DE102017219011B4 - Processing device - Google Patents

Abstract

Device for machining workpieces (10), in particular welding tongs, comprising two opposing holding brackets (13), two opposing joining tools (14), in particular in the form of welding electrodes, being arranged on the holding brackets (13), and the opposing joining tools (14) can be moved and / or driven relative to one another for machining workpieces, an area with tensile stresses (11) and an area with compressive stresses (12) occurring in the device (10) during workpiece machining, characterized in that the holding brackets ( 13) each have two biasing elements (20), a first biasing element (20) being designed as a compressive stress element and being arranged in the region of the holding bracket (13) in which compressive stresses occur during workpiece machining, and a second biasing element (20) as a tensile stress element executed and in the area of the bracket (13) is arranged in which tensile stresses occur during workpiece machining.

Description

The invention relates to a device for machining workpieces, in particular for joining workpieces.

Methods for joining workpieces are, for example, punch rivets, clinching, resistance welding, friction element welding, rivet welding, etc. In this connection, joining forces must be applied using a tool. These joining forces lead to a deformation of the structure of the tool used. Particularly in the case of the methods listed above as joining methods, high forces have to be applied, the tools sometimes having large projections, so that large deformations occur in the tool structures. In order to keep the deformation of the tool structures within limits, metallic structures with correspondingly large load-bearing cross sections are used. Depending on the level of joining force and the joining process, aluminum, copper or steel materials are used. Structures made of fiber-reinforced plastics are also possible.

Some joining methods tolerate little or no offset in the joining axis. The punch riveting with its particularly high joining forces is particularly worth mentioning here.

Handling devices, for example industrial robots, are used in many joining processes, especially in welding processes in large series. The welding processes are usually electric welding processes, the welding current being introduced into the workpieces to be joined by means of electrodes. In methods in which an alignment error can be tolerated within limits, such as resistance welding, for example, when the joining force is built up, there are tensions between the joining part structure and its clamping elements, the joining tool and the handling element. If the bending of the tool and the resulting misalignment and lateral misalignment are too large, these tensions can be released in the course of the joining process due to vibrations and the softening of the joining part material due to the welding process, and the welding electrodes on the surface are pushed joining workpieces. In addition to a quality-reducing influence on the weld spot quality, the stresses can also result in undesirable changes in the geometry of the part structure.

A low-deformation design of the support structures leads to high weight and / or to enlarged outer dimensions of the tool, which is why appropriately stable robots must be used. In addition to cost differences for industrial robots with different payloads, a higher payload of the industrial robot means that the overall handling speed is reduced. Even if the possible acceleration and speed of the individual robot axes remain the same, the same acceleration and speed profiles as for lighter tools cannot be used due to the higher weight of the tools and the resulting mass inertia. The undesirable tendency to vibrate in the overall system increases due to strong accelerations. The result is longer cycle times.

If the same joining forces are always used for a joining process, the construction of a support structure is conceivable in which the joining axis is aligned when the nominal force is applied. The problem here remains, however, that bending also causes a displacement perpendicular to the force axis. As already described, this so-called pushing creates a tension between the clamped joining part structure and the handling robot and, if necessary, would have to be compensated for by a correspondingly mounted tool holder. However, if different joining parts are joined with the same tool, as is customary in resistance welding, different electrode forces are required, so that this approach has proven to be disadvantageous.

Steel is often used as the material for the retaining bracket in punch rivet assemblies in order to implement tool structures that are as low in deformation as possible. These brackets are constructed in a C-shape and can quickly weigh 200 kg and more, depending on the radius and the required joining force. A well-known approach to reducing the total weight is the development of a weight-optimized support structure in which the force axis is perpendicular to the surface of the part to be joined when the joining force is applied and thus has no misalignment. These structures are to be designed for the respective geometry and are not optimized in terms of torsional rigidity, but can avoid the undesired misalignment due to the internal deformations of the structure. From the DE 10 2012 022 890 A1 as well as from the DE 198 19 721 A1 Devices for machining workpieces, in particular joining tools, have already become known, in the load-bearing structure of which individual pretensioning elements are introduced in order to counteract tensions occurring during operation.

However, it is not previously known from the prior art to compensate for the overall voltage state resulting during operation in different areas of a processing device. The well-known Devices still have the disadvantage that elements of the basic structure for absorbing the operating loads or the resulting overall stress state must have appropriate material thicknesses.

The object of the invention is to provide a device for machining, in particular the joining of workpieces, which avoids the disadvantages described.

According to the invention, this object is achieved by a device for machining workpieces with the features of independent claim 1. Advantageous further developments of the device result from subclaims 2-15.

A device for machining workpieces, in particular welding tongs, comprising two opposing holding brackets, two opposing joining tools, in particular in the form of welding electrodes, being arranged on the holding brackets, and wherein the opposing joining tools for machining workpieces can be moved and / or driven relative to one another , wherein an area with tensile stresses and an area with compressive stresses occur during workpiece machining in the device, is characterized in that the holding brackets each have two biasing elements, a first biasing element being designed as a compressive stressing element and being arranged in the area of the holding bracket in which compressive stresses occur during workpiece machining, and a second prestressing element is designed as a tensile stress element and is arranged in the region of the holding bracket, in the tension during workpiece machining tensions occur.

In all structures, tensile and compressive stresses occur when a force is applied, depending on the area of the structure. In theory, one could use springs in the affected areas that are subjected to tension or pressure. Springs, if they are in a preloaded state, have the property that a further spring travel only takes place when the preload force is exceeded. Prestressed screws should also be considered as such.

If permanent tensioning or pre-tensioning is specifically introduced into the structures of the tools, the structure can be pre-tensioned or pre-deformed against the loading direction of the joining process up to the maximum loading. The result would be that with the structure prestressed in this way, no more deformation occurs until the maximum joining force is reached.

Due to the fact that the deformation is accompanied by a deformation of the structure, the contact surfaces of the tool holders, such as setting heads for punch riveting, friction element welding or rivet welding, electrode holders for resistance welding, must be reworked accordingly or machined from the outset in such a way that the tools are Force direction aligned.

With these measures, a considerable weight reduction of the tool structure can be achieved, since the prestress can be introduced into structures whose degree of deformation would not be tolerable for the joining process.

A disadvantage of this procedure, however, is that the contact surfaces for the admission of the joining tools would have to be reworked or the deformations would have to be determined in the context of a simulation and the construction would have to be adapted accordingly so that the nominal dimensions of the construction are achieved after the preload has been applied. By using prestressing elements, the device according to the invention creates a possibility of introducing prestresses into a construction without the relevant construction connection dimensions being influenced. As with a spring that only undergoes further deformation in the preloaded state, for example a further change in the spring travel when the pretensioning force is exceeded, the pretensioning elements also behave.

It has proven to be advantageous if the pretensioning element has a pretensioning element.

In an advantageous embodiment, the biasing element has a passive clamping element. A passive clamping element is, for example, a screw or threaded rod that can be clamped using a nut.

In an alternative embodiment, the biasing element has an active clamping element. In this embodiment, the prestressing element can have, for example, a fluid cylinder, for example a hydraulic cylinder or a pneumatic cylinder. However, a drivable spindle, for example a thread, ball screw or roller screw, is also possible as an active clamping element. The spindle can be driven, for example, electrically, hydraulically or pneumatically, or also mechanically. It is advantageous that one element per supporting structure may be sufficient to compensate for the deformations of the overall structure. Also in the event that the required support structure geometry is used of deformation elements, a device with an active tensioning element can come into play.

In addition, it has proven to be advantageous if the pretensioning element also has a counter element, the tensioning element and the counter element being operatively connected such that a tension state that is proportional to the pretension of the tensioning element can be set in the counter element by means of the pretensioning of the tensioning element.

With the device according to the invention, compression or tension pre-stressing elements can be realized.

If the pretensioning element is a pressure pretensioning element, the counter element has a compressive stress state due to a tension-loaded tensioning element. For example, a pipe as a counter-element is pressure-prestressed, for example by using a tension-loaded screw in the pipe to determine a state of compressive stress proportional to the prestressing force F the screw is generated. For this purpose, the screw can be screwed into a fitting piece which is arranged in the tube and is countered to the tube by an undercut. The length of the fitting piece is dimensioned such that it is shorter than the pipe, so that by tightening the screw that is locked against the opposite end of the pipe, a tensile stress can be applied in the screw and the fitting piece, so that a compressive stress is induced in the pipe . The tube experiences no further deformation when an external compressive force is applied, as long as the set preload force is not exceeded.

If the prestressing element is a tensile prestressing element, the counter element has a tensile state due to a pressure-loaded tensioning element. For example, a pipe is tension-preloaded as a counter-element by, for example, a tension state proportional to the preload force in the pipe with a pressure-loaded screw F the screw is generated. To do this, the screw can be screwed into the pipe. A fitting piece is arranged in the pipe in such a way that its position is fixed in the direction of the pipe axis. This can be achieved, for example, by screwing a stopper into the tube on the side of the tube opposite the screw, the length of the fitting being dimensioned such that the sum of the lengths of the screw, fitting and stopper is longer than the tube , whereby a compressive stress can be applied in the screw by screwing the screw pressing against the stopper over the fitting, so that a tensile stress is induced in the tube. The tube does not undergo any further deformation when an external tensile force is applied, as long as the set preload force is not exceeded.

In an advantageous embodiment, the prestressing element has a circular cross section. A prestressing element with a circular cross section can be produced particularly inexpensively.

In an alternative embodiment, the prestressing element has a polygonal cross section.

In further alternative embodiments, the prestressing element has an oval or an elliptical cross section.

Furthermore, it has proven to be advantageous if the prestressing element has an extruded profile. By using an extruded profile, the device according to the invention can be produced particularly inexpensively. It has proven to be particularly advantageous if a receiving bore for a prestressing element is already contained in the extruded profile. Channels for receiving coolant lines, such as are required for resistance welding, for example, can already be included in an extruded profile. The extruded profile can be cut to length according to the respective geometric requirements and connected to a supporting structure, for example welded. This procedure guarantees a minimal and resource-saving use of materials.

In a further advantageous embodiment, the prestressing element has a stiffening element. By using a stiffening element, for example, the torsional stiffness of the prestressing element can be increased. The stiffening element can be connected to the prestressing element, for example by welding.

In a further advantageous embodiment, the counter element has an aluminum material. Basically, all suitable materials, in particular all metal materials, can be used for the counter element. However, aluminum offers weight advantages over most other suitable metal materials, especially over steel. Since the use of steel for the supporting structure is no longer necessary even for the high forces of punch riveting, the weight can be reduced considerably by using aluminum.

It has proven to be advantageous if the prestressing element is inserted into the device. As a joining process there are for example welding, gluing or screwing on. As an alternative, however, it is also possible to use a support structure, for example made from solid material, in which a recess, for example a bore, is provided for receiving a prestressing element.

The use of prestressing elements can also be used for secondary elements of the connection method. For example, in resistance welding, electrode holders are used on the electrode arms, to which the welding electrodes are in turn attached. For reasons of accessibility, the dimensions of the electrode holders are partially limited. The sometimes high electrode forces required for resistance welding cannot be achieved because the permissible fatigue strength of the electrode holder material is exceeded. This problem can be solved by using preloading elements.

Use in threaded spindle systems is also possible. Although threaded spindles could also be preloaded with a tension or compression screw depending on the load, this affects the pitch accuracy. First, the blank would have to be pre-stressed and only then would the thread be created. The reduction in cross-section could be included or a prestress compensation could be carried out. The use of the biasing elements at this point is therefore easier.

The use of the prestressing elements is suitable, for example, for C and X pliers for resistance welding, punch rivets, friction element welding devices, clinching and for stationary joining devices in C and portal construction, generally components with bending moment loads, such as those that occur with presses, threaded spindles or general supporting structures .

Further advantages, special features and expedient developments of the invention result from the subclaims and the following illustration of preferred exemplary embodiments with the aid of the figures.

• 1 eine Stanznietzange zum Stanznieten als C-Bügel gemäß Stand der Technik in einer Seitenansicht und einer dreidimensionalen Ansicht
• 2 eine Stanznietzange als optimierter C-Bügel gemäß Stand der Technik in einer Seitenansicht und einer dreidimensionalen Ansicht
• 3 eine Prinzipskizze eines Druckvorspannelements gemäß der Erfindung in Draufsicht, Seitenansicht und als Schnitt
• 4 eine Prinzipskizze eines Zugvorspannelements gemäß der Erfindung in Draufsicht, Seitenansicht und als Schnitt
• 5 ein Strangpressprofil in einer dreidimensionalen Ansicht
• 6 eine Schweißzange als C-Bügel mit Vorspannungselementen gemäß der Erfindung
• 7 eine Ausführungsform einer lineargeführten X-Zange aufgebaut mit Vorspannungselementen gemäß der Erfindung in einer dreidimensionalen Ansicht
• 8 einen Elektrodenarm mit Bohrungen zur Aufnahme von Vorspannungselementen

The pictures show:

• 1 a punch rivet pliers for punch riveting as a C-bracket according to the prior art in a side view and a three-dimensional view
• 2nd a punch riveting pliers as an optimized C-bracket according to the prior art in a side view and a three-dimensional view
• 3rd a schematic diagram of a pressure biasing element according to the invention in plan view, side view and as a section
• 4th a schematic diagram of a tension element according to the invention in plan view, side view and as a section
• 5 an extruded profile in a three-dimensional view
• 6 a welding gun as a C-bracket with biasing elements according to the invention
• 7 an embodiment of a linearly guided X-gun with biasing elements according to the invention in a three-dimensional view
• 8th an electrode arm with holes for receiving prestressing elements

1 shows a device for machining workpieces 10th in the form of punch riveting pliers for punch riveting in the form of a C-bracket according to the prior art. The forces used when joining materials lead to a deformation of the structure of the device 10th . In particular, the high forces used in punch riveting and the sometimes large projections bring about large deformations in the structure of the device 10th with yourself.

In operation occur in the areas 11 the device 10th Tensions on while in the fields 12th the device 10th Compressive stresses occur. To the deformation of the device 10th To keep it within limits, metallic structures with correspondingly large load-bearing cross sections are used. In processes in which an alignment error can be tolerated within limits, such as resistance welding, the joining force builds up tension between the joining part structure and its clamping elements, the welding tool and the handling element, usually an industrial robot. Is the bend of the device 10th and the resulting misalignment and lateral misalignment are too great, these tensions can be released in the course of the welding process due to vibrations and the welding of the joining material due to the welding process, and the electrodes are pushed on the sheet metal surface. In addition to a quality-reducing influence on the weld spot quality, the stresses can also result in undesirable changes in the geometry of the part structure.

A low-deformation design of the support structures leads to a high weight and / or to enlarged external dimensions of the device 10th , which is why suitable robots are used, which among other things leads to a reduction the possible handling speed leads. Even if the possible acceleration and speed of the individual robot axes is constant, due to the higher weight of the device 10th and the resulting inertia, the same acceleration and speed profiles are not used as in a lighter device 10th . Strong accelerations increase the tendency of the entire system to vibrate, which is why they should be avoided. The result is longer cycle times.

For the realization of a structure of the device that is as low in deformation as possible 10th Steel is often used as a material for the retaining bracket in punch rivet assemblies 13 used. Such C-shaped brackets 13 are in 1 recognizable and can quickly weigh 200 kg and more, depending on the radius and the required joining force. On the brackets 13 are joining tools 14 along a joining axis 15 arranged. By bending the bracket 13 in the operation of the device 10th there is a change in the joining axis 15 so that the joining axes 15 of the respective joining tools 14 no longer cursing.

2nd shows a device for machining workpieces 10th in the form of punch rivet pliers with optimized holding brackets 13 in the design as a C-frame with a lattice structure according to the prior art. The device has a weight-optimized support structure in which the joining axis 15 is perpendicular to the surface of the part to be joined when the joining force is applied and thus has no misalignment. Such support structures are to be designed for the respective geometry and are not optimized with regard to the torsional rigidity, but can avoid the undesired misalignment due to the internal deformations of the structure.

3rd shows a schematic diagram of a biasing element 20th in the form of a pressure biasing element according to the invention. A counter element 22 in the form of a tube is prestressed by using a tensioned screw as a tensioning element 21 in the pipe 22 a compressive stress state proportional to the preload force F the screw 21 is produced. The screw 21 is in a fitting 25th screwed that into the pipe 22 is arranged and against the pipe 22 is countered by an undercut. The fitting piece 25th is dimensioned in its length so that it is shorter than the pipe 22 is, by screwing in against the opposite end of the tube 22 locked screw 21 a tension in the screw 22 and the fitting 25th can be applied so that in the tube 22 a compressive stress is induced. The pipe experiences this 22 When applying an external compressive force, no further deformation as long as the pre-tensioning force is not exceeded.

4th shows a schematic diagram of a biasing element 20th in the form of a tension element according to the invention. A counter element 22 in the form of a tube is prestressed by using a pressure-loaded screw as a tensioning element 21 in the pipe 22 a tensile state proportional to the preload F the screw 21 is produced. The screw 21 is in the pipe 22 screwed in. In the pipe 22 a fitting piece is arranged such that its position is fixed in the direction of the pipe axis. In the exemplary embodiment shown, this is achieved in that on the screw 21 opposite side of the tube 22 a stopper 26 into the pipe 22 is screwed in, the fitting 25th its length is such that the sum of the lengths of screw 22 , Fitting piece 25th and stoppers 26 longer than the pipe 22 is, by turning the fitting 25th against the stopper 26 pressing screw 22 a compressive stress in the screw 22 can be applied so that in the tube 22 a tensile stress is induced. The pipe experiences this 22 When applying an external tensile force, no further deformation as long as the set preload is not exceeded.

5 shows an extruded profile 23 how to build the structure of the device for machining workpieces 10th Can be used. The locating hole is in the extruded profile 27 for a preload element 20th already included. The structure of the device 10th can be constructed, for example, from such extruded profiles welded together.

6 shows a device for machining workpieces 10th in the form of a welding gun with brackets 13 as a C-bracket with pre-tensioning elements 20th according to the invention. In the brackets 13 are prestressing elements 20th inserted. On the brackets 13 are joining tools 14 arranged in the form of two opposing welding electrodes. One of these welding electrodes is arranged such that it can be moved along its longitudinal axis, one of which is also on the corresponding holding bracket 13 arranged drive element 28 is drivable. By using prestressing elements 20th are biases in the device 10th Can be inserted in the form of welding tongs without affecting the relevant construction connection dimensions.

7 shows an embodiment of a device for machining workpieces 10th in the form of a linearly guided X-pliers, with preloading elements 20th is constructed according to the invention. Two joining tools that can be moved along their longitudinal axis 14 in the form of welding electrodes face each other on a drive element 28 for the translational movement of the joining tools 14 arranged. Here are the drive elements 28 each on holding brackets 13 arranged, each of the two retaining brackets two biasing elements 20th having. The bracket 13 are arranged one above the other, with the upper bracket 13 fixed to a frame 30th is arranged while the lower bracket 13 relative to the top bracket 30th along a linear guide arranged on the frame 29 is arranged movable. Due to the movability of the bracket 30th Workpieces of different thicknesses can be used together with the device 10th to be edited. The upper biasing element 20th of the upper bracket 13 is designed as a pressure biasing element, the upper biasing element 20th of the upper bracket 13 an area with compressive stresses in operation 12th represents. Likewise is the lower biasing element 20th of the lower bracket 13 designed as a pressure biasing element, the lower biasing element 20th of the lower bracket 13 an area with compressive stresses in operation 12th represents. In contrast, the lower biasing element 20th of the upper bracket 13 designed as a tension element, the lower bias element 20th of the upper bracket 13 an area with tensile stresses in operation 11 represents. Likewise is the top biasing element 20th of the lower bracket 13 designed as a tension element, the upper bias element 20th of the lower bracket 13 an area with tensile stresses in operation 11 represents

8th shows a bracket 13 in the form of an electrode arm with mounting holes 27 for holding prestressing elements 20th . Are the brackets 13 the embodiment of the device 10th according to 7 from prestressing elements 20th assembled, there is the bracket 13 the in 8th Embodiment shown from a piece of aluminum made from solid, in the receiving holes 27 are introduced into the biasing elements 20th are insertable.

The embodiments shown here are only examples of the present invention and should therefore not be understood as restrictive. Alternative embodiments contemplated by those skilled in the art are equally within the scope of the present invention.

Reference list

10th

Device for machining workpieces

11

Area with tensile stresses in operation

12th

Area with compressive stresses in operation

13

Bracket

14

Joining tool

15

Joining axis

20th

Preload element

21

Clamping element, screw

22

Counter element, tube

23

Extruded profile

25th

Fitting piece

26

Plug

27

Location hole

28

Drive element

29

Linear guide

30th

frame

Claims (15)

Device for machining workpieces (10), in particular welding tongs, comprising two opposing holding brackets (13), two opposing joining tools (14), in particular in the form of welding electrodes, being arranged on the holding brackets (13), and the opposing joining tools (14) can be moved and / or driven relative to one another for machining workpieces, an area with tensile stresses (11) and an area with compressive stresses (12) occurring in the device (10) during workpiece machining, characterized in that the holding brackets ( 13) each have two biasing elements (20), a first biasing element (20) being designed as a compressive stress element and being arranged in the region of the holding bracket (13) in which compressive stresses occur during workpiece machining, and a second biasing element (20) as a tensile stress element executed and in the area of the bracket (13) is arranged in which tensile stresses occur during workpiece machining. Device (10) according to Claim 1 , characterized in that the biasing element (20) has a clamping element (21) under bias. Device (10) according to Claim 1 , characterized in that the biasing element (20) has a passive clamping element (21). Device (10) according to Claim 1 , characterized in that the biasing element (20) has an active clamping element (21). Device (10) according to one of claims 2 to 4, characterized in that the prestressing element (20) further comprises a counter element (22), the prestressed tensioning element (21) and the counter element (22) are operatively connected in such a way that a tension state that is proportional to the bias of the tension element (21) can be set in the counter element (22) via the bias of the tensioning element (21). Device (10) according to Claim 3 , characterized in that the pretensioning element (20) is a pressure pretensioning element, the counter element (22) being in a tensioned state due to a tensioned tensioning element (21). Device (10) according to Claim 3 , characterized in that the pretensioning element (20) is a tension pretensioning element, the counter element (22) being in a tensioned state due to a pressure-stressed tensioning element (21). Device (10) according to one of the preceding claims, characterized in that the biasing element (20) has a circular cross section. Device (10) according to one of claims 1 to 7, characterized in that the biasing element (20) has a polygonal cross section. Device (10) according to one of claims 1 to 7, characterized in that the biasing element (20) has an oval cross-section. Device (10) according to one of claims 1 to 7, characterized in that the biasing element (20) has an elliptical cross section. Device (10) according to one of the preceding claims, characterized in that the prestressing element (20) has an extruded profile (23). Device (10) according to one of the preceding claims, characterized in that the biasing element (20) has a stiffening element. Device (10) according to one of claims 5 to 13, characterized in that the counter element (22) comprises an aluminum material. Device (10) according to one of the preceding claims, characterized in that the biasing element (20) is inserted into the device (10).

Images