JOININING METHOD AND JOINING DEVICE

Abstract

A method for joining joining elements to components, in particular for stud welding, comprises the steps of: providing a joining element having a first joining surface, and providing a component having a second joining surface; preparing the first or the second joining surface, wherein the preparation step includes detecting the state of the first or the second joining surface; joining the joining element to the component. The preparation step uses least one of the following detection methods: (i) an electrical contact resistance measurement, (ii) an electrical conductivity measurement, (iii) a fluorescence measurement, and (iv) a laser measurement.

Claims

1. A joining method for joining joining elements to components, the method comprising the steps of: providing a joining element including a first joining surface, and providing a component including a second joining surface; preparing at least one of the first joining surface or the second joining surface, including the step of detecting the state of the at least one first joining surface or second joining surface using at least one of the following detection methods: (i) an electrical contact resistance measurement on the joining surface, (ii) an electrical conductivity measurement on the joining surface, (iii) a fluorescence measurement on the joining surface, and (iv) a laser measurement on the joining surface; and joining the joining element to the component.

2. A joining method according to claim 1, wherein the electrical conductivity measurement includes the steps of: generating an electromagnetic generator field with a generator; moving the generator into the vicinity of the at least one first joining surface or second joining surface; inducing an electrical eddy current (i) in the material of the component or in the material of the joining element; and detecting, with a sensor, an electromagnetic response field generated by the induced eddy current (i).

3. A joining method according to claim 2, wherein the electromagnetic generator field has a frequency in a range of from 10 kHz to 2 MHz, in particular in a range of from 10 kHz to 500 kHz, and preferably in a range of from 20 kHz to 300 kHz.

4. A joining method according to claim 1, wherein the fluorescence measurement includes the steps of: supplying the at least one first joining surface or second joining surface with electromagnetic generator radiation created with a generator; exciting the atoms in the material of a coating on the at least one first joining surface or second joining surface; detecting with a sensor an emission of response radiation, released by the material, in particular the emission of light quantums.

5. A joining method according to claim 4, wherein the electromagnetic generator radiation used to excite the coating includes at least one of LED or laser radiation.

6. A joining method according to claim 1, wherein the detection method includes providing a generator and a sensor housed in a measurement probe having a diameter (D.sub.M) which is in a range of from 7 mm to 50 mm, in particular in a range of from 8 mm to 40 mm.

7. A joining method according to claim 1, wherein the detection step is carried out within a timeframe of no less than 0.1 s, and no greater than 2 s.

8. A joining method according to claim 1, wherein the contact resistance measurement includes the steps of: applying an electrical potential (U) to the at least one first joining surface or second joining surface with a contact probe; at least one of pressing the contact probe onto the at least one first joining surface or second joining surface with an increasing force (F), or increasing the value of the electrical potential (U) on the contact probe, detecting a resistance change (R) across the joining surface.

9. A joining device for joining a joining element including a first joining surface to a component including a second joining surface, the joining device comprising: a joining head including a retaining apparatus for holding the joining element to align the first joining surface with the opposed second joining surface, a detection apparatus for detecting a state of at least one of the first joining surface and the second joining surface, the detection apparatus including at least one of: (i) an electrical contact resistance measurement apparatus, (ii) an electrical conductivity measurement apparatus, (iii) a fluorescence measurement apparatus, and (iv) a laser measurement apparatus.

10. A joining device according to claim 9, wherein the detection apparatus is arranged on the joining head.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Embodiments of the invention are shown in the drawings and are explained in more detail in the following description, in which drawings:

[0048] FIG. 1 is a schematic view of a joining device according to one embodiment of the invention.

[0049] FIG. 2 shows a detail II from FIG. 1.

[0050] FIG. 3 is a graph showing count values in relation to a coating density from a fluorescence measurement on a joining surface.

[0051] FIG. 4 is a schematic view of a measurement probe for carrying out a fluorescence measurement.

[0052] FIG. 5 is a schematic view of a measurement probe for carrying out a conductivity measurement.

[0053] FIG. 6 is a graph used for conductivity measurement showing the conductivity, hardness and tensile strength of a material as a function of temperature.

[0054] FIG. 7 is a schematic view of an arrangement for contact resistance measurement.

[0055] FIG. 8 is a graph showing resistance in relation to force when carrying out a contact resistance measurement method.

[0056] FIG. 9 is a graph showing resistance in relation to voltage when carrying out a contact resistance measurement method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] FIG. 1 schematically shows a joining device, which is generally denoted by 10. The joining device 10 comprises a joining head 12, which is preferably secured to a robotic arm 16 of a robot 14. A carriage 18 is arranged on the joining head 12 so as to be movable along a joining axis 20. A retaining apparatus 22 is formed on the carriage 18, by means of which apparatus a joining element 24 can be retained. The joining element 24 comprises a shaft portion 26 on which the joining element 24 can be retained by means of the retaining apparatus 22, and comprises a flange portion 28. A first joining surface 30 is formed on a side of the flange portion 28 that faces axially away from the shaft portion 26.

[0058] The joining element 24 can be joined to a component 32, for example a metal sheet component of a vehicle body, by means of the joining device 10. The component 32 comprises a second joining surface 34 that can be aligned with the first joining surface 30 before the joining process begins.

[0059] In the present case, the joining device is designed for stud welding; however, it can also be designed for stud bonding/stud gluing. During stud welding, the joining element 24 is lowered onto the component 32 by movement of the carriage 18. A voltage is subsequently applied between the joining element 24 and the component 32, resulting in a flow of electric current. The component 24 is then lifted back up, resulting in an electric arc being drawn. The opposing joining surfaces 30, 34 become fused to one another as a result of the electric arc. The joining element 24 is then lowered onto the component 32 again, following which the electric arc is cut off on account of the electrical short-circuit. The whole fusion solidifies, and the joining element 24 is integrally bonded to the component 32.

[0060] A stud welding process of this kind is generally known. A tip ignition process may also be used in place of the drawn-arc ignition process.

[0061] The joining element 24 and the component 32 are preferably manufactured from aluminium alloys. The joining process is carried out using specific joining parameters. The joining parameters can optionally be set, namely depending on the state in particular of the second joining surface 34 before the joining process.

[0062] Determining the state of the second joining surface 34 can be used to adapt the joining parameters or to initiate further steps before beginning the joining process, for example an additional cleaning step in which the second joining surface 34 is supplied with a physical medium, such as a plasma gas or a snow jet.

[0063] A detection apparatus 40 used to detect a state can usually work entirely passively. In the present case, the detection apparatus 40 can, however, be designed as an active detection apparatus, in which the detection apparatus 40 excites the second joining surface 34, as schematically indicated by reference sign 36, at which point a reaction occurs at the second joining surface 34, as schematically shown by reference sign 38 in FIG. 1, which can be detected by the detection apparatus 40.

[0064] The detection apparatus 40 can, as shown, be mounted on the joining head 12.

[0065] Alternatively, as also shown in FIG. 1, the detection apparatus can be designed as a detection apparatus 40 that is separate from the joining head 12.

[0066] In FIG. 1, a diameter of the second joining surface 34 is indicated by DF. Preferably, a diameter D.sub.M, which can be covered by the detection apparatus 40 or 40 on the surface of the component 32, is greater than the diameter DF. For example, the detection apparatus 40 can comprise a measurement probe having a diameter D.sub.M that is preferably greater than DF.

[0067] FIG. 2 shows a detail II from FIG. 1. Here, it is schematically indicated that the component 32 can have a granular structure 42 in a surface layer, which structure can contain for example smaller grains 44 and larger grains 46.

[0068] FIG. 2 also shows that a coating or a covering 50 can be formed on the surface or on the second joining surface 34 of the component 32, which coating or covering can be for example an oil film, fat or hotmelt covering, or a covering of waxes, oils, polysiloxanes, or a covering of hydrocarbons, polymers, etc.

[0069] The materials or the composition of the coating 50 and a coating thickness 52 that is indicated schematically in FIG. 2 can have a significant impact on the above-described joining process.

[0070] FIG. 2 indicates that the excitation 36 can be for example wave-like and can excite, in particular atomically, materials of the coating 50, at which point reaction radiation 38 is subsequently released by the coating 50.

[0071] FIG. 2 thus shows an example of a detection apparatus in the form of a fluorescence measurement apparatus 40-1.

[0072] In this case, the joining surface 34 or the coating 50 thereof is supplied with electromagnetic radiation, in particular light radiation, the constituents of the coating 50 and/or of the underlying material of the component 32 being excited and then releasing reaction radiation 38 on account of the fluorescence characteristic, which radiation is often in a different wavelength range from the excitation radiation 36.

[0073] In particular, reaction radiation pulses can be released by the coating 50 or the component 32 and can be counted.

[0074] FIG. 3 shows a graph of a count n in relation to a coating density or thickness, measured in g/m.sup.2.

[0075] It can be seen that, as the density or coating thickness of the coating 50 increases on account of the larger number of atoms, which are excited on account of the excitation radiation and shifted into a higher energy state, this results in correspondingly higher counts.

[0076] The graph 56 shown in FIG. 3 can include a corresponding fluorescence curve 58, which can be linear in portions, but which moves into a saturation range, preferably based on the function of a delay element, as the coating strength increases.

[0077] FIG. 3 shows a plurality of measurement points having linear calibration portions on the fluorescence curve 58.

[0078] In order to be able to evaluate current second joining surfaces 34, the joining surface is preferably calibrated with respect to the material of the component 32 and/or the material or the main constituent of the coating 50. This makes it possible to compare current joining surfaces 34 with previously measured reference joining surfaces, on the basis of which the detection apparatus 40-1 has been calibrated, preferably for a plurality of different combinations of the material of the component 32 and a main constituent of the coating 50.

[0079] FIG. 4 is a schematic view of a detection apparatus 40-1 which contains, in a measurement probe or in a probe housing 60, a generator 62 for generating generator radiation 36-1 and a sensor 64 for detecting reaction radiation 38-1.

[0080] The diameter of the measurement probe 60 is indicated in FIG. 4 by D.sub.M1 and is preferably in a range of from 8 mm to 40 mm.

[0081] FIG. 5 shows a comparable embodiment of a detection apparatus 40-2 in the form of a conductivity measurement apparatus.

[0082] Here, a generator 62 for generating an electromagnetic field, in particular an alternating magnetic field, is arranged in a measurement probe 60. In this case, the measurement probe 60 also contains a sensor 64 for detecting a reaction field.

[0083] The material of the component 32 is, in the present case, preferably a non-magnetisable material. Consequently, on account of the alternating magnetic field 36-2, eddy currents i are induced in the material of the component 32, which in turn lead to the reaction field 38-2.

[0084] Detecting the reaction field 38-2 makes it possible to draw conclusions as to the conductivity of the component 32 in the region of the joining surface 34.

[0085] FIG. 6 shows, by way of example, a graph 66 in which the conductivity a (measured in MS/m), a hardness b (measured in Barcol) and a tensile strength c (measured in dN/mm.sup.2) are shown in relation to temperature, namely for an example material of the component 32.

[0086] Certain conclusions can be drawn from such a graph 66, if the conductivity is known, which can for example be detected by the detection apparatus 40-2 from FIG. 5.

[0087] The detection apparatus 40-2 from FIG. 5 is also preferably a calibrated detection apparatus, by means of which the previous, various reference joining surfaces 34 have been detected, the measurement values of which are compared with measurement values of current joining surfaces.

[0088] FIG. 7 shows a further embodiment of a detection apparatus 40-3 in the form of a contact resistance measurement apparatus.

[0089] Here, the detection apparatus 40-3 comprises a contact probe 70, which can be pressed by means of a force F onto the joining surface 34.

[0090] In addition, a potential in the form of a voltage U can be applied at the contact probe 70, which voltage can be adjusted. In the case of reference sign 74, a resistance between the contact probe 70 and the component 32 can be measured.

[0091] In the case of the contact resistance measurement, the contact probe 70 is either pushed gradually towards the joining surface 34 by means of an ever-increasing force, and/or the voltage U is gradually increased.

[0092] The first case results in a graph 76, as shown in FIG. 8. As the force F increases, the resistance R decreases. When a threshold value S is reached (corresponding to a resistance difference AR) it can be seen, for the solid line, that said line relates to a component 32 without or having only minor coatings. The dashed line in FIG. 8 shows the case in which a coating is present on the joining surface 34. As a result, even as the force increases, the resistance R remains largely constant up to a threshold value S, and then decreases abruptly. It can be seen here that a coating having a specific thickness that can depend on the value of S is present on the joining surface 34.

[0093] The corresponding graph 78 in FIG. 9 shows the alternative or additional variant in which the voltage U is increased gradually. In this case, too, the resistance R increases gradually. A resistance difference AR is in turn correlated with a threshold value S. In this case, too, if a coating is present the resistance R remains largely constant up to such a threshold value S, and then decreases rapidly.

[0094] A laser measurement apparatus can also be used to identify the surface condition on the first and/or on the second joining surface upon similar principle than the other measurement apparatus described above. The reaction radiation 38 to an excitation radiation 36 is measured and can be compared to a target figure, thus allowing a diagnostic of the surface condition to determine the correct procedure to be implemented before and/or during the joining step.

[0095] Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.