Method for Producing Load-Indicating Connection Components, and Corresponding Load-Indicating Connection Component

Abstract

The disclosure relates to a method for producing load-indicating connection components. A connection element (10) and a piezoelectric ultrasonic transducer (20) are provided and interconnected. The method comprises forming a layer structure on the surface (14) of the connection element (10). The layer structure comprises, in this order, proceeding from the surface (14) of the connection element (10): a first solder layer (16); a reactive layer (30); a second solder layer (22); and the piezoelectric ultrasonic transducer (20). The reactive layer (30) is designed for an exothermic reaction by activation with heat, with electromagnetic radiation or with electric current. Subsequently, the piezoelectric ultrasonic transducer (20) is pressed toward the connection element (10) in order to produce a specified contact pressure, and the reactive layer (30) is activated. The disclosure also relates to a load-indicating connection component of this type.

Claims

1. A method for producing load-indicating connection components (1), wherein a connection element (10), and a piezoelectric ultrasonic transducer (20) are provided and interconnected, the method comprising: a) forming a layer structure on a surface (14) of the connection element (10), which in this order proceeding from the surface (14) of the connection element (10) comprises, a first solder layer (16), a reactive layer (30), a second solder layer (22), and the piezoelectric ultrasonic transducer (20), wherein the reactive layer (30) has a thickness in a range of 10 μm to 100 μm and is adapted for an exothermic reaction by activation with heat, electromagnetic radiation, or electric current; b) pressing the piezoelectric ultrasonic transducer (20) toward the connection element (10) with a specified contact pressure; and c) activating the reactive layer (30).

2. The method according to claim 1, wherein the layer structure is formed by applying the first solder layer (16) onto the surface (14) of the connection element (10) and applying the second solder layer (22) onto the piezoelectric ultrasonic transducer (20), cutting to size a reactive bonding foil that comprises the reactive layer (30), placing the reactive bonding foil onto the first solder layer (16) on the connection element (10), and placing the piezoelectric ultrasonic transducer (20) onto the reactive bonding foil, wherein the second solder layer (22) points toward the reactive bonding foil.

3. The method according to claim 2, wherein the reactive bonding foil is cut to size in such a way that a shape of the reactive bonding foil corresponds to a shape of the piezoelectric ultrasonic transducer (20).

4. The method according to claim 2, wherein the reactive bonding foil is cut to size in such a way that a part of the reactive bonding foil is not covered by the piezoelectric ultrasonic transducer (20) after placing the piezoelectric ultrasonic transducer (20) onto the same.

5. The method according to claim 2, wherein the cutting to size of the reactive bonding foil is effected by means of laser cutting.

6. The method according to claim 1, wherein the layer structure is formed by coating a surface of the piezoelectric ultrasonic transducer (20) with the reactive layer (30) and placing the coated piezoelectric ultrasonic transducer (20) onto the surface (14) of the connection element (10), wherein the reactive layer (30) faces the surface (14) of the connection element (10).

7. The method according to claim 1, wherein the first solder layer (16) or the second solder layer (22) contains at least one adhesion-improving intermediate layer and a main layer comprising a solder material.

8. The method according to claim 1, wherein the specified contact pressure is specified in a range of 0.3 Mpa to 3 MPa.

9. The method according to claim 1, wherein the reactive layer (30) comprises a system of alternating layers, wherein the alternating layers are selected from Ni/Al, Al/Pd, Al/Ti, or Ti/Ni.

10. The method according to claim 1, wherein the surface (14) of the connection element (10) is zinc-plated.

11. The method according to claim 1, wherein the connection element (10) is fabricated from steel, stainless steel, high-alloy steels, special steels, titanium, TiAl6V4, aluminum, nickel, amagnetic steel brass, copper, or an alloy of one of the forgoing.

12. The method according to claim 1, wherein the connection element (10) is a screw having a screw head and the surface (14) of the connection element (10) is a surface of the screw head or a surface at an end of the screw opposite to the screw head.

13. A load-indicating connection component (1) obtained by a method according to claim 1, wherein the load-indicating connection component (1) comprises a connection element (10) and a layer structure arranged on the surface (14) of the connection element (10), comprising in this order proceeding from the surface (14) of the connection element (10) a reacted reactive layer (32) and the piezoelectric ultrasonic transducer (20).

14. A method for producing load-indicating connection components (1), wherein a connection element (10) and a piezoelectric ultrasonic transducer (20) are provided and interconnected, the method comprising: a) forming a layer structure on a surface (14) of the connection element (10), which in this order proceeding from the surface (14) of the connection element (10) comprises, a reactive layer (30), and the piezoelectric ultrasonic transducer (20), wherein the reactive layer (30) has a thickness in a range of 10 μm to 100 μm and is adapted for an exothermic reaction by activation with heat, electromagnetic radiation, or electric current, and wherein the surface (14) of the connection element (10) is configured to perform a function of a first solder layer and a surface of the piezoelectric ultrasonic transducer (20) is configured to perform a function of a second solder layer; b) pressing the piezoelectric ultrasonic transducer (20) toward the connection element (10) with a specified contact pressure; and c) activating the reactive layer (30).

15. The method according to claim 14, further comprising the step of cutting to size a reactive bonding foil that comprises the reactive layer (30), placing the reactive bonding foil onto the surface (14), and placing the piezoelectric ultrasonic transducer (20) onto the reactive bonding foil.

16. The method according to claim 14, wherein the layer structure is formed by coating a surface of the piezoelectric ultrasonic transducer (20) with the reactive layer (30) and placing the coated piezoelectric ultrasonic transducer (20) onto the surface (14) of the connection element (10), wherein the reactive layer (30) faces the surface (14) of the connection element (10).

17. The method according to claim 14, wherein the connection element (10) is fabricated from steel, stainless steel, high-alloy steels, special steels, titanium, TiAl6V4, aluminum, nickel, amagnetic steel brass, copper, or an alloy of one of the forgoing.

18. The method according to claim 14, wherein the connection element (10) is a screw having a screw head and the surface (14) of the connection element (10) is a surface of the screw head or a surface at an end of the screw opposite to the screw head.

19. A method for producing load-indicating connection components (1), wherein a connection element (10) and a piezoelectric ultrasonic transducer (20) are provided and interconnected, the method comprising: a) forming a layer structure on a surface (14) of the connection element (10), the layer structure comprising a first solder layer (16), a reactive layer (30), and the piezoelectric ultrasonic transducer (20), wherein the reactive layer (30) has a thickness in a range of 10 μm to 100 μm and is adapted for an exothermic reaction by activation with heat, electromagnetic radiation, or electric current, and wherein the first solder layer (16) is positioned either between the surface (14) and the reactive layer (30) and a surface of the piezoelectric ultrasonic transducer (20) is configured to perform a function of a second solder layer or between the reactive layer (30) and the piezoelectric ultrasonic transducer (20) and the surface (14) of the connection element (10) is configured to perform a function of the second solder layer; b) pressing the piezoelectric ultrasonic transducer (20) toward the connection element (10) with a specified contact pressure; and c) activating the reactive layer (30).

20. The method according to claim 19, wherein the connection element (10) is fabricated from steel, stainless steel, high-alloy steels, special steels, titanium, TiAl6V4, aluminum, nickel, amagnetic steel brass, copper, or an alloy of one of the forgoing.

21. The method according to claim 19, wherein the connection element (10) is a screw having a screw head and the surface (14) of the connection element (10) is a surface of the screw head or a surface at an end of the screw opposite to the screw head.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0060] Exemplary embodiments of the invention are shown in the drawings and will be explained in detail in the following description, in which:

[0061] FIG. 1 shows the connection of an ultrasonic transducer to a connection element by using a reactive layer system before reacting of the reactive layer system,

[0062] FIG. 2 shows the load-indicating connection component with the connected ultrasonic transducer,

[0063] FIG. 3 shows a schematic view of a pressing device for generating a defined contact pressure, and

[0064] FIG. 4 shows a comparative measurement between a load-indicating connection component according to the invention and two comparative examples.

[0065] In the following description of the exemplary embodiments of the invention like components and elements are designated with the same reference numerals, wherein a repeated description of these components or elements is omitted in individual cases. In the Figures, the subject-matter of the invention is only shown schematically.

[0066] FIG. 1 schematically shows the production of a load-indicating connection component 1. An ultrasonic transducer 20 and a connection element 10 are interconnected by using a reactive layer system 30.

[0067] In the situation shown in FIG. 1, the connection element 10 is a screw. The ultrasonic transducer 20 is to be connected to the surface 14 of the connection element 10 in the region of a screw head 12 of the screw. The connection is to be accomplished by a soldering process. For this purpose, the surface 14 is provided with a first solder layer 16, and a surface of the ultrasonic transducer 20 was provided with a second solder layer 22.

[0068] For example, the surface 14 of the connection element 10 and a surface of the ultrasonic transducer 20 can be provided with a tin coating as a first solder layer 16 and a second solder layer 22 in a simple way by means of the PVD method of sputtering.

[0069] For producing a stable solder connection between the connection element 10 and the ultrasonic transducer 20, the two solder layers 16 and 22 must be melted at least on their surfaces so that they can form a materially bonded (stoffschlüssige) connection. For this purpose a reactive layer 30 is provided, which comprises a reactive layer system of alternating layers. For example, nickel layers and aluminum layers are arranged in alternation. The reactive layer system is configured in such a way that after activation, for example via introduced heat, the thermal energy necessary for the production of the solder connection is released in an exothermic reaction.

[0070] In the layer system formed on the surface 14 of the connection element 10, the reactive layer 30 is arranged between the first solder layer 16 and the second solder layer 22. In the example shown in FIG. 1, the surface of the reactive layer 30 is chosen such that the same corresponds to the surface of the ultrasonic transducer 20, so that the ultrasonic transducer 20 completely covers the reactive layer 30. The total thickness of the reactive layer 30 is chosen such that the reaction of the reactive layer releases enough heat to at least melt the first and second solder layers 16, 22 and materially (stoffschlüssig) connect them to the reactive layer 30. After activation, the reactive layer 30 releases the heat within a short time so that the ultrasonic transducer 20 and the connection element 10 are hardly heated.

[0071] For activation of the reactive layer 30, activation energy must be supplied. In the example outlined in FIG. 1, a laser beam 42 therefor is focused from the side onto the reactive layer 30 by means of a laser 40 and in this way introduces the necessary activation energy at the edge of the reactive layer 30. When the reactive layer 30 is cut to size such that its surface area is greater than that of the ultrasonic transducer 20, the activation energy can also be introduced on the upper side of the reactive layer 30. After activation of the reactive layer 30, the same is heated via an exothermic reaction between the contained alternating layers, wherein the reaction spreads over the entire volume of the reactive layer 30 and melts the reactive layer as well as parts of the adjoining solder layers 16, 22.

[0072] In order for the melted layers to form an intimate connection and for possibly existing surface irregularities to be filled and compensated for by the melted material, it is provided to press the ultrasonic transducer 20 against the connection element 10 with a defined contact pressure during the soldering operation. In the example shown in FIG. 1, the pressing force necessary for generating the defined contact pressure is transmitted to the ultrasonic transducer 20 via a punch 50.

[0073] After cooling, the solder connection between the connection element 10 and the ultrasonic transducer 20 is produced and the punch 50 can be removed. As the reaction taking place in the reactive layer 30 is fast, bonding generally takes less than one second.

[0074] FIG. 2 shows a load-indicating connection component 1 obtained according to the method outlined in FIG. 1. The connection component 1 comprises the connection element 10, which in the present example is designed as a screw, and the ultrasonic transducer 20, which are materially (stoffschlüssig) connected by a solder connection. Between the surface 14 of the connection element 10 and the reacted reactive layer 32, parts of the first solder layer 16 are arranged, which has bonded to the surface 14 of the connection element 10 due to the reaction heat of the reactive layer 30 and has partly fused with the reacted reactive layer 32. Parts of the second solder layer 22 are located between the reacted reactive layer 32 and the ultrasonic transducer 22, wherein parts of the second solder layer 22 are fused with the reacted reactive layer 32.

[0075] FIG. 3 shows a schematic view of a pressing device 60 for generating a defined contact pressure for pressing the ultrasonic transducer 20 against the connection element 10 during the soldering operation.

[0076] The pressing device 60 comprises a base 61 on which the connection element 10 is placed together with the layer system, which is formed on its surface 14 and comprises the reactive layer 30 and the ultrasonic transducer 20. The pressing device 60 furthermore comprises a linear unit 62 for height adjustment. A linear guideway 63 comprising a movable carriage 64 and a stop 65 is mounted on the linear unit 62. A spring pin receptacle 69 with a platform 66 is attached to the carriage 64 of the linear guideway. The movable carriage 64 initially rests on the stop 65.

[0077] The platform 66 serves as a support for movable weights 67. In the example of FIG. 3 a single weight 67 is shown, but it is also possible to use several weights 67 in order to specify the desired pressing force. The spring pin receptacle 69 acts as a holder for a spring pin 68 whose function it is to transmit the pressing force to the ultrasonic transducer 20 as a defined contact pressure. The spring pin 68 therefor is pretensioned into a completely extended position by means of a spring. For transmitting the contact pressure, the spring pin 68 includes a punch 50 that acts as a contact surface at its end facing the ultrasonic transducer 20.

[0078] After placing the connection element 10 together with the layer system, which at least comprises the reactive layer 30 and the ultrasonic transducer 20, the stop 65 is lowered by using the linear unit 62, wherein the components connected to the movable carriage 64 received in the linear guideway 63, namely the spring pin 68, the spring pin receptacle 69, the platform 66, the weights 67, likewise are lowered following the stop 65.

[0079] During lowering, the ultrasonic transducer 20 is contacted via the punch 50 of the spring pin 68. During further lowering, the force exerted on the ultrasonic transducer 20 rises, while the spring pin 68 is increasingly retracted. For example, a spring action of the spring pin 68 can be chosen such that a pressing force in the range of 1 to 3 N up to complete retraction of the spring pin 68 is achieved.

[0080] After complete retraction of the spring pin 68, the spring pin receptacle 69 no longer rests on the stop 65 and moves in its linear guideway 63 relative to the stop 65, when the stop 65 is further lowered by means of the linear unit 62. As a result, the full weight force of the weight 67, the platform 66, the spring pin receptacle 69 and the spring pin 68 is transmitted to the ultrasonic transducer 20.

[0081] The pressing force correspondingly is specified by choosing the mass of the weights 67. The pressing force is transmitted to the ultrasonic transducer via the contact surface of the spring pin 68, wherein the contact pressure is defined by the weight force and the surface area of the ultrasonic transducer 20.

[0082] The size of the punch 50 of the spring pin 68 is to be chosen such that its contact surface as far as possible corresponds to the surface area of the ultrasonic transducer 20 facing the spring pin 68. The pressing device 60 is designed such that spring pin receptacle 69 and spring pin 68 are easy to change in order to ensure a fast adaptation to changing sizes of the ultrasonic transducer.

[0083] FIG. 4 shows a comparative measurement of the ultrasound propagation times for a load-indicating connection component according to the invention, in which the ultrasonic transducer is soldered to the connection element, as compared to two load-indicating connection components as comparative examples in which the ultrasonic transducer according to the prior art has been attached by glueing. The diagram of FIG. 4 represents the measured sound propagation time t for a time-of-flight measurement in dependence on the temperature T of the respective connection component.

[0084] In a time-of-flight measurement by using the ultrasonic transducer, an ultrasonic signal is emitted in the form of a time-limited pulse. The ultrasonic pulse passes through the connection element and is reflected at an end of the connection element. The reflected ultrasonic signal is then measured again as an ultrasonic echo. The sound propagation time t is the period of time that has passed since the emission of the ultrasonic pulse until receipt of the ultrasonic echo.

[0085] The load-indicating connection components used each include identical M12×50 screws made of steel as connection element. On the screw head of the M12×50 screws, ultrasonic transducers each are mounted.

[0086] What is used as an ultrasonic transducer is a piezoceramic having a diameter of 5 mm and a thickness of 0.5 mm.

[0087] In the load-indicating connection component according to the invention, the ultrasonic transducer has been soldered to the screw by using a bonding foil. For this purpose, both the screw head and the piezoceramic were provided with tin solder layers. For this purpose, tin layers having a thickness of 30 μm were deposited on the surfaces by a sputtering method.

[0088] For connecting the ultrasonic transducer to the screw, an Al/Ni bonding foil NanoFoil® having a thickness of 40 μm of the firm Indium Corporation was used, which was cut to size by short-pulse laser cutting to have the diameter of the ultrasonic transducer.

[0089] In both comparative examples, the ultrasonic transducer was glued onto the screws. For the first comparative example, an anaerobic acrylate glue was used, for the second comparative example an epoxy glue.

[0090] FIG. 4 shows the measured propagation times in dependence on the temperature for the three M12×50 screws. A first curve 101 shows the measured sound propagation times for the load-indicating connection component according to the invention. A second curve 102 shows the measurements of the sound propagation times for the first comparative example, and a third curve 103 shows the measurements of the sound propagation times for the second comparative example. For all three curves 101, 102, 103 it can be seen that the measured sound propagation time rises with increasing temperature.

[0091] Starting at −20° C., the propagation times of the screws incrementally increase with each temperature level. Rising the temperature is effected in 20 K steps. Up to the temperature level of 100° C., the curves 101, 102, 103 extend analogously. For the temperature levels 120° C. and 140° C., both glued ultrasonic transducers show signs of failure according to the comparative examples, recognizable by the abrupt upward deflections. The same are caused by the temporary loss of contact of the electrode on the side of the ultrasonic transducer facing the screw head. When users or automated measurement systems do not recognize these problems, this results in faulty measurements. What is likewise problematic, because not always recognizable immediately, are changes in the echo structure of the ultrasonic signals, which are caused by thermal influences or influences of the environment on the glue layer and its aging. These problems also lead to false measurement results. By using ultrasonic transducers applied by means of a bonding foil, said problems can be eliminated.

[0092] Thus, by comparison, the measurements shown in FIG. 4 clearly reveal that in the exemplary embodiment of the invention with a soldered ultrasonic transducer, the ultrasound propagation time can be measured reliably even at higher temperatures above 100° C.

[0093] The invention is not limited to the exemplary embodiments described here and the aspects emphasized therein. Rather, within the range indicated by the claims a multitude of modifications is possible, which lie within the scope of activities of a skilled person.

LIST OF REFERENCE NUMERALS

[0094] 1 load-indicating connection component [0095] connection element [0096] 12 screw head [0097] 14 surface [0098] 16 first solder layer [0099] 20 ultrasonic transducer [0100] 22 second solder layer [0101] 30 reactive layer [0102] 32 reacted reactive layer [0103] 40 laser [0104] 42 laser beam [0105] 50 punch [0106] 60 pressing device [0107] 61 base [0108] 62 linear unit for height adjustment [0109] 63 linear guideway [0110] 64 movable carriage of the linear guideway [0111] 65 stop [0112] 66 platform [0113] 67 weights [0114] 68 spring pin [0115] 69 spring pin receptacle [0116] 101 first curve [0117] 102 second curve [0118] 103 third curve