EP1640081A1 - Joining method and device for driving a joining tool - Google Patents

Abstract

The stamping machine (2) has a stamping tool (16) pushing a rivet against a top sheet (A). The top sheet rests on a bottom sheet (B). The river deforms the sheets and forcing them into a matrix (6). A cylindrical holder piece (22) presses the sheets down against the rim of the matrix. A cylinder (4) contains a first piston (12) with a piston rod pressing down on an intermediate piece and the stamp. There are hydraulic fluid connections (24,26) to chambers (10a) above and (10b) below the first piston. A second piston slides on the piston rod of the first piston and pushes on the holder piece. It has throttle channels (28) allowing hydraulic fluid to flow through it slowly.

Description

The present invention relates to a method and a device for actuating a joining tool for joining at least two plate-shaped workpieces of similar or different materials, in particular for punch riveting or clinching, and a method for operating such a device.

Numerous embodiments of drives for joining tools such as punch riveting and clinching devices are known. The most common drive form consists of a hydraulic cylinder for actuating a punch for the joining operation and a further hydraulic cylinder for actuating a hold-down, which exerts a hold-down force on the workpieces around the joint during the joining operation, see for example WO 93/24258 and EP 0675774. In the Method and the device according to EP 0675774, a "substantial" hold-down force is exerted before and during the joining process, which can be up to 1.5 tons according to the information in this document. In practice, holding-down forces of the order of, for example, 8-10 kN are used. Although this method has its advantages, the use of a large hold-down force before and during the joining process also has its disadvantages. For example, the large hold-down force during the joining process prevents unimpeded deformation of the punch rivet. The use of a large hold-down force before the joining process causes certain disadvantages in the combined stamped rivet bonding method, since the large hold-down force hinders the pressing and flow of the adhesive from the joining zone.

By an obvious prior use of the applicant, it is already known to exert a small hold-down force during the joining process by means of a spring and to increase the hold-down force by the end of the joining process, that the plunger of the hydraulic cylinder transmits a portion of the setting force via a stop connection on the hold-down. A similar arrangement is from the already mentioned EP 0675774 B1, in which a large hold-down force is exerted already before and during the joining process by its own hydraulic cylinder, which then increases towards the end of the riveting operation by a stop connection between the plunger and the hold-down piston according to information in this document at short notice to values up to about 5 tons becomes.

From WO 00/29145 it has already become known to withdraw the punch after the joining operation and, when the punch is retracted, to exert a hold-down force on the workpieces in order to reduce deformations of the plate-shaped workpieces (sheets) out of their plane. For this purpose, this document discloses two basic ways to achieve this. According to one possibility, a retaining device is provided for the hold-down device, which prevents yielding of the hold-down after the joining operation, when the lower leg of the usual in riveting C-frame springs back after returning the punch. According to the other possibility, the punch and the hold-down are simultaneously subjected to a high pressure during the joining operation via a stop connection, and after the joining operation, the punch is slightly retracted, whereupon the hold-down is again subjected to hydraulic pressure to exert a relatively large hold-down force. It is also mentioned in this document that a great or little or no hold-down force can be exerted during the joining process.

Furthermore, it is already known in the prior art to apply at least one small hold-down force before the joining operation in order to press the workpieces against each other before the joining operation and to hold them immovably and in particular to perform a rivet and workpiece control, see for example WO 93/24258.

The present invention has for its object to provide a method for joining and a device for actuating a joining tool for joining at least two plate-shaped workpieces of similar and different materials, which despite great simplicity and compact design offers the possibility to avoid an impairment of the joining process by the hold-down and yet to ensure a high-quality joint with minimal deformation of the workpieces outside the joint.

The method according to the invention is defined in claim 1.

In the method according to the invention, a high punching force is exerted during the joining operation for the joining process and substantially no hold-down force to allow unimpeded deformation of the joining region and simultaneously a high punching force and a high holding force for reducing material deformations of the workpieces and for producing a compacting effect after the joining process exercised in the joining area.

Under joining process is here, as usual, to understand the process between the beginning and end of the required to make the joint connection deformations. In the case of punch riveting, this is the process between the beginning and end of the penetration of the punch rivet into the workpieces to be joined. In the case of clinching, this is the process between the beginning and the end of the deformation of the workpieces into the joining zone.

The hold-down force exerted after the joining operation is to be selected such that bulges of the workpieces around the joint are carried out during the joining process and, furthermore, a certain compression effect is exerted on the workpieces in order to increase the connection quality and to achieve a sufficient final strength of the connection , Important in this context is that at the same time a high punch force is exerted on the joint to prevent the high hold-down force affecting the joint. The entire surface of the joint and of the surrounding workpiece area is thus subjected to high forces after the joining process, whereby, moreover, springback of the C-frame usually provided in such tools is also reduced. Another advantage of the method according to the invention is that the C-frame is lighter than that built in the prior art can be, since during the joining process essentially no hold-down force is applied and the C-frame therefore only has to absorb the punch force.

An embodiment of a device according to the invention is defined in claim 18.

According to the invention, this device has only a single hydraulic cylinder, which is subdivided by the main piston for the punch in a piston rod remote working chamber and in a piston rod side working chamber. The holding-down piston serving to operate the hold-down is disposed in the piston rod-side working chamber of the cylinder, and the portions of the piston-rod-side working chamber located on axially opposite sides of the hold-down piston are interconnected by fluid communication, so that the hold-down piston on its axially opposite sides with that in the piston rod side Working chamber prevailing pressure can be applied.

This structural design of the device makes it possible to carry out the method according to the invention explained above. For this purpose, it is provided in particular that the device has a joining position in which the piston rod facing away from the working chamber is subjected to a pressure for performing the joining process and the piston rod side working chamber is depressurized, and that it has a post-processing position in which both working chambers are subjected to a high pressure , So that after the joining process, a high hold-down force and a high punching force are exerted on the joint and the surrounding workpiece area.

Since thus only a single hydraulic cylinder with only two working chambers are required to operate the punch and the blank, the device comes with only two ports and two hoses, which reduces the design effort accordingly and in particular the hydraulic control is simplified. In addition, the invention allows a compact design of the device, since the main piston and the Hold-down piston in a sense interlock. An increase in stroke therefore has only a simple effect on the device designed according to the invention, whereas in the case of an attachment with two separate hydraulic cylinders, a stroke magnification has a double effect.

Another embodiment of a device according to the invention is defined in claim 19.

In this embodiment, although two hydraulic cylinders are provided. However, since two working chambers of the two cylinders are constantly connected to one another by a flow connection, the same advantages result in part as in the embodiment described above. So only two pressure medium connections are required, which in turn reduces the design effort and simplifies the hydraulic control.

An important advantage of the invention is that the joining process itself is not affected by any hold-down force. When setting punched rivets for example, this leads to the fact that the punch rivet in the workpieces can deform unhindered and informal. This results in a defined forming behavior of the rivet, which leads to a slightly larger bottom of the rivet than the punch riveting with high hold-down force. Cracks in the rivet can be avoided.

The method according to the invention can be used with particular advantage in conjunction with an adhesive method. In a further embodiment of the invention, it is therefore provided that an adhesive layer is provided between the workpieces, at least in the joint area, before the hold-down device is pressed against the workpieces. Since only a small hold-down force and during the joining process substantially no hold-down force are exerted in the inventive method before the joining process, the adhesive can be pressed freely during the joining process and flow out of the joining zone. The absence of a hold-down force during the joining process to a reduction of air bubbles between the workpieces, as will be explained in more detail.

A further reduction of the risk of air bubble formation can be achieved in a further embodiment of the invention in that punch rivets are used, in which the peripheral surface of the rivet shank is divergent, preferably cone-shaped, at least in a predetermined region in the direction of the rivet head. The rivet shank formed in this way exerts a force on the punch-side workpiece during the joining operation, which prevents or at least reduces the spring-back of the punch-side workpiece, so that the workpieces remain in abutment in the joining zone. This also reduces the risk of air bubbles, as will be explained in more detail.

As already mentioned, the invention further reduces spring-back of the usually provided C-frame, whereby the connection quality and final strength of the joint connection are correspondingly improved.

Further advantageous embodiments of the invention are defined in the dependent claims.

• Fig. 1 einen Längsschnitt durch ein Fügewerkzeug in seiner Grundstellung;
• Fig. 2 einen der Fig. 1 entsprechenden Längsschnitt durch das Fügewerkzeug in der Vorbearbeitungsstellung;
• Fig. 3 einen der Fig. 1 entsprechenden Längsschnitt durch das Fügewerkzeug in der Fügestellung und Nach-Bearbeitungsstellung;
• Fig. 4 einen Längsschnitt durch das Fügewerkzeug der Fign. 1 bis 3 mit einer Ventilanordnung für die hydraulische Steuerung des Fügewerkzeuges in seiner Grundstellung;
• Fign. 5 bis 8 der Fig. 4 entsprechende Darstellungen abgewandelter Ausführungsformen des Fügewerkzeuges und der Ventilanordnung.
• Fig. 9 einen in spezieller Weise ausgebildeten Stanzniet zur Verwendung mit dem Verfahren und der Vorrichtung gemäß der Erfindung.

Reference to the drawings, an embodiment of the invention will be explained in more detail. It shows:

• 1 shows a longitudinal section through a joining tool in its basic position.
• FIG. 2 shows a longitudinal section through the joining tool in the pre-machining position corresponding to FIG. 1; FIG.
• 3 shows a longitudinal section corresponding to FIG. 1 through the joining tool in the joining position and post-processing position;
• 4 shows a longitudinal section through the joining tool of FIGS. 1 to 3 with a valve arrangement for the hydraulic control of the joining tool in its basic position;
• FIGS. 5 to 8 of Fig. 4 corresponding representations of modified embodiments of the joining tool and the valve assembly.
• Figure 9 illustrates a specially formed punch rivet for use with the method and apparatus of the invention.

The joining tool 2 shown only schematically in the drawing serves for producing a joint connection between two (or more) plate-shaped workpieces A and B (sheets). In the illustrated embodiment, the joining tool 2 is a riveting tool for setting punch rivets N, although the joining tool 2 and another tool such. b. a device for clinching can be. Since punch rivets and punched rivet joints are basically known, this will not be discussed in detail.

The joining tool 2 comprises an actuating device in the form of a hydraulic cylinder 4 and a die 6, on which the workpieces A, B are supported. The cylinder 4 is supported on a C-frame (not shown), as is common in such joining tools.

The cylinder 4 has a cylindrical inner space 10, in which a main piston 12 with a piston rod 14 is slidably disposed. The piston rod 14 of the main piston 12 is fixedly connected to a punch 16 for setting the rivet N.

As shown in Figs. 1 to 3, the main piston 4 divides the cylindrical inner space 10 into a piston rod-facing upper working chamber 10a and into a piston rod-side lower working chamber 10b. In the lower working chamber 10b, a hold-down piston 18 is arranged, which is fixedly connected via a piston rod 20 with a tubular holding-down device 22. The hold-down piston 18 and its piston rod 20 surround the piston rod 14 of the main piston 12 coaxially and are slidably guided on the cylindrical inner wall of the cylinder 4 so that they are axially displaceable relative to the main piston 12.

The upper working chamber 10a can be pressurized or relieved of pressure via a pressure medium connection 24, optionally with a controlled fluid pressure (hydraulic pressure), while the lower working chamber 10b can also be acted upon or relieved of pressure via its own pressure medium connection 26 with a controlled fluid pressure. As indicated schematically in the figures, the portions of the working chamber 10b located on both sides of the hold-down piston 18 are connected to one another by a flow connection 28 connected, so that the axially opposite sides of the hold-down piston 18 are always acted upon with the same fluid pressure. The flow connection 28 may consist of one or more of the hold-down piston 18 penetrating holes or in other ways, for. B. by one or more longitudinal grooves on the outer periphery of the hold-down piston 18, are formed.

Further, a stopper connection 30 is provided between the piston rod 14 of the main piston 12 and the sleeve-shaped piston rod 20 of the hold-down piston 18, which is effective only in one axial direction, with movements of the main piston 12 in the direction away from the lower working chamber 10b (ie upwards in the figures).

The operation of the device described is as follows:

In Fig. 1, the device is in its normal position, in which the upper working chamber 10 a is held without pressure via the pressure medium connection 24 and the lower working chamber 10 b is acted upon via the pressure medium connection 26 with a relatively small fluid pressure. By prevailing in the lower working chamber 10b fluid pressure of the main piston 12 is pressed into its upper end position. On the hold-down piston 18 acts on its axially opposite sides of the prevailing in the lower working chamber 10b fluid pressure. Since the upper side of the holding-down piston 18 is larger than its underside by the cross-sectional area of the piston rod 20, a downwardly acting pressure difference acts on the hold-down piston 18. By acting between the two piston rods 14 and 20 stop connection 30 of the hold-down piston 18 is, however, held in a basic position in which he occupies the axial middle position shown in FIG.

The machining process for setting the punch rivet N and thus for producing the joint connection takes place in three steps:

In a first step, before the joining operation, the main piston 12 and the hold-down piston 18 are moved to a Vorbearbeitungsstellung in which the hold-down 20 and the rivet N are pressed against the workpieces A and B with a comparatively low force, s. Fig. 2. For this purpose, both working chambers 10a, 10b respectively acted on their pressure medium connection 24 and 26 with a low fluid pressure. Since the upper surface of the main piston 12 is larger than the underside thereof by the cross-sectional area of the piston rod 14, the plunger 8 exerts a corresponding downward punching force on the rivet N. Also, the hold-down piston 18 is pressed down due to the mentioned surface difference by the fluid pressure, so that the hold-down 20 exerts a corresponding hold-down force on the workpieces A, B. The punch force and the hold-down force need only be so large that the workpieces A, B are held immovably in contact with each other and with the die 6 and a rivet and tool control can be performed. The hold-down force is preferably less than 7.8 kN and may for example be of the order of 3 to 5 kN. In general, a hold-down force of less than 3.9 kN is sufficient. The stamping force is preferably less than 5 kN and may be of the order of 1 to 3 kN.

In the second processing step, the joining process, the device assumes the joining position shown in FIG. 3, in which the upper working chamber 10 a is acted upon via the pressure medium connection 24 with the fluid pressure required for the joining process, while the lower working chamber 10 b is depressurized via the pressure medium connection 26 is done. The main piston 12 then exerts via the piston rod 14 and the punch 16 the stamping force required for producing the joint connection on the joint 8 or the rivet N, see FIG. 3. Further, since the lower working chamber 10b is depressurized, the hold-down 20 has the joining process no function. It is understood that in hydraulic systems on the low pressure side there is always a residual pressure, so that the lower working chamber 10b can not be made completely depressurized. However, the resulting holding-down force, which is for example in the order of 0.3 to 0.5 kN, is negligible. Depending on the material of the workpieces used, a hold-down force of, for example, less than 4 kN no measurable influence on the workpiece properties. In any case, this applies to hold-down forces of less than 1.5 kN.

As already mentioned, dispensing with a significant hold-down force has the advantage that the punch rivet N can deform unhindered during the setting process, so that a defined forming behavior of the punch rivet occurs. Compared to a procedure with high hold-down force then comes to a slightly larger bottom of the punch rivet, which reduces the risk of cracking.

The required for setting the punch rivet N stamping force is in a usual order of z. B. 30 to 80 kN.

In the third processing step subsequent to the joining process, in which the apparatus is in a post-processing position likewise illustrated by FIG. 3, both working chambers 10a and 10b are respectively subjected to high fluid pressure via their pressure medium connections 24 and 26. This is expediently carried out such that the high fluid pressure prevailing in the working chamber 10a is maintained, while the working chamber 10b is subjected to the same high fluid pressure or a similarly high fluid pressure via the pressure medium connection 26.

To ensure that the deformation of the punch rivet during the setting process can end without hindrance, the pressurization of the working chamber 10b and thus the structure of the hold-down force is preferably carried out only a short period of time after completion of the setting process. This period of time is for example 0.2 to 0.3 seconds and is preferably greater than 0.1 seconds.

Due to the described pressurization of the working chamber 10a and 10b of the punch 16 is pressed against the rivet N due to the above-mentioned surface difference of the main piston 12 with a high punch force. At the same time, the hold-down 20 is pressed against the workpieces A, B due to the surface difference of the hold-down piston 18 with a large hold-down force. The high hold-down force has the purpose, any Deformations of the workpieces A, B to reduce around the riveting out of its plane and also in this area a certain compression effect on the workpieces A, B exercise to increase their final strength and thereby improve the quality of the connection. Further, since not only the hold-down 20, but also the punch 16 exerts a high force on the joint connection, a certain equalization of the force occurs. Furthermore, by the stamping force and the hold-down force, a return springing of the C-frame (not shown) is prevented or at least reduced.

The punch force and the holding force must be selected depending on the application to achieve these functions. Preferably, the hold-down force is greater than 5 kN and in particular greater than 7.8 kN. The stamping force is preferably greater than 5 kN and in particular greater than 6.5 kN.

The punching force and the holding force are maintained for a predetermined period of time. Subsequently, the device is returned to its basic position shown in Fig. 1 by the upper working chamber 10a is made depressurized via the pressure medium connection 24 and the lower working chamber 10b is acted upon by a low fluid pressure.

Fig. 4 shows schematically a joining tool 2, as described above with reference to FIGS. 1 to 3 has been described in connection with a valve arrangement of a (not shown otherwise) hydraulic control for operating the joining tool. The valve arrangement consists of two separate directional control valves 32 and 34, of which the directional control valve 32 is assigned via the pressure medium connection 24 of the working chamber 10a and the directional control valve 34 via the pressure medium connection 26 of the working chamber 10b, either to pressurize the working chambers 10a and 10b with or from Relieve pressure. The directional control valves 32 and 34 thus control the connection of the working chambers 10a and 10b each with a (not shown) Pressure control device (eg proportional valve) and a pressure relief area of the hydraulic system.

With regard to the operation of the hydraulic control can be applied to the above-described operation with reference to FIGS. 1 to 3 are referred to. In addition, please note:

In the basic position shown in Fig. 5, the directional control valve 32 assumes its pressure relief position, and the directional control valve 34 its pressurization position. In the pre-processing position of the joining tool, both directional valves 32, 34 are in their pressurization position, in which both working chambers 10a, 10b are subjected to a low pressure. In the joining position, the directional control valve 32 is in its pressurization position and the directional control valve 34 is in its pressure relief position in order to exert a high punching force and (essentially) no hold-down force. In the post-processing position, both directional valves 32, 34 are in their pressurization position to exert both a high punch force and a high hold down force.

The embodiment shown in Fig. 5 differs from that of Fig. 4 in terms of structural design of the cylinder assembly of the joining tool, wherein the Fig. 4 corresponding components of FIG. 5 are denoted by the same reference numerals, supplemented by the letter a. The joining tool of Fig. 5 differs from that of Fig. 4 in that instead of a common hydraulic cylinder 4, two cylinders 4a and 5a are provided, of which the cylinder 4a, the main piston 12a for the punch 16a and the cylinder 5a, the hold-down piston 18a for the hold 22a receives. A transverse wall 29 between the cylinders 4a and 4b, together with the hold-down piston 18a, defines a working chamber 31, which in the illustrated embodiment has its own pressure medium connection.

In that regard, the arrangement corresponds to conventional punch riveting tools with separate cylinders for the punch and hold-down. In contrast to the prior art punch riveting tools, however, in the embodiment 5, the piston rod side working chamber of the cylinder 4a and the working chamber 31 of the cylinder 5a by a flow connection 33 constantly connected to each other. The flow connection 33 may, as shown, outside of the cylinder or through the transverse wall 29 extend therethrough.

Due to the permanent connection between the piston rod-side working chamber of the cylinder 4a and the working chamber 31 of the cylinder 5a results in the arrangement of FIG. 5, the same operation as in the arrangement of Fig. 4. Thus, in the case of Fig. 5 satisfy two simple Directional valves 32 and 34 for controlling the pressurization and discharge of the individual working chambers. With regard to the operation of the arrangement of FIG. 5, reference may therefore be made to the description of FIG. 4.

6, the structural design of the joining tool shown there is identical to that of FIG. 5 with the hydraulic cylinders 4a and 5a. The only difference is that instead of the two directional valves (connected in parallel) 32 and 34, a bypass valve 36 and a directional valve 38 , which are connected in series, are provided.

The directional control valve 38 is adjustable between a (shown in FIG. 6) basic position and a working position. In the basic position, the directional control valve 38 blocks two pressure medium lines 37 and 39 with respect to the pressure source and the pressure relief area of the hydraulic system. In the working position, the directional control valve 38 connects the pressure medium line 37 to the pressure source and the pressure medium line 39 to the pressure relief area.

The bypass valve 36 is adjustable between a (shown in FIG. 6) basic position and a bypass position. In the basic position, the bypass valve 36 connects the pressure medium line 37 to the pressure medium connection 24a and the pressure medium line 39 to the pressure medium connection 26a. In the bypass position, the bypass valve 36 connects both pressure medium connections 24a and 26a to the pressure medium line 37.

The operation is as follows: In the basic position, the bypass valve 36 and the directional control valve 38, the positions shown in Fig. 6 a. For the Vorbearbeitungsstellung the joining tool, the directional control valve 38 is moved to its working position, in which it remains for the joining and post-processing position.

In the Vorbearbeitungsstellung of the joining tool, the bypass valve 36 assumes its bypass position, in which it connects the rod rod side and piston rod side working chamber of the cylinder 4 a and the working chamber 31 of the cylinder 5 a via the pressure medium line 37 and the directional control valve 38 with the (controllable) pressure source of the hydraulic system. For the joining position, the bypass valve 36 is moved back into its basic position, in which it now connects the piston rod facing away from the working chamber of the cylinder 4a with the pressure source and the piston rod side working chamber and the working chamber 31 with the pressure relief area. Finally, in the post-processing position, the bypass valve 36 resumes the bypass position in which all the working chambers are connected to the pressure source.

It should be noted that the valve arrangement of FIG. 6 can also be used in a joining tool of FIG. 4.

The joining tool shown in Fig. 7 corresponds in terms of its structural design largely to that shown in Fig. 6, wherein corresponding components with corresponding reference numerals, in which, however, the letter a is replaced by the letter b, are called. Different from Fig. 6, however, is that the flow connection 33 is missing. Rather, the working chamber 31b of the cylinder 5b has a fluid port 27b separate from the fluid ports 24b and 26b which can be pressurized or relieved of pressure via a pressure control valve 40 (e.g., proportional valve). The joining tool with the two cylinders 4b and 5b for actuating the punch and the blank holder therefore corresponds to a conventional joining tool.

The pressure medium connections 24b and 26b of the working chambers of the cylinder 4b are controllable via a bypass valve 36 and a directional control valve 38, which are identical to the corresponding valves of FIG.

In the basic position, the valves assume the basic position shown in FIG. 7. For actuation of the bypass valve 36 and the directional control valve 38 before, during and after the joining process, reference may be made to the description of FIG. 6. The pressure control valve 40 is operated to apply a relatively low pressure to the working chamber 31b in the pre-machining position, to a negligible pressure in the joining position, and to a high pressure in the post-processing position.

The arrangement of FIG. 7 offers the possibility of depressurizing the piston rod-side working chamber of the cylinder 4b in the post-processing position via the bypass valve 36, so that the stamping force exerted by the main piston 12b can be correspondingly increased.

The arrangement shown in Fig. 8 differs from that of Fig. 7 only in that the bypass valve 36 of FIG. 7 has been replaced by a bypass valve 36 b, which in the bypass position, the piston rod facing away and piston rod side working chambers of the cylinder 4 with each other, but they shuts off against the pressure source of the hydraulic system. In the Vorbearbeitungsstellung therefore both working chambers of the cylinder 4b are depressurized, so that no stamping force is generated. In this embodiment, therefore, no rivet detection is possible in the pre-processing position, whereas in all other embodiments, the ram in the pre-processing position exerts a punching force that can be used for rivet detection. Otherwise, the mode of operation of the arrangement of FIG. 8 corresponds to the mode of operation described with regard to FIG. 7.

In the embodiments of FIGS. 1 to 7, incidentally, the first step before the joining process can be performed in two stages in such a way that first the hold-down with the required comparatively low hold-down force is applied and only then the rivet on the stamp with a relatively low punch force is applied to the workpieces. This then makes it possible to depressurize the hold-down already a short period of time before setting the rivet, since the workpieces are pressed together by the attached rivet.

As already mentioned, the riveting method according to the invention can be combined particularly advantageously with the bonding to the hybrid joining technique "punch riveting-bonding". In this hybrid joining technique, an adhesive layer K is provided between the workpieces A and B, see Figs. 1-3:

In the above-described riveting method according to EP 0675774, in which a large hold-down force is exerted already before and during the joining process, the adhesive is enclosed by the hold-down pressure before the joining process within the inner joining zone. During the joining process, therefore, unimpeded pressing and flowing of the adhesive from the joining zone radially outwards is not possible. On the other hand, the large hold down force promotes springback of the punch side workpiece after being punched by the punch rivet. This in turn can lead to the formation of air pockets and channels in the adhesive layer.

In the method according to the invention, however, in which only a relatively small hold-down force and during the joining process substantially no hold-down force is applied before joining, is an unimpeded pressing and flow of the adhesive from the joining zone radially outwardly during the joining process substantially possible. In addition, the absence of a hold-down force during the joining process leads to a reduced springback of the punch-side workpiece A, which also reduces the risk of trapped air and channels in the adhesive layer K.

To further reduce this risk, punch rivets N 'are used in the combined punch rivet bonding as shown in FIG. The punch rivet N 'has in the usual way a rivet head N1 and a rivet N2. In contrast to conventional punch rivets, however, the peripheral surface N3 of the rivet shank N2 is not cylindrical, but slightly divergent in the direction of the rivet head N1. More specifically, the peripheral surface N3 has the shape of a cone with the cone angle α. Therefore, the punch rivet N 'is driven with its conical peripheral surface N3 in the joining parts A, B. (FIG. 3), the rivet shank N2, due to its conicity on the punch-side workpiece A, exerts a downward force which prevents spring-back of the punch-side workpiece A. The workpieces A, B therefore remain in the joining zone in abutment, so that a gap formation between the workpieces A, B and thus the formation of air inclusions and channels are prevented in the adhesive layer K.

The cone angle α must in any case be greater than 0 and is preferably in the range of 0.5 to 10 °, particularly preferably in the range of 1 to 5 °. As illustrated, the entire circumferential surface of the rivet shank N2 may be divergent. However, it is also possible to make the peripheral surface N3 in a foot region cylindrical and divergent only in the region between the foot region and the head N1. The axial length of this foot region is expediently chosen so that it corresponds to the thickness of the punch-side workpiece A.

The use of a stamped rivet N 'formed in this way in conjunction with the stamped rivet adhesive method designed according to the invention permits a particularly effective suppression of a gap formation between the workpieces A, B in the joining region and thus the formation of air bubbles and channels in the adhesive layer K.

Claims (26)

Method for joining at least two plate-shaped workpieces (A, B) of identical or different materials by means of a joining tool, a punch (16) for performing the joining operation at a joint (8) and a hold-down (22) for exerting a hold-down force on the a workpiece (6) supported workpieces (A, B), in which method: during the joining process, a high punching force for the joining operation and substantially no hold-down force are exerted to allow unimpeded deformation of the joining region, and after the joining operation, a high punching force and a high holding-down force are simultaneously exerted for reducing material deformations of the workpieces and for producing a compaction effect in the joining region. Method according to Claim 1, characterized in that the high punching force exerted after the joining operation and the high holding-down force exerted after the setting operation are maintained for a predetermined period of time. A method according to claim 1 or 2, characterized in that the high hold-down force is exercised only a short period of time after completion of the joining operation. Method according to one of the preceding claims, characterized in that the holding force exerted after the joining operation is greater than 5 kN, preferably greater than 7.8 kN. Method according to one of the preceding claims, characterized in that the force exerted after the joining operation stamping force is greater than 5kN, preferably greater than 6.5 kN. Method according to one of the preceding claims, characterized in that before the joining process, the hold-down (22) with a small Force against the workpieces (A, B) is pressed in order to hold the workpieces (A, B) immovably in abutment. A method according to claim 6, characterized in that the applied before the joining process hold-down force is less than 7.8 kN, preferably less than 3.9 kN. Method according to one of claims 1 to 7, characterized in that before the joining process, a small punching force is exerted to perform a check of the joint. A method according to claim 8, characterized in that the force exerted prior to the joining operation stamping force is less than 5.0 kN, preferably less than 2.5 kN. Method according to one of claims 1 to 7, characterized in that no stamping force is exerted before the joining process. Method according to one of the preceding claims, characterized in that between the workpieces (A, B) at least in the joining region, an adhesive layer (K) is provided before the hold-down (22) against the workpieces (A, B) is pressed. Method according to one of claims 1 to 11, characterized in that the joining tool is a setting tool for setting punched rivets (N). Method according to claims 11 and 12, characterized in that punch rivets (N) are used, in which the peripheral surface (N3) of the rivet shank (N2) is divergent at least in a predetermined region in the direction of the rivet head (N1). A method according to claim 13, characterized in that the peripheral surface of the rivet shank (N2) of the punch rivet (N3) used is formed conically in the predetermined area. Method according to one of claims 1 to 11, characterized in that the joining tool is a clinching tool (clinching tool). Method according to one of the preceding claims, characterized in that the punch (16) and the hold-down (22) by a common hydraulic cylinder (4) are actuated. A method according to any one of claims 1 to 15, characterized in that the punch (16) and the blank holder (22) in each case by a separate cylinder (4; 5) are operated. Device for actuating a joining tool for joining at least two plate-shaped workpieces (A, B) made of identical or different materials, comprising: a hydraulic cylinder (4) having a cylindrical interior (10), a main piston (12) with a piston rod (14), which is firmly connected to a punch (16) for the joining operation, wherein the main piston (12) divides the inner space (10) of the cylinder (4) into a piston rod facing away from working chamber (10a) and a piston rod side working chamber (10b), so that the main piston (12) on one side with the in the piston rod remote working chamber (10a ) prevailing pressure and on the axially opposite side with the pressure prevailing in the piston rod-side working chamber (10b) pressure can be acted upon, a holding-down piston (18) having a piston rod (20) which is connected to a holding-down device (22) for exerting a holding-down force on the workpieces (A, B), wherein the hold-down piston (18) with its piston rod (20) coaxially surrounds the piston rod (14) of the main piston (12) and is displaceable relative thereto, and wherein each of the two working chambers (10a, b) via a respective pressure medium connection (24, 26) optionally acted upon with pressure medium or depressurized, characterized in that the holding-down piston (18) is arranged in the piston rod-side working chamber (10b) of the cylinder (4) and the sections of the piston rod-side working chamber (10b) lying on axially opposite sides of the holding-down piston (18) are constantly connected to one another by a flow connection (28), then that the hold-down piston (18) is acted upon on its axially opposite sides by the pressure prevailing in the piston rod-side working chamber (10b). Device for actuating a joining tool for joining at least two plate-shaped workpieces (A, B) made of identical or different materials, comprising: a first hydraulic cylinder (4a) with a main piston (12a) which is fixedly connected to a plunger (16a) for the joining operation via a piston rod (14a) and the interior of the cylinder (4a) into a piston rod side working chamber and a piston rod remote working chamber divided, each of which can be acted upon by pressure medium via a respective pressure medium connection (24a, 26a) or relieved of pressure, a second hydraulic cylinder (5a) with a hold-down piston (18a) which is connected via a piston rod (20a) with a hold-down (22a) for exerting a hold-down force and which limits a working chamber (31), which are selectively pressurized or relieved of pressure can characterized in that the working chamber (31) of the second cylinder (5a) and the piston rod side working chamber of the first cylinder (4a) by a flow connection (33) are permanently interconnected. Apparatus according to claim 18 or 19, characterized in that the piston rod away from the piston rod side and working chamber via a respective directional control valve (32, 34) are selectively acted upon with pressure medium or pressure relieved. Apparatus according to claim 18 or 19, characterized in that the piston rod side and the piston rod away from the working chamber via a common bypass valve (36) and a common directional control valve (38), which are connected in series, optionally acted upon with pressure medium or pressure relieved. Device according to one of claims 18 to 21, characterized in that the main piston (12) and the hold-down piston (18) by a stop acting only in an axial direction (30) are connected to each other, so that the main piston (12) during a movement from a working position into a basic position the hold-down piston (18) entrains in a corresponding basic position. A method of operating a device according to any one of claims 18 to 22, characterized in that in a joining position during the joining operation, the piston rod facing away working chamber (10a) is acted upon by a pressure for performing the joining operation and the piston rod side working chamber (10b) is made substantially depressurized , so that the hold-down (22) substantially no hold-down force exerts. A method according to claim 23, characterized in that in a post-processing position after the joining process, the piston rod facing away and the piston rod side working chamber (10a, 10b) are each subjected to a high pressure, so that the punch (16) and the hold-down (22) after the joining process exert a high force on the joint (8) and the workpieces (A, B). A method according to claim 23 or 24, characterized in that in a Vorbearbeitungsstellung before the joining process, the rod end and piston rod side working chamber (10 a, 10 b) are subjected to a low pressure, so that the punch (16) and the hold-down (22) each have a small Apply force to the joint (8) and the workpieces (A, B). Method according to one of claims 23 to 25, characterized in that in a basic position, the piston rod side working chamber (10b) is acted upon by a low pressure and the piston rod facing away Working chamber (10 a) is made substantially depressurized, so that the main piston (12) is pressed in a serving as a basic position end position.

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