radially outer side of the bushing portion 74. The radial pins 78a, 78b engage, as is also illustrated in Fig. 2, in longitudinal slots 80a, 80b of the supporting sleeve 24, and therefore the rotary connecting member 64 and the supporting sleeve 24 are coupled in terms of rotation, but can be moved axially relative to one another, to be precise over the axial length of the longitudinal slots 80a, 80b. The testing apparatus 10 functions as follows: The testing apparatus 10 is guided in the axial direction from above in the direction of a stud 12 until a front end of the bush- ing portion 74 butts against the upper side of the stud 12. A rotary movement a is then introduced into the tension sleeve 34. The coil spring 44 causes this rotary movement to be converted into a rotary movement of the supporting sleeve 24, which, in turn, carries along the rotary connecting member 64 in the direction of rotation, and therefore the rotary connecting member 64, to be precise in particular the bushing portion 74 thereof, is screwed onto the stud 12. The coil spring 44 here is deformed preferably only to a slight extent, if at all.

As soon as the bushing portion 74 is seated on a flange or on the weld bead 18 and/or as soon as the annular surface 26 is seated on the upper side 16 of the workpiece 14, a first stage of this testing process is at an end. The screw connection between the rotary connecting member 64 and the stud 12 means that the rotary connecting member 64 and the stud 12 are connected axially to one another. As a result of the frictional engagement between the bushing portion 74 and the stud 12 and/or between the supporting sleeve 24 and the workpiece 14, continued rotation of the tension sleeve 34 in the same direction of rotation results in activation of the coupling thread engagement mechanism 28, 40 between the supporting sleeve 24 and the tension sleeve 34. This is because the coupling thread engagement mechanism 28, 40 is designed, in particular, to run counter to the thread engagement mechanism 20, 76 and is designed, in particular, in the form of a left-hand thread. On account of the fact that the supporting sleeve 24 is fixed by friction in the direction of rotation in relation to the workpiece 14 and in relation to the stud 12, continued rotation of the tension sleeve 34 thus results in rotation in relation to the supporting sleeve 24 such that the tension sleeve 34 is moved away in the axial direction from the workpiece 14. The rotary connecting member 64, and thus the stud 12, is subjected to an axial withdrawal force here via the coupling shoulder 48 and the axial bearing 72. This movement is a purely axial movement, such that a torque T to which the tension sleeve 34 is subjected is proportional to a withdrawal force F to which the rotary connecting member 64, and thus the stud 12, is subjected in the axial direction. In other words, following the elimination of any slack or tolerances, the angle of rotation a is proportional to the relative axial offset between the supporting sleeve 24 and rotary connecting member 64, as is indicated schematically at s in Fig. 1. If a torque defined in this way is applied and the weld connection 17 is not destroyed, the weld connection 17 is deemed to be sound.

The testing apparatus can then be removed by the tension sleeve 34 being rotated back in the opposite direction so that, first of all, the supporting sleeve 24 and tension sleeve 35 rotate relative to one another again until the sleeve end 30 strikes against the axial stop 42. Continued rotation then results in the rotary connecting member 64 being unscrewed from the stud until such time as the testing apparatus 10 can be removed from the stud.