EP4331742A1 - Method for monitoring a riveting process and riveting device having a process monitoring system - Google Patents

Abstract

The invention relates to a method for monitoring a punch riveting process and a riveting device with process monitoring. This includes a pressure generator, which is connected to a rivet attachment via a quick coupling with a self-closing hydraulic valve. A pressure sensor is arranged in a hydraulic area of the pressure generator, which can be used to determine the force generated by the rivet attachment.

Description

Field of invention

The invention relates to a method for monitoring a riveting process using a hydraulic riveting device with process monitoring. In particular, the invention relates to a hand-held hydraulic riveting device with a pneumatic-hydraulic pressure intensifier.

Background of the invention

It is known to equip riveting devices with a so-called process monitoring device. This is what the disclosure document shows, for example DE 102 48 298 A1 a riveting device in which a force-distance or force-time curve can be used to check whether a riveting process was carried out correctly. In particular, it is known to record a force-displacement or force-time curve and to check whether this curve lies within process windows stored in the process monitoring device.

For example, if the hole made for the rivet is too thick, the force increases more slowly, which is detected by the process monitoring device. In such a case, the process monitoring device can abort the riveting process or at least provide an error message.

With such riveting devices, particularly in loaded structures where failure of the rivet connection can occur would cause a high risk of accidents, such as in the areas of avionics and automotive, should be checked for quality.

The above-mentioned prior art relates to a hand riveting tool in which the handle has a cup-shaped housing for the pneumatic piston and in which a stroke of the pneumatic piston corresponds exactly to a stroke of the hydraulic piston.

The force, which corresponds to the tensile stress, can be measured by means of a force sensor, such as a strain gauge, which is located on the pulling device.

The disclosure document EP 3 360 647 A1 (Inventor Klaus Reitzig) shows a riveting device in which a pneumatic-hydraulic pressure generator is connected to a riveting attachment. The riveting attachment includes a working piston for a drawing or pressing tool, in particular a blind riveting device or a riveting bracket.

A modular system can thus be provided in which the pressure generator can be used for different types of pressing and drawing tools.

The integration of the process monitoring known from the prior art mentioned above would also be possible in such a tool system. However, this would require that each individual rivet attachment would have to be equipped with a force sensor and the corresponding connections. This is not only complex, but also disadvantageous in that there is a greater risk of the electronic parts attached to the rivet attachment being damaged when the tool is used.

Task of the invention

The invention is based on the object of providing an improved method for process monitoring of a riveting process and a riveting device designed for this purpose.

Summary of the invention

The object of the invention is already achieved by a riveting device with process monitoring and by a method for monitoring a riveting process according to one of the independent claims.

Preferred exemplary embodiments and further developments of the invention can be found in the subject matter of the dependent claims, the description and the drawings.

According to a first aspect of the disclosure, the invention relates to a riveting device with process monitoring.

A riveting device refers in particular to devices for setting punch rivets, blind rivets, rivet nuts, etc. Such a riveting device includes, for example in the case of a blind riveting device, a pulling device by means of which the rivet pin is pulled until it tears off. There are also rivet brackets that either have a die for forming the rivet on the side opposite the pressing device or are processed from both sides by means of the two-part rivet.

The riveting device includes a pressure generator.

The pressure generator is designed in particular as a pneumatic-hydraulic pressure generator. There will be one Pneumatic piston moves oscillating and hydraulic fluid is conveyed via a suction and pump valve during the setting process. This means that high pressures can be generated even with a compact device.

The pressure generator is connected to a rivet attachment via a quick coupling.

The quick coupling can have a self-closing hydraulic valve. This means that hydraulic fluid can be pumped from the pressure generator into the rivet attachment.

Alternatively, the quick coupling can include a mechanical interface, e.g. with displaceable pistons, via which the force generated by the pressure generator is transmitted to the rivet attachment.

The rivet attachment is the actual riveting tool and includes the working piston through which the pulling or pressing device is moved. The fluid moved by the pressure generator flows into the working piston during the setting process and can flow back after the work process has ended.

The system according to the invention is modular in such a way that various rivet attachments, for example blind rivet attachments, rivet brackets, etc., can be connected to the pressure generator via the quick coupling with the self-closing hydraulic valve.

The coupling can in particular be designed as a ball coupling. A reliable mechanical connection is created via the ball coupling.

It goes without saying that the rivet attachment is provided with a corresponding coupling piece, which can be connected to the quick coupling.

The quick coupling can preferably be operated without tools and can in particular be designed as a rotating or sliding sleeve.

According to the invention, a pressure sensor is arranged in a hydraulic area of the pressure intensifier, via which the force generated by the rivet attachment can be determined.

In order to determine the force directly or indirectly, the pressure within the hydraulic range of the pressure intensifier is used according to the invention.

It has been found that the tensile or pressing force generated by the riveting device can be reliably determined by measuring the pneumatic pressure in the pressure intensifier.

A setting process can be evaluated using corresponding values of a force/time or force/distance curve that can be determined in this way.

In the process monitoring, tolerance ranges within which the setting process must lie are stored specifically for the respective rivet and the respective rivet attachment.

If in the sense of the invention we are talking about a force-distance or force-time curve, it goes without saying that the pressure can also be used directly as a measurement variable in order to evaluate the setting process, since this is quite reliably linked to the tensile force. or pressing force is correlated.

Measuring the pressure is relatively easy to implement using a sensor and does not require a force transducer on the rivet attachment itself.

In a further development of the invention, the pressure sensor is arranged on an intermediate piece which is detachably connected to a main housing of the pressure generator.

The use of an intermediate piece also enables the corresponding riveting devices to be easily retrofitted with process monitoring.

All you have to do is remove the quick coupling and attach the intermediate piece to the main housing instead of the quick coupling.

The quick coupling can now be connected to the intermediate piece.

Since it only has to accommodate the quick coupling, the intermediate piece can be designed to be compact, in particular having a length of less than 5 cm.

The intermediate piece can in particular be connected to the main housing and to the quick coupling by means of a screw connection.

The pressure sensor is preferably designed as an absolute pressure sensor. Silicon, quartz or a metal is preferably used as the sensor material. In particular, the sensor can comprise a piazoelectric sensor, in particular made of zinc oxide or aluminum nitride. Alternatively, it can be a pressure sensor with a strain gauge.

The pressure sensor is preferably firmly connected to the intermediate piece, in particular screwed into the intermediate piece.

Preferably, the process monitoring uses at least two, preferably three time windows to check whether the force exerted by the rivet attachment is within a stored tolerance range.

In particular, a window can be in the elastic range in which the force is essentially linear and in which Hooke's law applies.

Another time window can be in the plastic region, in which the rivet begins to deform.

Finally, a third window can be located in the so-called flow area, in which the material flows in such a way that the curve flattens out again until, as with a blind rivet, the tear-off force is reached or, when using a rivet bar, the maximum force is reached.

The pressure sensor preferably has a measuring range of up to at least 500 bar, preferably up to at least 800 bar.

The riveting tool is designed in particular as a hand-held riveting tool.

According to one embodiment of the invention, the operating lever of the riveting device is arranged on the housing of the pressure generator.

In this embodiment of the invention, the pressure generator is carried by hand and also serves as an actuator.

In another embodiment of the invention, the pressure generator can also be arranged stationary and connected via a hydraulic line to a handle, which includes the actuator and the quick coupling for the rivet attachment.

The invention further relates to a method for monitoring a riveting process, wherein in particular a riveting device according to an embodiment described above can be used.

The procedure is used to monitor the setting of a punch rivet. Self-piercing rivets are used in particular to connect sheet metal pairs in car bodies. These have the advantage that no hole has to be drilled before the rivet is processed. In particular, the rivet punches out the required opening in the hole pairing itself.

In particular, the punch rivet is designed as a semi-hollow rivet. Such a semi-hollow punch rivet punches a hole in at least a first sheet metal layer, with the material of the punched hole flowing into the cavity of the rivet and forming a so-called slug there.

The closing head that forms on the opposite side is formed by the collar of the rivet being deformed by the die of the setting tool. Particularly in the case of semi-hollow punch rivets, it is intended that the lowest sheet metal layer is not punched through, but rather is formed into part of the closing head. When setting the rivet, a force-displacement and/or force-time curve is measured. In general, a setting process can be evaluated by measuring the force curve of the setting, checking whether the force curve corresponds to an empirically determined or calculated force curve (plus a tolerance window). For example, the force can be plotted against time. This is particularly simple because no force transducer, such as a strain gauge or piezo sensor, is required on the setting tool.

In the case of the riveting device mentioned above, which works as a pneumatic-hydraulic pump, the pump frequency can also be fixed depending on the design. This means that the pump frequency does not decrease or does not decrease significantly as the force increases.

A riveting tool is therefore preferably used in which the setting time is proportional to the distance traveled. This makes a particularly simple evaluation possible.

Alternatively, it is also possible to equip the setting tool with a displacement sensor. According to the invention, a first force-displacement and/or force-time window is defined empirically or by calculation and it is checked whether the force lies within the predetermined tolerance range within a predetermined time interval.

In particular, the time is measured from which the minimum setting force in the first window is reached, which elapses until a maximum force is reached which exceeds the maximum force of the first window.

The force-distance and/or force-time window measures whether the force F lies between a minimum force Fmin and a maximum force Fmax during a period t. If t is in a target range between tmin and tmax, the riveting process is OK while passing through the first window.

In this regard, the invention is based on the knowledge that with a punch rivet, in particular with a punched semi-hollow rivet, the force initially increases when the rivet punches into the sheet metal pairing. However, due to the flow of the material and/or the punching through of a first sheet metal layer, the force then drops again and then increases again to a maximum value at which the closing head is formed.

It has been shown that an evaluation of this first time window is particularly important when processing self-piercing rivets.

It is then checked in a second force-displacement and/or force-time window in which a closing head is formed whether the second force-displacement and/or force-time window lies within a predetermined tolerance range.

The second window also checks whether a force within a predetermined tolerance range is achieved over a predetermined period of time.

For example, if a punch rivet is processed that is defective on the closing head side, the force can increase dramatically. If, for example, an unsuitable die is used, which has a cavity that is too large, the force at the end of the setting process increases too slowly or the specified maximum force is not even reached.

In a further development of the invention, a third force-displacement and/or force-time window is provided, which overlaps the first and second force-displacement and/or force-time windows. The third window can in particular include the entire setting process from the start of punching to the formation of a closing head.

It is understood that in the third window the range between Fmin and Fmax is higher than in the first and second windows. The third measuring window begins in particular when the minimum force Fmin for the first measuring window is reached and ends when the maximum force Fmax is reached at the end of the setting process, i.e. when the closing head has formed.

This time interval must also match the respective setting process, which means that further possible errors in the setting process can be detected.

If the setting process is not carried out in one of the three measuring windows, the riveting tool can generate an error message.

Furthermore, the setting process can in particular be aborted before it is completed, especially if the first measuring window is not within the specified tolerance range.

As already mentioned at the beginning, the force-displacement or force-time windows can be determined empirically. A series of tests is carried out with a specific sheet pairing and a specific rivet and the tolerance range for the measuring windows is determined based on the test series.

Alternatively or in combination, such force-path and/or force-time curves can also be calculated, in particular based on the types of sheet metal used. The sheets can, for example, be divided into different groups, for example steel, aluminum and also a division based on strength. The method is preferably carried out in such a way that a program is executed on the riveting device.

In a first step, the user can enter the sheet metal pairing used into the device.

It goes without saying that, depending on the sheet metal pairing, an appropriately adapted rivet must be used. Particularly with semi-hollow punch rivets, the rivet must match the thickness of the sheet metal pairing used with a high degree of accuracy.

Suggestions for suitable rivets can already be stored in the device's memory from which the user can choose.

The rivet used can be entered manually. It is also conceivable to read the rivet used automatically, for example via a barcode or an RFID chip on the packaging from which the rivet is removed.

If the rivet is not suitable for use with the entered sheet metal pairing, the riveter will generate a corresponding message and inform the user that the use of this rivet is not permitted.

Information regarding the matrix to be used can also be stored on the device. For example, the display of the riveting device can show which die must be used for the selected rivet.

Based on the sheet metal pairing and rivet, the force-displacement and/or force-time windows are generated for the measurement process to be carried out. As explained above, these can be stored directly on the device as an empirically generated data set. The riveting tool can also do one Include an algorithm that calculates the force-distance and/or force-time window based on the respective sheet metal pairing and respective rivet.

The invention further relates to a riveting device which is designed to carry out the method described above.

The riveting device includes a memory and a processor. The memory contains data sets relating to the force-time and/or force-distance windows and/or an algorithm to calculate these. The riveting device can also include a display. This can in particular be designed as a touch screen.

Brief description of the drawings

• Fig. 1 ist eine Seitenansicht eines Ausführungsbeispiels eines Druckerzeugers.
• Fig. 2 ist eine Seitenansicht eines Ausführungsbeispiels eines Nietaufsatzes.
• Fig. 3 ist eine schematische Darstellung eines gesetztes Stanzhalbhohlniets.
• Fig. 4 zeigt schematisch einen typischen Kraft-Zeit-Verlauf.
• Fig. 5 ist ein Flussdiagramm eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens.

The invention will be described below with reference to an exemplary embodiment based on the drawings Fig. 1 to 4 be explained in more detail.

• Fig. 1 is a side view of an embodiment of a pressure generator.
• Fig. 2 is a side view of an embodiment of a rivet attachment.
• Fig. 3 is a schematic representation of a set semi-hollow rivet.
• Fig. 4 shows schematically a typical force-time curve.
• Fig. 5 is a flowchart of an exemplary embodiment of a method according to the invention.

Detailed description of the drawings

Fig. 1 shows a side view of an exemplary embodiment of a pressure generator 1, which in combination with the in Fig. 2 rivet attachment 30 shown can be coupled to a riveting device.

The pressure generator 1 includes a main housing 2 with a pneumatic connection 3.

In the main housing there is an oscillating pneumatic piston, which drives a hydraulic piston. The pressure generator is therefore designed as a pneumatic-hydraulic pump, in particular essentially as described in the EP 3 360 647 A1 is described.

In this exemplary embodiment, the entire pressure generator 1 is carried by hand.

In another exemplary embodiment, not shown here, the pressure generator is arranged in a stationary manner and is connected to a handle by means of a hydraulic hose.

The pressure generator 1 includes a quick coupling 5.

The quick coupling 5 is designed as a ball coupling and includes an integrated self-closing hydraulic valve.

The quick coupling 5 can be designed, for example, as a sliding sleeve.

The sleeve of the quick coupling 5 is pulled from the position shown here in the proximal direction in order to be able to uncouple the rivet attachment.

Between the main housing 2 and the quick coupling 5 there is an intermediate piece 10, which is intended for process monitoring.

The intermediate piece is screwed to the main housing 2.

In turn, the intermediate piece 10 includes a thread, in particular an internal thread, for the quick coupling 5 with the self-closing hydraulic valve.

The intermediate piece essentially extends the channel for hydraulic fluid leading to the quick coupling 5.

This axial channel 11 is shown schematically as a dashed line.

A channel 12 extends from the channel 11 in the radial direction to the pressure sensor 22.

In this exemplary embodiment, the channel 12 initially runs radially outwards and is then angled in the proximal direction.

This has the advantage that the pressure sensor 20 can be arranged approximately parallel to the main housing 2.

The pressure sensor can in particular be located in an arm 13, which is angled laterally in the proximal direction.

This arrangement is compact and protects the pressure sensor 20 from damage.

In this exemplary embodiment, the pressure sensor 20 is designed as a screw sensor and includes a thread 21 which is screwed into the intermediate piece 10.

The pressure sensor 20 also includes an output 22 in which the signal from the pressure sensor 20 can be picked up and forwarded to an external unit.

Instead of such an electrical connection 22, in an exemplary embodiment not shown here, a pressure sensor can also be used, which communicates with a process monitoring device via a wireless communication device.

The actual process monitoring device, which preferably includes a screen, is not shown here. However, such process monitoring devices are known and can in particular also be designed as a mobile device.

The corresponding parameters for the various rivets are stored within the process monitoring device.

If a setting process is not within the stored target values, the process monitoring device can output a corresponding signal (optical or acoustic) and/or display an error message.

Fig. 2 shows a side view of an exemplary embodiment of a rivet attachment 30.

The rivet attachment 30 is designed as a blind rivet attachment.

This comprises a coupling 31, which also has a self-closing hydraulic valve and which comprises a groove in which the balls of the quick coupling of the pressure generator engage in the assembled state.

The rivet attachment further comprises a housing 32 in which the working space of a hydraulic piston is located, via which the pulling device of the blind rivet attachment is operated.

The sockets for gripping the rivet pin are located in a conventional manner in a head piece 33 connected to the housing 32.

In this exemplary embodiment, the housing 32 can be pivoted via a pivot bearing 34. The pivot bearing includes a rotary feedthrough for hydraulic fluid.

This means that even hard-to-reach places can be reached in a simplified manner.

Fig. 3 shows a schematic sectional view of an already processed semi-hollow punch rivet, with respect to which the method according to the invention is used to evaluate the setting process.

The punching semi-hollow rivet 40 comprises an annular section which punches through the sheet metal and which forms a closing head 43 at the end of the setting process.

As shown in the illustration Fig. 3 To recognize, the semi-hollow punch rivet 40 completely punches through a first layer 41 of the sheet. A slug 44 is formed, which is arranged in the cavity of the hollow punch rivet 40 at the end of the setting process.

In this exemplary embodiment, the closing head is formed by the material of the rivet 40, by the slug 44 and by the formed sheet metal of the lower sheet metal layer 42.

Fig. 4 shows a schematic graphic of the time-force curve when setting the rivet.

The time is plotted dimensionlessly on the x-axis and the force is plotted dimensionally on the y-axis.

Due to the system, the force curve during the setting process is plotted from right to left in this representation.

Starting from the right, the setting process ends with a maximum force at which the closing head is formed. The maximum force is preferably adjustable on the riveting device and is adjusted depending on the rivet and sheet metal pairing.

Starting from the right, the force initially increases when the punch rivet hits the sheet metal pairing and begins to punch the sheet metal.

With a self-piercing rivet, in particular with a self-piercing semi-hollow rivet, the force then drops again within the first force window, especially when the first sheet metal layer is punched through.

It has been found that the time t1 within which the force lies in the first force window is crucial for evaluating the setting process of a semi-hollow punch rivet. A minimum time and a maximum time are defined for t1 (and also t2 and t3, not shown).

If t1 is not within a specified time interval, for example if the maximum force of the first window is exceeded early, the setting process is assessed as incorrect.

A region of plastic, approximately linear deformation then occurs until the second, upper force window is reached, within which the closing head is formed.

At the end of the setting process, the increase in force relative to time (or distance) decreases as material now flows into the die in which the closing head is formed. When a defined maximum force is reached, the setting process is ended.

The second force window defines a time interval t2 within which the closing head is formed. So t2 must also be within a specified interval.

For example, if an incorrect die is used in which the cavity is too large for the closing head, the force in the second force window increases too slowly.

The invention further defines a third window, which is characterized here as a distance-time window.

The third window is defined by time t3. This is the time period from reaching the minimum force of the first force window to reaching the specified maximum force Fmax at the end of the setting process.

t3 must also be within a specified range. Due to tolerances, the maximum force of the second and third windows is greater than force Fmax at the end of the setting process.

t2 and t3 can be measured either until the force Fmax is reached, or until the riveting tool ends the setting process with a slight delay when the force Fmax is reached.

The flowchart according to Fig. 5 shows schematically how the riveting device in Fig. 4 The evaluation of the setting process shown is started by the user. The user first enters a sheet pairing, in particular the thickness and type of sheets to be riveted.

A rivet is then either entered manually or read by the device.

If the rivet is not suitable, an error message is generated informing the user.

If the rivet is suitable, a data set with the first, second and third force windows is generated or read in from an empirically determined data set.

This data set corresponds to the representation Fig. 4 .

The setting process is then carried out, with an automated check being made as to whether the settings are in accordance with Fig. 4 specified value ranges for t1, t2 and t3 are adhered to in the respective window.

If this is the case, the setting process is evaluated positively, e.g. by showing on the display of the riveting tool that the setting process is OK.

If this is not the case, this will also be indicated by the riveting device.

The riveting device can include a memory in which the values of each individual setting process are stored. So can The quality of each individual setting process is documented as part of quality assurance.

The invention made it possible to reliably monitor the process even with riveting devices with a separate pressure generator.

Reference symbol list

1

pressure generator

2

Main body

3

Pneumatic connection

4

Actuator

5

Quick coupling

10

Intermediate piece

11

axial channel

12

Channel to the pressure sensor

13

boom

20

Pressure sensor

21

thread

22

Connection

30

Rivet attachment

31

coupling

32

Housing for the working piston of the rivet attachment

33

Headpiece

34

Pivot bearing

40

Semi-hollow rivet

41

1. Location

42

2. Location

43

Closing head

44

Slugs

Claims (15)

Method for monitoring a riveting process, wherein when setting a punch rivet, in particular a semi-hollow rivet, a force-distance and/or force-time curve is measured, characterized in that the force-distance and/or force-time curve in at least a first force-displacement and/or force-time window in which the rivet punches a sheet metal pairing, it is checked whether the first force-displacement and/or force-time window lies within a predetermined tolerance range,
and that in a second force-displacement and/or force-time window, in which a closing head is formed, it is checked whether the second force-displacement and/or force-time window lies within a predetermined tolerance range. Method according to the preceding claim, characterized in that in a third force-displacement and/or force-time window, which overlaps the first and second force-displacement and/or force-time windows, it is checked whether this is within a specified tolerance range. Method according to the preceding claim, characterized in that the third force-distance and/or force-time window begins when a minimum force of the first window is reached and ends when a predetermined maximum force is reached. Method according to one of the preceding claims, characterized in that the first, second and / or third force-path and / or force-time window is assigned a time t1, t2 and / or t3, the setting process being as is evaluated incorrectly if t1, t2 or t3 is not within a specified tolerance range. Riveting device comprising a memory and a processor, the riveting device being designed to carry out a method according to one of the preceding claims. Riveting device with process monitoring, in particular according to the preceding claim, comprising a pressure generator, which is connected to a rivet attachment via a quick coupling, a pressure sensor being arranged in a hydraulic area of the pressure generator, via which the force generated by the rivet attachment can be deduced. Riveting device according to the preceding claim, characterized in that the pressure sensor is arranged on an intermediate piece which is detachably connected to a main housing of the pressure generator. Riveting tool according to one of the preceding claims, characterized in that the quick coupling comprises a self-closing hydraulic valve. Riveting tool according to one of the preceding claims, characterized in that the quick coupling is arranged on the intermediate piece, in particular is releasably connected to the intermediate piece. Riveting device according to one of the preceding claims, characterized in that the process monitoring uses a pressure-time curve to check whether a riveting process is within a stored tolerance range. Riveting device according to the preceding claim, characterized in that the process monitoring uses at least two, preferably three time windows to check whether the force exerted by the riveting attachment is within a stored range. Riveting tool according to one of the preceding claims, characterized in that the pressure sensor is screwed into the housing, in particular the intermediate piece, from the outside. Riveting tool according to one of the preceding claims, characterized in that the pressure sensor has a measuring range of up to at least 500 bar, preferably up to at least 800 bar. Riveting device according to one of the preceding claims, characterized in that the pressure generator is designed as a pneumatic-hydraulic pump, with a pneumatic piston being moved in an oscillating manner, which drives a hydraulic piston, which in turn pumps hydraulic fluid into the riveting attachment via a pressure and suction valve. Riveting tool according to one of the preceding claims, characterized in that the riveting tool is designed as a hand-held riveting tool,
and/or that the intermediate piece has an axially extending fluid channel, from which a channel extends transversely, in particular vertically, which leads to the pressure sensor.

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