EP1459819A2 - Method and device for determining the degree of crimping of an interlocking connection between at least two components - Google Patents

Abstract

A method and a device for determining the degree of compression of a positive connection between at least two components is described, which can be produced by a cold-forming clinching method, in which the components to be connected are inserted between and through a die and a die which determines the spatial shape of the positive connection relative lowering of the plunger is pressed against the die, the entire positive connection being penetrated by an eddy current field using at least one eddy current sensor, and the measurement signals obtained by means of the eddy current sensor are used to determine the degree of compression of the positive connection.

Description

Technical field

The invention relates to a method and a device for determining the degree of compression of a positive connection between at least two components, which can be produced by means of a cold-forming clinching method, in which the components to be connected between a stamp and a die, which determines the spatial shape of the positive connection introduced and pressed against the die by lowering the punch relatively.

State of the art

DE 199 27 101 A1 describes a method and a device for clinching, in which two flat joining parts are firmly connected to one another by means of a cold-forming clinching process, which is also referred to as clinching. Enforcement joining, for example, in an article by Budde L. et al. "Punch riveting and clinching", the Library of Technology, Vol. 115, Verlag Moderne Industrie, Landsberg / Lech 1995, is characterized in particular by the fact that a form-fitting connection between two overlapping, usually flat-shaped parts to be joined the material to be joined is formed itself.

The cold forming is briefly explained below with reference to FIG. 2. Two generally flat joining parts 1, 2, for example two flat sheet metal parts, are pressed with the aid of a stamp 3 and a die 4 arranged opposite this, the joining parts 1, 2 being locally deformed approximately cylindrical. The stamp 3 has a largely conical stamping mandrel 31 which, when penetrating into the flat joining parts 1, 2 causes a material displacement which, in addition to a positive connection which forms, produces a positive locking effect between the two joining parts 1, 2, which leads to an undercut between the joining partners, the joining process usually being carried out up to a predetermined base thickness. For a qualitative description of the joint connection obtained by the clinching process, the punch stroke, which results from the vertical lowering movement and is referred to as the “X dimension”, is used to determine the bottom thickness of the clinch connection that is being formed. In addition to the X dimension, the so-called "flow dimension" is used for a complete description of the clinch connection, which represents a quantity for the volume of material pushed into the undercut within the joining area.

A clinch connection, as can be seen, for example, in the right part of FIG. 2, can therefore be characterized by two areas, namely the lowered floor area 5, in which, according to the exemplary embodiment, the two parallel sheet metal layers, which can have different wall thicknesses on the die and die side , have a constant base thickness in total, and the area of the so-called undercut 6, in which a mutual interlocking of the two sheets 1 and 2 is formed. The degree or extent of the spatial undercut is ultimately decisive for the strength of the entire clinch connection.

In order to be able to make a statement about the quality and the associated load and durability of such a clinch connection, the wall thickness in the floor area, i.e. determines the bottom thickness of the clinch connection after its manufacture. If one assumes that the volume fraction that is displaced from the floor area into the undercut area in the course of the clinching process is correlated with the floor thickness, then the flow mass can be inferred indirectly on the basis of the X dimension.

To determine the base thickness, the path covered by the stamp (X dimension) is usually manually or during the lowering process measured automatically and when a given punch stroke is reached, a floor thickness that can be achieved is determined. Depending on the spatial shape of the clinch connection specified by the stamp and die shape and the choice of material for the parts of the surface to be joined together, calibration values are determined in advance, on the basis of which actually measured floor thicknesses are correlated with X-dimension values. In addition, it is known, by online recording of the pressing force invested during the joining process, with which the stamp is pressed against the die, to determine location-pressing force diagrams by means of which the achieved joining force can be derived, which, as a further process parameter, provides information about the quality of the clinch connection enables.

Another alternative refined measuring method for determining the quality of a clinch connection is based on the determination of the individual thicknesses of the joining parts by means of the non-destructive ultrasound test method. Such an ultrasound process based on the pulse-echo principle enables differentiated and independent monitoring and measurement of the stamp and die side wall thicknesses of the joint parts within the floor area, which enables more precise statements about the quality of the joint zone and the individual material displacement behavior of the individual joint parts becomes.

DE 198 29 999 C1 describes a method and a measuring device for detecting the correct insertion depth in a pipe press connection using an eddy current device.

US Pat. No. 4,677,379 describes a non-destructive testing technique for crack testing on riveted joints, in which eddy current measurement is also used. The complex AC impedance values are used to evaluate the eddy current signals.

Presentation of the invention

The invention is based on the object of a method and a device for determining the degree of compression of a positive connection between at least two components, which can be produced by means of a cold-forming clinching method in which the components to be connected between a stamp and one which determines the spatial shape of the positive connection The die is introduced and pressed against the die by relative lowering of the punch, in such a way that the entire joining area of the clinch connection can be determined with the simplest and cheapest possible means. In particular, it should be possible to carry out an online control of the entire deformation process during the joining process, so that the clinching process as such can be monitored and regulated in order to ultimately significantly reduce the reject rate of clinch joining connections that are not to be used. With the help of the new type of measurement technology, which should preferably be carried out without contact, the joint area should be recorded as holistically as possible.

The solution to the problem on which the invention is based is specified in claim 1. The subject of claim 10 is a device for determining the degree of compression. Features which advantageously further develop the inventive concept can be found in the subclaims and in the further description, in particular with reference to the exemplary embodiments.

The method according to the preamble of claim 1 for determining the degree of compression of a positive connection between at least two components, which can be produced by means of a cold-forming clinching method and which serves for quality control of the clinch connection, is based in principle on the non-destructive eddy current test. In this case, the entire area of the positive connection is penetrated by an eddy current field by means of at least one eddy current sensor. It is essential that the eddy current field generated and detectable by the eddy current sensor is the positive one Connection penetrated both in the floor area and in the areas of their undercuts. The measurement signals raised in this way with the aid of the eddy current sensor are used to determine the degree of compression of the positive connection, which also serves for quality control of the clinch connection.

Through the targeted application of the known eddy current measurement technology to the special technical case of the quality inspection of joint connections, which can be produced by means of the cold-forming clinching method, a number of advantages over the previously known inspection methods can be mentioned: The use of known eddy current sensors is due to its simple technical structure can be implemented inexpensively. The eddy current sensors, which are mostly small and light in construction, work in contrast to the ultrasonic testing technology used up to now without any contact means or additional contact layers, so that their integration into the joining tools, such as punches or dies, which accomplish the joining process of the respective joining partner can be implemented without further major technical change measures. This makes it possible for the first time to carry out the deformation process in situ, i.e. to monitor during the production of the clinch connection and to generate control variables during the joining process which are capable of influencing the deformation process.

Finally, the eddy current testing technology is able to register material warping between the at least two joining partners that are to be used with one another with a high measurement resolution, whereby even the smallest deviations from an ideal joining process can be determined. This is also done at a very high measuring speed, which is ultimately a prerequisite for process integration during the joining process. Of course, however, it is also possible to examine clinch connections that have already been completed with the aid of at least one eddy current sensor for subsequent quality testing. The quality check can be done manually, by merely approximating one Eddy current sensors can be realized at the joint to be examined, or can also be carried out automatically with the aid of suitable manipulators.

Basically, the eddy current method is a non-destructive material test that is based on the principles of electromagnetic induction. The alternating current sensor essentially has a coil arrangement through which an alternating current flows, which, if it is positioned close enough to the clinch connection to be examined, induces near-surface eddy currents within the electrically conductive material of the clinch connection, which does not necessarily have to be ferromagnetic, the magnetic field of which Eddy current sensor coil acts back. A complex impedance can be assigned to the system, consisting of the coil and the clinch connection to be examined, which can, for example, be displayed on a monitor for visual evaluation. Starting from a clinch connection that is to be assumed to be error-free and ideal, eddy current measurement technology can be used to determine a reference value in the complex impedance plane, which serves as a fixed predetermined operating point. If subsequently clinch connections deviate from the ideal clinch connection, this is reflected in a deflection of the working point in the impedance plane, which serves as error detection or quality control.

In a particularly advantageous variant of the method, the at least one eddy current sensor is operated by means of a multi-frequency method at a number of different AC frequencies. By suitable selection of the different AC frequencies, it is possible to significantly increase the information content of the measurement signals and to significantly improve the measurement reliability and measurement accuracy by using optimized linking algorithms.

In particular when checking clinch connections consisting of ferromagnetic materials, for example made of ferritic steel, the use of an eddy current sensor is suitable together with a device for local Magnetization of the material at the joint of the clinch connection is particularly good. Small permanent magnets, for example, which are arranged with a predetermined polarization around the coil of the eddy current sensor are suitable for this purpose. Thus, the premagnetization can make the material to be examined of the joining partners appear magnetically more transparent, the penetration depth of the eddy currents which can be described by the skin effect being increased within the joining partners to be examined.

For process-integrated detection and ultimately monitoring of the deformation process, a device according to the invention for determining the degree of compression of a positive connection between at least two components, which can be produced by means of a cold-forming clinching method, consisting essentially of a punch and a die, provides at least one eddy current sensor, which in the Stamp and / or is integrated in the die. In this case, the eddy current sensor is designed and arranged in such a way that the eddy current field that can be generated by the eddy current sensor penetrates the entire positive connection, with a control and a measurement signal evaluation unit being connected to the eddy current sensor at the same time.

By arranging the eddy current sensor as spatially as possible relative to the stamp and / or die surface, the coil arrangement of the eddy current sensor being covered with at least one mechanically robust protective layer for the purpose of mechanical protection, which advantageously also represents the stamp and / or die surface direct penetration of the eddy current fields into the joining partners to be deformed guaranteed. In a particularly preferred embodiment, the protective layer covering the eddy current sensor consists of an electrically conductive stainless steel, through which the eddy current fields can pass almost unhindered.

Brief description of the invention

Fig. 1a, b

Messsituationen zur Erfassung des Verformungszustandes einer Clinchverbindung mit Hilfe eines Wirbelstromsensors,

Fig. 2

sequentielle Prinzipdarstellung zur Herstellung einer Clinchverbindung gemäß Stand der Technik,

Fig. 3

schematisierte Darstellung einer Stempel-Matrizen-Anordnung mit Wirbelstromsensor-Überwachung, sowie

Fig. 4

Messprotokoll für die Vermessung einer Clinchverbindung bei drei unterschiedlichen Messfrequenzen.

The invention is described below by way of example without limitation of the general inventive concept using exemplary embodiments with reference to the drawings. Show it:

1a, b

Measuring situations to determine the deformation state of a clinch connection with the help of an eddy current sensor,

Fig. 2

sequential schematic diagram for establishing a clinch connection according to the prior art,

Fig. 3

schematic representation of a stamp-matrix arrangement with eddy current sensor monitoring, and

Fig. 4

Measurement protocol for the measurement of a clinch connection at three different measurement frequencies.

WAYS OF IMPLEMENTING THE INVENTION, INDUSTRIAL APPLICABILITY

1 a and b each show a schematic representation of measurement configurations for determining the quality of a joint connection between two flat components 1 and 2, which were produced by means of a cold-forming clinching process. The components available are made of electrically conductive material such as connections made of aluminum or other materials such as steel.

In the exemplary embodiment according to FIG. 1a, an eddy current sensor 7 is arranged directly below the clinch connection between the two surface components 1 and 2. The eddy current sensor 7, which in the simplest case consists of a coil arrangement which is supplied with an alternating current of a suitable frequency, generates an alternating magnetic field, the magnetic field lines 8 of which penetrate the entire area of the clinch connection. The clinch connection is composed in particular of the base area 5, in which the press stamp deformed surface areas of the surface parts 1 and 2 have a largely constant base thickness, and the areas of the undercuts 6 together.

The particular advantage associated with the use of eddy current sensors relates to the fact that the alternating magnetic fields 8 caused by the alternating currents within the eddy current sensor largely pass through the surface components 1 and 2 without contact, in particular in the area of the joint connection, and in these areas eddy currents within of components 1 and 2 induce. The proportion of material in the surface components 1 and 2 that is fulfilled by the eddy currents is referred to as the interaction volume and is determined by the size of the eddy current sensor 7 and the frequency of the magnetic alternating field 8 that excites the eddy currents strongly influenced by the volume of material in the interaction area, in particular by the type and strength of the material deformations which are formed by the pressing. The AC impedance of the eddy current sensor 7 serves as a measurement signal for the registration of the eddy currents, which can be viewed as an image of the eddy currents that are formed.

The arrangement of the eddy current sensor 7 according to FIG. 1 a covers both the bottom area 5 and the areas of the undercuts at the joint 6. This results in the main advantage of the method according to the invention over the previously known checking methods, especially since the measurement signal emitted by the eddy current sensor 7 contains the information contains a total of the base thickness as well as the areas of the undercuts 6. For the evaluation of the measurement signals, there is therefore direct information available not only for the X dimension, but also about the areas of the undercut, which relate to the flow dimension. It is therefore no longer necessary to conclude on the basis of the measured soil thickness only the degree of deformation (flow) in the area of the undercuts 6 that ultimately determines the strength.

For this reason, the method according to the invention is ultimately distinguished by a higher level of measurement reliability and measurement accuracy, with a more differentiated assessment of the joining quality being possible in the entire volume of the clinch connection.

1 b shows a measurement situation in which the eddy current sensor 7 is arranged on the top of the clinch connection. In this case too, the alternating magnetic fields 8 completely penetrate the area of the clinch connection. This measuring arrangement should be chosen especially in cases where the rear of the clinch connection is not accessible.

The measurement situations shown in FIGS. 1 a and 1 b serve to illustrate a subsequent quality control of already existing clinch connections. If clinch connections are to be checked for their quality already during their manufacture, a stamp-matrix arrangement according to the exemplary embodiment in FIG. 3 is suitable, which corresponds to the stamp-matrix arrangement already described in the introduction to the description with reference to FIG. 2, however is additionally supplemented in the manner shown by an eddy current sensor 7, which is integrated either in the die 4 according to the left image or in the punch mandrel 31 according to the middle image. It is also possible to combine both variants with each other. With the aid of the stamp-die arrangement shown in FIG. 3, it is possible to monitor the deformation process within the flat components 1 and 2 during the production of the clinch connection and, if necessary, to derive control variables in order to have a direct influence on the joining process. A target / actual value comparison between the currently measured impedance values and corresponding reference values is suitable for this in order to obtain controlled variables, for example to change the press force invested or the punch stroke.

It is for evaluating the measurement signals obtained by means of the eddy current sensor, which include comprehensive information about the entire joining area It is necessary to separate the signal components that come from the bottom area 5 from those signal components that come from the areas of the undercuts 6 and to quantify both signal components as “X dimension” and as “flow factor”. This is possible using a multi-frequency test method, in which the eddy current sensor is operated with several different measuring frequencies, preferably separated from one another in time. The measuring frequencies are selected depending on the type of material and the shape of the clinch connection. Signal processing algorithms with a corresponding objective are used in particular for measuring signal evaluation, and regression analysis or the use of neural networks is particularly suitable for this purpose.

To assess the quality of each clinch connection measured, values for the respective X dimension and the flow dimension are used, which are determined using suitable calibration parts. 4 shows measurement results in a diagram, along the abscissa the number of measurements carried out and along the ordinate the X dimension. The first measured value in each case, which is surrounded by a circle, represents the calibration value with which the further measured X dimension values are compared. In the diagram shown in FIG. 4, series of measurements are carried out and shown on three different clinch connections, each with different X dimension values 0.5, 0.6 and 0.7. The greater the deviations from the specified calibration value, the more the quality of the respective clinch connection deviates from an ideal clinch connection (see in particular the three measured value outliers for the X dimension value 0.5 and the single point for 0.6).

LIST OF REFERENCE NUMBERS

1, 2

Flat component

3

stamp

31

stamp Dorn

4

die

5

floor area

6

Joining area, undercut

7

Eddy current sensor

8th

Magnetic alternating field lines

Claims (11)

Method for determining the degree of compression of a positive connection between at least two components, which can be produced by means of a cold-forming clinching method, in which the components to be connected are inserted between a stamp and a die, which determines the spatial shape of the positive connection, and by relatively lowering the stamp against the Die are pressed, the entire positive connection being penetrated by an eddy current field using at least one eddy current sensor, and the measurement signals obtained by means of the eddy current sensor are used to determine the degree of compression of the positive connection. Method according to claim 1,
characterized in that the spatial shape of the interlocking connection is characterized by at least two areas, namely a first spatial area largely compressed according to the stamp cross-section, the so-called floor area, the degree of compression of which is characterized by the distance covered by the stamp during the compression, the so-called X dimension , and a second space area enclosing the first space area, the so-called joining zone, in which the material of each of the two components is forced to flow laterally for the stamp movement and the degree of compression of which is characterized by the laterally displaced material volume, the so-called flow rate,
that the eddy current field penetrates the first and second spatial area, and
that the measurement signals each contain information about the X dimension and the flow dimension, which are separated as measurement results by means of a measurement signal evaluation and represent the degree of compression of the joint connection. Method according to claim 1 or 2,
characterized in that the eddy current measurement is carried out during the production of the positive connection, and
that the measurement signals obtained are used as online control variables for the pressurized lowering of the punch. Method according to one of claims 1 to 3,
characterized in that the eddy current sensor is operated by means of a multi-frequency method at several different AC frequencies. Method according to claim 4,
characterized in that the AC frequency is selected depending on the electrical conductivity of the components in the area of the positive connection. Method according to one of claims 1 to 5,
characterized in that the eddy current field originating from the eddy current sensor is superimposed by a quasi-static magnetic field which pre-magnetizes the components in the region of the positive connection. Method according to one of claims 1 to 6,
characterized in that the measurement signals obtained by means of the eddy current sensor are present as complex AC impedance values, with amplitude and phase or real and imaginary part, and
that the AC impedance values are assigned to at least one predetermined target variable on the basis of a signal processing algorithm. Method according to claim 7,
characterized in that a regression analysis or neural crosslinking is used as the signal processing algorithm. Method according to claim 5 or 8,
characterized in that the assignment of the alternating current impedance values to a specific target value is carried out by referencing with measured values calibrated according to known X dimensions and flow dimensions. Device for determining the degree of compression of a positive connection between at least two components, which can be produced by means of a cold-forming clinching method, in which the components to be connected are introduced between a stamp and a die, which determines the spatial shape of the positive connection, and by relatively lowering the stamp against the Die can be pressed, at least one eddy current sensor being integrated in the punch and / or in the die,
the eddy current sensor is designed and arranged in such a way that the eddy current field that can be generated by the eddy current sensor penetrates the entire positive connection, and a control and a measurement signal evaluation unit are connected to the eddy current sensor. Device according to claim 10,
characterized in that the eddy current sensor is arranged close to the stamp and / or die surface facing the components to be provided or limits it itself.

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