WO1998031500A1 - Fixing device for workpieces to be machined on several sides - Google Patents

Abstract

The invention relates to a novel fixing device for workpieces to be machined on several sides, whereby the axes (14, 15) of the drive spindle (4) or support spindle (5) carrying the clamping elements (7, 8) are inclined at an angle ( alpha 1 or alpha 2), which in reality is very small, in relation to the work bench (1) and the ideal workpiece axis (19). Fixing a workpiece between the clamping elements (7, 8) with a clamping force acting in an axial direction deforms the housings (2, 3) and their fixing means, which, at a predefined nominal value, makes it possible to obtain the coaxial alignment of the axes (14, 15) and thus the optimal clamping position of the workpiece. Clamping force values which deviate from the nominal clamping force result in additional deformations, which can influence the clamping position of the workpieces in such a way that compliance with tight dimension tolerances can no longer be guaranteed. According to the invention it is possible to adjust the height of at least one housing (3) by means of a support element (11) which can be displaced by a small angle ( beta ) in relation to the base plate (13). A scale (17) indicating the intensity of the clamping force allows for safe adjustment of the support element (11).

Description

 Holding device for multi-sided workpieces

description

The present invention relates to a holding device for multi-sided workpieces according to the preamble of the first claim.

Such holding devices are required in machine tools with which workpieces can be machined from different sides with different tools at a standstill. The workpieces are pivoted from one machining position into another with the aid of an angle switching device which is built into the machine tool and can be actuated via a control device. The holding device has the task of continuing to turn the workpiece into the individual machining positions without the application of machining forces or to support it at a standstill during machining.

EP 0547 554 B1 describes a workpiece holding device for workpieces to be machined on multiple sides on machine tools, in which the workpiece is clamped by means of a clamping force between two clamping pieces which can be moved in the axial direction and are provided with flat clamping surfaces.

For support and for transmission of motion, each of the clamping pieces is connected to a spindle, which is in each case mounted in a housing fastened to the work table of the machine tool. In addition to the drive spindle, the first housing accommodates the angle switching device connected to it, while the second housing houses the freely rotatable support spindle connected to a drive for generating the clamping force.

With increasing size of the clamping force, the clamped parts, such as the two housings with their fastening screws and the part of the work table lying between them, deform such that the axes of the two spindles each form an angle against one another form the level of the worktable and intersect in the area of the workpiece. Although these angles are very small, the deformations result in a change in the workpiece position compared to the ideal workpiece axis, which leads to impermissible dimensional deviations during machining. In addition, the deviating position of the clamping surfaces on the clamping pieces resulting from the deformations can also cause a not inconsiderable eccentricity of the point of application of the clamping force, which leads to an unstable clamping of the workpiece.

The object of the invention is seen in applying measures to reduce or completely eliminate the deformations caused by the clamping force on the generic device. According to the invention the object is achieved in a holding device of the generic type in that at least one of the housings is provided with means which counteract the inclination of the axis of the associated spindle under the action of the clamping force with respect to the clamping plane of the machine tool and at least at a certain value cancel that force. Advantageous further developments of the inventive concept can be found in the subclaims.

The means used in the context of the invention produce in the respective housing an inclination of the spindle axis which is opposite to the inclination which is set by the clamping force. The aim of the setting is that the spindle axis runs horizontally at the nominal value of the clamping force and that the two axes of the holding device are set coaxially.

The idea of the invention is realized with the aid of an inclination of the foot in the base of the housing, which can be combined with a stepless height adjustment. The idea of the invention can also be realized with support parts arranged on an outside of the housing and having adjustable support forces. In addition, within the scope of the invention a pressure medium operated support cylinder are provided, which in conjunction with a drive cylinder to generate the clamping force prevent inclinations of the spindle axis in each load level.

In the case of a holding device with inclinations on both housings, these are designed such that when a defined value of the clamping force is reached, the workpiece has reached the clamping position provided for the machining processes.

Accordingly, the two housings are designed so that the axes of the drive spindle and the support spindle each have an inclination in the unloaded state with respect to the clamping surface of the work table and intersect in the area of the workpiece to be clamped. When loaded with a certain nominal clamping force sufficient for most workpieces, the loaded components of the machine tool deform so that the axes of the drive and support spindles are set coaxially and the clamping surfaces are parallel to one another. In this state, the workpiece has no deformation or change in position due to the clamping relative to the parts of the machine tool; Any precision machining can now be carried out on them.

So that workpieces with a clamping force deviating from the nominal value can also be machined with the holding device according to the invention, provision is made on at least one of the housings, especially on the one with the lower bending rigidity, with which a small height compensation can be carried out. With the help of this measure, the point of intersection of the two axes is shifted in a simple manner in the direction of the height-adjustable clamping piece, thus minimizing the deformation of the workpiece as a result of the inclined position of the clamping pieces. For height adjustment is a device at the foot of the base of the respective housing works on the incline plane principle. For this purpose, in addition to a wedge, a construction with a support part, the adjustment of which is carried out with the help of a fine thread, is used. A scale indicating the clamping force enables the required setting to be made before the workpiece is inserted.

When using support parts, simple housings that are not modified by additional measures and are easy to manufacture are used. Each support part is used on the side facing away from the clamping pieces on a housing bearing attached to the upper edge of the housing and on an abutment attached to the work table or to a base plate molded onto the respective housing. The support parts are designed so that not only a backlash-free but also a support acted upon by a support force can be set, which results in an inclination of the axis.

As supporting parts, for example, threaded spindles with a right-left thread are provided, which can be adjusted steplessly with a defined supporting force after installation in the bearing points. Support cylinders operating with a pressure medium can also be used in machine tools in which there are hydraulic systems. The precise setting of the supporting force with the aid of the storage pressure of the system is particularly advantageous, possibly via an intermediate store, which can be adjusted to the pressure value corresponding to the supporting force.

A parallel connection of one or more support cylinders is suitable for a machine tool in which the clamping force is used with a working cylinder fed by a hydraulic system. With an adapted dimensioning of the piston diameters of both cylinders, this solution can be used to achieve completely deformation-free clamping on the side of the second housing regardless of the size of the clamping force. In another development of the invention, the stability of the support of a housing can be improved by attaching two or more support parts. A particularly effective embodiment in the context of the invention is a connection of the first to the second housing by means of one of the support members specified above. For this purpose, a housing bearing is attached to a suitable location in each of which an eye of the support member is inserted and adjusted with a supporting force becomes. In order not to hinder the use of the processing tools in the vertical direction, the attachment of two support links outside this area is recommended. With the present embodiment, the power flow is limited to the two housings and the support members, so that additional abutments are unnecessary. For the machining of workpieces of different lengths, in addition to moving one of the housings on the work table, the supporting members only have to be lengthened or shortened. In the case of support members designed as threaded rods, it is sufficient, for example, to provide threaded bolts of different lengths, which can be inserted on one side into the nut piece arranged in the middle. For hydraulic support links, the length can be changed by adding or removing parts of the piston rod.

The deformations of the two housings, which are caused by the clamping force and reduce the accuracy of the workpieces, can be prevented according to the above either by constructive changes to the housings themselves or, in the case of unchanged housings, by external support measures. Thus, the most suitable measure can be selected for different applications with the help of the inventive solutions.

For a better understanding of the invention, reference is made to the accompanying drawings, which show the following in detail: Figure 1 Simplified representation of the holding device without a workpiece;

FIG. 2 holding device with a workpiece clamped at the nominal value of the clamping force;

FIG. 3 basic representation of the deformations with a clamping force exceeding the nominal value;

FIG. 4 deformations of a workpiece with low bending stiffness with a clamping force exceeding the nominal value;

Figure 5 Reduced deformation of the workpiece to Figure 4 after a height adjustment of the second clamping piece;

FIG. 6 height adjustment of the second clamping piece by means of a support part adjustable with a fine thread;

Figure 7 section A - B to Figure 6;

Figure 8 view in direction D against the base of the second housing in an enlarged view.

Figure 9 housing with threaded rod ^' as a support member;

Figure 10 housing with pressure medium-filled support cylinder;

FIG. 11 housing as in FIG. 10 with an additional working cylinder for generating the clamping force;

FIG. 12 supporting parts suspended from the housings of the two housings;

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are performing. This enables, for example, the use of comparatively large clamping forces in housings with relatively low rigidity.

On the other hand, whether only one housing is to be supported in a specific holding device depends on the relation of the stiffnesses of both housings. In the case of very different stiffnesses, it may therefore suffice to provide only the housing with the lower stiffness with a support.

A hydraulic fluid is particularly suitable as a pressure medium for the support members, with which list pressures of several hundred bar can be transmitted. In the support according to FIG. 10, the pressure load can take place during the entire operating period of the holding device, irrespective of the intervals in which the clamping force is applied. It is different with an embodiment according to FIG. 11, in which the pressure load of the entire system only takes place during the time in which a workpiece is clamped. The operating modes of the supports just mentioned have an influence on the selection of hydraulic fluid and seals.

In principle, designs with a gaseous pressure medium are also conceivable, especially if a corresponding system is already available in the production plant. In such cases, the control of the holding device must take into account the other characteristics of the pressure medium.

Claims

claims 1. Holding device for workpieces to be machined on several sides, with two clamping pieces, which receive the workpiece with the aid of a clamping force acting in the axial direction and have flat clamping surfaces, of which the first clamping piece by means of a rotatable drive spindle mounted in a first housing with an angle switching device and of which the second clamping piece by means of a rotatable and axially displaceable support spindle mounted in a second housing and connected to a drive generating the clamping force and in which the two housings are mounted on the work table of a machine tool, characterized in that at least one of the housings (2 or 3) is provided with means which counteract the inclination of the axis (14, 15) of the associated spindle (4, 5) under the action of the clamping force (Fk) relative to the clamping plane of the machine tool and at least cancel this force at a certain value. 2. Holding device for multi-sided workpieces according to claim 1, characterized in that the spindle (4,5) in the unloaded state with its axis (14, 15) by a beveling of the base (13) of the housing (2,3) caused inclination by the angle (a 1, α 2). 3. Holding device for multi-sided workpieces according to claim 2, characterized in that the base (13) by one along one with the angle {a 1,. 2) against the work table (1) inclined surface slidable foot (11) is completed. 4. Holding device for multi-sided workpieces according to claim 3, characterized in that the housing (2,3) is provided with an additional height adjustment. 5. Holding device for multi-sided workpieces according to claim 3 or claim 4, characterized in that a guide, preferably a tongue and groove arrangement is provided between the foot (11) and a plate (20) molded onto the base (13). 6. Holding device for workpieces to be machined on several sides according to claim 4, characterized in that the base (13) of the housing provided with the height adjustment (3) against the work table (1) is completed by means of a support part (16) which can be adjusted with a fine pitch . 7. Holding device for multi-sided workpieces according to claim 6, characterized in that the support screw (16) on a with the base (13) attached to the work table (1), preferably with one adapted to the dimensions of the support screw (16) Recess (25) provided base plate (23) is guided. 8. Holding device for multi-sided workpieces according to one of claims 3 to claim 7, characterized in that a preferably the deviation from the nominal value of the clamping force (Fkn) indicating scale (17) is provided for the adjustment of the base ^' (13). 9. Holding device for workpieces to be machined on several sides according to claim 1, characterized in that the respective housing (2, 3) is supported with a support part which is articulated on a housing bearing and an additional bearing point. 10. Holding device for multi-sided workpieces according to claim 9, characterized in that that a continuously adjustable threaded rod (31) is used as the support part with a right-left thread. 11. Holding device for workpieces to be machined on several sides according to claim 9, characterized in that a support cylinder filled with a pressure medium (32) is used as the support part, in which the support force can be adjusted by means of a pressure value which can be controlled on a connected pressure accumulator (33). 12. Holding device for multi-sided workpieces according to claim 10 or claim 11, characterized in that the spindle axis (14, 15) in the unloaded state caused by the set on the support member supporting force (Fs) inclination by the angle (o. 1, α 2) has. 13. Holding device for multi-sided workpieces according to claim 11, characterized in that in addition to the pressure accumulator (33) in the second housing (3) built-in working cylinder (34) for the clamping force is connected, both cylinders (32 and 34) so are dimensioned so that no inclination of the axis (15) occurs regardless of the pressure value. 14. Holding device for workpieces to be machined on several sides according to one of the claims 9 to 13, characterized in that the supporting part is supported against an abutment (35) attached to a base plate (38) connected to the housing (2, 3). 15. Holding device for workpieces to be machined on several sides according to one of the claims 9 to claim 13, characterized in that the supporting part at one each outside the effective range of Machining tools attached bearing point (37a, 37b) of the two housings (11,12) is articulated and set. 16. Holding device for multi-sided workpieces according to one of claims 9 to claim 15, characterized in that two symmetrical to the central plane of the respective housing (11, 12) attached support parts are provided. 17. Holding device for multi-sided workpieces according to one of the claims 11 to claim 16, characterized in that a hydraulic fluid is used as the pressure medium. 18. Holding device for workpieces to be machined on several sides according to one of the claims 11 to claim 16, characterized in that a gas, preferably compressed air, is used as the pressure medium. 19. Holding device for workpieces to be machined on several sides according to one of the preceding claims, characterized in that in the case of housings (2, 3) with very different bending stiffnesses, one of the means is only provided for the housing (3) with the lower bending stiffness. 20. Holding device for multi-sided workpieces according to one of claims 2 to 8 in conjunction with one of claims 9 to 14 or claim 16 to claim 18, characterized in that in one of the housing (2 or 3) an angle change on the base (13) is made and in the other housing (3 or 2) a supporting part is articulated against an abutment (35).