Method and device for press-through joining

Abstract

The invention relates to a method for clinching at least two superimposed joining parts (B1, B2) with a punch (11) in a joining direction (A) into a die (12), comprising the following steps: (a) detecting a force acting between the punch (11) and at least one of the joining parts (B1, B2), (b) detecting a path traveled by the punch (11) along the joining direction (A), (c) generating at least one mapping of the path measurement data to the force measurement data in the form of a first measurement result, (d) determining an initial total thickness (D1) of the joining parts (B1, B2) before the punch (11) penetrates the joining parts (B1, B2), (e) providing a reference force-displacement curve with an upper limit curve (H1) and a lower limit curve (H2). (f) Providing a target value (Z) for the final total thickness of the clinch element,the method further comprises the following steps: (g) creating a normalized reference force-displacement curve with an upper limit curve (H1) and a lower limit curve (H2) from a plurality of force-displacement curves determined for different material thicknesses, (h) transforming the first measurement result into a normalized force-displacement curve, (i) determining whether the normalized force-displacement curve lies outside the limit curves (H1, H2) at at least one point, (j) outputting a first error signal if the normalized force-displacement curve exceeds the upper limit curve (H1) and / or falls below the lower limit curve (H2) at at least one point.

Description

[0001] The invention relates to a method for clinching at least two superimposed parts by pressing the parts with a punch into a die in a joining direction to form a clinch element, wherein the method comprises acquiring force measurement data of a force acting between the punch and at least one of the parts, acquiring displacement measurement data of a path traveled by the punch along the joining direction, assigning the acquired displacement measurement data to the acquired force measurement data in the form of a first measurement result, determining an initial total thickness of the parts before the punch penetrates the parts at a first time point, providing a reference force-displacement curve, wherein the reference force-displacement curve has an upper limit curve and a lower limit curve, and providing a target value for the final total thickness of the clinch element.

[0002] To join two overlapping parts, for example, sheets of metal, by forming, they are placed between a punch and a die. The punch is lowered onto the parts and pressed down, forcing the material into the die, where an anvil can be used to create a die cavity. The initial total thickness of the two overlapping parts is the sum of their individual thicknesses, meaning that the initial total thickness varies from one joining operation to the next.

[0003] A method for joining at least two overlapping sheets with a variable total thickness using a clinching device, in which the penetration depth required for joining the sheets is adjustable, wherein the current total thickness is determined by means of the control system before joining the sheets and the penetration depth is set depending on the total thickness, is known from EP 3 020 489 B1.

[0004] From US patent 2001 / 0002506 A1, a device and a method for mechanically joining metal sheets are known, which are used for the automation of production and have sensors and actuators with which process parameters, for example different sheet thicknesses, can be stored.

[0005] From DE 10 2019 207 885 B3, a method and a device for process monitoring in a mechanical joining process are known, wherein a multitude of measured values ​​are received during the execution of the joining process. The measured values ​​relate at least two process variables to each other. A number of Fourier coefficients are determined from the measured values ​​using a Fourier transform, the number of which is reduced to a two-dimensional subspace. This is intended to enable more precise process monitoring.

[0006] WO 2018 / 178186 A1 concerns a method for producing a forming-joined connection between at least two components, in which an auxiliary joining element and / or a component material of one or more of the components is formed by a continuous force, whereby the applied force and the settling distance are recorded during the setting process. Difference quotients are repeatedly calculated from the difference between successively applied forces and the difference between settling distances and compared with at least one reference value. The setting process is terminated in the range of an increase in process force as soon as the difference quotient reaches or exceeds a predetermined reference value.

[0007] In clinching or press joining of components, individual parameters of the joining process are monitored. Specifically, the force applied by the punch and the punch's displacement are recorded to draw conclusions about the quality of the process. For a specific material pairing with defined material properties and thicknesses, a reference curve is conventionally determined to show what the force-displacement curve should look like as a measurement result, ensuring that the resulting product or clinch element meets the specified quality requirements. A curve envelope is then fitted around this reference curve and stored as a reference value in the control system for process monitoring.If the measured force and displacement values ​​lie outside the envelope curve, a message is issued indicating that the parameter values ​​are outside the specified tolerances; the process may be aborted. This requires that a reference curve and an envelope curve are created and stored for each material pairing and for each punch with a corresponding die for each joining process, and that process monitoring is configured for each material pairing. However, problems arise when working with material pairings whose properties are not defined with sufficient precision or whose material properties are subject to comparatively large fluctuations, which can be the case, for example, with cast materials, especially aluminum castings.The material thickness of castings varies, so a final value, for example for the total thickness of the clinch element after joining, and especially the target bottom thickness, can change for each joining operation.

[0008] The object of the present invention is to provide a method and a device with which a joining process with a high range of fluctuations in input parameters can be monitored for small deviations.

[0009] This problem is solved by a method with the features of the main claim and an apparatus for carrying out the method with the features of the dependent claim. Advantageous embodiments and further developments of the invention are disclosed in the dependent claims, the description, and the figures.

[0010] The method for clinching at least two superimposed parts by pressing the parts with a punch into a die in a joining direction to form a clinch element, wherein the method includes acquiring force measurement data of a force acting between the punch and at least one part, acquiring measurement data of a path traveled by the punch along the joining direction, creating at least one mapping of the acquired path measurement data to the acquired force measurement data in the form of a first measurement result, determining an initial total thickness of the parts before the punch penetrates the parts at a first time point, providing a reference force-displacement curve, wherein the reference force-displacement curve has an upper limit curve and a lower limit curve, and providing a target value for the final total thickness of the clinch element, provides forthat a normalized reference force-displacement curve with an upper limit curve and a lower limit curve is created from a plurality of force-displacement curves determined for different material thicknesses; that the first measurement result is shifted to a normalized force-displacement curve; that it is determined whether the normalized force-displacement curve exceeds the upper limit curve and / or falls below the lower limit curve at at least one point; and that a first error signal is output if the normalized force-displacement curve exceeds the upper limit curve and / or falls below the lower limit curve at at least one point. The creation of the first measurement result from the acquired displacement and force measurement data and their assignment is carried out, in particular, in the form of a force-displacement curve.where this assignment is advantageously carried out by an analysis unit in the form of a computer or a,

[0011] Data processing is performed by the analysis unit. The transformation of the initial measurement curve into a standardized force-displacement curve, specifically its displacement, stretching, compression, or rotation, can also be carried out by the analysis unit. The analysis unit, which is a data processing device (e.g., a microprocessor) with standard components, also determines whether the standardized force-displacement curve deviates from the upper and / or lower limit curves of the standardized reference force-displacement curve. Furthermore, it ensures that an initial error signal is generated. This error signal can be output audibly, visually, and / or tactilely to inform an operator of the deviation.The error signal can also be output in such a way that the process being carried out on a corresponding device is interrupted in order to initiate further measures, for example a check of the joining point or a change in the process parameters.

[0012] First, the total thickness of the overlapping parts is determined before a punch penetrates one or both parts, or when the opposing surfaces of the parts are in contact. This determines the actual material thickness of the pairing, which then forms the basis for the subsequent process. Care is taken to ensure that any gaps between the parts are completely eliminated, meaning that flat parts lie flush against each other. Any adhesive present is partially or completely displaced before the total thickness is determined. During this process, the parts, especially sheet metal, may already be plastically deformed or develop slight indentations. These changes caused by the descending punch are factored out when determining the total thickness, for example...This is achieved by adding compensation factors or allowances based on measured values ​​or empirical data to determine the material thickness. The determined material thickness in the joining area forms the basis for the subsequent process and was recorded by process monitoring. If changes occur in the materials used, particularly the material thickness of the parts being joined, either during the joining process or during a sequence of several joining processes, and if there are large fluctuations in the relationship between the force and displacement measurements, small deviations from the desired target value or the reference force-displacement curve are difficult to detect for the specific process at hand.By creating a standardized reference force-displacement curve with its associated tolerance ranges and transforming, shifting, stretching, and / or rotating the initial measurement result, which is typically a force-displacement curve, into a standardized force-displacement curve, the curves are approximated. While their shape and profile may be fundamentally similar, they could have different slopes or positions on the reference force-displacement curve diagram. Transforming, especially shifting and superimposing, the initial measurement results, assigning them to the standardized force-displacement curve, and comparing them to the standardized reference force-displacement curve prevents misinterpretations. This means that even with a wide range of starting materials, particularly varying sheet thicknesses, only one reference curve is needed for process monitoring. This simplifies machine setup and the manufacturing process.

[0013] In a training course, the initial total thickness of the joining parts is determined at a first time point before the punch penetrates them. A target value for the final total thickness of the clinching element is then provided. A displacement measurement point of the joining parts is determined at a second time point after the punch has been pressed into the die. Subsequently, it is determined whether the displacement measurement point at the second time point deviates from the specified target value for the final total thickness by more than a predefined tolerance value. If such a deviation is detected, a second error signal is issued. Providing a target value for the final total thickness of the clinching element defines a parameter against which the quality of the joint can be assessed.If, after the punch has been pressed into the die, it is determined at a second point in time, particularly towards the end of the punch's joining movement, that a predetermined target value has not been reached and is outside a specified tolerance range, a second error signal can be generated. The manner of output and the consequences of this second error signal can be the same as for deviations from the force-displacement curve. In addition to monitoring deviations during the joining process and controlling the joining procedure, the final result of the joining process is also used to assess the desired quality. The final overall thickness of the clinched element, i.e., the joined component, serves as the basis for this assessment.

[0014] Further training stipulates that at least one, and in particular all, joining parts must contain a metal or a metal alloy, in particular aluminium or aluminium compounds; in particular, a joining part must contain or consist of aluminium casting material.

[0015] The standardized reference force-displacement curve and the standardized force-displacement curve contain, or are supplemented in a further development process, with joining component data, whereby the standardized reference force-displacement curve is provided in a manner appropriate to the joining component data. Joining component data includes, in particular, materials, material thickness, and surface finish, which can have a significant influence on the force-displacement diagram and on the final overall thickness.

[0016] The initial total thickness of the parts to be joined before pressing is determined, for example, by observing the force profile during the movement of the punch in the joining direction. The analysis unit, for instance, determines whether a defined threshold for force increase is present. If there is a gap or clearance between two parts to be joined, a small initial force will be observed during the first contact of the punch with the first part until both parts are in flat contact. As soon as this occurs, the joint deformation of the parts begins, with the aim of the punch moving the material of both parts into the die. This joint deformation causes a significant force increase. If a significant force increase is detected when monitoring the joining movement of the punch in the joining direction, the determined joint part thickness, which is derived from the displacement measurement data at that time and, if applicable, from the subsequent measurement data, is used to calculate the final thickness.The initial total thickness, which can be determined to account for allowances due to minor deformations, is set as the basis for the further procedure.

[0017] To obtain the normalized force-displacement curve of the current joining pair, in one embodiment the first measured value, in the form of the force-displacement curve, is shifted along an abscissa by a first displacement factor, so that, for example, the curve is shifted from a determined force onset point as the starting point. Alternatively or additionally, the first measured value or the force-displacement curve is shifted along an ordinate by a second displacement factor to define a common starting point or a starting point that lies within a tolerance range around a starting point of the normalized reference force-displacement curve. The respective displacement factors along the abscissa and / or ordinate are preferably calculated from the initial total thickness and / or the final total thickness, whereby the respective displacement factors are determined based on empirical data and stored in the process control.The shift factors are calculated in particular by a computer or a data processing unit, for example in an analysis unit, for the respective measured values ​​in the system control.

[0018] In a further development of the method, at least two, and in particular three or more, combinations of components, each consisting of two components, are used as the basis for the reference force-displacement curve. The sum of the individual material thicknesses differs from the material thicknesses of the other material combinations. For each combination of components, force measurement data is recorded for a force acting between a punch and at least one component. Displacement measurement data for the punch along the joining direction are recorded to measure the distance traveled by the punch along the joining direction. The recorded displacement measurement data is correlated with the recorded force measurement data in the form of a first force-displacement curve, and a corresponding curve is generated, in particular by an analysis unit.The initial total thickness of the components being joined is determined before the punch penetrates the components by recording the force increase at a first time point. The final total thickness of the clinching element is then determined at a second time point using the punch. The first force-displacement curve is shifted to a normalized force-displacement curve. An upper limit curve and a lower limit group are assigned to this normalized force-displacement curve to define a tolerance range. In a further step, a target value for the final total thickness of the clinching element is assigned to this reference force-displacement curve. This target value must be achieved to meet the specified quality requirements of the process monitoring.

[0019] The device for clinching at least two components into a clinch element, comprising a punch and a die, a force measuring device for recording the force applied by the punch, and a displacement measuring device for recording the displacement traveled by the punch, and configured to perform the method described above, includes an output device for issuing an error message if the standardized force-displacement curve and / or the final total thickness are outside specified limits. The output device may issue a visual, haptic, and / or audible error message and / or interrupt the operation of the device so that the device can be checked and, if necessary, reconfigured.

[0020] Exemplary embodiments of the invention are explained in more detail below with reference to the figures. The figures show: Figure 1 - a force-displacement diagram for three component pairings; Figure 2 - a schematic representation of a standardization; Figure 3 - normalized force-displacement diagrams; Figure 4 - a schematic representation of the procedure; Figure 5 - a force-displacement curve with a target value range; Figure 6 - a partial view of a clinching device in its initial position in longitudinal section; as well as Figure 7 - a representation according to Figure 6 after the successful insertion of the joint.

[0021] In the Figure 6A schematic longitudinal section shows a device 10 for clinching. A punch 11 is slidably mounted in an upper tool carrier 10.1 in and against the joining direction A. Opposite the upper tool carrier 10.1 is a lower tool carrier 10.2, in which a die 12 with an anvil 12.1 arranged concentrically to the die 12 is located. Both the punch 11 and the anvil 12.1 are coupled to an electronic control unit (not shown) that controls the device 10. For example, drives for the punch 11 and the anvil 12.1 are moved along and against the joining direction A, so that a defined resistance can be applied to the punch 11 during the joining process, or the forming process of the parts being joined can be controlled.Two parts, B1 and B2, are inserted between the die 12 and the punch 11. The punch 11 is in a position where it is already in contact with the upper part, B1. There is a gap between the tool holder 10.1 and the top surface of the die 12, so that the punch 11 is already pressing the two parts, B1 and B2, together. A joining process and a joint forming of the two parts, B1 and B2, have not yet taken place. The punch 11 rests against the top surface, B10, of the upper part, B1, while the die 12 rests against the bottom surface, B20, of the second part, B2. In this position, where the two parts, B1 and B2, are in planar contact, the distance between the punch 11 and the die 12 is equal to the initial total thickness, D1, of the joining pair. The initial total thickness D1 is determined via displacement measurement data, which record the distance traveled by the punch 11 in the direction of the die 12.For example, starting from a fixed distance between punch 11 and die 12 in a neutral position, the distance traveled by punch 11 until a measured, significant increase in force is detected is subtracted to calculate the initial total thickness D1. This increase in force is determined by sensors. The force increase occurs when punch 11 presses the upper joining part B1 flat onto the lower joining part B2, eliminating any play between the two parts. At this point, the joint deformation begins, although punch 11 has not yet penetrated both joining parts B1 and B2. The initial total thickness D1 is determined before each joining operation of the newly inserted joining parts B1 and B2 and serves for process monitoring.

[0022] In the Figure 7The end of the joining process is shown; the punch 11 has moved into its final position, and the anvil 12.1 has also moved downwards in the joining direction A into the lower tool holder 10.2, so that the material of the two joining parts B1, B2 has moved into the cavity within the die. The path that the punch 11 traveled from the state of Figure 6 up to the state according to Figure 7 The distance traveled is called the penetration depth DTi. The difference between the initial total thickness D1 and the penetration depth DTi results in the final total thickness in the bottom area of ​​the clinch joint.

[0023] In the Figure 1The displacement is plotted on the x-axis (abscissa) and the force on the y-axis (ordinate) when joining two parts B1 and B2. The force-displacement curves are exemplary; three curves are shown for material pairings with maximum material thickness K1, nominal material thickness K2, and minimum material thickness K3. The displacement and force measurement curves between the maximum material thickness value K1 and the minimum material thickness value K3 all lie within a tolerance range suitable for manufacturing. A challenge in clinching parts B1 and B2 with varying material thicknesses is that the target values ​​must be dynamically adjusted during the joining process. Particularly when processing castings, material thicknesses can vary considerably from batch to batch, and potentially even within a single component. Therefore, the actual initial total thickness D1 must be determined before each joining process.To ensure sufficient quality, the target base thickness or the final total thickness in the base area of ​​the joint is recalculated each time, depending on the initial material thickness. Both the force applied at the end and the final position of the punch 11 and, if applicable, the anvil 12.1, depend on the current, actual initial total thickness D1 of the material pairing. The process control for the drives of the punch 11 and the anvil 12.1 is designed to exhibit the smallest possible deviations from the specified force-displacement curve, or to remain within the narrowest possible tolerance range of the respective specified curve, i.e., the reference force-displacement curve. The machines or fixtures 10 for clinching exhibit very high accuracy, allowing the process monitoring to be set to a correspondingly sensitive level.If the variations within the material pairings with regard to material thickness are comparatively large, the output parameters with regard to the material pairing fluctuate more than the sensitivity of the process deviation for the force-displacement curve of the machine, so that if only one reference curve is used as a basis, erroneous error messages may occur.

[0024] To make process monitoring less error-prone while still maintaining the highest possible precision, a transformation is performed, which is described in the Figure 2The process is shown schematically. The measured force-displacement curve, as the first measurement, is transformed into a normalized curve using the measured material thickness. Further data can be incorporated into the transformation process, such as the materials used, surface finish, surface treatment, temperatures, or other material properties. A transformation is then performed on these values ​​so that the normalized force-displacement curve F'(x') is calculated from the measured force-displacement group F(x).

[0025] In the Figure 3A large number of such normalized force-displacement curves are shown for different material thickness pairings and, where applicable, different materials. The measured force-displacement curves F(x) were shifted along the abscissa and / or ordinate, whereby the respective shift parameters along the abscissa and ordinate can be determined by prior analysis procedures. The shift parameters depend, for example, on the material thicknesses, the materials used, and the like. As in the Figure 3 As shown, after the actual penetration of the punch 11 into the material begins, which is characterized by the steep increase in force, a similar profile is observed for the respective curves. From this multitude of standardized curves, a reference curve for process monitoring is created in order to set up a device for performing clinching. This process is described in the Figure 4 schematically represented.

[0026] To set up the device, a large number of material pairings are measured during the joining process, and a force-displacement curve is created for each joining operation. Only those curves that meet the quality requirements are used. These curves are normalized and combined into a reference curve for process monitoring. This reference curve forms the basis for process monitoring, ensuring that the values ​​shown in the lower box of the device are maintained during the subsequent production of joined parts. Figure 4The described procedure can proceed as follows. Here, too, both the initial total thickness D1 and the force-displacement curve are measured during joining. The measurement result is normalized and compared with the reference curve of the process monitoring. If it is found that the reference curve or the tolerance range defined around the reference curve has been exceeded, an error message is issued; if applicable, a positive message is issued indicating that no error has occurred. Additionally and alternatively, the final total thickness is used as a quality criterion, with this being displayed as the target value at the end of the force-displacement curve.

[0027] An example of a reference force-displacement curve is in the Figure 5 shown, with an upper limit curve H1 and a lower limit curve H2 as envelopes, which were placed around the individual normalized force-displacement curves, which according to the Figure 3have been shifted as close to each other as possible. Either a single reference force-displacement curve is calculated from these curves as a normalized reference force-displacement curve, or the curves H1 and H2 are arranged around the family of curves. Top right in the Figure 5The final total thickness value is entered as the target value Z, as is the target value for the applied force. As long as the actual force-displacement curves during joining lie within the target range Z, it can be assumed that the joining process requires no correction. However, as soon as the force-displacement curves during joining lie outside the upper limit curve H1 or the lower limit curve H2, and / or the target range Z is not reached, an error message is issued so that the process can be checked and corrected if necessary. Possible errors within the process include, for example, changes in the material, breakage of the punch 11, breakage of the die 12, contaminants present between the parts being joined B1 and B2, or similar issues. The operator then checks the process.

Claims

1. A method for clinching at least two superimposed parts (B1, B2) by pressing the parts (B1, B2) with a punch (11) in a joining direction (A) into a die (12), comprising the following steps: (a) acquiring force measurement data of a force acting between the punch (11) and at least one of the parts (B1, B2), (b) acquiring displacement measurement data of a path traveled by the punch (11) along the joining direction (A), (c) generating at least one mapping of the acquired displacement measurement data to the acquired force measurement data in the form of a first measurement result, (d) determining an initial total thickness (D1) of the parts (B1, B2) before the punch (11) penetrates the parts (B1, B2) at a first time point, (e) providing a reference force-displacement curve, wherein the reference force-displacement curve has an upper limit curve (H1) and a lower limit curve (H2),(f) Providing a target value (Z) for the final total thickness of the clinch element, , characterized by the fact that The procedure further comprises the following steps: (g) creating a normalized reference force-displacement curve with an upper limit curve (H1) and a lower limit curve (H2) from a plurality of force-displacement curves determined for different material thicknesses, (h) transforming the first measurement result into a normalized force-displacement curve, (i) determining whether the normalized force-displacement curve exceeds the upper limit curve (H1) and / or falls below the lower limit curve (H2) at at least one point on the normalized reference force-displacement curve, (j) outputting a first error signal if the normalized force-displacement curve exceeds the upper limit curve (H1) and / or falls below the lower limit curve (H2) at at least one point.

2. Method according to claim 1, characterized by the fact thatThe method further comprises: (a) determining a displacement measurement point of the joining parts (B1, B2) after the punch (11) has been pressed into the die (12) at a second time point, (b) determining whether the displacement measurement point at the second time point deviates from the specified target value (Z) of the final total thickness by more than a specified tolerance value, and (c) outputting a second error signal if such a deviation is detected.

3. Method according to any of the preceding claims, characterized by the fact that at least one, in particular each, of the joining parts (B1, B2) comprises a metal or a metal alloy, in particular aluminium or aluminium compounds, in particular aluminium castings.

4. Method according to any of the preceding claims, characterized by the fact that The normalized reference force-displacement curve and the normalized force-displacement curve contain joining part data, and the normalized reference force-displacement curve is provided to match the joining part data.

5. Method according to any of the preceding claims, characterized by the fact that The initial total thickness of the joining parts (B1, B2) before being pressed by the analysis unit is determined by exceeding a defined threshold of force increase.

6. Method according to any of the preceding claims, characterized by the fact that The transformation is carried out by shifting the first force-displacement curve along an abscissa by a first shift factor and / or along an ordinate by a second shift factor, wherein in particular the first and / or second shift factor is calculated depending on the initial total thickness (D1) and / or final total thickness.

7. Method according to any of the preceding claims, characterized by the fact thatTo create the reference force-displacement curve for at least two joining part combinations where the sum of the individual material thicknesses differs from the material thicknesses of the other joining part combinations, the following steps are performed: i. Acquisition of force measurement data of a force acting between a punch (11) and at least one of the joining parts (B1, B2), ii. Acquisition of displacement measurement data of a path traveled by the punch (11) along the joining direction, iii. Creation of at least one mapping of the acquired displacement measurement data to the acquired force measurement data in the form of a first force-displacement curve, iv. Determination of an initial total thickness of the joining parts (B1, B2) before the punch (11) penetrates the joining parts (B1, B2) by acquiring a force increase at a first time point, v. Determining a final total thickness of the clinch element using the punch (11) at a second time point, vi.Transforming the first force-displacement curve into a normalized force-displacement curve, vii. Assigning an upper limit curve (H1) and a lower limit curve (H2).

8. Method according to claim 7, characterized by the fact that The reference force-displacement curve is assigned a target value (Z) of the final total thickness of the clinching element.

9. Device for clinching at least two joining parts (B1, B2) to form a clinch element, comprising a punch (11) and a die (12), a force measuring device for detecting the force applied by the punch (11) and a displacement measuring device for detecting the distance traveled by the punch (11), which is configured to carry out the method according to one of the preceding claims, and an output device for issuing an error message if the normalized force-displacement curve and / or the final total thickness are outside specified limits.

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