EP4079454A1 - Method and device for attaching a tensioning structure on a workpiece - Google Patents

Abstract

In a machining method according to the invention, a workpiece (11) is positively positioned and clamped on a first positive-locking structure (24). In this setting, the workpiece can be machined or machined in some other way. Before it is unclamped again, a second positive-locking structure (28) is attached to the workpiece (11) in a further processing step. The workpiece (11) is then unclamped and clamped again at the second positive-locking structure. Further machining processes can be carried out on the workpiece (11) in the new clamping. The production of the second positive-locking structure (28) during the clamping of the workpiece (11) in the first clamping ensures that the processing carried out in the second clamping fits dimensionally precisely to the workpiece structures produced in the first clamping.

Description

The invention relates to a method for attaching a clamping structure to a workpiece, a method for clamping and machining a workpiece, and a device for attaching a clamping structure to a workpiece and machining the same.

When machining workpieces, five-sided machining and, in many cases, six-sided machining is often required. During processing, in particular mechanical machining, the workpiece must be clamped firmly and in the correct position. For this purpose, the workpiece is typically held in a corresponding clamping device.

To clamp workpieces, beat the EP 1 071 542 B1 and the DE 10 2007 008 132 B4 suggest forming a form fit structure on the workpiece near its base. the DE 10 2007 008 132 B4 discloses the production of form-fitting structures both with a multi-tooth embossing jaw and with a single-tooth stamp or with a toothed roller, each for serial production of the form-fitting structure. Corresponding coupling structures, which are used for clamping and are arranged on the clamping jaws of a vice, are assigned to this positive-locking structure. Such a clamping has to be space-saving and proven resilient, so that almost complete five-sided machining of the workpiece is possible.

However, there are cases that require the workpiece to be re-clamped so that it can also be machined on surfaces and areas that were not accessible in the first clamping.

To this the EP 3 943 244 A1 proposed to provide a clamping device with clamping teeth suitable for holding pre-embossed workpieces with top jaws into which the outer contour of the partially machined workpiece is machined. The partially machined workpiece can be inserted into the inner contour of the top jaws formed in this way and clamped therein.

The workpiece is machined in the first clamping with a dimensional reference to the workpiece in the coordinate system specified by the clamping device. All structures created on the workpiece are aligned to this coordinate system. If the workpiece is to be re-clamped, the relationship between the surfaces already machined and the coordinate system of the first clamping must not be lost. Otherwise, the surfaces and structures machined in the second clamping would not be dimensionally accurate in relation to the structures produced in the first clamping.

Proceeding from this, it is the object of the invention to provide a method and a device with which workpieces can be precisely machined in several clampings.

The method according to claim 1 initially serves in general to attach a plurality of clamping structures to one Workpiece. For this purpose, the workpiece is preferably first transferred to an embossing station, gripped between two embossing jaws and provided with the desired first embossing structure by a movement of the embossing jaws towards one another.

In a subsequent step, the workpiece can be transferred to a processing machine or station and can be gripped and clamped there in a clamping device on the first embossing structure. For this purpose, the holding device can be in the form of a clamping device which has two clamping surfaces which can be adjusted at a distance from one another and between which the workpiece can be clamped. The clamping device can have first coupling structures which engage in the first positive-locking structure already present on the workpiece. The workpiece is thus held in a first clamping.

After the workpiece has been clamped, it is in particular machined in the processing machine, with material being removed and the shape of the workpiece being changed at least locally.

To continue processing, it may be necessary to re-clamp the workpiece. For this purpose, the attachment of a second positive-locking structure may be desired. For this purpose, an embossing mandrel is now used, which is spatially movably guided in at least two directions by a corresponding positioning device, for example the work spindle of the processing machine. A first direction is oriented transverse to the embossing mandrel. A second direction is oriented longitudinally (axially) to the mandrel. This allows the embossing mandrel at laterally spaced locations to the Be moved toward the workpiece to penetrate its surface and create a depression by plastic deformation. The preferably, but not necessarily, equidistant row of indentations produced in this way can later be used by a holding device for positively locking or mixed positively locking and frictionally locking clamping of a workpiece, which can then be subjected to machining.

The embossing mandrel is preferably held in a tool holder and can be used with this in a machine spindle and also stored in a tool magazine. The embossing mandrel is held in the tool holder in a fixed orientation (with respect to a rotation about its axial direction). The axial direction is parallel to the embossing direction in which the embossing mandrel is moved during embossing. An alignment surface, e.g., a Weldon flat, may be provided on the shank of the stamping mandrel, by means of which the stamping mandrel can be fixed in the tool holder in a desired orientation. Due to the resulting angular relationship between the embossing mandrel and the machine spindle, all depressions of the form-fitting structure to be produced can be produced in the same angular orientation. The indentations may be truncated pyramidal indentations. However, it is also possible to use other shapes, e.g.

Said process, in which a row or a field of indentations is applied to a workpiece by means of the embossing mandrel, can be carried out repeatedly on the workpiece in order to enable different clampings in succession. In doing so, the position of the Workpiece between two provided with corresponding teeth holding jaws clearly defined by the form-fitting structure formed by depressions. If further indentations, i.e. another form-fitting structure, are created in this clamping using an embossing mandrel and these are then used in a further clamping for aligning and fixing the workpiece, the accuracy of the first clamping is transferred to the further (second) clamping.

A vise held in a machine tool can be used as a holding device for fixing the workpiece during the embossing process. The embossing mandrel can be connected to the machine spindle of the machine tool. The embossing mandrel can be fastened in a tool holder and kept ready in a tool magazine in order to be transferred to the machine spindle as required or to be deposited back into the tool magazine by the latter. The machine spindle accommodates the tools for processing the workpiece or, if necessary, the embossing mandrel. The tools and the stamping mandrel can be exchanged in and out of the machine spindle using a tool changer or by directly approaching the tool holder with the work spindle in the so-called pick-up process.

In principle, it is possible to produce the form-fitting structure on the workpiece both for the first clamping and for the second clamping by means of the embossing mandrel. According to claim 5, however, an advantageous method is claimed in which the positive-locking structure for the first clamping is produced on the workpiece in a pre-stamping station. The pre-embossing station can, for example, be a station that processes a blank before it is processed initially receives, for example, between two toothed jaws, each having a plurality of embossing teeth. By reducing the distance between the jaws, the teeth of the two jaws penetrate the workpiece and create the desired form-fitting structure. After this positive-locking structure has been attached to the workpiece in the pre-stamping station, the workpiece is transferred to a holding device according to claim 5 . This holding device can be a vice which, together with the workpiece clamped therein, can be guided into and out of the machine tool as required. In the vise, the workpiece is held at its (first) form-fit clamping structure. Corresponding teeth of the clamping jaws of the vise penetrate into the form-fitting structure and hold the workpiece in place in a form-fitting and/or mixed form-fitting and frictional manner. In this state, the workpiece can be subjected to machining such as milling, drilling or the like. Furthermore, a series of indentations can be applied to the clamped workpiece by means of a tool (eg stamping mandrel) exchanged in the machine spindle, which form the second positive-locking clamping structure for a second clamping. The indentations are preferably produced by means of the embossing mandrel by plastic deformation of the workpiece. The indentations can be arranged in one or more rows or as a field to form the second form-fit clamping structure. To this end, two or more rows of depressions can be arranged parallel to one another. The depressions in the rows can be aligned with one another or offset from one another, "staggered". A multi-row arrangement of indentations can be used to enable higher holding forces.

Both the first and the second positive-locking structure are used exclusively for clamping the workpiece. Otherwise the form-fitting structure has no function for the workpiece and its subsequent use.

After the attachment of the second positive-locking structure, the partially machined workpiece can be released from the holding device and clamped in some other way. This can take place both inside a machine tool and outside of it, for example by the workpiece being taken out of a machine tool together with the holding device and being detached from the holding device at a correspondingly equipped work station. It can then be clamped on the form-fit clamping structure created with the embossing mandrel in the same vise or in another vise and returned to the same or another machine tool.

The object mentioned at the outset is also achieved with a device according to claim 7:

The device according to the invention includes a holding device for holding and fixing the workpiece, an embossing mandrel for generating a positive-locking structure on the workpiece, and a device for receiving the embossing mandrel and a positioning device for position-controlled guiding of the embossing mandrel. This device can be formed by a machine tool, which is assigned a corresponding embossing mandrel. The device for accommodating and guiding the embossing mandrel can be a machine spindle, as is otherwise provided for accommodating and guiding tools for machining workpieces. The positioning device for position-controlled movement of the embossing mandrel is then formed by the positioning device of the machine spindle.

The machine tool can have a control device with a machine control program that specifies a movement of the embossing mandrel in such a way that it produces a series of indentations on the workpiece that form the positive-locking structure. This is achieved by the work spindle of the machine tool, which is provided with the embossing mandrel, guiding the embossing mandrel in a repeated infeed and retraction movement and lateral displacement movement.

The device can also include a pre-embossing station for producing a first positive-locking structure. In addition, the holding device provided for fixing and holding the workpiece can be a vise whose clamping surfaces have holding teeth. The shape of the embossing mandrel can be matched to the shape of the retaining teeth. For example, the indentations on the workpiece created by the embossing mandrel can match the shape of the retaining teeth. For this purpose, the shape of the indentations corresponds, for example, to the shape of the holding teeth, or the indentations produced by the embossing mandrel are slightly smaller than the holding teeth, so that the holding teeth are seated firmly in the workpiece. The difference in size between the indentations and the retaining teeth can be within the range of the elastic deformability of the workpiece. However, it is also possible to measure the difference in size in such a way that the retaining teeth cause further plastic deformation on the workpiece when they engage in the depressions when the workpiece is clamped.

• Figur 1 eine Werkzeugmaschine zur Bearbeitung des Werkstücks in schematisierter Perspektivdarstellung,
• Figur 2 die Werkzeugmaschine nach Figur 1 in ausschnittsweiser schematisierter Darstellung,
• Figur 3 ein Rohling mit einer Formschlussspannstruktur zum Spannen in der Werkzeugmaschine nach Figur 1 und 2,
• Figur 4 einen Spannbacken mit von ihm gehaltenem Werkstück in schematisierter Darstellung,
• Figur 5 einen Prägedorn zur Erzeugung einer (zweiten) Formschlussstruktur an dem Werkstück und
• Figur 6 einen Prägebacken zum Prägen des Werkstücks zur Erzeugung einer ersten Formschlussstruktur.

Further details and variants of the method according to the invention and the associated device are the subject of the drawing, the associated description and dependent claims. Show it:

• figure 1 a machine tool for machining the workpiece in a schematic perspective view,
• figure 2 the machine tool figure 1 in a partial schematic representation,
• figure 3 a blank with a form-fit clamping structure for clamping in the machine tool Figure 1 and 2 ,
• figure 4 a clamping jaw with a workpiece held by it in a schematic representation,
• figure 5 an embossing mandrel for producing a (second) positive-locking structure on the workpiece and
• figure 6 an embossing jaw for embossing the workpiece to produce a first positive-locking structure.

In figure 1 a machine tool 10 is illustrated, which is used for machining a workpiece 11 . The workpiece 11 is in figure 1 and illustrated symbolically as a cube in the other figures, the workpiece 11, but also having any other suitable shape. The workpiece 11 is preferably made of metal, such as steel or an aluminum alloy. The material of the workpiece is ductile at least to the extent that depressions can be produced in it by embossing.

The machine tool 10 is provided with a holding device 12 which is designed, for example, as a vise and is set up to fix the workpiece 11 in place. The holding device 12 is in turn received by a workpiece carrier 13 or another holder which holds the holding device 12 stationary in the machine tool 10 or moves it as desired.

The machine tool 10 has a work spindle 14 which is assigned a rotary drive (not shown in the figures). The work spindle 14 can be moved in one, two or more directions X, Y, Z by means of a positioning device 15 that is only indicated schematically. At the same time or alternatively, the workpiece carrier 13 can be set up to move the holding device 12 in one or more directions X, Y, Z.

The machine tool 10 is assigned a tool magazine 16 which holds ready a number of tools 17 held in tool holders, for example drills, milling cutters or the like. The tool holder with such tools 17 can also be arranged in the work spindle 14 . For transferring tool holders with tools 17 from the tool magazine 16 to the work spindle 14 and for the return from the work spindle 14 to the tool magazine 16, a tool changing device can be provided. This includes, for example, a gripper that is not shown in more detail in FIG. Alternatively, the movement of the work spindle 14 can be used to change tools if the tool magazine 16 is arranged in the range of movement of the work spindle 14 (pick-up method).

Also arranged in the tool magazine 16 is at least one stamping mandrel 18 which is preferably mounted on a tool holder and which can be coupled to the work spindle 18 like a tool 17 . This illustrates figure 2 :

In figure 2 the holding device 12 designed as a vise is illustrated, which holds the workpiece 11 between two clamping jaws 19, 20 for machining. The two clamping jaws 19, 20 are kept movable towards and away from each other. They each have a receiving surface 21 lying in a common plane, as in figure 4 is illustrated using the example of the clamping jaw 20 . A clamping surface 22 is provided at right angles thereto, on which holding teeth 23 can be provided. These are designed, for example, in the shape of a truncated pyramid and engage in a form-fitting manner in a corresponding first form-fitting structure 24. The form-fitting structure 24 is formed by a series of indentations 25 stamped into the workpiece 11, which have preferably been introduced into the workpiece 11 by plastic deformation of the latter.

figure 6 1 illustrates an embossing tool that is designed similarly to a clamping jaw and has a row of embossing teeth 27 . The embossing teeth 27 can be designed in the shape of a truncated pyramid in order to produce depressions in the shape of a truncated pyramid. The flanks of the truncated pyramid-shaped embossing teeth 27 can be flat or curved. However, the embossing teeth can also be configured in the shape of a pyramid, a truncated cone, a cone or the like.

To produce the positive-locking structure 24 with its indentations 25, a blank (workpiece 11) is held between two embossing tools 26, one of which is in figure 6 is exemplified. The two embossing tools 26 are moved towards one another in a force-actuated manner. The embossing teeth 27, which are in the form of a truncated pyramid, for example, penetrate the workpiece 11 and produce the depressions 25. These depressions 25 form the first positive-locking structure 24, on which the workpiece 11 is received in the machine tool 10 for machining. However, the workpiece 11 cannot be machined in the area of the positive-locking structure 24 and also not on its side facing the holding device 12 . If this is to happen, it must be re-clamped.

In order not to lose the dimensional reference to the first clamping, the workpiece 11 can be provided with a further positive-locking structure 28 by means of the embossing mandrel 18 at points that have already been machined or at other points that are still free and no longer to be machined, as is shown in figure 3 is indicated at the top right. The second span structure 28 may be a straight row of indentations 30, a curved row, a double row, or an array of indentations.

The embossing mandrel 18 preferably has only a single embossing tooth 27a, which is attached to the outermost end of the embossing mandrel 18 on the face side. The opposite other end 29 is designed as an ordinary tool shank. The embossing tooth 27a preferably matches the embossing teeth 27 of the embossing tool 26 in terms of shape and size. At least that part of the embossing mandrel 18 which penetrates into the workpiece 11 during embossing, that is to say corresponds in size and shape to the indentation 30 to be produced, is regarded as the embossing tooth 27a. However, it is also possible to provide an embossing mandrel with two or more embossing teeth at the tip (distal end). The embossing tooth 27a can be designed in the shape of a truncated pyramid in order to produce depressions in the shape of a truncated pyramid. The flanks of the truncated pyramid-shaped embossing tooth 27a can be flat or curved. However, the embossing tooth can also be configured in the shape of a pyramid, a truncated cone, a cone or the like.

By means of the device described so far, the method according to the invention is carried out as follows:

First, the workpiece 11 is placed in the holding device 12 . The position of the workpiece 11 is defined by the holding teeth 23 . The indentations 25 of the first positive-locking structure 24 have preferably already been produced in a preparatory work step, for example in that the blank forming the workpiece 11 has been received between two embossing jaws 26 and has been embossed by them.

The machine tool 10 is now equipped with a tool 17 from the tool magazine 16 by transferring it to the work spindle 14 and coupling it to it becomes. The workpiece 11 can now be machined with the tool 17, for example driven in rotation, by exercising corresponding movements of the work spindle 14 and/or the holding device 12 in the X, Y or Z direction. The holding device and/or the work spindle can also be pivoted about one or more of these directions X, Y, or Z if the machine tool 10 is set up for this.

To carry out the machining, in particular machining, it is possible to change the tool 17 one or more times, for example using a tool changer or the pick-up method. When the machining is finished and a previously inaccessible area of the workpiece 11 is to be machined, the workpiece 11 must be unclamped and clamped in again. In order to enable unclamping and clamping without loss of accuracy, the second form-fitting structure 28 is first attached to the workpiece 11, while the workpiece 11 with the first form-fitting structure 24 is still held firmly between the jaws 19, 20. For this purpose, the tool holder with the embossing mandrel 18 is first exchanged in the work spindle 14 . The work spindle 14 is then as shown figure 2 As can be seen, positioned in the vicinity of the workpiece 11 and translated into a desired rotational position in which the stamping tooth 27a has the desired orientation. The work spindle 14 is now moved in the infeed direction (Z-direction) towards the workpiece 11 until the embossing tooth 27a penetrates the surface of the workpiece 11 and a depression 30 is produced by plastic deformation. Once this has happened, the work spindle 14 is moved back in the Z direction (axial direction of the work spindle) until the embossing tooth 27a disengages from the workpiece 11 . The work spindle 14 is now offset laterally, for example in the X direction (or also in the Y direction or another lateral direction). The offset is just as large as the desired distance between two adjacent depressions 30 from each other. The work spindle 14 is now moved again in the Z-direction in order to allow the embossing tooth 27a to again penetrate into the workpiece 11 in order to produce a desired indentation 30 by plastic deformation. This process is now repeated until the desired form-fitting structure 28 ( figure 3 ), i.e. a series of individual depressions 30 has been produced. Once this has taken place, the workpiece 11 can be re-clamped. For this purpose, the holding device 12 can be brought out of the machine tool 10 and re-clamped by means of suitable manipulators or by hand. For this purpose, the clamping jaws 19, 20 are initially moved slightly away from one another, so that the workpiece 11 is released. The workpiece 11 is then rotated and turned in such a way that the second (new) positive-locking structure 28 is pulled in front of the holding teeth 23 of the tightened ones, that is to say towards one another, until they again hold the workpiece 11 in place.

The second positive-locking structure 28 can be a straight, equidistant row of indentations 30 or any other arrangement of indentations 30 that fits the clamping teeth of clamping jaws that are provided for the second clamping. The second form-fitting structure 28 preferably matches the first form-fitting structure 24 in terms of shape, size and division, which is produced by means of embossing jaws 26 . Thus, both the first form-fitting structure 24 and the second form-fitting structure 28 fit equally to the retaining teeth 23. This despite the indentations 25 of the first form-fitting structure 24 have been produced in parallel and the depressions 30 of the second form-fitting structure 28 have been produced in series.

When re-clamping from the first form-fitting structure 24 to the second form-fitting structure 28, the workpiece 11 can also be used in a second, different holding device, for example a larger or smaller vice. In any case, however, the accuracy of the first clamping is transferred to the second clamping by making the second form-fitting structure 28 in the machine tool 10 on the workpiece 11, which is held on the first form-fitting structure 24.

In a machining method according to the invention, a workpiece 11 is positively positioned and clamped on a first positive-locking structure 24 . In this setting, the workpiece 11 can be machined or machined in some other way. Before it is unclamped again, a second positive-locking structure 28 is attached to the workpiece 11 in a further processing step. The workpiece 11 is then unclamped and clamped again at the second positive-locking structure 28 . Further machining processes can be carried out on the workpiece 11 in the new setup. The production of the second positive-locking structure 28 during the clamping of the workpiece 11 in the first clamping on the first positive-locking structure 24 ensures that the processing carried out in the second clamping fits dimensionally precisely to the workpiece structures produced in the first clamping.

References:

10

machine tool

11

workpiece

12

Holding device, vise, workpiece clamping device

13

workpiece carrier

14

working spindle

15

positioning device

16

tool magazine

17

Tool

18

embossing mandrel

19, 20

clamping jaws

21

bearing surface

22

clamping surface

23

clamping tooth/retaining tooth

24

interlocking structure

25

Depressions of the first form-fitting structure 24

26

embossing tool

27, 27a

stamping teeth

28

interlocking structure

29

End

30

Depressions of the second form-fitting structure 28

Claims (14)

Process for clamping and machining a workpiece, in which: a positive-locking structure (24) is produced on a workpiece (11) in a pre-stamping station (26), the workpiece (11) is clamped in a holding device (12) at its positive-locking clamping structure (24), the clamped workpiece (11) is subjected to machining, characterized,
that the clamped workpiece (11) is provided with an embossing mandrel (18) at various spaced-apart points with local plastic deformation of the workpiece (11) with indentations (30) pressed into its surface, and that the workpiece (11) is picked up by a clamping device (12) at the indented depressions (30). Method according to Claim 1, characterized in that a workpiece clamping device which is arranged in a machine tool (10) is used as the holding device (12). Method according to one of the preceding claims, characterized in that the embossing mandrel (18) is connected to a machine spindle (14) of a machine tool (10). Method according to claim 3, characterized in that the machine spindle (14) holds the embossing mandrel (18) in a non-rotating manner and in a sequence of indenting and moving in offset movements to create a series of indentations (30). Method according to one of the preceding claims, characterized in that after the indentations (30) have been created, the workpiece (11) is clamped by means of the embossing mandrel (18) with the same holding device (12) in which it was held during the creation of the indentations (30 ) was held by the embossing mandrel (18). Method according to one of the preceding claims, characterized in that the embossing mandrel (18) is connected to the tool spindle (14) and is guided by the latter to carry out the embossing process. Device (10) for attaching a clamping structure (28) to a workpiece (11), with: a holding device (12) for holding and fixing a workpiece (11), an embossing mandrel (18) for producing indentations (30) at various spaced-apart points on the workpiece (11) with local plastic deformation of the same, a device (14) for receiving and guiding the embossing mandrel (18) and with a positioning device (15) for the position-controlled movement of the embossing mandrel (18). Device according to claim 7, characterized in that the holding device (12) belongs to a machine tool (11) and that the device (14) for Recording and guiding of the embossing mandrel (18) is a machine spindle (14). Device according to Claim 7 or 8, characterized in that the embossing mandrel (18) is held in a tool holder. Device according to one of Claims 7 to 9, characterized in that the device (15) for the position-controlled movement of the embossing mandrel (18) is a spindle positioning device (15) of a machine tool (10). Device according to one of Claims 7 to 10, characterized in that the holding device (12) has clamping surfaces (22) on which holding teeth (23) are arranged. Device according to Claim 11, characterized in that the retaining teeth (23) are arranged in a row and are equally spaced from one another. Device according to one of Claims 11 or 12, characterized in that the retaining teeth (23) have a uniform shape. Device according to one of Claims 11 to 13, characterized in that the embossing mandrel (18) has a shape that matches the holding teeth (23).

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